Hep with crank length for a new chainset

James Newton
James Newton Posts: 70
edited August 2011 in Workshop
I'm looking at getting a new chainset and wanting peoples opinion on crank lengths...

Inseam - 33"
Height - 5ft 11"
Weight - 65kg

I ride with a 165mm crank length on my track bike. My road bike crank length is 175mm, but they came on the bike as a complete, which I planned to change anyway.

I do like to spin the cranks so shorter is definitely my personal preference.

What I'm wanting to know is, if 165mm is going to be too short on my road bike and if 170's will be the better all round option?

The options on the chainset are 165, 170, 172.5 and 175mm.

Thanks in advance!

Comments

  • Wamas
    Wamas Posts: 256
    I have 33" inseam and was recommended 175mm on my bikefit.
    Although I use 172.5mm on both my road bikes.

    I would go with 172.5, if you prefer them slightly shorter, although I can't image you would notice much difference either way. 170mm is probably on the short side.
  • Wirral_paul
    Wirral_paul Posts: 2,476
    For your height and more importantly leg - 172.5. 175 would be more suited to a time trial bike for you. The shorter cranks should help spin at a higher cadence
  • Thanks guys! Anyone else got any input?
  • ba68
    ba68 Posts: 156
    I don't think you'll notice a huge difference in terms of cadence but do bear in mind that the saddle height and possiblly the position will need to be altered to maintain the same leg extension so this will affect the ride position.

    Incidentally I am 6' and 34" in seam and have just changed from a 175 to a 172.5 due to a change of chain set.
  • I've just been thinking about that actually...

    Am I right in thinking say for example, if I went from 175mm cranks to 170mm cranks I'd need to heighten the seatpost height by 5mm get desired leg extension?
  • ba68
    ba68 Posts: 156
    Yes. The pedal centre will be 5mm closer to the seat when you leg is fully extended so in theory you will need to raise the saddle by the same amount, raising the saddle will also shift the distance between the saddle and the bar, although only by a couple of mm, so you may want to shift the saddle forward slightly. You may not notice the difference, I guess it depends how precise your current setup is.
  • Bobbinogs
    Bobbinogs Posts: 4,841
    This comes up a few times and it is probably worth reading this:

    http://bikedynamics.co.uk/FitGuidecranks.htm
  • Bobbinogs wrote:
    This comes up a few times and it is probably worth reading this:

    http://bikedynamics.co.uk/FitGuidecranks.htm

    That's brilliant and extremely helpful! I think I'm decided on 170mm cranks now, much appreciated Bobbinogs!