[ÆX]

so i was driving 10 hrs alone yesterday and it leaves a lot of time to
think about stuff. i generally think about how to totally change
DH bikes to make them work better, be more fun to ride and of
course go faster.


so most of us run the your seat height as high as possible so
pedaling is as efficient as possible. straighter legs on down stroke.
at some point depending how tall you are your seat height effects
your cockpit room. you need this room to correct form a buck,
extend to absorb a lander, space to bunny hop higher rock sections.


so. my idea is to run like 190+ cranks. and a 1'' higher BB giving the
same leg extension on down stroke but then when the cranks are
level you have more cockpit room for maneuvering . now before you
say low bb's are the stuff let me explain. when you corner level
pedaled its generally in a berm b/c you are level pedaled to pump the
corner to gain speed. on sketchy corners you are foot out weighting
your outside foot i hope. this would be the same as low BB short
cranks.


so, what you gain is longer cranks for more leverage, power when
you get the chance to pedal.

more "seat" to seat room for more aggressive riding. hop more
rocks, finesse around on top of you bike, more space for big landers.

 

[motomike]

Sounds interesting. I'd like to see you try it out!

 

[beaverbiker]

it is a very very interesting thought. but what about slowing down the pedal stroke RPM's due to the increased diameter/circumference in your pedal stroke circle? for shorter dh courses that might be a problem. i'm a tall dude, so i like long cranks. it's just a bummer that no one makes a bike that i can feel comfortable running 180's on.

 

[ÆX]

i think you see people spinning like mad on DH bikes b/c they run 165-170's .

you don't have to ride like that and you wouldn't with long cranks.

i like to put it in a big gear and mash rocking the bike side to side
with big wide bars.

 

[stoney]

That sounds like a good idea. You also get more bb clearance... I'd like to give that a go.

 

[Superdeft]

about 100 16 year-old kids just put their sundays on ebay...


In all seriousness though, it's fresh thinking like what bcd posted that will usher in the next wave of frame geometry when people start going out on a limb and trying new things.

 

[dG video]

A bike with a higher BB and longer cranks wont feel as stable on the straight stuff though. Atleast thats what I think.

 

[Secret Squirrel]

A bike with a higher BB and longer cranks wont feel as stable on the straight stuff though. Atleast thats what I think.

With sag the way it is....I don't think you'll notice it.

 

[ÆX]

A bike with a higher BB and longer cranks wont feel as stable on the straight stuff though. At least thats what I think.

you would ride bend legged more, but your bars sure would feel
LOW!

i was only thinking 190mm cranks and a 1'' higher bb.

but to do a real test some 210's with 2'' higher bb would be fun to try.

my friend had some 210 bullseyes back in the day. it was a weird ride.

 

[stoney]

but if it's a wide bb, ala Giant DH Team, you get a more stable stance which will lead to more stability.

 

[OGRipper]

Interesting thought. Depending on what length you ride now the distance between your two pedals is going to get significantly bigger. That could really screw with your pedaling. Could also mean your front foot will overlap your tire, especially on a 29er, no?

 

[sanjuro]

Don't forget about the flip side to longer cranks/more leverage: harder to spin.

Now dh is not road or xc. Maybe DH only a few pedal strokes out of a corner is all that is required. But 4x certainly has high pedal revolutions.

 

[Bicyclist]

Sounds weird. I'd try anything once though.

 

[ÆX]

Interesting thought. Depending on what length you ride now the distance between your two pedals is going to get significantly bigger. That could really screw with your pedaling. Could also mean your front foot will overlap your tire, especially on a 29er, no?

with your feet wider apart, isn't that a stance you would take not to get knocked over by say, a large gust of wind?

it is something i would like to feel.

there is plenty of room for your feet to front tire.
i think this would be best using platforms due
to needing ot put your feet out more and a slower
pedal stroke.

 

[OGRipper]

I still see some issues but Alex I like the way you think, and people with negative attitudes like mine right now never build anything. Give it a shot and let us know.

 

[Biscuit]

Interesting.

I like the idea for a few reasons:
For me downhill pedalling is usually high torque, out of corner sprints, or short bursts between sections. I don't think spin is nearly as important.

It would keep from destroying cranks and pedals, and the occasional over the bars from mistiming a pedal.

When you need a low bb is usually in crank-down flatter corners. With this setup, your weight would be as low or lower through the flat corner.

Maybees:
You could pump more agressively through big rock gardens.

Your seat height while cornering (pedal down) is higher. Not necessarily bad, but different.

Your seat height while sitting & pedaling is, well, different. You get more leg extension, but your leg will come higher as well. That is the hardest part about sitting and pedaling IMO. Hard on the knees and hard on the muscles. I guess you could set up your seat to a point where it wouldn't be detrimental at all. It's just interesting.

Bar height is confusing as well. I think sitting & pedaling would be a beneficial setup. Cornering, crank down, would work well too - essentially the same as most bikes now. Not sure about steeps and gnarly rocks though. Could be more difficult to get off the back. But your seat to bb length could actually be set up to be lower than standard, giving you more room to move around.

Negatives:
Your foot gets closer to the tire. Not really an issue with slack dh angles, but I've seen it on park and slalom bikes.

The bike may not feel as stable. I think head angle has more to do with this than bb height, but it will affect the feel of the bike.

Stress on the cranks would be amplified. Which means more weight.

Availability of long cranks.

 

[bikenweed]

Profile used to make 190mm cranks. Who wants to try them first?



A lot of the taller BMX racers would use them. 185mm is also pretty common in BMX racing.

 

[ssk]

Would a compromise of 180's and a 0.5" bb height increase be worth the effort? 180's are a readily available size in XT or even Profiles.

 

[mandown]

interesting idea. i see the extra weight being a factor. i see the benefit of having extra room to pull the bike up. i doubt there would be much extra clearance as you would need to run a bigger chainring to keep a similar gear ratio. i think the idea might make more sense for taller people with longer legs. the spin pattern would be tougher for people with shorter legs. when seated and pedaling, you need to consider what this will do to your knees through the whole pedal stroke. the longer crank arms will shove your legs more into your chest on the up part of the stroke. the shorter your legs are, the more noticeable it will be.

 

[CRoss]

I would be concerned with how high the pedal is going to be at the top of the pedal stroke. With 190 cranks and the BB 1" higher your leg is going to have to bend more. You might get more extension but you will also get more compression (bending of the leg). Changing the seat height is a way to give you more extension and less compression. By raising the BB and lengthening the crank arm you are raising the seat at the bottom of the pedal stroke but lowering it at the top.

When you do one or two legged squats you hit a point at the bottom of the squat where it is very hard to go back up. If you stay above this low point it is easy to go up and down repeatedly. Imagine having to pass this point with every pedal stroke.

I think having the higher BB on straight fast sections is going to be less stable. Your center of gravity will be higher. You could bend your legs more to lower your body but you will be giving up some amount of suspension travel in your legs. This is going to make it more difficult to absorb large holes and g-outs on courses like Mt. Snow and Snowmass.

 

[stgil888]

Re: the issue of using a wider BB to add stability: many manufacturers have tried wider bottom brackets. They do feel more stable. However, with wider bottom brackets comes wider hubs and rear ends to maintain a decent chainline. To fit the wider rear end, the cranks have to go out even further (spacers...etc). What you end up with is a surprisingly natural foot position that feels great cruising along. The problems show up when you start turning. A super wide BB puts your inside pedal (if down or level) farther away from the centerline of the bike.

There are lots of complications that come with a wider BB package, and I have a feeling this problems would be exacerbated by longer cranks. If you look at how many trails have developed, they have grooves through rocks and roots where most riders' tires go. As your pedals get farther from the centerline of this groove, they are more likely to encounter obstructions--many of them immovable.

 

[w00dy]

I ran a set of 185 profiles (which I'd be willing to donate in the name of science). They were fine sitting down and pedalling, but it was hard to stand up and crank with them. I found that I had to move my body up and down a lot more and it didn't feel very efficient or smooth. Definitely too much stroke for my legs.
I'm about 6' and 180mm cranks are my usual length of choice.

 

[no skid marks]

**** up the handling so you can sit down? and loose rev's to get the beast moving easy? Hmmmm I don't think so. Who sits down anyway,oh and the seat will be even more in the way. Not to mention that the hight of the high foot will just be whacky.
Sorry if this sounds negative.
It seems like you want a DH road bike BCD.Drop bars next?

 

[vitox]

alex this one i dont buy, im with you halfways but i think the cons have to outweigh the benefits.

for starters the gain from increased leverage when powering the bike, and the one from the wider stance, have to be quite big to counteract the stability loss from the way higher bb. i would tend to think that so long cranks are past optimal biomechanic (patineto where are you...) and that would mean all there we are left with is to gain from the wider stance, which percentually wouldnt be more than say 15%? i also dont think the center of mass will be lowered any much because of a wider stance.

that and the practical complications from a design like it, for instance at some point your feet might start hitting the frame, and on many swingarms it would be impracticable without much wider bbs.


i know i might come off a bit negative but im sure you much prefer me typing this!

saludos

 

[Udi]

I agree with the above two.
Pedalling isn't the primary objective in DH, handling is. While pedalling is definitely part of the equation, it definitely doesn't form a major part of most real runs.

Trying to hold speed through sections is usually a much bigger issue than trying to gain it. And this is where a low BB and a low COG come in handy; since most places that involve losing speed are - you guessed it - corners.

As a sidenote, having a low frontend and high BB is also going to leave for an awkward hand to foot distance. Why do you think the sunday frontends are specced so low? to match the BB.

 

[Thrillkil]

my only concern is that with longer cranks, wouldn't the "dead zone" at the top and bottom of each stroke be accentuated?

 

[Sandwich]

Anybody ever toy with this?

 

[Downhillbiker23]

Super interesting idea,
Originally thought 190 plus, there goes any hopes of ground clearance
but wiht your idea of raising the BB an inch that is doable

But then you get to cornering. high bb=bad cornering.
and corning, you drop your outside foot, with such long arms, your bound to hit something

 

[Sandwich]

but if you're outside foot is dropped it would be the same effective distance to the ground, or even lower. Cornering in berms would take some investigation though.

 

[Wa-Aw]

This might be handy for taller riders. Bikes these days seem to be more and more taylored to riders under 6ft. But I can't see how anyone short could pedal effectively with this set up. High RPM pedaling is generally more efficient and more stable, it was the roadies who told us that.

 

[SCARY]

Just stick a dropper post on it a be one with it.I don't know anyone who runs their post "as high as possible"anyway.

I run mine,so when my pedals are level,and the bike is leaned over,the seat lands in the crook of my knee area.Allowing me to lean the bike over as much as possible,and not hitting my thigh,limiting the lean and mobility.

 

[Verskis]

Do people really sit and and pedal on DH bikes, especially on DH races?
My seat is as low as it can go without touching the rear tire at bottom out, otherwise it hinders my movement on the bike. The seat is slightly above my knees when standing on leveled pedals.
At the races I'm always standing when pedaling, but we do have very short courses here in Finland.

 

[Sandwich]

I guess I didn't realize that BCD had originally intended this as a seated measure, but I liked the though more for standing and rock garden clearance. Your COG should remain the same if the crank compensates for an increase in BB height, except for in berms where you might have your pedals level. I hate pedaling a 165mm crank arm with an 83mm BB. It feels so uncomfortable.

 

[jonKranked]

so i was driving 10 hrs alone yesterday and it leaves a lot of time to
think about stuff. i generally think about how to totally change
DH bikes to make them work better, be more fun to ride and of
course go faster.


so most of us run the your seat height as high as possible so
pedaling is as efficient as possible. straighter legs on down stroke.
at some point depending how tall you are your seat height effects
your cockpit room. you need this room to correct form a buck,
extend to absorb a lander, space to bunny hop higher rock sections.


so. my idea is to run like 190+ cranks. and a 1'' higher BB giving the
same leg extension on down stroke but then when the cranks are
level you have more cockpit room for maneuvering . now before you
say low bb's are the stuff let me explain. when you corner level
pedaled its generally in a berm b/c you are level pedaled to pump the
corner to gain speed. on sketchy corners you are foot out weighting
your outside foot i hope. this would be the same as low BB short
cranks.


so, what you gain is longer cranks for more leverage, power when
you get the chance to pedal.

more "seat" to seat room for more aggressive riding. hop more
rocks, finesse around on top of you bike, more space for big landers.

lol wut? maybe on an xc bike, not a DH bike.

 

[jonKranked]

not to mention sourcing crank arms that are 195 or longer and could withstand DH riding would be difficult; profile's max out at 190.

 

[Wa-Aw]

How does having a higher seat and longer cranks arms possibly give you more effective seat room?

 

[Verskis]

How does having a higher seat and longer cranks arms possibly give you more effective seat room?

If you adjust your seat height for maximum pedaling efficiency, the seat will be lower with longer crankarms, because it's the distance from the pedal at the most downward position to the top of the seat that matters. Now when the cranks are leveled, you have more seat room with longer cranks.

Thinner pedals will also mean the seat is lower, but that does not give more seat room, since the pedal thickness affects also when the cranks are leveled.


Having said that, I still think increasing the BB height and crank length on DH bikes is not a good idea, I don't care about seated pedaling that much.

 

[HAB]

Bigger problem with this plan: The idea that the distance from the bottom of the pedal stroke to the seat is what matters most for pedaling efficiency is wrong. What makes pedaling a bike with a low seat uncomfortable and inefficient is more the tight distance between the top of the pedal stroke and the seat, i.e. the very acute angle ones knee must bend to in this position. Making the crank arms really long isn't going to help here. Basically you're going to end up with a bike with a high BB that's going to feel really weird in berms and such when you've got the cranks horizontal, and isn't going to be any easier to pedal. Admittedly you would have better BB clearance which is cool but I don't see it possibly being worth it.