Bicycle Mechanics - Crank Length
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03-20-09, 09:23 AM
I'm just in the planning stages of building up a bike ('86 Schwinn Traveler Frame). I was thinking about what size cranks I'll need. I have a 32" inseam. When I put that into a crank length calculator I found online ( Crank Length Calc (http://www.machinehead-software.co.uk/bike/cranks/cyclist_crank_length_calculator.html) ) it recommended 166.6 mm. So, basically 167.5mm. Browsing ebay and whatnot, it seams that there are a lot more options for 170mm. I don't want to be too OCD about this but is there a noticeable difference in 2.5 mm?
03-20-09, 09:34 AM
Use 170s. Better a bit long than to short. Roger
03-20-09, 09:35 AM
Are you going by pants size or by pubic bone height? The inseam that matters on your bike is actually closer to your pubic bone height. Using the inseam length of your pants in a sizing equation or calculator will give you inaccurate results.
And, no, 2.5mm is not that much difference. Dont worry about it. Most people can comforatble ride cranks between 165 and 175 mm without noticing much difference. Nobody who buys a production bike gets to chose optimum crank length and that doesn't seem to be a problem.
My advice is: If you like spinning easy gears: use shorter cranks; if you like pushing harder gears use longer cranks.
And if you currently have a bike and you like it, see what length the cranks are on that and use the same on your new bike.
03-20-09, 09:50 AM
Thanks, to both of you. I measured my inseam, in bare feet on a hard floor to my pubic bone (or as close as I could get.)
I'm just getting back in to riding after several years of nothing. I was never much of a spinner, so maybe 170mm will be the way to go.
03-20-09, 10:25 AM
170 mm gives you many more options with crank models as it is a very common size.
There have been numerous studies to try to equate recommended crank length to riding inseam measurements and the general concensus is it doesn't matter much and is more personal preference than science.
Lennard Zinn did an extensive study with a wide variety of riders and crank lengths from, IIRC, 160 to 220 mm long. He had to conclude there was no correlation of crank length with inseam in regards to power output or rider efficiency. He was very disappointed as he makes custom cranks but was honest enough to report his findings. :)
I ride both 170 and 175 mm cranks on different bikes and barely notice the difference.
03-20-09, 10:33 AM
Sooooo....don't overthink it. K.I.S.S.
03-20-09, 06:14 PM
I have an interest in crank length and I would say that its better to go a fraction shorter than a fraction longer. I know of no disadvantages of being a fraction short but going a little too long will start to hurt your knees.
Anyway with a 32" inseam either 165mm or 170mm will be fine. 170mm is as long as I would go for your inseam though.
03-20-09, 06:55 PM
Are you converting it into a fixie, or are you rebuilding it into a geared bike?
Most folks going for a fixie prefer shorter cranks because it reduces the chance of a pedal-strike, which can have unpleasant consequences, so the 165 might be preferable, and there are plenty of 165 track/fixie cranks.
Longer cranks give you better leverage though, so if it's a road bike you're building up, a 170 would be better.
03-20-09, 07:27 PM
It's also easier to spin quickly with shorter cranks. Depends on what you're using this bike for. If you're doing more climbing, definitely go for longer cranks. If it's a fixed gear, go shorter. Or, in lieu of anything else, go for what's cheaper!
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