15.5.08
retro pr0n
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ibald
bike nerd
i was discussing replacement cranks for somebody's bike and the question of crank length came up.. somehow i ended up with a short essay:
my opinion is shared by a vast amount of pro riders, coaches and ergonomists (is that a word). don't get anything longer than 172.5. i use 170 which is probably a bit long for me, 165's would be better but i couldn't get any.
most people use cranks that are too long. you need to be 6'+ (or have freakishly long legs) to use 175s. cranks too long will push your knee angle under 90 deg on dead top centre, this is not good for your knees, they don't like to push out from an acute angle like that, you know it aches when you stand up from a crouch... it's the same thing. there is no physical detriment i have been able to find from using shorter cranks (apart from possible inefficent cadence, but that's what gears are for).
it's a problem for mass market bikes that they use mass market parts which for economies of scale are punted out at whatever size they decide will bolt onto the majority of frames, on "tiny" and "small" frames you will get 170s; "medium" will be 170 or 175 and "large" and "extra large" will be 175. 4 frame sizes, 2 crank lengths... you get the idea.
people argue that you need good long cranks to get decent leverage. this is utter nonsense on a bike with gears, yes crank length makes a difference but this can be compensated for with the geary gubbins. singlespeeds and fixed wheel have their own concerns but still too long is too long (there are exceptions - specific hill climb events will benifit but we're talking short term use). lots of singlespeeders complain about having sore knees; this is less to do with the lack of gears and more to do with the added stresses of a misproportioned bike setup.
i've argued this with people before and it makes even more sense to me written down. take my opinion as you wish but i'm right :)
my opinion is shared by a vast amount of pro riders, coaches and ergonomists (is that a word). don't get anything longer than 172.5. i use 170 which is probably a bit long for me, 165's would be better but i couldn't get any.
most people use cranks that are too long. you need to be 6'+ (or have freakishly long legs) to use 175s. cranks too long will push your knee angle under 90 deg on dead top centre, this is not good for your knees, they don't like to push out from an acute angle like that, you know it aches when you stand up from a crouch... it's the same thing. there is no physical detriment i have been able to find from using shorter cranks (apart from possible inefficent cadence, but that's what gears are for).
it's a problem for mass market bikes that they use mass market parts which for economies of scale are punted out at whatever size they decide will bolt onto the majority of frames, on "tiny" and "small" frames you will get 170s; "medium" will be 170 or 175 and "large" and "extra large" will be 175. 4 frame sizes, 2 crank lengths... you get the idea.
people argue that you need good long cranks to get decent leverage. this is utter nonsense on a bike with gears, yes crank length makes a difference but this can be compensated for with the geary gubbins. singlespeeds and fixed wheel have their own concerns but still too long is too long (there are exceptions - specific hill climb events will benifit but we're talking short term use). lots of singlespeeders complain about having sore knees; this is less to do with the lack of gears and more to do with the added stresses of a misproportioned bike setup.
i've argued this with people before and it makes even more sense to me written down. take my opinion as you wish but i'm right :)
Labels: bikes
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