Would there be a noticeable difference in going to a 172.5 crank from a 170? I know this has come up before, but it’s usually the other way around (i.e., going to a 170 from a 172.5). I just picked up a 172.5 crank thinking that the .5 mm difference would be negligible. Has anyone ever done this and found any faults/issues with it?
It might take a bit of time to adapt, but once you adapt, I doubt you’d notice any difference. I race on 180’s, but I’ve ridden 172.5’s on a borrowed bike without any problems. Shorter is almost always an easier change than longer…
Would there be a noticeable difference in going to a 172.5 crank from a 170? I know this has come up before, but it’s usually the other way around (i.e., going to a 170 from a 172.5). I just picked up a 172.5 crank thinking that the .5 mm difference would be negligible. Has anyone ever done this and found any faults/issues with it?
NO
I am going to go from 180’s to 200’s. Shall be interesting how it goes. I rode some 200 power cranks for a while indoors and did not notice any difference.
Dave
Lennard Zinn reports a test he did in which riders of all sizes produced the most (or nearly the most) power with 150mm cranks. Shorter may actually be better.
I ride 180’s on all my bikes. Last weekend I captained for a blind stoker at a tandem rally. The captains cranks on her bike were 170’s. I could not believe how tiny they felt and how inefficient I felt pedaling them.
What is your inseam?
35". Why, you buying me some new slacks? 
How tall are you and what is your leg length?
My grandfather, my father, and myself were all Olympic coaches. My grandfather was 5’ 9" tall, and rode 170.0 cranks. My father was 5’ 7" and rode 170.0 cranks. I’m 5’ 10" and ride 172.5
What this means is that it all depends upon your inseam. My grandfather and father although different in height both had the same inseam of 30 inches. My inseam is 32.
Mike Fraysse
That’s actually not surprising. Peak power will likely come at the highest cadence you can generate, and higher cadence will be easier with shorter cranks. The key to remember is that peak power and sustainable power are not the same thing, especially depending on the length of your race.
Crank length doesn’t make much difference after adaptation, but were I to choose it based on anything, I’d choose it based on race duration. For events requiring higher power, I’d race shorter cranks. For long course, longer cranks to accompany the lower cadences (there is a metabolic cost to lifting your leg up and down; research is inconclusive on the breakpoint of this cost and on cadence in general) that help to minimize metabolic cost. So were I a short-course athlete, 175. I focus on long course, so 180. But really, I doubt it makes too much difference at all unless they are obviously too long (i.e. impinge your hips at the top of the pedal stroke), something which is much more likely for triathletes who do most racing in the aerobars.