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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 11-19-09, 01:22 PM   #1
wearyourtruth
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formula/program for converting speed to RPM and vice versa?

is there a formula or program that allows me to convert my mph to rpm based on my gear ratio? or vice versa. just curious really but i haven't found anything online.
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Old 11-19-09, 01:39 PM   #2
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diameter(mm)*pi*rpm*60/1609344
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Old 11-19-09, 01:44 PM   #3
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There's this thing called Google... took me about 7 seconds.
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Old 11-19-09, 02:00 PM   #4
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http://sheldonbrown.com/gears/

Set to "MPH @ 100 RPM" (or "KPH @ 100 RPM"). Once you know your speed at 100 RPM, it' pretty easy to calculate your RPMs at other speeds.

E.g.: If 15 MPH = 100 RPM, then new RPM = [X/15 * 100], where "X" is the new speed.
If your new speed equals 16 (meaning, "X"), then your new RPM = [16/15 * 100] = 106.7 RPM.
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Old 11-20-09, 03:02 PM   #5
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http://software.bareknucklebrigade.c...it.applet.html
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Old 11-20-09, 03:11 PM   #6
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Yeah ^^^ What he said. Rabbit does exactly what you want. You can also download the applet so you don't have to go to that webpage every time you want to calculate.

http://software.bareknucklebrigade.com/ (click "Outside Browser")
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Old 11-20-09, 06:20 PM   #7
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Quote:
Originally Posted by wearyourtruth View Post
is there a formula or program that allows me to convert my mph to rpm based on my gear ratio? or vice versa. just curious really but i haven't found anything online.
RPM of the wheel? Or RPM of your feet (cadence)?

If RPM of the wheel, then gear ratio is completely irrelevant. See adriano's formula (which appears to be correct).

If RPM of your feet, it's only slightly more complicated. You'll need to use gear ratio to determine wheel RPM.
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