Different crank lengths on different bikes?

Richvelo

Hi, I'm hoping someone may be able to offer some sound advice, my road bike has 175mm cranks and this year I have bought a cross bike to serve as a winter bike and to have a dabble in a few cross races, I've been mainly on the cross bike now for the last month and a half and coincidently I'm having problems when running in one of my knees.
I have just thought it may be worth checking the crank length and general position on the CX bike and the crank length in 172.5mm
Is this a bad thing? I'm presuming it may be and even if I adapt to it over the winter I may have problems again in the spring, but It's not a huge difference is it or is it.
I'm 6 foot tall.

Confused

Rich

dru

2.5mm between crank arms won't be a big difference and you probably wouldn't be able to tell the difference.

The 175 sounds in the right ball park for a 6 footer.

Don't overthink it.

lucan

2.5mm difference? I have socks that vary in thickness that much! :shock:

CoachFergie

All the research on power, efficiency and fatigue between 145mm and 190mm cranks suggest no significant differences.

GiantMike

On my most used bike I have different crank lengths: MTB 175mm. Road bike 172.5mm. Cross Bike 170mm. I can't tell the difference between any of them (except the road bike is terrible off-road).

cougie

For months I used 1 bike that had different length cranks !

Can anyone tell what length their cranks are without looking ? 2.5mm is bugger all.

Nack

I agree with all the previous posters about different crank lengths making no difference at all.

The only thing to remember is to adjust saddle height accordingly if you get a new chainset with different crank lengths to the one you were using previously.

sub55

I can tell the difference in my bikes. Should point out that i`m excessively tall and all my bikes except one have 180mm cranks ,the exception is the track bike which is shod with 170mm . I can certainly tell and my power figures aren't as good

Richvelo

Thanks for all the replies, I was wondering how such a small difference could affect me.
I'll check saddle position again and carry on.

Thanks again

Rich

sub55

cadseen wrote:

If your tall you probably wont notice much diferrence, more likely notice if cranks are to long if your shorter.
Smaller cranks will allow you to spin faster and may be more useful in road races and sprinting etc.
Larger cranks can suit slower pedalling when rolling larger gears in time trials.

Neither lengths should cause knee or any problems. You must rember id you increase the crank length by say 5mm that you will also need to lower the saddle by 5mm.

that`s over simplistic , it don't work like that

bigpikle

dont forget its 2.5mm in RADIUS, so means a 5mm difference in the diameter of the circle you make with the pedal. With different lengths on different bikes it does mean the muscles and joints etc are following a different path many thousands of times on each ride. It does seem logical therefore that it could have a negative effect over time...

I've got bikes with 172.5 and 175mm cranks and have been assured by a Retul bike fit expert it does matter and isnt ideal, but frankly, I cant feel any difference when both bikes are set up properly. Thats not to say it isnt having an impact though????

ColinJ

I've got different length cranks on the same bike! I'm 6' 1" and normally ride with 175 mm cranks but my left crank cracked earlier in the year and I happened to have a 170 mm left crank in my junk box so I stuck that on.

It so happens that my left leg is significantly shorter than my right and I was getting a lot of backache on my bike. I found that not having to stretch down quite so far with my shorter leg has helped reduce the backache.

I didn't notice that my pedalling action felt different. In fact, I forgot that the replacement crank was shorter until I noticed that my back wasn't aching as much as before and wondered why.

Alex_Simmons/RST

Bigpikle wrote:

I've got bikes with 172.5 and 175mm cranks and have been assured by a Retul bike fit expert it does matter and isnt ideal, but frankly, I cant feel any difference when both bikes are set up properly. Thats not to say it isnt having an impact though????

Get a different expert.

Cranks length is over rated as needing to be perfect (IOW there isn't a perfect crank length), all one needs do is make sure saddle height and fore-aft is adjusted slightly.

Ride the crank length(s) you feel good on.

Richvelo

Ok there seem to be a range of opinons, my original question was whether there could be problems when swapping from a summer bike with 175mm to a winter bike with 172.5mm.

A few have said that that amount of difference would not be noticable which I would agree with in that I probably wouldn't notice at the time, but if it didn't matter then would cranks all be the same length?

That said I would imagine that if I reguarly swapped between the different bikes on a daily or weekly basis then I would prob suffer no ill effects but only swapping on a summer / winter basis could that be troublesome at each change over?
(provided the saddle height / position is ok)

Alex_Simmons/RST

Richvelo wrote:

That said I would imagine that if I reguarly swapped between the different bikes on a daily or weekly basis then I would prob suffer no ill effects but only swapping on a summer / winter basis could that be troublesome at each change over?
(provided the saddle height / position is ok)

Plenty of people have bikes with different crank lengths, and race on them.

I used to ride/race 165s, 170s and 175s on different bikes in the same week, depending on the ride/race I was doing. Provided the bike is set up right, it matters little.

Nowadays I have had to standardise to 170s on all bikes, as riding with a prosthetic leg has meant a range of pedal restrictions I didn't have before (e.g. limited knee flexion, no ankle joint, fixed components that are somewhat unforgiving against one's skin). I could go shorter but can't go longer.

Alex_Simmons/RST

cadseen wrote:

Smaller cranks will allow you to spin faster and may be more useful in road races and sprinting etc.
Larger cranks can suit slower pedalling when rolling larger gears in time trials.

You'll probably find pedal speed remains similar though.

Cadence may be a little lower on a longer crank but the pedal is traveling a greater distance per revolution.

cadseen wrote:

Neither lengths should cause knee or any problems. You must rember id you increase the crank length by say 5mm that you will also need to lower the saddle by 5mm.

Usually you find the amount to modify saddle height is not the same as the difference in crank length. Everyone will be different in this respect.