Re: Crank Length

Postby danose on Wed 25/Mar/09 12:01pm

JohnnyC wrote:Yeah I would think a mountain bike would benefit alot more from longer cranks, and even in road cycling where you've also got hills you would definitely need the longer cranks.


on the road - only if you stand to climb - and the price you pay on the flat means it's not worth it IMHO. I find 175s definitely uncomfy on the road (and 170s a touch too spinny)

offroad - well you don't sit and spin like on the road, well not for aeons anyway
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Re: Crank Length

Postby JohnnyC on Wed 25/Mar/09 12:09pm

danose wrote:
JohnnyC wrote:Yeah I would think a mountain bike would benefit alot more from longer cranks, and even in road cycling where you've also got hills you would definitely need the longer cranks.


on the road - only if you stand to climb - and the price you pay on the flat means it's not worth it IMHO. I find 175s definitely uncomfy on the road (and 170s a touch too spinny)


How come the change in crank length only comes in to effect when standing? I thought the extra leverage would be needed either way
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Re: Crank Length

Postby cyclenutnz on Wed 25/Mar/09 12:43pm

We have these really great things for increasing leverage on a bike, they're called gears. To get more power out of longer cranks you have to apply more force (or increase foot velocity which is also extra physical cost), there is no magic power increase.

Crank length choice should be dependent on position and rider feel considerations. If in doubt - go shorter.
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Re: Crank Length

Postby RHYSy on Wed 25/Mar/09 12:48pm

I reckon go with the longest cranks you can handle (ie: comfort/gut clearance) without sacrificing cadence (ie: maximum cadence).

There is a lot of research done on crank length, but they often use stupid lengths - 120 to 220. In the 170 to 177.5 range, not a heck of a lot of difference. So, go with what feels right.
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Re: Crank Length

Postby danose on Wed 25/Mar/09 1:04pm

JohnnyC wrote:How come the change in crank length only comes in to effect when standing? I thought the extra leverage would be needed either way


if you were strong enough maybe - for me long cranks + seated climbing = sore knees and no more speed, though it'd be interesting to hear xcguys comments (he's recently gone from 170s to 175s on the road)
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Re: Crank Length

Postby XCrazy on Wed 25/Mar/09 1:08pm

One part of the article confused me. Slightly paraphrased " By going to shorter cranks we were able to lower seat height 50-70mm". If you shorten cranks do you not need to raise seat height to maintain same leg extension??? :eh:

I'm really keen to try 170mm on my mtb, mainly for lower cadence sections which people might find weird. I find at lower cadence I have a lot of knee wobble at the top of my pedal stroke and seem to "flop" through this part of the stroke. I'm guessing shorter cranks would help this. Its just a mission to track down shorter cranks to try cause they cost a lot to buy new :(
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Re: Crank Length

Postby specializedman on Wed 25/Mar/09 3:42pm

I ride over 20 hours a week on a bike with 175mm cranks then on the 1 hour a week I ride my race bike with 172.5mm crank's I cant feel a difference,

I would be interested in testing maximum cadence between the bike's however as I can hit a pretty reliable max cadence....
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Re: Crank Length

Postby Spokes on Wed 25/Mar/09 3:54pm

cyclenutnz wrote:We have these really great things for increasing leverage on a bike, they're called gears. To get more power out of longer cranks you have to apply more force (or increase foot velocity which is also extra physical cost), there is no magic power increase.

Crank length choice should be dependent on position and rider feel considerations. If in doubt - go shorter.



3 of my bikes dont have gears. HTH.
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Re: Crank Length

Postby cyclenutnz on Wed 25/Mar/09 3:57pm

SpecMan - difference in cadence for same CPV (circumferential pedal velocity) from a 2.5mm change is not large.
If your max on 175 is 150rpm then same CPV would give 152.2rpm on 172.5. It would be hard to reliably measure that sort of difference given how long max cadence can be sustained for and the limitations of measuring devices (SRM goes to 0.5s but that may only be 10-20 samples).

Spokes - 0ne of mine doesn't, it has shorter cranks but I don't notice the difference (I am unusually careful about accounting for equipment difference when matching positions, I suspect that many of those who can tell the difference are less rigourous). With your singles/fixies you have a choice for increasing leverage - change the rear cog or change the crank. One of those options sounds cheap and easy and the other...
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Re: Crank Length

Postby Oli on Wed 25/Mar/09 4:04pm

Less rigorous? I don't THINK so! :D
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Re: Crank Length

Postby cyclenutnz on Wed 25/Mar/09 4:12pm

Does your method involve lasers?
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Re: Crank Length

Postby Spokes on Wed 25/Mar/09 4:15pm

cyclenutnz wrote:
Spokes - 0ne of mine doesn't, it has shorter cranks but I don't notice the difference (I am unusually careful about accounting for equipment difference when matching positions, I suspect that many of those who can tell the difference are less rigourous). With your singles/fixies you have a choice for increasing leverage - change the rear cog or change the crank. One of those options sounds cheap and easy and the other...


Where Im coming from is BMX racing, so need the length for a good snap out of the gate but if its to long its hard to hold high cadence once you are at speed.
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Re: Crank Length

Postby wgtngrl on Wed 25/Mar/09 4:57pm

Really interesting article - thanks 4 posting. I'm off home to check my crank lengths :)
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Re: Crank Length

Postby johnL on Wed 25/Mar/09 5:23pm

on the lowering of the seat, its not about leg extension but the top of the stroke to create the correct angle that allows force and breathing. A rider in Belge I know well just went to longer cranks and the QuickStep bike fit guru raised the seat to maintain the angle at the top of the stroke (where the most power is generated). It takes some thinking when we only think in terms of reach.

i do believe that 70-50mm is out by a factor of 10 though
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Re: Crank Length

Postby XCrazy on Wed 25/Mar/09 5:55pm

johnL wrote:i do believe that 70-50mm is out by a factor of 10 though


70-50mm did strike me as a rather massive change to compensate for a relatively small change elsewhere :crazy:
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