Road Cycling - Fit - nobody ever talks about crank length

When it comes to fitting a bicycle, no one ever seems to talk about what might be the most important part when it comes to fit: the length of the crank. Seems logical to me that if my leg length (or more properly, my femur length) is 12 percent longer than someone who's properly fitted on a 175 mm crank, then I ought to be riding a crank that's 12 percent longer. That would have me riding a 185 mm crank. Do Campy or Shimano even build cranks that long? The answer is no, which raises the question: Why?

What do you guys think about crank length? Why does no one even talk about it, especially Shimano and Campy?

Here's a link to a discussion on crank length. Seems to make sense to me. http://www.nettally.com/palmk/Crankset.html

Welcome to the forums! And thanks for the link, it looks like my 167.5mm crank is a bit to small for me.

I disagree with Mr. Palms formula so much, I think he should have a big disclaimer. I ride a 172.5 crank, after upgrading from a 170. The 172.5 is considered longish for someone with my inseam, using the standard rules of thumb. Using the Palm formula, I'd be using something like a 180.

I like a longer crank, and think there is a benefit when climbing, due to the longer lever-arm. But to accomodate them you have to lower the saddle, and still get more knee bend at the top of the spin. So the trade off is additional knee stress, plus, IMO, a weaker leg position at the start of the down stroke. Those reasons, plus the cost of good crankset, are enough to keep me from experimenting.

That said, I'm sure there are a lot of tall people out there who would safely benefit from something longer than the stock 175mm cranks on a tall frame.

It reminds me of the Biopace/Ovaltech debacle of about 15 or 16 years ago, when the bicycle component makers came out with ovalized chainrings. Computer simulations showed they would lead to a more efficient pedal stroke. In practice, they made it difficult to spin smoothly, and were shunned after being on the market a couple of years. Still, I'll bet there are some people out there that find they work better, and advocate their use.

for more discussion of crank length check out:

http://www.thankstomycranks.com/

for custom cranks see:

http://www.hscycle.com/

i run 175 on the mtb and 170 on the road. i'm trying some 172.5s on the new road bike(hey they were dura ace and they were free--of course if they cause knee pain even "free" isn't a bargain and i'll go back to my 170s).

good luck.

There was a really good article about this in the Rivendell Reader. I'll dig it up and see what was there.

If I remember correctly, he (Grant Petersen) said it was all a bunch of hoo-ha, that 170mm is good enough for most everyone with 700c wheels.

He also said that a properly designed 650c bike should have a really low bottom bracket and shorter cranks, like 160mm.

Ive always considered crank size the starting point of bike fit.
Specialised TA make cranks from 150 to to 185. Even their sizing guide is a bit conservative.UK company Thorn also have a wide range, but their cranks are a bit cheaper then TA
Given a crank size, you can then determine the bottom bracket height, and the toe-clip clearance to the front wheel. Instead, people often raise the BB on small bikes and bodge to geometry to give clearance with too-large .
Many fitting guides ignore crank size . The research into crank sizing is very poor.
Often smaller independant bike builders have a better sense of ergonomics than the big bike companies.

http://www.peterwhitecycles.com/fitting.htm

http://simon.trinhall.cam.ac.uk/bike/cranks.html

Wow, this is pretty interesting. I was thinking about moving to a shorter crank set to eleminate some of the knee bend I have.
Thanks for the info. :thumbup:

Knee flexibility, ankling habits, cadence preference, and femur length all are relevant parameters. I am no help on this issue -- I am a pretty average 5'8" guy who wears 30-inch trousers and happily pushes 170mm cranks on-road and off.