I rode 170mm for a couple of years and then put some 175mm cranks on, simply because I found some nice 175mm ones cheap - I couldn’t tell the difference, or I got used to it really fast.
Just put on some 165mm ones so I can get ground/toe overlap clearance (its a cx bike) - I’m curious if I’ll notice a big difference changing the crank length by 10mm…
If you consider inseam lengths from shorties to giraffes (eg 730mm - 865mm, 18.5%) and calculate a proportional change, the small difference between 165 and 180 (9%) doesn’t correlate, the giraffes should be on cranks closer to 200mm if shorties are on 165mm.
Leonard Zinn has plenty to say about this, and makes some looooong cranks too. (And I just clicked Spirito’s link, which also has plenty to say about it )
Also, torque is the cross product of a force acting on a lever arm (τ = r × F), for a force of 1000N (~100kg rider with all their weight on one pedal) on a 165 & 175mm crank, the torque is: 0.165 or 0.175m*1000N = 165 or 175Nm, a 6% increase in torque.
depends on BB height (cue H)
Which is probably one of the reasons why 200mm cranks aren’t all that common.
If a frame is built with BB drop that will allow ~170~175 cranks to work OK without pedal strike whacking 200mmm cranks on is asking for trouble. Conversely if you build a frame for long cranks then put short cranks on the BB is to high.
If crank length was proportional to leg length and hence frame size BB drop would also vary with frame size causing H’s head to explode.
It depends on the event,
If your doing a itt or ttt or similar event your down on the line,
But if your doing sprints where you will be slowing and sitting up on the banks a 175 could be dangerous.
)