Crank length query

SLX01
SLX01 Posts: 338
edited March 2012 in Road buying advice
I am used to riding a compact 172.5 road bike crank but have started to build a TT bike for duathlons. I have been offered a cheap carbon 170 (not compact) which is a bargain but obviously shorter. Would fitting this be bad move just to save money or should I stick to a 172.5. I was thinking that moving to a non compact the shorter length may be an advantage?

Comments

  • rake
    rake Posts: 3,204
    not sure of the reasoning there, shorter cranks help with cadence but non compact gears are higher. some use longer cranks for tt, depends how long your legs are as well.
  • maddog 2
    maddog 2 Posts: 8,114
    I'd stick with a 172.5

    plenty of cheap non-compact cranks out there
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • SLX01
    SLX01 Posts: 338
    rake wrote:
    not sure of the reasoning there, shorter cranks help with cadence but non compact gears are higher. some use longer cranks for tt, depends how long your legs are as well.

    Somehow I got it into my head that regular cranks are harder to spin due to the gearing so shorter crank length would reduce that somehow?? I knew I should have paid more attention in physics at school! :lol:
  • cougie
    cougie Posts: 22,512
    FWIW - I dont see how 2.5mm make any difference in the scheme of things. you alter your leg length far more than that depending on where you sit on the saddle. 2.5mm on that distance is negligible.
  • MichaelW
    MichaelW Posts: 2,164
    The difference between 172.5 and 170 is marginal but so is the time difference in a TT race. If you are going to the bother of building a specialist TT bike, may as well optimise it for the correct crank length for your legs, gears and riding style, whatever that is.
  • Crankbrother
    Crankbrother Posts: 1,695
    Give it a go ... They always say only make changes in 5mm inrements so in that scheme of things it's not gonna cause that much trouble ... Changing saddles often causes that much difference ...

    One question ... What exactly are you thinking of changing from, to? ... And on what bike?
  • SLX01
    SLX01 Posts: 338
    MichaelW wrote:
    The difference between 172.5 and 170 is marginal but so is the time difference in a TT race. If you are going to the bother of building a specialist TT bike, may as well optimise it for the correct crank length for your legs, gears and riding style, whatever that is.

    I did try 172.5 on the bike but found that my knees came up fairly high and restricted my diaphram so I did think that 170 may reduce this and improve my technique/performance on aerobars.
    Opinion does seem to be its not that greater deal so I will give it a go I can always change the chainset later if it is really not suitable.
  • bristolpete
    bristolpete Posts: 2,255
    I run 165mm cranks on my Venge as I have short inseam and have to say I love it. Much better pelvis rotation, can keep a higher cadence, feels so much better and I wish I had done it years back. Feels like a free gear on the bike. If I were TT'ing I would definitely run 165mm.

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