Crank length questions

[bedraggled]

Do you have the same length cranks on every bike or does it vary from bike to bike?
Can you tell the difference if you swap between crank lengths?
Which do you prefer?

All my bikes have 175mm but got some 170mm, wondering if my knees will object if I use them.

 

[hamster]

The point of crank length is to match to the dimensions of your leg, giving the most efficient positioning for your muscles to act to best effect. (As an example, look at bad kids bikes which have adult cranks, where feet pedal exaggerated circles).

Over the years I have shifted towards exactly the same crank length on everything (170mm). The most surprising difference was shifting from 175 to 170 on my singlespeed. Gearing stayed the same but I was faster AND found seated climbing easier.

There is this argument trotted out that longer cranks give more leverage. Indeed they do. However changing gear achieves the same effect.

 

[Nob]

I’ve been on 177.5’s since 79 & as they are comfortable for me I’m not going to change...why fix it if it ain’t broke & I don’t need any knee leg troubles as I age by anykind of experimenting with other lengths.....

 

[jim haseltine]

I used to ride 170 on my winter bike because cheapness and 177.5 on my other road bikes. It might have been imagination or a gain in fitness after the winter but the hills seemed easier on longer cranks - other than that I couldn't feel any difference. I also had 165mm on a fixed time trail bike - again, felt no difference when riding.
I've standardized on 175mm for years now - mainly because the longer cranks weren't easily available in the group sets I started using. I'd like to blame my current poor performance in hilly stuff on shorter cranks but I really suspect that advancing age and increasing body weight have more effect than a couple of mm of crank.

 

[hamster]

I’ve been on 177.5’s since 79 & as they are comfortable for me I’m not going to change...why fix it if it ain’t broke & I don’t need any knee leg troubles as I age by anykind of experimenting with other lengths.....

Exactly - stick with what suits. I once did a tour having just switched to 175. I had knee pain all week. I suspect it was due to the extra articulation of the knee (to get over top dead centre, and being too bent at the start of the power stroke).

 

[Old Ned]

I've got 170 (6 3/4") on my 'classic' road bikes and a mix of 172.5 and 175 on my 'classic' MTB's and modern road bikes. TBH, I don't really notice any difference. When I first started TT'ing back in the early 60's it was discovered by my LBS that I had a mix of 6 1/2" and 6 3/4" Stronglight 49D cranks on my bike. I'd been given them by an older guy who was having a clear-out. I had no idea there was anything wrong.

 

[Jonny69]

I have traditional 165mm track cranks on my fixed gear bikes. My on-road geared bike has modern mtb cranks which pretty much all seem to be 175mm and I can definitely feel a difference. The 175s feel too big for me for a road bike. They're bearable, but it does feel like I'm wanging my legs around too much and it feels inefficient.

 

[mattr]

I'm switching to shorter cranks across the board. (going down to 165)
Knees will tend to complain if you go longer (if you are close to your limit), if your knees complain when you go shorter, it's *extremely* unlikely to be the crank length that did it. More likely something else you've changed (saddle height and setback will need altering if you change crank length)

Only issue i've had with going shorter is that now i need to do it on everything i ride for more than an hour at a time. Some people do notice the shorter cranks, others don't.
Some don't even notice odd length cranks, but that baffles me.

 

[Old Ned]

Some don't even notice odd length cranks, but that baffles me.

When mine were odd I was only 14 or 15 and didn't know any different. I'm sure I'd feel it now though :roll:

 

[Holiocornolio]

I switched from 175 to 170 a while back. I thought I noticed a difference for the first few pedal strokes and then I decided I was imagining it. There probably is a small difference in my pedaling efficiency but not enough for me to really notice or care about. I still have 1 bike with 175mm cranks and I honestly don't notice a difference, even over longer rides. As someone else has posted I think going to a longer crank is going to create more issues than going shorter will, but the small difference between 170 and 175 isn't enough for most people to need to worry about.