I think I'm remembering right. Isn't there a Martin paper that tests a decent sample size of athletes over quite a large range of crank lengths? I want to say it was a huge length range, from something around 120mm to 220mm. Pretty sure he presented this data at a seminar at the Serotta Symposium earlier this year. The interesting thing being, I believe he found the data to suggest the most efficient crank length was around 140mm (not remembering for what size rider). Anybody else seen/remember this paper?

Jim, sorry if any of this is incorrect. This is just off memory and I haven't gone back to re-read yet.

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-Joe S.

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I guess I may have had my 54 tooth on that day maybe even my 53 - Use your little internet Calculator and you tell me - was it the 53 or 54 :)

His studies of 16 bike racers of various heights doing maximal sprint power tests of under four seconds duration on cranks of 120, 145, 170, 195, and 220mm showed no statistical difference between crank lengths. Seat height to the pedal was maintained throughout, but fore-aft saddle position and handlebar height were not readjusted with crank length changes, despite variations with crank length of pedal-to-knee relationship and saddle-to-bar drop. This also led to Martin’s assertion that he could see no point to positioning the knee over the pedal spindle.

-Crank length matters: Not so, says Martin, who did research showing that maximum power varies by, at most, a few percent depending on crank lengths. And we're not talking about the difference between 170mm and 172.5mm either - Martin experimented with fulcrums as short as 120mm and as long as 220mm. Between 145mm cranks and 195mm cranks, maximum power output across all riders, short and tall, varied by a total of 1.6 percent. He did say he prefers 165mm arms for time-trialing, simply because they allow a rider to get lower on the bike, which is more aerodynamic, while preserving a good hip angle, which is essential for power production, which apparently isn't compromised by shorter crankarms.

Not so, says Martin, who did research showing that maximum power varies by, at most, a few percent depending on crank lengths.

He did say he prefers 165mm arms for time-trialing, simply because they allow a rider to get lower on the bike,

He did say he prefers 165mm arms for time-trialing, simply because they allow a rider to get lower on the bike,

Your hip angle will be open more than before.

again, i don't get it. if my bike now has 175s, and i switch them our with some 165s, you're saying i should lower my seat ??

wouldn't i be raising my seat ??

what am i missing here? think about the knee angle at bottom dead center.

A side benefit for those encumbered by UCI requirements is that the raising of the seat and shifting it back (to accomodate keeping the knee in the same spot relative to the pedal spindle at the start of the power stroke) when implementing shorter cranks will also make it slightly easier to meet both the 5cm saddle offset and the limits on extension lengths since the body is effectively shifted rearward relative to the BB.

In Reply To

  i understand what you are saying, but your hip angle won't change at all relative to the extended leg.

Interesting. It kind of implies that we each have a power band, just like a car engine, that has the most power between certain degrees of flexion. For example when your leg is almost straight the power you can deliver is less than if it's bent more, and if you're knee is at right angles the leg similarly is less powerful than when it's a little more open.
A shorter crank arm would do a better job of keeping you in your power band. Wouldn't make much difference for someone whose leg can deliver the same energy at any angle between top and bottom of a pedal stroke.

Apologies if this was already raised as I didn't read all the posts in the thread, sorry.

I'm actually not agreeing or disagreeing with the short crank idea. Just trying to understand why the OP was seeing a positive result for short cranks with a tall rider.

I'm on whatever stock crank came with my Cervelo Dual, and I've got a lot more training to do before I need to think about crank length. I like the long crank distributing load across a larger group of muscles idea but I'm not sure I believe it. Isn't it just the same group just stretched/contracted more?

Bottom line is you're right: Once your pedalling technique is good you pretty much have to try out different crank lengths with a power meter to see if it's worth changing. But how would you be able to test for endurance? If you've trained with one crank length wouldn't you be naturally inclined to favour that length in long comparison rides since your muscles aren't used to the range of motion associated with the new crank?