Originally Posted by
531Aussie
However, don't forget the long crank conundrum:
they may provide more leverage, but they're a little harder to push, because you're relatively lower over the pedal through most of the downstroke, due to having to lower the saddle for the reach at the bottom of the stroke, and coz of the extra length coming up higher through the top of the stroke
That only applies if you are using cranks that are too long (ie most small riders). Most tall riders are using small cranks, whatever size they select. Their angles of movement are smaller than a med rider with med cranks.
I think it is best to consider, for any sized rider, what length is a medium crank. This will differ according to rider size.
Then consider for that rider, what is a long and a short crank.
eg a 175mm is very long for a small rider, a bit long but OK for a medium rider, a small size for a tall rider.
Considering the effort involved in turning cranks, firstly we need to fix the work-rate of the rider. Assuming this is constant, then longer cranks generate more torque so can turn a bigger gear at a slower cadence.
Cadence is NOT the constant, a big rider on big cranks will spin more slowly.