my fisher ferrous has 440mm = 17.3" chainstays. which is the same number you got empirically. it came w/ a sram drivetrain. i believe you can run a sram f. derailleur w/ shimano shifters, but can't mix and match sram r. der's & shimano shifters because of 1:1 actuation ratios for sram and 2:1 for shimano. there may be a workaround, but it's nice that you are trying to build the bike with off the shelf components that are readily available.
Frame design
- Thread starter Ted Wojcik
- Start date
Quite a few years ago, Shimano had a policy of only selling complete parts picks to a manufacturer. This made the manufacturer have unused parts if they wanted to use someone else's shifters or brakes or headset, etc. SRAM found that it was very difficult to get any OEM content because of this. A law suit evolved claiming a violation of free trade in the USA. Shimano concentrated on making Shimano compatible with Shimano. Sram's shifters were available to work with Shimano dérailleurs, but now it looks like SRAM wants to run their own dérailleurs and seem to have mostly the 1:1 shifter ratio. The Attack range is all that remains Shimano compatable. I really would like to keep frame design open to any component, but now it seems for the 29er's, there may be choices that offer advantages. I don't really think that a .3" longer chainstay is going to make the design inferior, but to optimize all aspects is the intent. At one time, it was possible to make sub 20lb hardtails. When I was asked how it was done, I answered it was a little bit of weight saved everywhere. To try to make this bike as nimble as possible, I want to make sure attention is paid everywhere.
Here is a quick shot of a frame I'm finishing up, so the jig will be empty for the MonkeyView attachment 93409
View attachment 93410 Butt.
View attachment 93410 Butt.
The frame you are finishing? 29er?
Do certain tubes get "stamped" with 26 or 29 or road etc? Because on that bottom bracket/chainstay shot I can make out a 29 label on the chainstay tube.
Do certain tubes get "stamped" with 26 or 29 or road etc? Because on that bottom bracket/chainstay shot I can make out a 29 label on the chainstay tube.
No marks on the tubes to identify frame type. The 29 you see is part of a heat treat number for aircraft grade 4130. The frame is a messenger bike built with straight gauge chainstays.
Thanks for the reply. Sounds like it should be a sturdy bike for someone to pedal like crazy for many years.
I haven't forgot about this frame. I have to finish some client's frames and I'm waiting for some tubing. Any suggestions on braze-ons or other details?
how about a stage race number plate under the front of the TT.
then make a little sign that says "best east coast 29er"
Other Details......hmmmmm.......I think you mentioned that you'd also do a rigid fork to go along with the suspension fork for the "Monkey Butt" - if so, it would be cool if that fork matched up nicely with the rear triangle. So for example, a unicrown fork rather than a segmented fork since I think all of the builds I've seen from you feature non-segmented seat stays (ass opposed to say Sycip or the On One look).
Who ever said it was?
Down tube fender mounts?
What are your plans for cable stops? I'd like to see the option of running full housing for the rear brake.
segmented forks and 29ers aren't the best of friendsWho ever said it was?
please elaborate
neither are reality and your comments...
I think we are the ones asking for you to explain.
Segmented forks have been done by On One, Waltworks builds em, as do others.
I'm genuinely curious to learn more about why you made the statement, so please do elaborate. I know I'd find it helpful if you did.
who are you referring to? and why are segmented forks bad for 29ers?
Yep, count another as perplexed. What exactly makes segmented forks and 29r's a bad blind date?
Off hand, On one, Walt, Retrotec, Sycip, Hunter, Iglehart, Bontrager, DT, Fetish, Black Sheep, and a few others make them. Granted, Bontrager, DT, and Fetish are carbon or Alu, but in essence they're still segmented. Kinda hard to call any of those guys slouches with a torch indieboy.
Ok, you snuck in before I did. Iglehart indeed does make one. We can all sign up to win one over at dirtrag. If you really wanted to we could drag Walt into this. He loves talking about this kinda nonsense.
Off hand, On one, Walt, Retrotec, Sycip, Hunter, Iglehart, Bontrager, DT, Fetish, Black Sheep, and a few others make them. Granted, Bontrager, DT, and Fetish are carbon or Alu, but in essence they're still segmented. Kinda hard to call any of those guys slouches with a torch indieboy.
Ok, you snuck in before I did. Iglehart indeed does make one. We can all sign up to win one over at dirtrag. If you really wanted to we could drag Walt into this. He loves talking about this kinda nonsense.
edit this:
from his site:
"The Penguin is a well dressed bird for all occasions. A super all purpose bicycle with the endurance racer in mind. A full compliment of Columbus Life tubing brought together around 29'ers (700c wheels)...Of course the frame is paired with the traditional new england segmented crown fork...
The Penguin is the culmination of twenty years mountain biking and building experience assembled for the rider who values practicality and function above all..."
Please show me a fork that is not a lever...
the fork won't see a larger bending moment because its segmented. furthermore, if it is designed correctly and manufactured right it will be fine.
<- happy segmented disc fork rider
what about running cables through the frame?
The point I think he is making is that it is not an OPTIMAL design for such a long fork. There are not very many butted fork blades available in sufficient weight and butt profile to make a segmented fork for a long crown to axle 700c offroad wheel.
Judging what a small builder can do in the US against what some company that has 300 forks at a time produced in asia is not fair.
Someone who only makes 100 or so forks a year, TOTAL (of all wheel sizes, etc..) can't get access to custom drawn and profiled tubing to make an optimal segmented fork.
The added length of the fork blade in a segmented fork is crucial to this analysis.
Because segmented forks just recently came back into vogue all the fork blades that a small builder can get are optimized for uni-crown or brazed crown construction. Usually you then end up using either straight gauge tubing (way heavier than a good unicrown blade), or butted tubing of about the right profile fdesigned for a different application for a segmented fork.
For a long travel suspension corrected segmented 29'er fork you would need a fork blade of 460mm or more before you start mitering it. That's long! Most anything on the market that is that long is also pretty tapered at the dropout end, making adding the disc tabs a real chore, and uglying it up.
The reputable builders who build segmented 29er forks are doing them for shorter A-C lengths only.
My guess would be that those folks who are making longer segmented disc 29'er forks are building a fork that has nothing but disadvantages when compared to unicrown fork in that same length, and that they are making it out of inferior materials to achieve aesthetic goals and marketshare.
If any of those guys are ponying up to get 30 sets of legs drawn at a time I'll withdraw my criticism, but otherwise, it's yet another case of Fad and Fashion Over Function, which I think is a criticism that can be applied to a large part of the designs we are seeing built around 700c wheels for offroad use.
That's my two cents.
I can't wait to see the finished product of this thread. For something that was designed by committee on an internet messageboard (a truly Orwellian tragedy), I think this will be a pretty cool frame!
I think you are trying to make a point unique to your vantage point.
Whether or not it is economical to make an OPTIMAL segmented fork is an entirely new question and wouldn't be resolvable without a working definition of the word OPTIMAL.
At the risk of repeating myself I'll say it again. If the fork is segmented or of a unicrown design the maximum bending stresses the forks will see will be the same if A-C are the same. For a basic example consider the On One fork (segmented 470 mm A-C) and the Surly KM fork (unicrown 468 mm A-C). These will have a global max bending stress within 99.57% of one another as it is a function of A-C under idenitical loading conditions. Both will take you out and back on a bike ride without issue.
Whether or not it is economical to make an OPTIMAL segmented fork is an entirely new question and wouldn't be resolvable without a working definition of the word OPTIMAL.
At the risk of repeating myself I'll say it again. If the fork is segmented or of a unicrown design the maximum bending stresses the forks will see will be the same if A-C are the same. For a basic example consider the On One fork (segmented 470 mm A-C) and the Surly KM fork (unicrown 468 mm A-C). These will have a global max bending stress within 99.57% of one another as it is a function of A-C under idenitical loading conditions. Both will take you out and back on a bike ride without issue.
Let's save the dialog. I have a set of nice fat uni fork blades for the fork.
Segmented forks. Work verses benefit. Tell me the benefit in factual terms.
Segmented forks. Work verses benefit. Tell me the benefit in factual terms.
Esteemed Mr Wojick,
I'm with you, the one and only benefit of segmented forks I can see, besides looking pretty bitching, is well...
When building custom forks in normal length you have a few more parameters to play with in terms of tube selection or offset with a segmented though. For a light rider you could likely build a lighter fork. When optimal strength-weight is really important, I'll take a uni-crown any day. Plus it's 4 less miter cuts and significantly easier fixturing.
Donkey-
I guess my vantage point is the real world then?
The parts to make the forks to an equivlanet strength-weight ratio are not available. That is a very important consideration from my point of view. If something is of no benefit, why do it?
I'm with you, the one and only benefit of segmented forks I can see, besides looking pretty bitching, is well...
When building custom forks in normal length you have a few more parameters to play with in terms of tube selection or offset with a segmented though. For a light rider you could likely build a lighter fork. When optimal strength-weight is really important, I'll take a uni-crown any day. Plus it's 4 less miter cuts and significantly easier fixturing.
Donkey-
I guess my vantage point is the real world then?
The parts to make the forks to an equivlanet strength-weight ratio are not available. That is a very important consideration from my point of view. If something is of no benefit, why do it?
I'm going to second Mickey on this. Benifits, I've always considered the bulk of segmented forks to be stiffer, which lends itself well to the longer AC of the 29" world. As a brief disclaimer I have yet to touch a segmented 29" fork. But at the end of the day it still comes down to "what can you make, and make well." I thought Doberman was trying to produce a light segmented 29" fork...but my memory is hazy at this hour.
But is it really Orwellian, it doesn't seem psuedo-utopian enough?
It is cool to get these explanations and again I think this frame would look great with a unicrown fork up front.
I appreciate it when people make posts that have explanations and reasons behind them (which Indieboys initial post did not)
And ultimately Ted has the final say on what becomes of this frame - I appreciate his asking us folks for some input.
It is kinda wild doing a frame via a message-board like this, but ultimately I think the finished product might just rock. Especially if we keep the input and lively and so far friendly and positive dialogue going.
Cheers,
Mark
I appreciate it when people make posts that have explanations and reasons behind them (which Indieboys initial post did not)
And ultimately Ted has the final say on what becomes of this frame - I appreciate his asking us folks for some input.
It is kinda wild doing a frame via a message-board like this, but ultimately I think the finished product might just rock. Especially if we keep the input and lively and so far friendly and positive dialogue going.
Cheers,
Mark
I have resisted telling this story because it could be taken as sour grapes. This is how the segmented fork came to be. In 1985 or so, one of my clients came to me requesting a fork suitable for his new Merlin Ti mtn. frame. This was a time when frame builders were squishing and bending tubes to make frames "more vertically complient and torsionally rigid. His name was Ted Stear. He said he wanted a fork to match the ride characteristics of the Ti frame. I wondered how I was going to do this without making an armload of forks to try. I made a tubular steerer crown assembly that could accommodate a variety of 1" fork blades. We used sections of butted top tubes, straight gauge tubing and straight 1" fork blades to find a feel that went along with The more flexible Ti frame, or so we thought. This was done in the same light as an early Bontrager fork that used a machined crown-steerer. At that time, Fat City and Merlin were across the parking lot from each other. Ted took his bike to show the "Torque-Fork" to the guys at Merlin and everyone asked, "why didn't he just weld the blades to the cross tubes?", missing the point of being able to try different fork blades. The next thing we know, the Yo Eddy fork was born. About the same time Koski forks became available. From what I understand, the Koski Bros. were the originators of the unicrown fork. Their forks had a larger diameter and thinner gauge fork tube and became my unicrown fork of choice. Great action and minimum welding. The fork I'm going to provide with the Monkey Butt follows this original guideline. I have included a drawing of the original Torque-Fork crown.View attachment 93445
To bring up another point on rigid forks, with the almost exclusive use of suspension forks on production mtn. bikes and carbon forks on road bike, the stock list of fork blades is pretty bleak. A custom builder's creativity is limited by the materials available to him. Almost no heat-treated fork blades any more, so most of the rigid forks we would build or buy are really middle of the road based on the quality of tubing in the fork. Paying $350 for a fork built with straight gauge 4130 reflects the labor to build the fork, not something that is measurably better in function. Segmented forks do look cool, though.
It is interesting regarding the lack of steel fork blad tubing. I've owned 4 different road bikes now and so far the fork I've liked the least was a carbon fiber Kinesis fork that came on my Jamis Quest. I prefered the steel fork on an old Univega Suprasport and the current steel fork on my old Specialized Sirrus over the carbon fork that came on the Quest. And the best fork I've had on a road bike was the fork on my Serotta Colorado LT. I miss that bike, but had to sell it and the money from the sale went to take care of some important matters. I'm also glad to hear from time to time from the new owner of the bike who's thoroughly enjoying it and riding it like it should be ridden (which is often!).
Thanks for some of that MTB rigid fork development history Ted. Good stuff.
Maybe its been a tough week for me and my brain ain't a workin'...
Ted, Are you saying that you will be making a unicrown fork? I like the looks of segmented forks, but what I would like best is a rigid fork that performs well. Do you feel that unicrown forks perform better? In the end, I won't care what it looks like (painted to match the frame helps though).
I had a builder make me a segmented disk fork for a 29er. Prior to that I had been riding a Kona P2 unicrown V-brake fork on my 26er. I think I liked the cheap Kona fork better. But I don't know why.
Ted, Are you saying that you will be making a unicrown fork? I like the looks of segmented forks, but what I would like best is a rigid fork that performs well. Do you feel that unicrown forks perform better? In the end, I won't care what it looks like (painted to match the frame helps though).
I had a builder make me a segmented disk fork for a 29er. Prior to that I had been riding a Kona P2 unicrown V-brake fork on my 26er. I think I liked the cheap Kona fork better. But I don't know why.
I think it is going to be a unicrown fork. The pdf ted posted was an illustration of that early on segmented fork right??
Monkey Butt - whatever happens with this bike it seems like the rear third of it should be painted red don't you think?
Monkey Butt - whatever happens with this bike it seems like the rear third of it should be painted red don't you think?
Yup, the fork will be a unicrown very similar to the old Koski forks. The blades I have are a large diameter, thin wall tube and will give the bike a nice ride when on rigid. Rigid forks work in "splay". 29er forks that are suspension corrected (long) need to be a large diameter to keep a reasonable amount strength and rigidity. A quick frame builders engineering axiom, increase a tubes WALL THICKNESS by a factor of x, strength goes up by x and rigidity goes up by x. Increase it's DIAMETER by x, strength goes up by 2x and rigidity goes up by 4x. Now you know why aluminum frames have big tubes, to increase strength and reduce the amplitude of frame flexure. This is done to give aluminum frames an acceptable fatigue life. That is why they ride like they do. Have you ever seen an aluminum spring? If I have my son do a drawing in Solid Works of both a unicrown and a segmented fork with the tubing profiles I'm sure we would get a real engineer's take on the flex characteristics in each fork. I can tell you that the fork with the largest diameter blades will be the stiffest. If the blades diameter tapers, we can see where the fork blades will flex the most. Those early Koski forks has a large diameter at the dropout and because of this the front brake had a great feel. The bent fork blades had less of a tendency to "unwind" with the brake on. This kept the pad stable on the rim. I want the big diameter at the dropout to add strength and rigidity for the disc caliper.