Crank length

EKE_38BPM

I've just bought and fitted 175mm cranks on my fixie. As everything else is the same its easy to pinpoint any differences in how the bike feels.

I'm quite long in the trouser department (I've got long legs too) so when I saw these longer cranks, I thought they might suit me better than cranks more suited to Santa's helpers (RC, BJUK, CW etc), but I have to say that it feels like much harder work than using 170mm cranks.

Is there a mechanical advantage to using a longer crank? I can't feel the difference (as in I don't feel my feet lifting higher at the top of the stroke or stretching more at the bottom) but it definitely feels harder to get going. No computer, so I can't quantify anything, but I wonder what difference different crank lengths have on things like power, torque, acceleration, stamina etc. I certainly feel more tired after a ride now than I did before, but I've been using 170mm cranks for about 25 years and these new cranks for not even 25 hours. Maybe I just need to get used to them?

itboffin

Could be that babies gear you're pushing :P

EKE_38BPM

itboffin wrote:

Could be that babies gear you're pushing :P

I'm pushing just under 76". I do like the look of 52x18, its nothing like a baby gear.

The Rookie

Longer cranks increase you leverage (although 170 to 175mm is a circa 3% increase) and should make it easier to pull away, where it should count against you is a speed where your feet have to travel further (again circa 3%), either something else has changed or your memory is playing tricks!

Simon

itboffin

EKE_38BPM wrote:

itboffin wrote:

Could be that babies gear you're pushing :P

I'm pushing just under 76". I do like the look of 52x18, its nothing like a baby gear.

I found a 14t freewheel the other day and one a brief second i though oooow that plus a 53t up front :shock: then my knee twinged and i remembered the 2 torn ITB's back in 2009. plus some mornings my BSO is frankly not cricket.

yes all very silly

EKE_38BPM

itboffin wrote:

EKE_38BPM wrote:

itboffin wrote:

Could be that babies gear you're pushing :P

I'm pushing just under 76". I do like the look of 52x18, its nothing like a baby gear.

I found a 14t freewheel the other day and one a brief second i though oooow that plus a 53t up front :shock: then my knee twinged and i remembered the 2 torn ITB's back in 2009. plus some mornings my BSO is frankly not cricket.

yes all very silly

102.2" would be a massive gear. On the BSO that weighs a few ton, I would predict another torn ITB for ITB when pulling away from a set of lights, up hill, in heavy traffic, at night.

veronese68

Simple answer is MTFU, what did you expect? Surprised it took this long for someone to say it.
Morereasonable answer is, as Simon says, the longer crank should give a mechanical advantage being a longer lever. I've nearly always used 175mm cranks but recently rode a bike with 170mm and didn't notice the difference in crank length. I used to ride the same bike with 175mm cranks but there was a gap of a couple of months between the two so any small difference is lost in the mists of time and senility.
I'd have thought a man of your stature would have always been on 175mm. Like you said your not a little fella.

meanredspider

Your feet have to travel further with the longer cranks (3cm per rotation - 2 metres a minute at around 70rpm) - I'm not sure it's really significant. You will also be stretching your movement a bit further. Probably really mostly just the need to MTFU

UndercoverElephant

I suspect your position isn't quite right on the new bike, check the saddle fore/aft in relation to the BB.

Gussio

175mm cranks on all my bikes. Considered shorter for the SS/FG to reduce the likelihood of pedal-strike, but didn't bother in the end. Only time I have tried shorter cranks is on a track bike at Herne Hill, when TBH I was more worried about crashing than how much difference 5mm makes.

rjsterry

On a similar line, I've recently had to replace my 42T inner ring with a 39T due to availability, and I've been very surprised just how much easier the 39T (about 7% smaller) is to turn.