I have just sent Crisp Titanium a video and a few photos of me on my bike pedaling to nowhere, so the ‘design process’ is starting to move along. I’m still far away from making component choices, I hope, but I’m trying to get ahead of the ball since there are so many questions, including this one that has come completely out of left field.
What crank arm length should I choose?
I’ve been running 170mm cranks since I started riding, but shorter seems to be all the rage these days, including this guy, who is my height and rides 165mm.
Apparently there are many reasons why shorter is better with crank arms, but my favorite one is that it can potentially put less stress on the knees and hips. My hips are fine, but I’m willing to try nearly anything to fix up my left knee.
I know at least one of you who is experimenting with 165s. Anybody else going shorter than you used to and liking it…or not?
The Vicious Cycle 
My road bikes have 170mm cranks, but my time trial bike came with 165mm cranks. Can’t say I notice all that much difference. I’m not sure I could tell them apart in a “blind test” between the two. Hard to say for sure as they’re totally different bikes. Perhaps I should swap the cranks across to a road bike and give it a go. Shorter does seem to be all the rage right now!
It seems that shorter cranks make for a more aero position, so I suppose having those on your TT bike makes sense. I might have read that sprinters, on the other hand, prefer longer cranks, maybe for more torque? It might depend on what you need them for!
I rode 170s for years on my road bike, until I got into my mid-50’s. A bike fit exactly 2 years ago (prior to my first 44/5 trip) had my fitter advising me that 165s would help with some minor issues with my knee, and he was right. Swapping the Ultegra cranks was easy enough, if a bit pricey, and I haven’t looked back since.
My gravel bike came with 170s, and after a year and several hard gravel events I will be swapping to 165s this spring. Reducing crank length means raising the seat post by about the same amount, so it’s subtle but meaningful change in my opinion. Luckily changing cranks on SRAM is easier, since you can just buy the crank arms instead of the whole crankset like the Shimano Ultegra on my road bike. The other benefit for shorter riders on smaller frames, it reduces toe overlap just that much more. I notice it more on my gravel bike due to the more vigorous bike handling.
Great news on the knee! We are both not tall, so all this makes some sense to me.
I think I’ll start with 165s and give it a go. I am leaning towards SRAM at the moment, so that makes the decision even easier.
Forget 165mm. 150 might be the go-to now: https://www.cyclingnews.com/features/why-is-jonas-vingegaard-using-tiny-150mm-cranks/