okay so what are the benefits and down sides to going longer.
i know that ergonomically i use a 175 but can i get more performance by using different lengths?

Used 175’s with gears and went to 180’s for the ss.More torque with the longer arms,quite noticable at slow speed especially on thrutchy stuff when you’re about to stall out.I was getting new cranks anyway so made sense,dunno whether I’d swap just for longer arms tho.

You’ll get more power for a given ratio due to the extra leverage, but if you aren’t over 6ft it might be an idea to make your ratio easier if you are spinner. I’ve always been happy to grind a bigger gear on 175’s (6ft) but it’s supposed to be better for you to spin a smaller gear.

I have always thought longer cranks were intended for taller riders.

For mere mortals I would’nt have thought the extra few mm’s would make a seriously noticable diference. Do you think your 175’s are holding you back?
I found some gains in performance by perfecting my cleat position.

I would say that 175’s would be fine, and had been pointed out crank lenght should be based on height…not fashion!

I am 6’2″ and have long thighs and have been running 170mm cranks on my singlespeed for 5 years with no issues, infact the shorter cranks lets you spin faster on the flats where a singlespeed is at more of a disadvantage!

SSP

am sticking with the 175’s but am interested in the issues of flat terrain and RPM.

my legs can go round fast but there is a point where they go no faster so i thought a longer crank arm might allow greater speed on flat for the same RPM.
but slow speed it might make it a bit unstable.

ultimatly my legs are good with 175 so i will stay there .
and i just got a pair of xtr 952. the ultimate in my opinion.
cheers guys

Given the same gearing and rpm your speed will be the same regardless of crank length.What will change is the speed your foot moves!As the crank arm gets longer so does the distance your foot moves to complete one revolution (2 x Pi x crank length).If the time it takes to complete one revolution is conatant (rpm) your “foot velocity” has to increase (compared to shorter crank arm length).Basically longer is better for low rpm shorter is better for high rpm.

Taken from Mike Burrows book “Bicycle Design”

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