Crank Lengths

Building a new race bike soon. Have always just used whatever cranks happened to be lying around but am gonna buy some nice ones for a change. Have never used anything but 165mm. Should I bother looking into whether longer cranks might be a good idea, or just stick to 165 til forever? What lengths are youse guys running? Gonna drop a bit of coin so wanna get the right ones.

Discuss.

How tall are you? I’d say match your crank length to your femur length, and lean towards a shorter crank for road riding.

  • Longer cranks give you more leverage, equivalent to slightly reducing your gear ratio. Shorter cranks do the opposite. On a road bike you’ll adjust your gearing to whatever end result you want, so there’s no net difference, at least in terms of leverage. Neither “gives you more power”.

  • Longer cranks mean larger pedal circles, so it makes sense to me that this should roughly match your leg length. If a tall runner with long legs ran with the small steps of a much shorter person, barely lifting their feet off the ground, it would be underutilising their muscles. Likewise if a shorter runner was taking huge strides, lifting their knees up to their chin, they’d be putting unnecessary strain on their joints. That’s obviously an exaggerated example, but you know what I mean.

  • I had some knee pain caused in part by my knees moving laterally when I pedalled. I switched from 172.5 to 165, and immediately noticed a big improvement. I think the less acute bending at the top of the pedal stroke was the trick. I’m slightly shorter than average (177cm). Also, the majority of my riding was on fixed bikes with 165 cranks, so I don’t think my muscles had learnt how to deal with the longer cranks in my road bike.

  • Triathlon and TT guys are now favouring shorter cranks, as you can a slightly lower position without your knees hitting your chest.

  • I read somewhere that the difference in gear ratio between 165 and 175 cranks is equivalent to the change from a regular to a compact crankset, so you may want to adjust your chainrings accordingly.

Hmm that was longer than expected. I’ve been thinking a bit about this lately, if you couldn’t tell.

I’m looking for a crankset for Swuzz Jnr’s next bike.
Am thinking about going from 150 -> 165.
He’s 153 tall. Pedal to saddle (t-t) is 79cm.
Partly in anticipation of growth.
The more I read about performance effects, the more inclined I am to stay with the 150’s.
The more I watch eBay/gumtree/FB listings, the more inclined I am to grab a mega deal on some 170’s.

Argument, got some nice 165s for sale?

If you ride a track of 42 degrees or steeper and do a lot of sprints or mass start races I’d advise getting 165s. I stubbed my toe on the bank of a 32 degree track once, and that was with 165s.

For TT events where you’re staying mostly in the lane you could get away with longer.

I agree with Rhys, always 165mm unless you’re well tall or TTing.

^I’m going to disagree with the 165mm crank recommendations.

If you have a look at all the bikes at world/national level, pretty much no one uses 165mm cranks anymore.
170mm is normal even for shorter riders (sub 170cm) and a lot of guys/girls are using 172.5 or whatever length they use on road just to keep a familiar feeling set up.
I had 165mm for years because it’s what came with my bike, I changed to 170mm and it didn’t affect my ability to spin smaller gears. Also, I don’t know if it was psychological or an actual mechanical advantage that I could notice but it did seem easier to stay on top of bigger gears (96-98).

Very interesting comments!

I wish I had a set of 170mm so I could do a decent A/B. At the end of the day I’ll always be a slow old hack anyway, but as I said above, it’d be nice to be able to make an informed choice before parting with a heap of cash if there’s a better option.

Matthias, did you change to 170mm because a coach told you to or something, or did you just take a punt?

If it makes any difference (doubt it but whatevs), my body dimensions are very average in most respects. I think I’m about 5’10", I always ride approx. 55cm square frames and am neither particularly heavy nor stick thin. Have got average length limbs too. The only thing I can think of that’s a bit of an anomaly is the size of my feet. They are fecking huge. No idea if that would have any bearing on desirable crank length though.

Maybe I should just buy some 170mm and see how they go. If, although unlikely, they feel really shit, I’ll just sell them and cut my losses. If they feel better or exactly the same, I guess that’s sort of a win either way.

I was informed by more experienced riders that 170mm would be better for me, wether they had any good reasons for giving that advice I don’t remember. I think if the majority of top level track riders are using longer cranks then it’d be a safe bet to get 170s. It might feel a little different for a start but chances are with in a ride or two you wont even notice anymore. Chances of pedal strike are very very low even at DISC, you’d have to be doing sub 25km/h I reckon and even then you’d probably lose front wheel traction before hitting the pedal.

Cheers for the input.

Was just brought to my attention that we actually have some square taper 170mm road cranks at home. Grouse. Provided they don’t throw the chain line out too far, I’ll give them a go.