Hi,
I just wondered how people worked out which length cranks suited them best. Trail and error sounds expensive. I currently use 170mm. Am I likely to notice a difference with 175? I'm not that tall, but tend to use high gears so wondered if longer cranks might even be better.
Sticking with 170 would be playing safe, but I've been keeping an eye out for parts for a new bike, and started to wonder whether I'm unnecessarily limiting my choices.
Tony S
Crank length - how to choose, and does it matter?
It's one of those things where there are as many theories as there are crank lengths!
If you have a look at various race training books you'll find various formula for working it out, indeed a hunt around the 'net will probably find some too. They broadly seem to agree that a male with an average leg length should have 170mm cranks on a road bike and perhaps 175 on an MTB. Don't ask me what average leg length is though!
Just to muddy the waters Mike Burrows recently did an article based on some other research that suggested cranks can be much shorter - he swapped his (c)170 for (c)150 and said he got on fine.
Oh yeah, just to be awkward, single speeders use slightly longer ones for better leverage and fixers use slightly shorter ones for better ground clearance on corners.
If you have a look at various race training books you'll find various formula for working it out, indeed a hunt around the 'net will probably find some too. They broadly seem to agree that a male with an average leg length should have 170mm cranks on a road bike and perhaps 175 on an MTB. Don't ask me what average leg length is though!
Just to muddy the waters Mike Burrows recently did an article based on some other research that suggested cranks can be much shorter - he swapped his (c)170 for (c)150 and said he got on fine.
Oh yeah, just to be awkward, single speeders use slightly longer ones for better leverage and fixers use slightly shorter ones for better ground clearance on corners.
Observation suggests:
Lankies can get away with virtually any length cranks.
The shorter you are the more important you get something that fits.
There isn't nearly enough choice off the peg or custom.
Shops will tell you 'not to worry' about length as your knees give out.
Accomodating five footers and six footers on 170s is like putting a 1ft stem on all bikes.
It boils down to this - cranks are quite an expensive component to stock a range of sizes for and an area where off the peg bikes can nail their price point by homogeneity. Thinking about the issue is too much hassle/cost. If the back of you knees describe an acute angle at tdc they're too long. Your cranks that is, not your legs.
Lankies can get away with virtually any length cranks.
The shorter you are the more important you get something that fits.
There isn't nearly enough choice off the peg or custom.
Shops will tell you 'not to worry' about length as your knees give out.
Accomodating five footers and six footers on 170s is like putting a 1ft stem on all bikes.
It boils down to this - cranks are quite an expensive component to stock a range of sizes for and an area where off the peg bikes can nail their price point by homogeneity. Thinking about the issue is too much hassle/cost. If the back of you knees describe an acute angle at tdc they're too long. Your cranks that is, not your legs.
It seems obvious to me that shorter legs require shorter cranks.
I've changed two of my bikes over to 165mil cranks from 170 (29" inside leg), and though you might think a decrease of 5mil is niether here nor there,personally I've found it to be much better for me. Especially when out on a long,all day ride.
Now, if doing a ride on one of the bikes with 170's,at the end of the day I can definitely tell the difference. i.e. the knees ache.
Eventually, I'll put 165's on all the bikes. It's just the right size for me.
I've changed two of my bikes over to 165mil cranks from 170 (29" inside leg), and though you might think a decrease of 5mil is niether here nor there,personally I've found it to be much better for me. Especially when out on a long,all day ride.
Now, if doing a ride on one of the bikes with 170's,at the end of the day I can definitely tell the difference. i.e. the knees ache.
Eventually, I'll put 165's on all the bikes. It's just the right size for me.
pioneer wrote:It seems obvious to me that shorter legs require shorter cranks.
My wife is 5' 3" and only stopped getting knee pain when she went to 155mm cranks. Her speed and endurance on solo and input on the tandem went up immediately. The problem is short cranks are not widely available and are expensive when you find them or are old fashioned designs (e.g. TA cyclotourist). Shimano used to do (may still do?) a 160mm basic crank set that fits shorter people but even that might be too long for women around 5' of whom there are many.
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Yorkshireman
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- Location: North Hykeham, Lincoln.
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Hm! I recently changed my crankset from 28, 38, 48 / 170mm to 22, 32, 44 / 175, and the only thing I've noticed is the change (for the better) in gearing. I forgot to change the saddle height, but I don't seem to have any problems ... yet 
PS
I'm 5'2" if that matters ... Who said short arse?
PS
I'm 5'2" if that matters ... Who said short arse?
Colin N.
Lincolnshire is mostly flat ... but the wind is mostly in your face!
http://www.freewebs.com/yorkshireman1/
Lincolnshire is mostly flat ... but the wind is mostly in your face!
http://www.freewebs.com/yorkshireman1/
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piedwagtail91
- Posts: 258
- Joined: 23 Jan 2007, 9:18pm
i don't think it makes a difference.
when i noticed a crack in one of my cranks the day before a club standard ride ,i swapped it for another. after 160 miles when i came to take it off to get another from the shop i realised i done the ride with odd length cranks, 172.5 175.
when i told the shop owner, a clubmate, he said he had his best ever year racing on odd length cranks, he didn't realise until mid season but left them anyway.
when i noticed a crack in one of my cranks the day before a club standard ride ,i swapped it for another. after 160 miles when i came to take it off to get another from the shop i realised i done the ride with odd length cranks, 172.5 175.
when i told the shop owner, a clubmate, he said he had his best ever year racing on odd length cranks, he didn't realise until mid season but left them anyway.
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piedwagtail91
- Posts: 258
- Joined: 23 Jan 2007, 9:18pm
piedwagtail91 wrote:fatboy wrote:piedwagtail91,
Given that most people actually have odd length legs why shouldn't they have odd length cranks?
that what i think, but was told the difference needs to be made up in the pedal thickness for some reason.
What you were told just seems wrong to me. If you've got different length legs then surely each leg will want to make a slightly different size circle not one that's a bit higher. Anyway, what do I know
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly
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piedwagtail91
- Posts: 258
- Joined: 23 Jan 2007, 9:18pm
fatboy wrote:piedwagtail91 wrote:fatboy wrote:piedwagtail91,
Given that most people actually have odd length legs why shouldn't they have odd length cranks?
that what i think, but was told the difference needs to be made up in the pedal thickness for some reason.
What you were told just seems wrong to me. If you've got different length legs then surely each leg will want to make a slightly different size circle not one that's a bit higher. Anyway, what do I know
i agree ,i usually make up my own mind on crank length. i don't think 2.5 mm makes a noticeable difference, if you think a lot of fuss is made over crank length you want to see some of the stuff they debate on the time trial forum,. the aerodynamic loss of a qr skewer as opposed to an allen key type (pitlock type) being recent topic !