crank length

granda

how important is crank length i.e. does it matter if its 170mm or 175mm as surely 5mm difference couldnt make that much difference and if so can it be offset by moving the saddle backwards or forwards

bcmf

As with most stuff it really depends on the rider.
I found that moving from 170 to 175 made a huge difference. Felt like I got more power and my banged up knees felt a huge benefit.
I believe the general consensus is that for 'spinning' shorter cranks are better but for mashing longer cranks.

smacl

I would have thought a longer crank would be equivalent to a slightly lower gear, as your foot is travelling a greater distance per revolution of the crank, and you are getting more leverage on the crank.

Beasty

For some people it seems to make a big difference. As smacl says there is a gearing impact

For me, my road bike has 175mm cranks, and my track bike 165mm, but tbh I could not tell the difference between the two (although I'm on fixed gear on the track bike, which probably overshadows any other changes)

Nwm2

granda wrote: »

how important is crank length i.e. does it matter if its 170mm or 175mm as surely 5mm difference couldnt make that much difference and if so can it be offset by moving the saddle backwards or forwards

Not as much effect as you might think:

granda

thanks for the replies so if i've got a 172.5 crank length with my 172cm height would i be ok or should i go shorter(my crank length before was 170)

doozerie

granda wrote:

thanks for the replies so if i've got a 172.5 crank length with my 172cm height would i be ok or should i go shorter(my crank length before was 170)

It really depends on who you ask as some people have very strong feelings about whether crank length makes a difference. I'm slightly under 172cm height and my preference is always 170mm cranks, but I believe that if you really get down to the nitty gritty of it it's the length of your femur that is considered more relevant than your total height. I've always thought that foot length should really play a part too but I don't recall seeing that raised in some of the age-old heated discussions on the topic that I've read. Some, perhaps much, of such discussiona depends on how much you value the theory that your knee should by either directly above, or slightly behind, the ball of your foot when the crank is at 3 o'clock position - I don't have any real faith in that particular rule of thumb personally.

Part of my bias in favour of shorter cranks is that I've had various knee issues down through the years. Longer cranks means a lower saddle with the result of an even greater change of angle at the knee at the high point of crank rotation - it's another judgement call as to whether you believe the few millimetres of difference in crank length will count for any real difference on knee stress, but I've always tried to avoid it.

Incidentally, at some point or other 175mm cranks seemed to become standard on mountain bikes. My own MTB has these too and my perception is that this is overall harder on my knees. An MTB has such a variety of other differences about it though that it could be argued that any issues I've noticed are due to factors other than crank length.