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Crank arm lengths

alp777alp777 Posts: 211
edited April 2009 in Road beginners
I picked up a new bike today that should have had 172.5mm cranks but it has been fitted with 170mm.

Should i change them? will it make much difference?

Posts

  • brownboshbrownbosh Posts: 602
    It depends on personal preference, bike type and use and inside leg measurement.
  • HonestAlHonestAl Posts: 406
    If you're pretty tall, long legged, 170 is "too short" for your legs in principle. I'm sure someone here can point you at some learned treatise on the geometry of your frame, length of your inside leg etc. How tall are you / how long is your inside leg? I've got pretty short legs (31 inches ish) and have fitted 170s on all my bikes, but I suspect you won't feel it's like night and day.
    "The only absolute statement is that everything is relative" - anon
  • richaricha Posts: 1,634
    Does it matter having 172.5 on one bike and 175 on another.

    What are the advantages of a long cranks? I am 5'10" and have 32" legs.

    Cheers,
    Rich
  • RichA wrote:
    Does it matter having 172.5 on one bike and 175 on another.

    What are the advantages of a long cranks? I am 5'10" and have 32" legs.

    Cheers,

    Longer cranks means more leverage. MTbs tend to have 175 length cranks whereas road bikes might be 170 to 172.5. Riding MTB requires occasions where short, steep technical sections have to be climbed/got over. The extra leverage allows the rider to get over easier. Road biking on the other hand lends itself to a smoother pedalling action in which 'spinning' the cranks more quickly is more efficient. Shorter cranks means the cranks will rotate around a shorter radius thus meaning each revolution takes less time.

    In practice, I don't know if you'd notice it. I notice the difference on my MTB (175s)and Road bike (170s)when cycling on the road. However, this could be down to lighter bike, less rolling resistance, larger wheels. better aerodynamics etc.

    Also those with longer legs would need longer cranks. I find the 170s fine for me (5' 9'' and 30 inch inside leg).
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