Frame design

[Ted Wojcik]

How about a discussion of some of the challenges in designing a 29er frame. Let's talk about making a frame with an 18" seat tube and using a front dérailleur. When done, I will build the frame and we will have a local 29 fan test it. We'll call it Monkey Butt.

[tozovr]

with the 18" ST and a front derailleur the main issue is the operating angles of the actual derailleur right? So the tube either needs to have a crazy angle (steep?) or you need to manipulate it right? In steepening the angle you effectively shorten the Top Tube...then you get Toe overlap issues and possible fork crown interference.

If we call it monkey butt, the front should be brown and the back, Blue. :clapping:

[Ted Wojcik]

Actually, the biggest problem is if we make the chainstays short enough for good climbing/traction, there is an issue with the front dérailleur hitting the rear tire when on the small ring. If the chainstays are long enough to minimize this issue, the wheel base gets long and steering starts to slow down in addition to the decrease in traction. As this discussion goes on, I will present some drawings with exact dimensions as well as recommendation on how we might address these challenges.

[tozovr]

I'm cheating...FTW, Darrell and I just chatted about this on the Sinister 29er a few months back ;)

to keep a sub 17" seat tube angle the seat tube got a nice dogleg in it.

http://www.ridemonkey.com/mountain-bike-photos/data/500/14391th_IMG_3001.JPG

I spoke with Chris a week or two ago, sounds like you guys are kicking ass!

RJ

[Angus]

Ted,
Great to have you aboard an on RM! I have admired your quality for years.
I am not a frame designer (nor do I play one on TV). But I will be watching this thread to see what develops, as I am an avid 29er fan. Cheers...

[MMcG]

I'd say put a little bend in it - get the chainstays to around 17" and find an older Shimano rear derailleur (say an old XT or LX or something - one of the models that Surly used to recommend on the Karate Monkey) and then have at it.

Also now that so many new tires are coming out - design considerations should also include the ability to run as wide a tire as possible should a rider prefer to go that route, but with a design that would allow for ample chainring clearance for at least a two ring set up.

Another thought would be a seat tube to top tube brace on the frame to provide for a slightly more sloping top tube which could provide a little more clearance for the rider.

Just a few thoughts on my end.

[MMcG]

I had another thought here.

What about some type of sliding rear dropout setting or slotted dropouts at different chainstay lenghts. So for example, an east coaster or a short chainstay advocate could run the frame in a short chainstay mode, but a west coaster or a fireroad type of guy could lengthen the chainstays a tad for his or her preference? Could this be done via Paragon Sliders or perhaps some type of system like they utilize on the Evil Sovereign?

[Ted Wojcik]

This is the dialog I'm looking for. I'm on the way to the shop now, so I will continue this chat later in the day. Let's see what grows out of this.

[Stray_cat]

I'd certainly like to see a 29er using a shorter wheel base. Most of the ones I've tired I've though to myself "hey I'm on a big bike." I'd say do what ever you have to do to get those chainstays short.

[MMcG]

This is the dialog I'm looking for. I'm on the way to the shop now, so I will continue this chat later in the day. Let's see what grows out of this.

Ted - thanks for starting up this thread. Should make for a real solid conversation here. I made it a sticky so it will stay on top for people to see easily.

All the best,

Mark

[Toddre]

This should be interesting to follow... Can't wait to see how it turns out..Maybe it will help me with some tweaking of some frame designs I'm working on for future projects...of course, the frame here is too small again...lol

[MMcG]

This should be interesting to follow... Can't wait to see how it turns out..Maybe it will help me with some tweaking of some frame designs I'm working on for future projects...of course, the frame here is too small again...lol


We'll just get you a really Long seatpost! ;)

[Possum]

How about a 17.75" chainstay? 73.5deg STA?

When you say 18" seat tube, do you mean "traditional" 18" seat tube (i.e. for a rider that would normally ride an 18" (c-c) frame in a 26" bike)? This would be roughly a "medium" sized frame, with an ETT of 23.75-24"?

At this size, I don't see toe overlap being a problem, unless you get into like a 71deg STA, unless your rider has Sasquatch feet.

I see your primary drivers here being a)clearance with the front der and the rear tire and b)sufficient mud clearance for the rear tire while still being able to fit 3 chainrings and not use a 120mm wide bb.

My suggestion would be a 73mm shell, so that you can put the stays a little farther outboard. You're probably still going to have to do some of your own custom bending to get enough clearance for a Rampage and be able to use all 3 rings.

I honestly think the front derailleur location takes a back seat to this issue.

Thoughts?

[sportcult]

How about a braze on style front derailler? You could just have a little arm to place it where you need it.

[eMcK]

Great thread.

Rather than the 73mm shell, perhaps go with a press-in bering design as used on quite a few road bikes and the new Pivots. This should give plenty of space to get those chainstays wide enough for 2.3's and some mud.

I would give up my front derailer for some really short chainstays, but I would guess to be in the minority there. I like the Wolfhound style split seat tube, but it would seem to preclude the use of a front derailer, although I wonder if an E-type or braze on would work.

What I would like to see other than short chainstays: Longish top tube (~24") slackish head angle (~70) to go with a higher rake fork, and slackish (~71) seat angle. High BB, at least 12", maybe a bit more. Some extra standover would be great also, with either an extended seattube or a small brace, ala 1st gen El Mariachis.

I happened to be looking at a custom 20" wheeled kid's bike today with the Wojcik name on it.

[MMcG]

An E-type is a good idea. Is anyone utilizing that type of set up on any custom frames?

The slacker HT angle with the higher rake fork makes sense for rigid, but if one were to use a suspension fork, about the slackest you could go would probably be 71 degrees don't you think?

I'd love to hear thoughts about a seat tube angle as slack as 71 degrees.

[Frank Tuesday]

An E-type is a good idea. Is anyone utilizing that type of set up on any custom frames?

The slacker HT angle with the higher rake fork makes sense for rigid, but if one were to use a suspension fork, about the slackest you could go would probably be 71 degrees don't you think?

I'd love to hear thoughts about a seat tube angle as slack as 71 degrees.

This is how I view it, and the idea I designed my geo with.

Set your seat relative to the handlebar position to adjust the correct cockpit length and weight distribution for seated position. Once you have that, choose the BB position that gives you the cockpit size and weight distribution that you want for a standing position. Of course, if you buy into KOPS, this is heresy.

[MMcG]

This is how I view it, and the idea I designed my geo with.

Set your seat relative to the handlebar position to adjust the correct cockpit length and weight distribution for seated position. Once you have that, choose the BB position that gives you the cockpit size and weight distribution that you want for a standing position. Of course, if you buy into KOPS, this is heresy.


Frank - perhaps you could throw up a photo or two of your bike to provide some visual examples of this. That would be greatly appreciated.

And Welcome to Ridemonkey!!

Cheers,

Mark

[tozovr]

AGreat thread.

Rather than the 73mm shell, perhaps go with a press-in bering design as used on quite a few road bikes and the new Pivots. This should give plenty of space to get those chainstays wide enough for 2.3's and some mud.

I would give up my front derailer for some really short chainstays, but I would guess to be in the minority there. I like the Wolfhound style split seat tube, but it would seem to preclude the use of a front derailer, although I wonder if an E-type or braze on would work.

What I would like to see other than short chainstays: Longish top tube (~24") slackish head angle (~70) to go with a higher rake fork, and slackish (~71) seat angle. High BB, at least 12", maybe a bit more. Some extra standover would be great also, with either an extended seattube or a small brace, ala 1st gen El Mariachis.

I happened to be looking at a custom 20" wheeled kid's bike today with the Wojcik name on it.


I'm sporting 71.5° head Tube angle with the 73° ST...24" TT and the 17.5" seat Tube (center of BB to top of ST). 73mm wide BB shell and no way in hades to run a big ring. 12.75" BB height

This was based on quite a few rides on different stuff available and most importantly, what Darrell, Frank and I wanted out of a 29er here in the depths of New England. This was a very specific thing for us, hence no provisons for a big ring etc.

We didn't really worry about mass market appeal, just our vision. It works awesome for us, but I know there are folks out there who would hate my bike.

[MMcG]

I'm sporting 71.5° head Tube angle with the 73° ST...24" TT and the 17.5" seat Tube (center of BB to top of ST). 73mm wide BB shell and no way in hades to run a big ring. 12.75" BB height

This was based on quite a few rides on different stuff available and most importantly, what Darrell, Frank and I wanted out of a 29er here in the depths of New England. This was a very specific thing for us, hence no provisons for a big ring etc.

We didn't really worry about mass market appeal, just our vision. It works awesome for us, but I know there are folks out there who would hate my bike.


I took a parking lot spin on D's Simon Bar last night. Holy Crap - that's one helluva nice bike that Simon Bar! You guys done good! :thumb:

[tozovr]

I took a parking lot spin on D's Simon Bar last night. Holy Crap - that's one helluva nice bike that Simon Bar! You guys done good! :thumb:

You should try one without the gonky H-bars...and gears :busted:

Pretty stoked Darrells fork turned out breaking in very nicely.

[MMcG]

You should try one without the gonky H-bars...and gears :busted:

Pretty stoked Darrells fork turned out breaking in very nicely.


I loved those Gonky H-Bars. And his fork was very nice!

[eMcK]

An E-type is a good idea. Is anyone utilizing that type of set up on any custom frames?

The slacker HT angle with the higher rake fork makes sense for rigid, but if one were to use a suspension fork, about the slackest you could go would probably be 71 degrees don't you think?

I'd love to hear thoughts about a seat tube angle as slack as 71 degrees.

Some of the newer 29" forks on the market have a bit higher rake, the Fisher OE Fox F29 comes to mind, along with the Minute and the Maverick, although I'd have to sit down and do some figuring to see what the trail would be with a slacker head angle.

The slack seat tube with a longish top tube, paired with a shorter stem would get my weight further back over the rear of the bike, helpful to get the front wheel up and over things, and to stay more centered on the bike on steep downhills.

[MMcG]

Some of the newer 29" forks on the market have a bit higher rake, the Fisher OE Fox F29 comes to mind, along with the Minute and the Maverick, although I'd have to sit down and do some figuring to see what the trail would be with a slacker head angle.

The slack seat tube with a longish top tube, paired with a shorter stem would get my weight further back over the rear of the bike, helpful to get the front wheel up and over things, and to stay more centered on the bike on steep downhills.

I think the Maverick is 47.3mm of offset and one of the Manitous might be 48mm.

Thanks for the reply. might that slack of a seat tube angle cause you to "loop out" a bit on climbs? Whattya think?

[Ted Wojcik]

I'm sorry about the delay in posting here, but I have to make bikes during the day and the computer is kept at home to keep the shop's environment from eating it.
This is going to generate a long discussion. Let me lay out some ground rules. (really there are no rules, but we do have limitations) Every frame/bike builder has restrictions, his stock list, that is the available tubing, drop-outs, braze-ons, and other needed fittings, and available components. I would like to use readily available parts. If we start designing a frame to use proprietary components, there will be a time when the project will be obsolete. Lets think on the long term. You will find out how challenging designing a bike to suit a large assortment of riders can be. I don't want the identity of the bike to be lost in compromises, but it needs to be as universal in appeal as possible. I'm going to build this frame with steel because the stock list is so big and I am committed to that material. We will talk about why as we go forward.
We need to decide on the components and fork. I will tweak the geometry and weight distribution as the build progresses, after all, 25 years of frame design shouldn't go to waste. We will find there are ways of making the bike handle the way we want without a predetermined trail number. We will use a ratio called stability index that includes fork offset, head angle, wheel diameter and mass, and center of gravity placement. Because fork offset is provided by the fork manufacture, we are constrained in geometry. I will set the head angle last. Let's select the component group and fork first.

[pinkshirtphotos]

sliding vertical dropouts with the disc mount built into them would be really cool.

[Possum]

I vote Reba fork and XT components. Nice, durable, reliable, fairly affordable. Also fairly standard. No goofy H-bars or any other "specialty" type items.

I think everyone is going to learn a good deal on this. I know I learned a lot when I built my frame. Producing the drawing was an education in and of itself, in terms of learning how much changing one aspect changes several others. Then actually putting the frame into the jig and getting it all to work was another level of education.

[Psychic_Pimp]

This promises to be a fun discussion, indeed.

I had another thought here.

What about some type of sliding rear dropout setting or slotted dropouts at different chainstay lenghts. So for example, an east coaster or a short chainstay advocate could run the frame in a short chainstay mode, but a west coaster or a fireroad type of guy could lengthen the chainstays a tad for his or her preference? Could this be done via Paragon Sliders or perhaps some type of system like they utilize on the Evil Sovereign?

Another option to make a frameset more versatile is what Frank the Welder has done with the Simon Bar and others. Interchangeable dropouts could be used so that one could run a track end or vertical drops. Different sizes of vertical drops could also be machined. That way the same frame could be configured geared with longer or shorter chain stays so it could be set up as a fire road bomber or rock crawler without messing with sliders or slots.

[tozovr]

I agree about building the bike for across th eboard acceptability. I think every single person here has an idea about what makes a perfect 29er for themselves....unfortunately that bike might be a nightmare for someone else.

I was lucky to work with Frank, as many have been to work with Ted...to find someone who can translate what you dig, into angles and dimensions. I can tell you what I like and don't like about certain bikes, but can not articulate that in number at times. Since the Simon bar, that has changed quite a bit. So instead of maybe tossing out things like "short stays" or steep HA, maybe just talk about what you have and why it rocks or sucks for you and where you ride?

lastly, I don't think the current reba platform is a good basis as it will undoubtedly change to the next gen of offset...I pray it does anyhow LOL. They'd be crazy to keep it at 38mm. Maybe the manitou or th enew Fox...not so much the Maverick DUC32 (as much as I LOVE mine)-it's just too uncommon.

[Ted Wojcik]

I understand that Fox has made the first of their 29er forks OEM only. I will try to pry one out of their hands for this project. I'll let you know as soon as I talk to the rep. I think XT is a good idea as well as Paragon slider drop outs.

[pinkshirtphotos]

ted, you can order the new fox 29er fork from bti i think.

[Ted Wojcik]

Unless things have changed recently, Fox does not sell through distributors. I have an OEM account with FOX, but I was told they had an exclusive deal with Fisher for the first of the 29" forks for 1 year. I could be wrong, but I will check tomorrow.

[ByStickel]

One nice solution to clearance issues is elevated chainstays. Sure, they look old-fashioned, but they allow for easy tire clearance. Biggest issues for a 29er happen at the tire/chainring/fr. der. junction. Most , but clearly not all, of those problems are solved by e-stays.

Front derailleurs stink, especially on 29ers. Since we're talking east coast here (crossing myself), I'd love to see a 2x9 20/32 crankset, sans bashguard, with the rings pushed out as far as possible without increasing Q.

Using an old-school bottom swing front der (non-universal pull) will gain you a few precious millimeters, but where are you going to find them? Unfortunately, top-swings would allow for lower, stiffer chainstay location on an elevated bike.

Ted, will you let me in on your beadless welding secret? Pretty please? I'll be up in the neighborhood this coming week and could bring my trusty Huntsman and some turkey leftovers...

PS: fox forks are currently available through retailers, in the retail-offset (not G2). O.E. accounts will have access after 1 year.

[tozovr]

I understand that Fox has made the first of their 29er forks OEM only. I will try to pry one out of their hands for this project. I'll let you know as soon as I talk to the rep. I think XT is a good idea as well as Paragon slider drop outs.


Ted, They'll sell you one of the Non-OE forks (44mm offset as oppose dto 46 IIRC?) but Gary Fisher has the lockdown on the G2 offset until '08 sometime. You or Chris can likely EP a normal one though.

RJ

[sportcult]

An E-type would be cool so you could just take it off if you want to run 1x9 or single (as I would). It would complement the versatility of the slider dropouts.

[Ted Wojcik]

The problem with dérailleur clearance is that the tail end of the cage hits big tires with short chainstays when on the small ring. When standing and cranking hard, there is enough tire deflection that it will require more that a millimeter or two clearance. Do we limit tire size or compromise chainline? The new cranks from Shimano kinda' prevent screwing with chainline, but offer great stiffness. Because 29" wheels have such a big rollout, we could live with a 20 tooth small ring and a 2X9, but we are leaving the realm of off the shelf parts. Elevated chainstays still won't increase the tire to cage issue. I'm going to do some precise measurements and a drawing and we can see how much room we have and work with that. It will be a few days before I can post the drawing because of some software issues. I had a bad virus that required reformatting my 'puter, so I can't convert my CAD files to a postable format right now. I will try to straighten that out over the weekend

[MMcG]

My vote would be for a Fox F29er fork - that fork is getting great reviews and it has a 44mm offset (the non Fisher OEM one) which is a great middle ground for a 29er frame. Perhaps Mike B. could help out with some Stan's wheelset for this. He's a RM regular and works for Stan's.

Perhaps we could get Brian HCM to offer up some Hope bits for the build as well (headset, seatpost collar, skewers)

I think the frame should be done up in the Signature Red, White and black or perhaps a Ridemonkey themed paint scheme (with some type of light to dark green fade scheme to it).

I could go on and on I guess.

I still wonder if there isn't a way to find pile of New Old STock Shimano front derailleurs that could get the job done. I had one on a small Karate monkey and ran my wheel all the way forward in the drops with an Exiwolf tire and had plenty of tire clearance. I knew I shoulda kept that front derailleur!

This thread kicks ass! Let's keep it going folks!

[MMcG]

One nice solution to clearance issues is elevated chainstays. Sure, they look old-fashioned, but they allow for easy tire clearance. Biggest issues for a 29er happen at the tire/chainring/fr. der. junction. Most , but clearly not all, of those problems are solved by e-stays.

Front derailleurs stink, especially on 29ers. Since we're talking east coast here (crossing myself), I'd love to see a 2x9 20/32 crankset, sans bashguard, with the rings pushed out as far as possible without increasing Q.

Using an old-school bottom swing front der (non-universal pull) will gain you a few precious millimeters, but where are you going to find them? Unfortunately, top-swings would allow for lower, stiffer chainstay location on an elevated bike.

Ted, will you let me in on your beadless welding secret? Pretty please? I'll be up in the neighborhood this coming week and could bring my trusty Huntsman and some turkey leftovers...

PS: fox forks are currently available through retailers, in the retail-offset (not G2). O.E. accounts will have access after 1 year.

Steve - welcome to the Monkey!!! Stoked to have you hear and contributing to this thread.

Cheers,

Mark

[BikeGeek]

This thread kicks ass! Let's keep it going folks!
Interesting reading so far. I don't know enough about frame geometry to participate, but I'm looking forward to seeing where this goes.

:thumb:

[Ted Wojcik]

Hi Steve! If I taught you how to weld like that, what would set my frames apart from the rest. LOL. Practice, man, practice. I'm leaving for Ct. Tuesday to eat the bird, but I should be back Friday. Give the shop a call if you want to stop by.

[tozovr]

I still wonder if there isn't a way to find pile of New Old STock Shimano front derailleurs that could get the job done. I had one on a small Karate monkey and ran my wheel all the way forward in the drops with an Exiwolf tire and had plenty of tire clearance. I knew I shoulda kept that front derailleur!

This thread kicks ass! Let's keep it going folks!



1x9 rules!

[MMcG]

1x9 rules!

1x9 is a good way to go - or 1x8 or whatever you so desire in back. But it sounds like Ted has in mind a more versatile design that someone who wanted to run 2 or three rings could utilize.

If we are going to keep this more East Coast specific than a 2x9 with one of those custom Ted Wojcik basguards would be just the ticket. :thumb:

[MMcG]

Hi Steve! If I taught you how to weld like that, what would set my frames apart from the rest. LOL. Practice, man, practice. I'm leaving for Ct. Tuesday to eat the bird, but I should be back Friday. Give the shop a call if you want to stop by.

Ted - where will you be heading in CT?

I live in Burlington - perhaps we could meet for a cup of coffee or something if you'd like.

All the best,

Mark

[MMcG]

Another thought for this thread is in addition to a suspension fork, it would be pretty cool to include a rigid fork option as well since many 29er folks enjoy the precision that a rigid fork provides.

[sportcult]

Another thought for this thread is in addition to a suspension fork, it would be pretty cool to include a rigid fork option as well since many 29er folks enjoy the precision that a rigid fork provides.

Yay rigid! :clapping:

[Ted Wojcik]

My idea here is to come up with a design I could ride. I'm 60 now and need all the gears I can get. These challenges face all builders, so if we can find a way to deal with them. I'm sure we will find more usable 29er's in the market place. Of course there will be a rigid fork to go with it. I think that we might end up with some custom fabricated chainstays, slider dropouts, and a geometry that will tolerate adjustable chanstay length. When chainstay length changes, there can be quite an influence on handling. I'll tell you a story about that later in the build. I just want to throw out some fodder for thought here. 27.5" rear wheel?
Hey Mark, we are going to Kensington. (South of Hartford) I will be tied up until Friday on our way home. If there is time in there, I'd love to have a cup of coffee

[pinkshirtphotos]

ted, 27.5 has been tried before on road bikes. never really stayed around. i honestly dont see it becoming a big deal either. a 26 inch rear wheel with 29 front would be better especially when being able to chose tyres

[Bullitboyz]

Hey Mark, we are going to Kensington. (South of Hartford) I will be tied up until Friday on our way home. If there is time in there, I'd love to have a cup of coffee

hey let's make it a party... i'm in!

love this discussion, thanks Ted! .. but where was it 2 years ago when i was lookin for a Wojcik 29er? :disgust: (I guess I'll just suffer with my Wojcik 650b for now)

can you do a curved top tube with steel to provide more standover clearance for the shorty riders? (that's not a request, just wonderin)

. a 26 inch rear wheel with 29 front would be better especially when being able to chose tyres

oh and ^^^ BARF. in my opinion, 26" rear wheel negates 90% of the benefits of the 29er concept. but if that's your thing, then just have the 26er's geometry customize to account for the bigger front hoop.

[Ted Wojcik]

The first of the 29er's was really done by Bruce Gordon in the mid 80's. He called them Rock and Road. He used a Hakapallita tire that weighed over 1000 grams and I think that is what prevented it from more popularity. It had quick disconnects on the cables so you could swap back and forth between drop bars and flat bars. Great bike and a great idea that was delayed by tire availability. Scot Nicol and Cannondale did a bike with 26" front and 24" rear. Great bikes to do trials like trail riding. And we can't forget about the 96er thing. A lot of riders like this combo. Motorcyles routinely use different tires front and rear. The thing that will make 27.5" wheels work WILL be tires. 27.5" (650B) is the most popular wheel size in many other countries so I think we will see this gain some acceptance. It will be a better fit for those with shorter legs and gearing is less affected by the big roll out of the larger wheel size. One of the biggest advantages that I have seen for 29" wheels is for single speeds where the inertia of the large wheels keep the bike going through the rough stuff without shifting. Now if we can address the challenges of making a traditional drive train work with big wheels, we will have made a contribution to the sport and bring the advantages of big wheels to a traditional mountain bike. All I'm saying is let's look at all options.

[sportcult]

I think 29 front, 650b rear has merit. I was riding a 96er before my 29er and there are some aspects I miss. If the 27.5 truly has a compromised feel between the sizes it would rule on the back. 29 on the front is set for me. I haven't found any disadvantage to that yet. I don't believe the claims that the rear is 90% of the 29er advantage. Anyone who is running a suspension fork on a hardtail has already acknowledged that there is a big difference between the effect of the front end and the rear when it comes to traction, rolling over stuff, and pedalling sensation. I am very tempted to try a 97.5er...

[WishIWereRiding]

Can I comment, even if I'm from CA?

I'd like to see the frame designed for the Fox F29 @ 100mm of travel. I either want 100mm or rigid (actually I want both, I just don't want to bother with 80mm).

[MMcG]

Can I comment, even if I'm from CA?

I'd like to see the frame designed for the Fox F29 @ 100mm of travel. I either want 100mm or rigid (actually I want both, I just don't want to bother with 80mm).

Welcome to the Monkey!

Your comment on the Fox fork makes me wonder if somewhere down the line we'll see a Fox 29er Talas model on the market.

[eMcK]

My thoughts on fork and components:

Fork: Fox. The Reba is probably due for a change soon. The jury is still out on whether Manitou has got their QC and customer service back on track. That said I really like the Minute 29" fork I rode a few times. That leaves us with the Fox, or maybe the RST, which seems to be a heck of a lot of fork for the money.

Components: We are pretty much locked into external bearing 2 piece cranks if we want off the shelf parts. I say stick with proven stuff, something at the LX or XT level, perhaps for the whole bike. I've been testing a bike with an almost straight LX grouppo (including hubs) and have very little to complain about.

I've tried 2 27.5 bikes , and I have rims and tires waiting for hubs and spokes to finish the build. While tire selection will never be great, the one tire out now is just about perfect for east coast style trails. Deeper tread, real cornering knobs, should shed mud acceptably. I would have no problem going to a 27.5 tire to get shorter chainstays and front derailer clearance.

[MMcG]

My thoughts on fork and components:

Fork: Fox. The Reba is probably due for a change soon. The jury is still out on whether Manitou has got their QC and customer service back on track. That said I really like the Minute 29" fork I rode a few times. That leaves us with the Fox, or maybe the RST, which seems to be a heck of a lot of fork for the money.

Components: We are pretty much locked into external bearing 2 piece cranks if we want off the shelf parts. I say stick with proven stuff, something at the LX or XT level, perhaps for the whole bike. I've been testing a bike with an almost straight LX grouppo (including hubs) and have very little to complain about.

I've tried 2 27.5 bikes , and I have rims and tires waiting for hubs and spokes to finish the build. While tire selection will never be great, the one tire out now is just about perfect for east coast style trails. Deeper tread, real cornering knobs, should shed mud acceptably. I would have no problem going to a 27.5 tire to get shorter chainstays and front derailer clearance.

How about one of each and we can do a comparo. ;)

If this is going to be an 18" seattube design - then perhaps it makes the most sense to stick with the original concept of a 29er. Since the "challenge" part of making a frame like this work and have it be geared is part of the "fun" of this excercise.

Just my two cents.

With that said - I wouldn't mind giving a 27.5er a try - especially at my 5'9" height at some point to see how it works for someone like me.

[-dustin]

The first of the 29er's was really done by Bruce Gordon in the mid 80's.
it that why he comes off so grumpy, because he doesn't get credit for the first 29er?

come on, pal, crack a smile! DW looks more pleased than BG.

http://www.cyclingnews.com/photos/2007/tech/shows/nahmbs07/nahmbs076/Bruce_Gordon_NAHBS_Best_in_Show_award.jpg

[MMcG]

My idea here is to come up with a design I could ride. I'm 60 now and need all the gears I can get. These challenges face all builders, so if we can find a way to deal with them. I'm sure we will find more usable 29er's in the market place. Of course there will be a rigid fork to go with it. I think that we might end up with some custom fabricated chainstays, slider dropouts, and a geometry that will tolerate adjustable chanstay length. When chainstay length changes, there can be quite an influence on handling. I'll tell you a story about that later in the build. I just want to throw out some fodder for thought here. 27.5" rear wheel?
Hey Mark, we are going to Kensington. (South of Hartford) I will be tied up until Friday on our way home. If there is time in there, I'd love to have a cup of coffee


Ted - Feel free to send me an email or private message and I'll give you my telephone number.

Safe Travels for the Turkey Day Festivities!

[MMcG]

I think 29 front, 650b rear has merit. I was riding a 96er before my 29er and there are some aspects I miss. If the 27.5 truly has a compromised feel between the sizes it would rule on the back. 29 on the front is set for me. I haven't found any disadvantage to that yet. I don't believe the claims that the rear is 90% of the 29er advantage. Anyone who is running a suspension fork on a hardtail has already acknowledged that there is a big difference between the effect of the front end and the rear when it comes to traction, rolling over stuff, and pedalling sensation. I am very tempted to try a 97.5er...


I know that Davis Carver of Carver Bikes and www.bikeman.com Bath Ski and Sports up in Maine has tried out this 27.5/29er combo on one of his Carver hardtails. That seems to be a better combo than 69er in my eyes, but I've also been on a couple of 69ers that I cobbled together and although it wasn't as good as a 29er - with the right frame and fork - it was better than dual 26" wheels to my estimation and my riding preferences.

[Possum]

I've got no problems with the 29/27.5 combo. It's not for me (I like the full 29 thing), but I've got no problems for it.

I do agree with MMcG, though on doing the "full 29" treatment on this bike. I kind of feel that if this is a "learning process" to see what compromises have to be made and what creativity came come about to make this thing work, using a 27.5 rear to gain that tire clearance on shorter stays is a bit of a copout.

What kind of stay length are we talking about here?

I know all you East Coast guys seem to like super short stays and high bbs, but I've found with good design, you don't have to have 16.5" stays on a 29er. My Rock Lobster had +/-17" stays, and my Badger has 17.75" stays, both with +/-12" bb heights. The Badger is a better climber AND descender. We've got plenty of tight and twistys in KC, and we have no shortage of rocks. I used to be in the "must have the shortest stays I can get" camp, but this new bike has me re-thinking some of that.

So what kind of chainstay length are we actually talking about here?

[sportcult]

I definitely think 96 kills a regular 26. Like I said, the 29 front seems like all positive, no negative as long as you have the geometry right. I've done bike switches on rides and found that a 29 wheel on a decent rigid fork feels almost exactly as compliant as a 26 wheel with a 3 inch travel fork, however the 29 wheel then adds its ability to roll over features that would stop a 26.
The problem with 29ers and acceleration is that even if you make the wheel light the inertia is going to be disproportionately greater because it increases with the square of radius. For that reason, the 650b will feel much closer to a 26 when accelerating while still being a (hopefully) good compromise in rolling effect. Since some of the mechanics of wheel performance are exponential and some are linear there should be a critical point where the inertia vs rolling resistance strikes the optimum balance. Since wheel size has been pretty arbitrary, it seems that it would premature to assume that one of the current sizes has pegged that point precisely. Maybe it's 27.5, maybe it's 29, maybe it's 28.1...That balance point will be shifted based on the average size of obstacle that the wheel has to overcome, i.e. what kind of trail you ride on...duh.

[MMcG]

So what kind of chainstay length are we actually talking about here?


I think that is what is cool about this thread. We have ideas but in a sense it is somewhat of a blank canvas. I doubt we'll see a frame with a 17.9" chainstay - yet I also doubt (maybe not) that we'll see something with a 16.5" chainstay either. We'll get to decide what "works best" perhaps.

I would love to hear about rider size/height and chainstay length. Does it make sense to have slightly longer stays for those folks who may be pushing 6'4" and up let's say. For example, if a rider is 6'9" tall - would longer stays (within reason) make sense for that person compared to the chainstay length that might be "optimal" for someone my height at 5'9" tall? Or doesn't that matter?

[WishIWereRiding]

Does it make sense to have slightly longer stays for those folks who may be pushing 6'4" and up let's say. For example, if a rider is 6'9" tall - would longer stays (within reason) make sense for that person compared to the chainstay length that might be "optimal" for someone my height at 5'9" tall? Or doesn't that matter?

I think it makes a big difference, and I wish that production bikes in different sizes where all different. Currently production frames are too similar, and the smaller sizes get the worst compromizes.

I'm not into the 27.5 idea, only because I think we should prove what can be done with 2 29" wheels. 278.5 should be another project. I also don't want to think about 2 different wheels and tires etc.

[Ted Wojcik]

I'm sorry for being away, but I have bikes to make during the day. We have a great discussion going here. First what I would like to do is determine how short we can make the chainstays with a given tire to give adequate clearance with the tail of the front dérailleur. If we can't reach an acceptable design here to make a traditional (read Shimano) drive train function, we will decide if we want a 29"wheel only design or do we want the ultimate mountain bike without restricted wheel selection. Let's decide on a rear tire and size. I have a new XT crank on order and I will make a bottom bracket chainstay assembly to check and verify how much room we will have based on the tire chosen. I talked to Fox today and I cannot buy a 29er fork as an OEM, but I can have a local bike shop get me one as an aftermarket part. They did give me an engineering drawings so we can design the frame.

[MMcG]

Ted - so you want to work with the most current XT or equivalent front derailleur available correct? I thought I read somewhere that Shimano had made some recent changes in their front derailleur designs to help provide a little more rear tire clearance - I'm not positive, but maybe it is something a fellow Monkey could look into for this thread.

As for a rear tire - I wonder if we can get Kenda to "buy" into this thread and provide a Nevegal or Small Block 8 or something else in their line-up.

It would be really cool if we could get MikeB from this forum to join in on this thread. He's a STan's employee - maybe a good source for the wheelset? Just thinking out loud here.

Mark

[Psychic_Pimp]

Ted - so you want to work with the most current XT or equivalent front derailleur available correct? I thought I read somewhere that Shimano had made some recent changes in their front derailleur designs to help provide a little more rear tire clearance - I'm not positive, but maybe it is something a fellow Monkey could look into for this thread.


Mark

The Shimano site does claim that the new XT front derailleurs have been redesigned for better tire clearance both for the cage tail and behind the seat tube.

[sportcult]

I'm cheating...FTW, Darrell and I just chatted about this on the Sinister 29er a few months back ;)

to keep a sub 17" seat tube angle the seat tube got a nice dogleg in it.

http://www.ridemonkey.com/mountain-bike-photos/data/500/14391th_IMG_3001.JPG

I spoke with Chris a week or two ago, sounds like you guys are kicking ass!

RJ

If it had modular dropouts like this Sinister, you could run any size wheel you wanted in the back, geared or single, etc...The dropout for a 26" wheel would have a hole or slot far forward and way down, the 27.5 would be in the middle and the 29 would be back and up. That way the rest of the bike wouldn't change, BB height, HT angle, standover would be constant regardless of rear wheel choice. In addition, if each dropout size were slotted the owner could adjust chainstay length for different handling or tire clearance. It would actually be pretty simple and perhaps make a bike that pleases most of us? Then we can argue about paint schemes!

[ByStickel]

The big problem is always going to be the front derailleur. I believe that there is the possibility of a semi-cageless design that could free things up for 29, but we're obviously talking about a non-standard part... so you either have der cage tire overlap or you don't.

If you don't then you're stuck with long WEST-COAST stay lengths, and we don't want that. Even 650b out back will increase stay length over a traditional 26er. The greater traction of the larger tires will help to mitigate some of the losses due to the length, but they still harm the balance and quickness of the bike.

Since the 29er wasn't considered when multi-speed components were designed, I see this as an area where it's OK to have proprietary pieces, like a special chainline crank or funky front der. The bike will be compromised without it. Someone smart (like me :-P ) with money (not me :-( ) should develop a new standard front der for 29.

Or there's Schlumpf. Or Rohloff.

[ByStickel]

And most builders are making the mistake of running a straight seat tube down to the BB. This gives an inappropriate angle for the front der because those ders aren't designed for so much BB drop.

(I know that Shimano now offers the XT -and maybe others- in two different CS-to-ST angles. I haven't checked them to see if either is appropriate for 29er)

Curving the bottom of the ST increases clearance and corrects for front der angle.

But it takes a mighty thick tube to heat-bend it and a mandrel-bent tube can get pricey for tooling set-up.

[Ted Wojcik]

I wish I could afford to have some custom dropouts machined for this project, but I can't. The closest thing to that is going to be Sliders by Paragon. I can't post the first of the drawings yet, but 17.5" chainstays, 2.5" BB drop with 73 degree seat tube will allow the use of a Shimano XT front der. M771 or M773. They are for a seat tube chainstay angle of 63-66 degrees. Do we have a consensus on the tire yet? Right after Turkey day, I will make a mock up to check the clearances.

[sportcult]

17.5"? So what's the deal with all the frames, like Niner and GF, that have 17.3" chainstays and straight seat tubes? They have problems with the granny gear? (Please pardon my ignorance of drivetrains with more than one gear...)

[eMcK]

I wish I could afford to have some custom dropouts machined for this project, but I can't. The closest thing to that is going to be Sliders by Paragon. I can't post the first of the drawings yet, but 17.5" chainstays, 2.5" BB drop with 73 degree seat tube will allow the use of a Shimano XT front der. M771 or M773. They are for a seat tube chainstay angle of 63-66 degrees. Do we have a consensus on the tire yet? Right after Turkey day, I will make a mock up to check the clearances.

I've been pretty happy with the Nevegal. Going wide enough to fit this tire would leave plenty of room for everything smaller.

[eMcK]

But it takes a mighty thick tube to heat-bend it and a mandrel-bent tube can get pricey for tooling set-up.


How about a 3 piece seaat tube with cut, mitered and welded lower sections to effectively "bend " the seat tube in the front derailer clamp area?

[-dustin]

you guys are making me want to go measure my Willits.

[pinkshirtphotos]

ted you have a pm

[nmr8]

Front derailleurs stink, especially on 29ers. Since we're talking east coast here (crossing myself), I'd love to see a 2x9 20/32 crankset, sans bashguard, with the rings pushed out as far as possible without increasing Q.

but doesn't pushing the rings out induce a lot of chain dropping?

[Ted Wojcik]

We will try to keep the chainline as close to the 50mm that Shimano recommends as possible. Monday, I will order the parts to build a "mule"
Do to the Holiday ext week, things will slow down a bit, but bare with me here, and I will share the process of building a true custom frame. Ride Monkey will have control of the helm as this ship sails into unchartered seas. Kinds' corny, huh?

[MMcG]

How are the tubes bent for say the Karate Monkey - is that a difficult and costly process for a custom builder to undertake? IF the newer Shimano front derailleurs provide more clearance, the bent seat tube idea may be worth exploring a little bit more. When I ran my Karate Monkey (a small) I was able to run a Bontrager Race wheel with an Exiwolf in back and an older XT front derailleur with the rear wheel all the way forward in the horizontal dropouts (I didn't need to use their Monkey nut to move the rear wheel back a little) in a 2x9 set up and the bike shifted just fine in all gears.

The thing that irked me the most on the Karate Monkey for these parts (Connecticut) was the low bottom bracket. I know some guys are running 170 and even 165mm cranks to address this issue - but again - this is another compromise that this Ted Wojcik Project could address.

Ted - do you want this to be a total in house thing or would you be willing to have collaborators contribute. For example - you may have to go with Paragon Sliders - but perhaps there is someone here on the Monkey with the ability to produce a different type of sliding or adjustable or multiple dropout set up.

Just thinking with the collective power of the Monkey and the web and the riding community - perhaps folks wouldn't mind stepping up to the table to assist with items/hard work/parts for this project.

Best to all,

Mark

[jncarpenter]

Fred (Wolfhound) & I have been discussing the challenge of adding a front der. to his split ST frames....one way we discussed was using an E-type with the backplate removed....like such:

We'll see how effective it is over the long haul.

[Ted Wojcik]

I would welcome inputs on this project, but lets try to be able to repeat the component. Doing a one time design that would be too expensive to repeat won't help this thing go forward. Paragon sliders are not a problem, bent tubes are. I would like to use some of the air hardening steel that is available to keep the frame light and strong. That tubing isn't not going to like being bent. I'm pretty conservative in my frame designs. I hate returns. I'm definitely a "form follows function" guy. But whatever ideas are thrown out there, let's take a look. I'm willing to learn, too. Remember every time we deviate from the norm, it will probably require some special fixtures for construction. The frame needs to be straight and stay straight. As the frame flexes, let's make sure the wheels stay in plane, that is no head tube or rear axle twist. Too much flexibility will make the bike feel unsteady through stutter bumps and lose precision in tight technical stuff. Also, we don't need fatigue cracks showing up later.

[MMcG]

I think the e-type could be the best front derailleur option if this frame is to have a straight seat tube.

Probably OEM items but I noticed today while visiting a shop that Specialized is using a sort of bolt on front derailleur (pseudo e-type?) on their FSR Stumpjumper 29er and a few of their other FS bikes (like their new Pitch 5.5" travel bike).

Since this isn't a true "custom" frame for one specific individual - what were you thinking of in terms of top tube length for the 18" seat tube frame?

[Angus]

The derailers found on the Specialized bike are E-types with the bracket removed and a Custom mount on the frame which should be easily recreated...

[El Caballo]

All these problems get solved so quickly if you just use a wider chainline...~10mm wider BB, offset chainstays ~5mm to drive side to get a dishless rear wheel with standard 135mm hub, stronger wheels, plenty of room for big tires, everyone wins except the people who nerd out about 10mm of Q factor.

[MMcG]

10mm wider - meaning an 83mm bottom bracket shell?

[Ted Wojcik]

I don't think that the new XT crank/BB will allow that much more shell, but I'll take a look at how much of a shift that setup will take. I won't be able to take a look until this week and I'll be some what unavailable until after the holiday.

HAPPY THANKSGIVING !!

[eMcK]

All these problems get solved so quickly if you just use a wider chainline...~10mm wider BB, offset chainstays ~5mm to drive side to get a dishless rear wheel with standard 135mm hub, stronger wheels, plenty of room for big tires, everyone wins except the people who nerd out about 10mm of Q factor.

For shorter rides, I don't notice much change in q-factor, but when I'm looking at long days in the saddle (touring, solo 24 hour, etc) 10mm more on an already too wide crank is too much.

The new XT won't work with an 83mm shell. Truvativ and Race Face make ISIS BB for that size, and I beleive Phill Wood will make a 83mm sqaare taper BB up if you ask.

I'm not aware of any external BB Shimano cranks that work with an 83mm BB. Truvativ, Race Face and maybe a few others have soem DH oriented cranks that work, but this all seems to be getting away from the idea of an East Coast XC bike.

[tozovr]

The Saint's are available in 83mm...not too heavy and sexy looking to boot.

But the point is moot...Ted is looking for realistic solutions to 29er problems on a trailbike for more than one person...this isn't a design exercise in what works best for an individual. Normal parts for a normal rider on a sweet frame.


Ted, what do you feel would be some good points for a 29er? I think Ted is likely more qualified to tell us what tends to work, whereas we can tell him what we like, what works for us and what doesn't.

I mean hell, I know I love how my 29er rides etc, but that is because Darrell and I fed some valid info into the computer that is FTW, and he gave us his interpretation of our data, in the form of 6061.

I respect what everyone here is saying and the ideas put forth but I think we start to micro-manage the whole thing.

[Ted Wojcik]

My idea here is to make a 29er frame that rocks in New England Single Track. I want the frame to be light, quick, and be able to use components of the owners choice. Unfortunately, Shimano kinda' dictates the layout. We might find out that other parts will work the best, but I would prefer that any body's parts will work. How short do the chainstays need to be? How short are your's and are they too long? Why? It has been agreed upon that 29" wheels have better traction, so we might get away with something greater than sub 17". I will try to make the bike steer like the single track bike we all love, but I'm really looking for input on all the other feature the Monkees are looking for in the ideal 29er. I think an LX/XT/XTR crank is a good standard because of the popularity of Shimano parts and the 22" small ring is really needed with the big wheels. It would be good if the bike would suit a broad cross section of riders. The crank, front dérailleurs and.dropouts will be here this week, but with the holiday, I won't get to do much. I will tack together a chainstay, BB, seatube assembly and we will take a look at what we have to work with and settle on a rear triangle design.

[WishIWereRiding]

Do you think that because sliding dropouts make the rear triangle smaller, that compliance is effected?

I would think that a CS @ or shorter than 17.25" would be worth doing. That would make it shorter than allmost all production bikes and most custom bikes as well. That is of course if you can get the FD to work. Otherwsie, just make them as short as will fit without having to get too creative with the ST junction and angle. Have we desided on a STA?

[eMcK]

A few actual measurements of some stuff in the basement:

Bianchi Sok SS 08 17 1/4 74º
Raleigh XXIX SS 07 17 3/8 73º
Fisher Paragon 07 17 3/8 72º
Ventana Full-sus 18 1/4 74º
Custom steel SS 17 5/8 ?

Forgot to measure my KM at home but Surly lists it at:

Karate Monkey 17 73º

I haven't found any of these bikes particularly well suited to NE single track, although they all work just fine. I don't see any reason to go with super short chain stays for traction reasons, as all 29er's I've ridden can claw their way up almost anything with a minimum of technique compared to 26" bikes. The 26" bike I'm currently testing gets gobs of traction, but the rider needs to really use some technique to keep the front end from wandering and coming up on steep climbs. I have a feeling the longer chainstays and steeper seat angles used on many 29er"s make it a comparative no brainer to climb the steep loose stuff.

Personally though I'd give up some of the climbing ability to get a bit more playfulness in the bike. It takes a pretty solid pull to get the front end to come up for log piles and the like. The big wheels seem to require less lift to clear similar size obstacles as a 26", but I like the feel of a bike that wants to get up on it's rear wheel, something I think can be accomplished by a slacker seat angle, shorter chainstays and a higher BB.

This may not be what Ted has in mind of course, but when I think of an east coast single track hardtail, this is how I want it to ride.

[MMcG]

A few actual measurements of some stuff in the basement:

Bianchi Sok SS 08 17 1/4 74º
Raleigh XXIX SS 07 17 3/8 73º
Fisher Paragon 07 17 3/8 72º
Ventana Full-sus 18 1/4 74º
Custom steel SS 17 5/8 ?

Forgot to measure my KM at home but Surly lists it at:

Karate Monkey 17 73º

I haven't found any of these bikes particularly well suited to NE single track, although they all work just fine. I don't see any reason to go with super short chain stays for traction reasons, as all 29er's I've ridden can claw their way up almost anything with a minimum of technique compared to 26" bikes. The 26" bike I'm currently testing gets gobs of traction, but the rider needs to really use some technique to keep the front end from wandering and coming up on steep climbs. I have a feeling the longer chainstays and steeper seat angles used on many 29er"s make it a comparative no brainer to climb the steep loose stuff.

Personally though I'd give up some of the climbing ability to get a bit more playfulness in the bike. It takes a pretty solid pull to get the front end to come up for log piles and the like. The big wheels seem to require less lift to clear similar size obstacles as a 26", but I like the feel of a bike that wants to get up on it's rear wheel, something I think can be accomplished by a slacker seat angle, shorter chainstays and a higher BB.

This may not be what Ted has in mind of course, but when I think of an east coast single track hardtail, this is how I want it to ride.


So are you saying you'd like a bike that would be a bit easier to manual, wheelie, loft the front end for playing on rocks and whatnot? A bike that was a tad bit easier to do small drops and to do wheelie drops and whatnot?

[El Caballo]

It doesn't matter whether the BB shell is wider or not, so long as the spindle length produces a 5mm wider chainline.

You don't even need weird parts. All Truvativ ISIS and square taper cranks, for instance, use a 113mm BB as standard, so all you need for the offset rear is a standard 68x122mm BB -- available from Shimano for about $20.

Yes, this means the XC cranks with integrated spindle won't work, because Shimano didn't want to add 10 extra grams and put a bolt on the drive side like BMX cranks use. As mentioned, you have to use Saints, ISIS, or square taper.

I don't personally think this is much of a sacrifice considering that it fixes all the other problems and uses standard, currently-available parts.

Note for the Q-factor nerds: external BB cranks are wide as hell. A set of Truvativs or Middleburns plus an extra 10mm is probably the same width as a set of new XTs. So I don't think the "too much extra Q" argument is necessarily true.

[eMcK]

So are you saying you'd like a bike that would be a bit easier to manual, wheelie, loft the front end for playing on rocks and whatnot? A bike that was a tad bit easier to do small drops and to do wheelie drops and whatnot?

MMgG,

BINGO.

[MMcG]

MMgG,

BINGO.

I'm right there with ya sir! :clapping::thumb:

[sportcult]

I'm right there with ya sir! :clapping::thumb:

Ditto.

A 29er that could pop up easy and roll would be unstoppable...

[Ted Wojcik]

It appears that the Saint crank/BB system will solve some problems. I might be missing something, but I think that it will require the 150mm rear hub as well to keep the chainline as recommended. What this would mean is that if this frame design went into the market place, it would have to use Shimano Saint if we used up to date parts. Square taper cranks are in the same category as dinosaurs, I'm not a great fan of ISIS. Some manufactures did okay with it, but I have three cranks in the shop with a loose crankarm spindle interface. What is the general opinion on crank/BB selection? I have no problem with asymmetrical frame design, but I would like to keep component selection more versatile. Sooner of later, this frame will end up in somebody's hands that won't realize the design requires special components and then it will be said that Ted Wojcik builds his frames with bad alignment.

[eMcK]

It doesn't matter whether the BB shell is wider or not, so long as the spindle length produces a 5mm wider chainline.

You don't even need weird parts. All Truvativ ISIS and square taper cranks, for instance, use a 113mm BB as standard, so all you need for the offset rear is a standard 68x122mm BB -- available from Shimano for about $20.

Yes, this means the XC cranks with integrated spindle won't work, because Shimano didn't want to add 10 extra grams and put a bolt on the drive side like BMX cranks use. As mentioned, you have to use Saints, ISIS, or square taper.

I don't personally think this is much of a sacrifice considering that it fixes all the other problems and uses standard, currently-available parts.

Note for the Q-factor nerds: external BB cranks are wide as hell. A set of Truvativs or Middleburns plus an extra 10mm is probably the same width as a set of new XTs. So I don't think the "too much extra Q" argument is necessarily true.

I'm in complete agreement that we can use avaliable parts to get the chainline you are looking for, but the idea here (at least as I'm interpreting it) is to use "standard" parts, not ones that will sooner rather than later stop bing supported by the major component makers.

Shimano has stopped production on the UN-7X series BB, the selection of ISIS is getting smaller, and I don't see the major's going back to 3 piece setups anytime soon.

For the record I think the newer external BB cranks are a pretty crappy solution to a problem created by ISIS and Octalink. Higher Q-factor, no real ability to adjust chainline, crappy bearing life, seal drag, expensive...did I miss any? For most XC style riding the old square taper standard was perfectly fine. All my current personal bikes are spinning on at least 2+ year old Shimano square taper BB's, some are over 5 years old.

From what I can tell Ted wants to design this bike around modern components, which means external bearing BB cranks, for better or worse.

[Ted Wojcik]

If possible, I would like to build this frame to use stuff we are still going to be able to buy in 5 years. Oops, I just dropped my crystal ball. I have a ridable mountain bike in the shop that I built in 1984. Fortunately, I still have some N.O.S. parts to keep it going for a while. Remember Freewheels?

[eMcK]

It appears that the Saint crank/BB system will solve some problems. I might be missing something, but I think that it will require the 150mm rear hub as well to keep the chainline as recommended. What this would mean is that if this frame design went into the market place, it would have to use Shimano Saint if we used up to date parts. Square taper cranks are in the same category as dinosaurs, I'm not a great fan of ISIS. Some manufactures did okay with it, but I have three cranks in the shop with a loose crankarm spindle interface. What is the general opinion on crank/BB selection? I have no problem with asymmetrical frame design, but I would like to keep component selection more versatile. Sooner of later, this frame will end up in somebody's hands that won't realize the design requires special components and then it will be said that Ted Wojcik builds his frames with bad alignment.

My idea on cranks would be based on the type of riding this bike is set up for.

Riding around on technical trails for a few hours a time? Wide cranks such as the Saint are A-OK.

A more all-purpose bike that might see some multi-hour epics with large sections of climbing and non-technical terrain interspersed with tech sections? I'd like to see something with a lower q-factor.

Your's and everyone else's mileage may vary though.

[MMcG]

Ditto.

A 29er that could pop up easy and roll would be unstoppable...

This is some thoughts I had posted months and months ago and I thought I'd bring it back here for this thread as it seems somewhat relevant.

My 29er woods bike musings:

Okay,
What do you guys think of a frame set up like this - sort of like a 29er "woods" bike if you will:
1. Seat tube angle 72.5 degrees
2. Head tube angle of 71 degrees with a 4" fork up front (Reba I guess)
3. 16.9" chainstays (possibly a hair shorter as I'd be running this single speed)
4. 23" or 23.25" Effective Top Tube length (with a nice slope to it, maybe even with an evil sovereign like brace on it)
5. 16" or so seat tube with a long post
5. but here's the kicker - a high bottom bracket - say 13.5"

How do you think something like that would ride?? Would the higher bottom bracket help make it easier to loft the front end up over or up on to logs or rocks and whatnot?

The short stays would help keep the rear wheel under me when I was standing and climbing right?

Just for reference - I selected that ETT length based on my previous (and current bikes) and my 5'9" height.

Whattya think???


I'd now change that selection of a Reba to either a new Fox F29 or one of the new RST 100mm air forks which are supposed to offer great bang for the buck and have a 44mm offset.

I had a Single speed in mind when I initially posted this, but I wouldn't object to this type of design in a 2x9 or 1x9 configuration either.

Just thought I'd throw this out there.

Is a bottom bracket that is that high insane? If so, what about say a 12.5 or 12.75" bottom bracket?

[Ted Wojcik]

I think I'll wait until I have the chainstay length worked out before I get into the frame geometry. Cockpit size is something that can be talked about at any time. B.B. height, I would like to turn into drop, that is how far the B.B. center is below axle center. Angles will be talked about at length and I'll offer up some surprises here.

[tozovr]

So are you saying you'd like a bike that would be a bit easier to manual, wheelie, loft the front end for playing on rocks and whatnot? A bike that was a tad bit easier to do small drops and to do wheelie drops and whatnot?


sounds like a bike with shorter stays ;)

[MMcG]

sounds like a bike with shorter stays ;)

Indeedy it does! :monkeydance:

[El Caballo]

I'm in complete agreement that we can use avaliable parts to get the chainline you are looking for, but the idea here (at least as I'm interpreting it) is to use "standard" parts, not ones that will sooner rather than later stop bing supported by the major component makers.
[...]
From what I can tell Ted wants to design this bike around modern components, which means external bearing BB cranks, for better or worse.

Really? The average production life of any post-square-taper standard has been about three years, because they all suck. If external bearing 68/72mm BB cranks are still the standard in five years I will eat a bug.

We've gone through Octalink V1, Octalink V2, ISIS, and now external BBs, and all are doomed. First, there's not enough room in a BB shell for a thicker axle and decent bearings, and if you shove the bearings outboard, you get all the stiffness, friction, sealing, mud-packing, and Q factor problems we all know and hate.

(An aside: everyone knows that we need larger diameter BB shells to really solve the problem. Whether this means the BMX standards of Spanish or Mid BB, Cannondale's BB30, or something else, things are going to change because they have to.)

In the meantime, this is an XC hardtail. If you are so rad that you can break a square taper spindle, you can buy the 83mm Saint integrated cranks. For the rest of us, there are plenty of blingy square taper cranks in production (Middleburn, TA Cyclotouriste) and plenty of cheapies as well (Sugino, Shimano). Current BB production includes UN-5X for the cheap and Phil Wood and Action-Tec for the bling. What are the odds of anyone building Octalink V1 BBs in five years?

[tozovr]

Really? The average production life of any post-square-taper standard has been about three years, because they all suck. If external bearing 68/72mm BB cranks are still the standard in five years I will eat a bug.

We've gone through Octalink V1, Octalink V2, ISIS, and now external BBs, and all are doomed. First, there's not enough room in a BB shell for a thicker axle and decent bearings, and if you shove the bearings outboard, you get all the stiffness, friction, sealing, mud-packing, and Q factor problems we all know and hate.

(An aside: everyone knows that we need larger diameter BB shells to really solve the problem. Whether this means the BMX standards of Spanish or Mid BB, Cannondale's BB30, or something else, things are going to change because they have to.)

In the meantime, this is an XC hardtail. If you are so rad that you can break a square taper spindle, you can buy the 83mm Saint integrated cranks. For the rest of us, there are plenty of blingy square taper cranks in production (Middleburn, TA Cyclotouriste) and plenty of cheapies as well (Sugino, Shimano). Current BB production includes UN-5X for the cheap and Phil Wood and Action-Tec for the bling. What are the odds of anyone building Octalink V1 BBs in five years?


$55 a season is cheap...cheaper than one lift ticket.:busted:

[Ted Wojcik]

We all know that Shimano has been answering questions we never asked for a long time. The cold hard reality is that obsolescence has been the marketing strategy of our Asian friend for some time. The most enduring design has been the square taper and for many reasons, would be my choice. Our components require updating, not because of short life by design, but short life by ending manufacture. When most of my clients pick up their new frame, they are seldom looking forward to equipping it with old school parts. The problem with a bigger shell to accommodate bigger bearings is the taps (?), reams, or other machining required to produce the new design. The LBS wants parts that are available from any distributor and doesn't want to get another batch of tools to service it. And speaking of service, how about the poor bike tech? Another tech school to attend. This design needs to be versatile enough to use any components. I don't want to reinvent the bicycle here. let's see what we can do with what we have and make the frame to present production standards.

[MMcG]

Square taper would be fine by me. You can still get high quality cranks (Middleburns come to mind) and there are still bottom brackets of high quality available are there not?

Is the BB width the main issue with how long the chainstays can be anyway? I don't know the answer - just throwing the question out there.

[sportcult]

Wow, I've had just the opposite experience...I've rounded out many a square taper spindle while having nothing but good experiences with ISIS. I've taken my crank arms on and off many, many times and the interface is still just as tight as the first build. This includes Race Face, Truvativ, and Middleburn mixed and matched with several BB's. My longest lasting, never die cranks and BB are Shimano XTR M950's. I got a very used set 10 years ago and 5000+ miles later I'm still torquing on them on my 29er single speed. I still haven't used the newer external types yet.

[tozovr]

Wow, I've had just the opposite experience...I've rounded out many a square taper spindle while having nothing but good experiences with ISIS. I've taken my crank arms on and off many, many times and the interface is still just as tight as the first build. This includes Race Face, Truvativ, and Middleburn mixed and matched with several BB's. My longest lasting, never die cranks and BB are Shimano XTR M950's. I got a very used set 10 years ago and 5000+ miles later I'm still torquing on them on my 29er single speed. I still haven't used the newer external types yet.


me too...same same (except I have used externals and dig them)

[eMcK]

Sounds like a standard English BB shell in either 68 or 73 will allow everyone to use what they have/want.

[capt.crispy]

I still have a set of 9 year old race face sguare taper cranks and they work fine but I have to take them off every now and then and clean and retighten them more often than my external bb race face and saints.

Although I agree the siants would be wierd and alot of people wouldn't realize you need that specific chainline for the frame .

[sportcult]

Something seems very backwards here. Designing a frame around a specific Shimano part seems like the best way to guarantee that it will be obsolete and incompatible with anything else in 2 years.
If we're trying to plan ahead for 5 years down the road, maybe we should assume that the component companies will make a modification to the front derailler that gives it the proper clearance to work with the flooding market of 29ers...

[sportcult]

So where does the tire hit the derailler? On the tail of the cage? On the cable pulley? Does anybody have a picture? I held up a low clamp XT front derailler to my frame and it doesn't look like the tire would interfere with it unless it was all the way up against the cable pulley. It would take pretty short stays to reach that.

[MMcG]

This frame has 17" chainstays - and look how close the rear tire (and it is not a big wide tire) comes to the front derailleur without any bend to the seat tube. And from the picture that's with the chain in the middle ring too.

http://i109.photobucket.com/albums/n60/MMcG25/doberman29er.jpg

[eMcK]

Ted,

how would a seat tube/BB junction like this work? The small tube could be set at a steep angle to get some tire clearance for the front derailer cage, while the actual seat tube could be angled to get the effective seat tube angle wanted.
http://www.ridemonkey.com/mountain-bike-photos/data/500/26009seat_tube.jpg

No need for fancy bending, just an extra miter or two and a bit more work with the welder.

[Psychic_Pimp]

Ted,

how would a seat tube/BB junction like this work? The small tube could be set at a steep angle to get some tire clearance for the front derailer cage, while the actual seat tube could be angled to get the effective seat tube angle wanted.
http://www.ridemonkey.com/mountain-bike-photos/data/500/26009seat_tube.jpg

No need for fancy bending, just an extra miter or two and a bit more work with the welder.

I was just thinking about this same type of solution and trying to remember where I have seen this done, perhaps pics from the handmade bike show?

The question is, what is this a solution to? It can allow more clearance between the tire and seat tube but it won't make more room for the derailleur. The derailleur has to stay centered around the BB and chainrings. Moving the seat tube forward necessitates using an E-type derailleur mount but doesn't move it forward.

[MMcG]

Is it really really difficult to bend the seat tube ever so slightly in the right spot? For example - the guy who builds those wolfhounds has significant bends in a lot of his tubes that he uses? couldn't the seat tube be bent just sliglty to allow for a bit more clearance and still accept a standard front derailleur?

Brant at On-One gave me permission to post this as an example:

http://images.fotopic.net/?iid=yqqdih&noresize=1&nostamp=1&quality=70

Although it still seems like an e-type or a modified e-type like Specialized is doing these days is the way to go.

[MMcG]

Sorry for the ginormous photo.

Perhaps I should just provide a link instead?

[jncarpenter]

Sorry for the ginormous photo.

Perhaps I should just provide a link instead?
...looks fine on my monitor ;)

[MMcG]

That is good.

Here's something that Brant put out there and It how has me thinking and wondering.

Are shorter stays better for Single Speeding vs. geared riding where you could have the ability to stay in the saddle longer on climbs?

[eMcK]

I was just thinking about this same type of solution and trying to remember where I have seen this done, perhaps pics from the handmade bike show?

The question is, what is this a solution to? It can allow more clearance between the tire and seat tube but it won't make more room for the derailleur. The derailleur has to stay centered around the BB and chainrings. Moving the seat tube forward necessitates using an E-type derailleur mount but doesn't move it forward.

The main problem with the front derailer I've seen is tire contact with either the cable pinch bolt, and/or some other part of the cable leverage mechanism. Rotating the front derailer forward would free up a bit more space behind the seat tube.

If you look closely at the bike below you can see where the rear tire is overlapping the front derailer. I saw this bike at Interbike and the tire was firmly pressed into the front derailer. It may have been a preproduction sample, as the geoemtry on the Jamis website seems to long and steep(17.72", 73º) to have this much contact. http://www.jamisbikes.com/usa/bikes/08_bikes/images/08_bike_images/08_DRAGON_29.jpg

The other idea here was to not lock someone into an E-type derailer and help keep the seat tube out of the way if a slacker angle was used(which I'm all for).

[Ted Wojcik]

The main problem as I see it, is the tail of the front dérailleur cage hits the tire. Now as the new stuff has all the crap for top/bottom pull cables, it gets more complicated. E type answers the cable routing issue. I have the parts coming to build a mock up to check these clearances. Sorry about the delay, but we will have to wait until after I eat the bird.

Happy Thanksgiving

[Possum]

Bending a seat tube is a bit of a bitch.

First, you generally need to use a softer tube, like 4130, as the "better" tubing is a little more brittle and will generally kink/fail when you bend it.

Second, you generally have to create your own mandrel for bending a tube. You've got to decide on the radius you want, and the route a mandrel out of plywood or some other material with the correct tubing OD radiused into it. Fill your tube with sand, and the start bending.

You also (generally) have to use straight-gauge tubing, because you will kink your tubing at the butt interface on butted tubing (usually).

It's not generally something that a builder wants to invest the time in unless he/she plans to do it on a somewhat regular basis (like Curtis Inglis at Inglis/Retrotec).

I have 17.75" chainstays on my bike, with a 73mm shell. We still had to hand-bend the Zona stays a bit more than stock to get sufficient clearance for my 2.3 Resolutions. You may think that 17.75" is "long", but my bike manuals very well. There's more to a custom bike build than just the raw numbers on the drawing. Many other factors can add in to make this bike handle the NE singletrack.

With these wider tires and short stays, you also run the risk, as someone pointed out, of catching the cage with the side knobs of the tire.
^^looks like Ted and I were typing at the same time^^

[MMcG]

I have 17.75" chainstays on my bike, with a 73mm shell. We still had to hand-bend the Zona stays a bit more than stock to get sufficient clearance for my 2.3 Resolutions. You may think that 17.75" is "long", but my bike manuals very well. There's more to a custom bike build than just the raw numbers on the drawing. Many other factors can add in to make this bike handle the NE singletrack.




Your 17.75" chainstay frame - is it a Badger by any chance?

[Psychic_Pimp]

The main problem with the front derailer I've seen is tire contact with either the cable pinch bolt, and/or some other part of the cable leverage mechanism. Rotating the front derailer forward would free up a bit more space behind the seat tube.

If you look closely at the bike below you can see where the rear tire is overlapping the front derailer. I saw this bike at Interbike and the tire was firmly pressed into the front derailer. It may have been a preproduction sample, as the geoemtry on the Jamis website seems to long and steep(17.72", 73º) to have this much contact.

The other idea here was to not lock someone into an E-type derailer and help keep the seat tube out of the way if a slacker angle was used(which I'm all for).

If you're still referring here to the drawing you posted earlier, I do understand what you're trying to do and why. Here's the problem; the seat tube where a clamp-type derailleur attaches must be perpendicular to the bottom bracket or the cage won't match the chain rings' radius properly. Moving the bottom of the seat tube forward of the bb center to any appreciable degree would throw that off and necessitate an E-type der. It's a catch-22. Often the simple fixes just give you a different problem to deal with.

The frames I have seen with bent seat tubes still have a place to clamp on the derailleur that is directly in line with the bb. The Karate Monkey, Sinister Simon Bar, the new Specialized, and the fancy Scandal Mark posted all have this.

As an aside, it is possible that the problem you point out with the Jamis could be cured by simply using a low-clamp derailleur. My XXIX+G came with a low clamp and it was a pretty tight fit. I tried a high clamp like the one on that Jamis and it didn't help.

I have actually run into three different derailleur/tire interference problems on 29ers so far; back end of cage, cable pinch bolt, and the cable itself crossing too close to the tire.

[tozovr]

Bending a seat tube is a bit of a bitch.

First, you generally need to use a softer tube, like 4130, as the "better" tubing is a little more brittle and will generally kink/fail when you bend it.

Second, you generally have to create your own mandrel for bending a tube. You've got to decide on the radius you want, and the route a mandrel out of plywood or some other material with the correct tubing OD radiused into it. Fill your tube with sand, and the start bending.

You also (generally) have to use straight-gauge tubing, because you will kink your tubing at the butt interface on butted tubing (usually).

It's not generally something that a builder wants to invest the time in unless he/she plans to do it on a somewhat regular basis (like Curtis Inglis at Inglis/Retrotec).

I have 17.75" chainstays on my bike, with a 73mm shell. We still had to hand-bend the Zona stays a bit more than stock to get sufficient clearance for my 2.3 Resolutions. You may think that 17.75" is "long", but my bike manuals very well. There's more to a custom bike build than just the raw numbers on the drawing. Many other factors can add in to make this bike handle the NE singletrack.

With these wider tires and short stays, you also run the risk, as someone pointed out, of catching the cage with the side knobs of the tire.
^^looks like Ted and I were typing at the same time^^

FTW's process, as told by him...

http://www.ridemonkey.com/mountain-bike-photos/data/500/143915.JPG

http://www.ridemonkey.com/mountain-bike-photos/data/500/143916.JPG

[eMcK]

If you're still referring here to the drawing you posted earlier, I do understand what you're trying to do and why. Here's the problem; the seat tube where a clamp-type derailleur attaches must be perpendicular to the bottom bracket or the cage won't match the chain rings' radius properly. Moving the bottom of the seat tube forward of the bb center to any appreciable degree would throw that off and necessitate an E-type der. It's a catch-22. Often the simple fixes just give you a different problem to deal with.

The frames I have seen with bent seat tubes still have a place to clamp on the derailleur that is directly in line with the bb. The Karate Monkey, Sinister Simon Bar, the new Specialized, and the fancy Scandal Mark posted all have this.

As an aside, it is possible that the problem you point out with the Jamis could be cured by simply using a low-clamp derailleur. My XXIX+G came with a low clamp and it was a pretty tight fit. I tried a high clamp like the one on that Jamis and it didn't help.

I have actually run into three different derailleur/tire interference problems on 29ers so far; back end of cage, cable pinch bolt, and the cable itself crossing too close to the tire.

The drawling I posted was pretty sloppy and perhaps didn't get at what I wanted. The shorter tube would still be centered on the BB, mimicking a steep seat tube angle, while the actual seat tube would give a "vitual" angle of whatever was wanted by the builder or rider, effectively separating the seat tube angle from the front derailer mounting position. This can be accomplished with an E-type front derailer also, but I'm not a fan of the top-swing style derailer, mostly because they fill up with mud and freeze much more easily than the tradition swing type.



What I was after was a steep seat angle for derailer clearance and and a slacker one to position the rider a bit futher back, I was hypothesizing this was one possible answer that avoided bending tubes and an E-type derailer.

[Psychic_Pimp]

The drawling I posted was pretty sloppy and perhaps didn't get at what I wanted. The shorter tube would still be centered on the BB, mimicking a steep seat tube angle, while the actual seat tube would give a "vitual" angle of whatever was wanted by the builder or rider, effectively separating the seat tube angle from the front derailer mounting position. This can be accomplished with an E-type front derailer also, but I'm not a fan of the top-swing style derailer, mostly because they fill up with mud and freeze much more easily than the tradition swing type.



What I was after was a steep seat angle for derailer clearance and and a slacker one to position the rider a bit futher back, I was hypothesizing this was one possible answer that avoided bending tubes and an E-type derailer.

Ah, I think I understand for real now, I was not seeing that you wanted to mount the der. on the short tube. The length of the shorter tube would be rather longer than I had imagined, especially if you use a high clamp derailleur. Well, as an extra added bonus, the extra 9 or more inches of seat tube is sure to offend weight weenies.

[greenchris]

^^^^
Weight weenies don't ride steel bikes.

[Possum]

Your 17.75" chainstay frame - is it a Badger by any chance?

Yup. The baby blue one that you've seen on mtbr.

[MMcG]

Yup. The baby blue one that you've seen on mtbr.


Did you select the chainstay length or did Rob Pennell? BTW, that's a gorgeous bike.

[Possum]

The overall bike is pretty close to the 19" Dorothy, with a few tweaks that Rob and I discussed. The chainstay is the standard, and Rob and I discussed it a bit, and I decided to go with his recommendation.

The bike rides extremely well as a whole package. I have no problems with manuals or un-weighting the front end during seated climbing (I prefer to do as much climbing as possible seated if I have gears). There's no tipover fears, but I can get the front end as light as I want it with body position.

That's part of the reason that I keep driving questions about the chainstay length, b/c so many people keep talking about the need for short chainstays on a 29er. I've ridden short(ish) chainstays, and these are "longer" at 17.75, and the bike rides extremely well.

It simply made me re-think my whole "gotta have super short stays" thing.

Thanks for the compliments on the bike. I gotta get back out on it. I taco'd the front wheel in Arkansas and then started a bunch of work on my house. Gotta get that wheel built back up (Flows this time).

[MMcG]

Perhaps shorter stays are more effective for Single Speeds than geared bikes. Maybe the initial 17.5" that Ted mentioned would be fine. Perhaps there are other "tweaks" to the frame to make it easy(ier) to manual, wheelie, loft the front end. Perhaps a taller head tube might help with that?

I'm really digging this thread. Let's keep the thoughts and ideas and even the ramblings flowing folks. :thumb:

[MMcG]

Just to update things a bit. I met Ted for coffee on Thanksgiving and he's got a lot of great ideas cooking for this frame and bikes in general. Super nice guy too! :thumb:

[sportcult]

I'm also doing my research. I should be riding a bike with 16.75" stays by the end of the week. I'll report back what differences I feel compared to my current 17.9" setup...

[MMcG]

I'm also doing my research. I should be riding a bike with 16.75" stays by the end of the week. I'll report back what differences I feel compared to my current 17.9" setup...

Going for one of the Origin-8 Scouts are ya?

[sportcult]

Yeah, I wanted to get tozovr's Simon Bar frame, but that didn't work out, so I opted to go ahead and try the Scout. It's cheap and if I'm going to try short stays, might as well have the option of going as short as possible.

[MMcG]

Yeah, I wanted to get tozovr's Simon Bar frame, but that didn't work out, so I opted to go ahead and try the Scout. It's cheap and if I'm going to try short stays, might as well have the option of going as short as possible.

Cool - send me a PM as to where you are getting it from.

Best,

Mark

[bcd]

Welcome to the Monkey!

Your comment on the Fox fork makes me wonder if somewhere down the line we'll see a Fox 29er Talas model on the market.

soon, hahaha

[bcd]

what about 2x5. putting the granny in the middle position.
i am all about it. 94mm bcd is back with fsa 4 bolt!
44x29 front with 12-16-21-26-32 dishless rear wheel. plenty of
range. then w/o a granny so far into the center your f der should
clear any fat tire w/17 cs no bent seat tube.


https://www.bti-usa.com/images/thumbnails/large/fs/fs1102.jpg

[MMcG]

what about 2x5. putting the granny in the middle position.
i am all about it. 94mm bcd is back with fsa 4 bolt!
44x29 front with 12-16-21-26-32 dishless rear wheel. plenty of
range. then w/o a granny so far into the center your f der should
clear any fat tire w/17 cs no bent seat tube.


https://www.bti-usa.com/images/thumbnails/large/fs/fs1102.jpg

This is interesting stuff. ARe these new cranks for 2008?

[bcd]

This is interesting stuff. ARe these new cranks for 2008?

the carbon ones are yes. 2x9 is not new really,
but i think it would work for 29er app real well.

4x94 bcd is new.

used to be 5x94.

[MMcG]

I thought the 4x94 bcd was new.

Not sure about the five speed rear cassette though? Why not 2x8 or 2x9? Won't work as well?

[bcd]

I thought the 4x94 bcd was new.

Not sure about the five speed rear cassette though? Why not 2x8 or 2x9? Won't work as well?

it would work fine. i am just so sold on dishless rear and
minimizing the amount of parts you need to ride a bicycle.

i like ss but for all around geared bike i have found i don't
need 9 speed cass.

[MMcG]

it would work fine. i am just so sold on dishless rear and
minimizing the amount of parts you need to ride a bicycle.

i like ss but for all around geared bike i have found i don't
need 9 speed cass.


I hear ya. I think the goal for this "project" however is to design a frame that anyone could put components on and ride it.

With that said - your 2x5 drivetrain idea sounds pretty damned cool.

[bcd]

I hear ya. I think the goal for this "project" however is to design a frame that anyone could put components on and ride it.

With that said - your 2x5 drivetrain idea sounds pretty damned cool.

well a 2x9 could bolt on too. the main concern an any short cs 29 geared bike is f der to fat rear tire. there are only two way of going about it.

rotate the seat tube around the bb center.
move the f der out from the tire by
A - widening the bb width.
B - only run 2 rings in the front.

no miracle cure out there that i see.
pretty cut and dry.
alex

[indieboy]

running two chainrings on mtns is the way to be son

[Ted Wojcik]

I measured a WTB Exiwolf 2.3 and got a rolling diameter of 29.375 with about 45 lbs of air. Here is the beginning of our drawing showing a chanistay length of about 17.25 without any magic. Remember the first of Fat City bikes had chainstays of 17.25" and started the tradition of New England Single Track. As we go on we will try to have a weight distribution close to a 26" wheeled bike using 16.75" chainstays. With the use of Paragon sliders, we can set the distance from the tire to the seat tube to a minimum distance.
Stay tuned.

[sportcult]

What's the range on the paragons? It would be cool if the sliders were placed such that the chainstay length was 17.25 with them all the way back for those running gears, while single speeders could run them shorter.
What went into your bottom bracket drop number of 2.25?

[MMcG]

I like something along the lines of sportcult's idea. Paragons at 17.25 for gears, but maybe with the ability to slide them in even more for single speeders or 1x8 or 1x9 or 1xwhatever riders. :thumb:

[Ted Wojcik]

What will happen is the sliders will alloy a few different tire sizes without rubbing on the seat tube. I think we will end up using an e-type front dérailleur to keep clearance. As we go on I'll talk a bit about B.B. drop and it's effect on stability. I think 2.25" drop with give about a 12.3 B.B. height with tire squish. With the 2.3 Exiwolf.

[sportcult]

What will happen is the sliders will alloy a few different tire sizes without rubbing on the seat tube. I think we will end up using an e-type front dérailleur to keep clearance. As we go on I'll talk a bit about B.B. drop and it's effect on stability. I think 2.25" drop with give about a 12.3 B.B. height with tire squish. With the 2.3 Exiwolf.

What length fork is that assuming? (a-c)

[Ted Wojcik]

I haven't set the fork length yet, but I'm voting for 80mm travel. I would draw the frame around an a-c length of 485mm

[MMcG]

An 80mm fork sounds good to me for this type of singletrack carver bike. If someone prefers a slightly slacker front end - well they'd still have that type of option to go 100mm and slacken things out a tad. It seems to make more sense than the opposite - setting it at 100mm and then if someone wanted less travel they'd have a wicked steep HT angle.

Man I can't wait to see this frame and thread evolve.

[Ted Wojcik]

Good morning. If you would like to take a look, here is the drawing we are working on. I will put in the details later today

[MMcG]

I like the slope of that Top Tube. :thumb:

[Ted Wojcik]

Here is the drawing,. More detail will be added as things go on. Photos coming soon

[pinkshirtphotos]

if i understand correctly your toe will be in the path of the tyre when you are at 3 and 9? is this with all 29ers or just your frame (never really cared to notice before)

[sportcult]

Just built up a new frame with some interesting numbers that relate to this project. Here are some pics:

Frame: Origin-8 Scout29 (size 18")
4130 chro-moly

chainstays as shown are 16.75"
BB height is 12.75", shell is 68mm
rear tire is Kenda Karma 1.9
Fork is 490mm a-c

side view to give an idea of the geometry:
http://www.pullpedalpaddle.com/Images/bikepron/scoutside.jpg

tire clearance:
http://www.pullpedalpaddle.com/Images/bikepron/scoutclearance.jpg

As you can see this is nearing the practical limit on stay length. With a little wider bottom bracket and manipulated or machined stays and bridges, larger tires could be accommodated at this length. With this size tire there is also clearance for a standard XT front derailler.

[MMcG]

That's a cool frame - looks choppered a bit with that Niner fork though (still bent is it?)

[MMcG]

Ted - that bb drop on the frame = what in terms of BB height?

Your drawings have helped me understand what bb drop is - thanks for that.

Is that now a 17" seat tube instead of an 18?

The Monkey Butt - I like it.

Best,

Mark

[Ted Wojcik]

It looks like there is toe clip overlap, but because the crank arms are away from the centerline, and the wheel will travel in an arc about the steering axis, I don't think there will be any interference. With a tire diameter of 29.375 and a B.B. drop of 2.25, that will give us a B.B. height of 12.4375 not considering tire squish. This design can easily be changed to an 18" frame if we want, It seems that we already have someone willingl to buy a 17", so I thought I would save time and draw it as a 17.

Ted

[sportcult]

That's a cool frame - looks choppered a bit with that Niner fork though (still bent is it?)

It's at 50mm rake right now. I'm still trying to figure out if I like it better or worse than 60mm...60mm was pretty cool.

[Psychic_Pimp]

Ted, I would like to hear your take on extending and gusseting the seat tube like the Scout. Perhaps its just an aesthetic issue for me but the ever-extending seat post bugs me somehow.

What are the pros and cons, from the mind of the frame builder, of making that seat tube, say 21" and giving it a gusset for support?

[Ted Wojcik]

The issue I have with an extended seat tube with a gusset is that when the gusset is welded on, there is significant distortion of the top part of the tube. This makes reaming the tube a bit of a PIA. I like to use an externally butted seat tube and the butted section is not long enough to allow much of an extension. I think it is best to have a good amount of the seatpost go below the top tube seat tube intersection and prefer not to have any more steel in the frame than needed

[tozovr]

if i understand correctly your toe will be in the path of the tyre when you are at 3 and 9? is this with all 29ers or just your frame (never really cared to notice before)

I find it particularly hard to continue forward progress when my wheel is at 3 and 9:busted:

[MMcG]

It looks like there is toe clip overlap, but because the crank arms are away from the centerline, and the wheel will travel in an arc about the steering axis, I don't think there will be any interference. With a tire diameter of 29.375 and a B.B. drop of 2.25, that will give us a B.B. height of 12.4375 not considering tire squish. This design can easily be changed to an 18" frame if we want, It seems that we already have someone willingl to buy a 17", so I thought I would save time and draw it as a 17.

Ted

I like that bottom bracket figure -should still keep it within 12" or so even if someone were to run Stans and low PSI in their tires.

Will this design feature sliding dropouts or standard vertical rear dropouts?

[Ted Wojcik]

I will put up some photos over the weekend. Sub 17" stays with sliders XT front der, 2.3 tire, and LX crank. I'm trying to make a 29er mainstream.

[indieboy]

i don't get whats wrong with "long" stays

[Ted Wojcik]

What I'm trying to do here is make a 29" wheeled mainstream mountain bike that shines in New England single track. The priority is the ability to turn and burn, point and shoot. Long bikes don't make the grade. The challenge is big wheels. The bike needs a long front center, that is the distance from the bottom bracket to the front axle, to prevent toe overlap and short chainstays to weight the rear wheel to help with lofting the front wheel. We know that a 29" rear wheel has more traction, but the bigger front wheel is heavier, so lofting will be harder. Light weight is important. It is the mass of the bike that needs to change direction, so the lighter the better. Short bikes mean less steel. When it is all done, we will see what the road tester has to say. I have put the chainstay/B.B. assembly together today and I'm happy with the way things are going. Stay tuned

[sportcult]

Rode the 16.75 stays today for the first time. I'm not going to comment fully on it until I've had a week or so in the saddle, but they do make an immediate difference in pulling the front up. The high (12.75) BB also allows you to carry much more speed through rock gardens...There may be a couple drawbacks as well, but I need to get used to the whole new setup before coming to any conclusions...