Crank length

nigelgos
nigelgos Posts: 128
edited November 2013 in Road buying advice
I'm looking at upgrading the groupset on my Allez 2011. Looking at the geometry for the 56" frame the stock crank is a 172.5mm. The 105 is a great price at Merlin Cycles atm but only 170mm. Would this matter? or maybe be a better size for me?

My inside leg is ~85.5cm and I'm 179cm tall.


Edit: actually I've just re-measured the inside leg using the 'book between legs method' and I'm ~85.5cm.

According to this (http://www.machinehead-software.co.uk/b ... lator.html) I'm about in the middle of a 170/172.5 so my thinking is that a 170mm crank would be fine for me.

Comments

  • napoleond
    napoleond Posts: 5,992
    Wouldn't matter a jot. You'd just need to raise your saddle by the 2.5mm
    Insta: ATEnduranceCoaching
    ABCC Cycling Coach
  • 86inch
    86inch Posts: 161
    NapoleonD wrote:
    Wouldn't matter a jot. You'd just need to raise your saddle by the 2.5mm

    Maybe, maybe not... "my standard" crank length is 172.5mm which i am used to. If that changes to 170 or 175 i can tell immediately, and my legs do not thank me for it........It has been ever thus for 30 years. So i'm not exactly a newbie :wink:

    Up to the OP, but i'd advise caution before switching, and try to keep all bikes similar.
  • sungod
    sungod Posts: 17,356
    NapoleonD wrote:
    Wouldn't matter a jot. You'd just need to raise your saddle by the 2.5mm

    or reduce it by 2.5mm to keep same maximum extension

    :)
    my bike - faster than god's and twice as shiny
  • StillGoing
    StillGoing Posts: 5,211
    edited November 2013
    At the risk of repeating this yet again. Your crank length determines your seat height. You don't want to be over extending at the bottom of the pedal stroke so will set the seat height accordingly. However, if the cranks are too long and you've set the seat height for the correct extension at the bottom, your leg is going to be over compressed at the top of the pedal stroke. This can reduce the ability to get your maximum power out and cause injury. The correct length crank gives the correct angles at the top AND bottom of the pedal stroke.

    There's plenty who think it's hokum, but unless you've done back to back tests using a power meter, you probably wouldn't notice the effects. I moved from 170mm cranks to 165mm cranks after back to back tests with a power meter. The figures were there in black and white to show the results. Same cadence and same gear, just different length cranks and a revised seat height to suit.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • napoleond
    napoleond Posts: 5,992
    sungod wrote:
    NapoleonD wrote:
    Wouldn't matter a jot. You'd just need to raise your saddle by the 2.5mm

    or reduce it by 2.5mm to keep same maximum extension

    :)

    No, if you got a shorter crank you'd need to raise your saddle to keep the same max extension
    Insta: ATEnduranceCoaching
    ABCC Cycling Coach
  • cycleclinic
    cycleclinic Posts: 6,865
    I ride 170mm to 177.5mm cranks and can switch between them all with no issues so I would say it is a non issue. Some TT bike have really short cranks for tall riders.
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • sungod
    sungod Posts: 17,356
    NapoleonD wrote:
    sungod wrote:
    NapoleonD wrote:
    Wouldn't matter a jot. You'd just need to raise your saddle by the 2.5mm

    or reduce it by 2.5mm to keep same maximum extension

    :)

    No, if you got a shorter crank you'd need to raise your saddle to keep the same max extension

    oops, i misread the op, thought he was going longer for some reason
    my bike - faster than god's and twice as shiny

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