• 07-15-2011
    Roar
    Crank length - how critical when you are short?
    Hi there -

    I have done a bit of reading on this on the forums and it seems that a lot of people feel that it's not a huge deal to have 172.5mm cranks if your optimal length is 170mm... but I am assuming we're talking about your average sized man....

    I am 5'2" (female, 30 inch inseam).

    I need to swap to a compact double. I have Campagnolo Record on the bike at the moment, and it's older, so it's 10 speed. I am therefore at the mercy of eBay...and there haven't been any 170mm lately, but loads of 172.5mm....

    I saw some crank-arm-length-calculator online once, and I think I came up with my optimal crank arm length to be 165mm, but that's not going to happen because the shortest arm Campy makes is 170mm.

    So, clearly, 170mm is better, but is 172.5 going to be a big deal when I am this far off my optimal length to start with?

    Many thanks for your opinions.
  • 07-15-2011
    Dave Hickey
    I'm 5'7".. I have bikes with 165, 170, and 172.5 cranks.

    The bike with 172.5 cranks was just changed from 170 for the same reason you list above. I found the crankset I wanted but they didn't have it in 170mm... No issues at all

    I really cannot tell any difference.
  • 07-15-2011
    Daren
    Don't get a Campy crankset.:p

    The difference in lengths is going to either increase the load you place on your knees at the top of your pedal stroke, make you rock side to side on your saddle at the bottom, or both. As long as you don't have any knee issues and your saddle height is adjusted properly you shouldn't have any issues.
  • 07-15-2011
    wim
    Quote:

    Originally Posted by Roar View Post
    So, clearly, 170mm is better, but is 172.5 going to be a big deal when I am this far off my optimal length to start with?

    In spite of all the crank length advice found on the internet, there is no optimal crank length. In addtion, a 2.5 mm change (stack of just two dimes) is easily taken care of by the elasticity of connective tissue and muscle unless you're grossly misfitted on your bike and are sitting at a bizarre extreme of a fit dimension.

    Most people going 2.5 mm longer would lower their saddle by 2.5 mm to regain their old saddle height. But there are knowledgeable riders who would not change saddle height. They would just let the natural flexibility of the human body take care of this very small change. I've always followed the "do nothing" procedure when changing crank lengths and it's been good for me.
  • 07-15-2011
    V3T
    You could also keep your current crank arms and swap the chainrings, but you would need to find a set of chainrings with the correct BCD with 50T, or maybe 51T. Probably easier said than done...
  • 07-15-2011
    Roar
    Cool. Thank you.
  • 07-15-2011
    Roar
    Dumb question - but am I correct to assume I can't use a newer 11speed setup on my 10 speed?
  • 07-15-2011
    namillis
    Great point. On the other side, I'm 6'3" and based on those optimal lengths I computed years ago I would need a longer than average crank (I forget how long). Well, my bikes always come stock with 175mm cranks and that's what I've always ridden. Spending extra money on cranks that are slightly longer doesn't make sense. So here I am, perfectly happy on my 175mm cranks. Heck, if I got longer cranks I'd probably worry about dragging the ground on corners!
  • 07-15-2011
    gamara
    If you wanted to go the 11spd route, the cheapest route would be to buy a new 11spd gear cam for your lever. This will involve a rebuild of your right shift lever to give it the extra click needed for 11spd. I know that there are companies out there that sell this. Then the other parts needed will be a new 11spd chain & the cassette. Your 10spd rear derailleur should be fine. That is your cheapest route. Otherwise you will have to buy a new set of levers if you didn't want to do a rebuild.
  • 07-15-2011
    haasezlube
    I personlly had this question quite a few years back and found an uncanny amount of tech articles written by well known individuals on how to do formal measurements to fit yourself accuate crank lengths but at the end the all the calculations there are only more calculations to be considered or abstract data such as knee design internally or surgical mods as which i have! All the best calc's i have seen would indicate at my height that i require a 175mm length but in real life use that hurts my surgically enhanced knee so i dropped to a 172.5 and NO more pain!! My wife which is 5'1" at 103 measures out to a 155 mm or so they say and after spending a bit of time and money to have a custom crankset made up we then purchased her new bike with SRAM Apex Cranks which only come down to a 165mm in size and she actually preferred them while climing but likes her thirds 160mm custom set for the long flats and or down hills! I hope this did not make your hunt more confusing but i only aim to say that i find there to be a lot of details involved in finding the "IDEAL" crank length and that sometimes many close ones can all do the same or very simalar trick!!
  • 07-15-2011
    Camilo
    Do you have to use a Campy crankset with Campy 10 speed components?
  • 07-15-2011
    pwork
    I am 5'7" and probably the most un-flexible member on RBR. I'm more of a MTBr and love a 175 crank on the trail. I feel like the road runner @ 90rpm; I'm a masher. However, I just recently went from a 172.5 double to a 165 compact (cheap crank to try it) and love the difference. I did adjust the saddle some to make up for the difference. My back hurts less and I'm able to spin more freely; lot less TDC dwell. Bottom line, you might want to pick a cheap crank to experiment.
  • 07-15-2011
    Roar
    Interesting pt re picking up some inexpensive cranks to try it.

    I would, except I don't think I know enough to buy something that would work with my setup. And I am not doing my own wrenching....

    But it's appealing.