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170mm cranks aren't more powerful than 165mm

Really good read on importance of crank length with some data on power transfer: https://www.powercranks.com/cld.html

A study demonstrated 145mm cranks had the best power transfer and the author theorizes that knee bend (reduced by shorter cranks) has a much greater effect on power transfer, despite the commonly held belief that longer crank length contributes to more power.

He also goes on to say that longer cranks tend to have higher pedal speed, and it is harder to apply power to a pedal that is moving faster. It's also arguably harder to apply power on the backstroke with longer cranks even though it's easier on the forward stroke.
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April 30, 2015 05:16 PM
From: San Francisco
15 posts
2 bikes
This is cool! Id like to see the crank lengths tested on a SS mountain bike course tho. 145 would probably be noticeably bad at 40rpm up a steep hill. Just theorizing though.
April 30, 2015 06:00 PM
From: San Diego, CA
780 posts
9 bikes
I think that comfort has more to do with overall power output, like zeb said, 145 up hill would not be comfortable and would decrease the power
April 30, 2015 06:14 PM
From: East Bay, California
356 posts
3 bikes
I wish it included how many people this was tested for. One or two people is hardly enough to conduct a "study". This study also changes a lot with the geo of a bike. Technically speaking from physics power=work/time, work=forceXdistance therefore if the same force is being applied, then the longer distance from a crank arm will mean more work, which therefore means more power.

I think what needs to be taken away from this is the it didnt really make too much of a difference from 145 to 170mm.
April 30, 2015 06:17 PM
From: Los Angeles
419 posts
45 bikes
Powercranks is quite possibly the ugliest website. Must be a zombie site from the early 90's
May 1, 2015 04:58 AM
I would think they should apply this study to all types of cycling where power transfer is a big deal. When I bought my first crank set, someone told me to go around 170 in order to push higher gears. But this applies mostly to track and road cycling and not so much MTB or cross.
May 1, 2015 03:19 PM
From: Las Vegas, NV
372 posts
3 bikes
I'm buying 170's next to finish my build. 165's are way to spinnyand a disadvantage when t comes to climbing since you have no leverage.
May 1, 2015 09:31 PM
From: Miami, FL
59 posts
1 bike
A friend of mine had the opportunity to use those power cranks for a few months,
a year or so ago. He said that they did make a difference with leg strength and pedalling technique.
Shorter cranks will give a smoother more even torque output through the pedal stroke than longer cranks. But you need the leverage (torque) to push bigger loads. Gears, hills or head wind.
Have you ever tried riding a kids bike with short cranks? It's shit. Sure you can spin, sort of. But there is no leverage so the gearing is quite low. The kid is pedalling flat out at walking pace. But if you change up the ratio they can't get it moving. No leverage.
It's all a compromise. Cranks short enough to spin and long enough for the leverage.
This guy talks about crank lengths too.
And heaps of other bike fit topics.
May 2, 2015 11:49 AM
From: Gold Coast. Australia
179 posts
2 bikes

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