Join Date: Aug 2005
Location: Awesome, Austin, TX
Bikes: Specialized Roubaix, Interloc Impala, ParkPre Image C6
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First you need to know how many teeth are on the front chainrings and the rear cogset. Typical fronts include 53/39, 50/34 or in a triple, 52/42/30. Yours could be different. The tooth count is usually stamped on the ring but if you can't find it, count 'em.
For the cogset, again, each gof should have a stamp with the tooth count or you can count 'em.
Once you have all that, google "sheldon Brown gears" and you'll find a link to his gear ratio calculator. After putting in the info for your chainring and cogset, it'll calculate ratios, gear inches and MPH given a certain RPM.
Oh yeah...you'll need to know your wheel diameter (likely 700) and your crank arm length.
2014 Specialized Roubaix2003 Interloc Impala2007 ParkPre Image C6 (RIP)