Crank Length

Secteur

My bike (the only bike I have ever had) has 175mm cranks.

Having never ridden anything else, I have no idea about this. They feel fine to me, but I have no comparison.

What is the benefit / difference with different length crank (and what sizes do they come in?)

How would I know if a shorter crank would suit me - is this "pro bike fit" territory?

Thanks.

Wirral_paul

Its a pretty basic fit requirement really - bikes tend to come fitted with an appropriate crank length depending on the frame size.

It' you have long legs, ie approx 6ft or more then 175mm will be about right for you on a road bike. I'm 5ft 10in and ride on 172.5mm for a road bike and 175mm on a time trial bike. Shorter cranks help you spin your legs a bit easier, while longer gives more leverage.

So how tall are you? Inside leg length??

Secteur

I'm a hair's width under 6' tall, and I think I have long legs - I seem to recall my inside leg is 33" but I need to check this.

I tend to ride with a high cadence (90-95) wherever I can - I find this suits me better.

The 175's I have dont feel wrong, but I have no comparative experience to really know.

PS yes it is a "standard" road bike

Wirral_paul

If you're spinning at 95rpm and it feels comfortable then I dont think you have any worries really. Maybe a full bike fitting might suggest otherwise for maximum efficiency from your leg muscles, but your sizing would suggest (to me at least) that your cranks are probably just fine.

thescouselander

I believe crank length can make a significant difference. When I changed my bike earlier in the year my average speed suddenly went up over night. The only reason I can think of for such a difference was the size of the crank arms. My old bike was equipped with 172.7mm arms and the new one has 175mm arms.

On the new bike I find myself pushing a higher gear than on the old bike - I realise the overall effect should be that effective gear ratio is the same but that fact is I am regularly arriving at work up to a minute faster than on my old bike. I guess the fit is just better and that has lead to some efficiency gain somehow.

MichaelW

Wirral_Paul wrote:

Its a pretty basic fit requirement really - bikes tend to come fitted with an appropriate crank length depending on the frame size./quote]

but only if you use a medium ish style frame (M-L)
If you are medium sized then any commonly available crank size will be OK although some may be a mite better for some riding styles.
If you are very tall or short then you are usually stuck with the same cranks as medium sized riders.

For any one rider, longer cranks suit a slower pedalling style at higher gear and shorter cranks suit faster cadence in lower gears. The power input/output remains the same but optimized pedalling may result in some gains.