Cranks Size

Discussion in 'Beginners' started by Farky, 6 Jun 2008.

  1. Farky

    Farky Senior Member

    West London
    Morning all,

    Quick question; how do you know what size crank-set you need? I see there are a number of options like 167mm, 172mm and 175mm as just a few examples.

    I'm pretty new to all this so sorry if it seems like a dumb question!
  2. ASC1951

    ASC1951 Guru

    Not a stupid question at all and your average LBS youf won't be very helpful.

    Sheldon Brown again -
    You will soon find that his site is most people's starting point for good advice.

    I'm 5' 6" and I use 170mm cranks on geared road bikes and 172.5mm off road. I have tried 165s for fixed riding but found that I couldn't generate the leverage on hills, so I went back to 170s for that too.
  3. rickangus

    rickangus Über Member

    west sussex
    The ideal crank length is 21% of your 'actual' leg length (as opposed to leg length for trousers).

    To calculate, measure your height in metric, no shoes, standing against a wall. Then sit on floor, back to wall, and measure your height again - may have to get someone to help.

    Subtract smaller number from larger - that is your leg length; take 21% of that and that is your ideal crank length. If it comes out to one of the above figures your in luck!
  4. ASC1951

    ASC1951 Guru

    Farky, it also depends on what sort of riding you do. It's normal to have longer cranks for MTB because you aren't spinning so much and at low speeds on steep stuff the extra leverage is more important than efficiency. for road riding go for the one nearest your 'ideal' length.

    Standard adult cranks come in 170, 172.5 and 175. 165s take a bit more finding. It's not that critical for the recreational rider and unlike frames no-one ever has cranks made to measure.
  5. betty swollocks

    betty swollocks large member

    Almost everyone rides 170 on road and 175 off. Suggest you do the same.
    Experiment later on if you want.
  6. Steve Austin

    Steve Austin The Marmalade Kid

    I've used cranks from 170 to 180 on and off-road. Being a big lad with long legs anything shorter than 175 feels really uncomfortable to me.
    the 180's were fine for SSing off-road as you have loads of leverage, but a bit tricky to spin fast. Must admit they were excellent for turning over a big gear at speed though.
    Whatever the science my opinion is that you should use whatever cranks you feel comfortable with, and they should be of corresponding length to the users legs. ie long cranks=long legs

    Just for interest Magnus Backstedt has been experimenting with 190 cranks. So worth trying some different sizes. i'm settled on 175 on and off-road now
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