Originally Posted by
iamtim
It took me a while to figure out skid patch calculation: turn your gear ratio into a fraction and then divide the top by the bottom. If the result is an integer, that's the number of skid patches. If it's fractional, than the number of skid patches is the bottom number. So in the case of a 48 tooth chainring and a 16 tooth cog you've got 48/16 = 3, so 3 skid patches. In the case of a 48 tooth chainring and a 17 tooth cog you've got 48/17 = 2.82, so 17 skid patches.
I'm pretty sure that's wrong.
According to S. Brown and other sites I've seen, it boils down to simplifying the ratio, then taking the bottom number of the fraction (or "denominator") for the number of skid patches.
Example:
42/16 will simplify to 21/
8. You have 8 skid patches.
44/16 will simplify to 11/
4. You have 4 skid patches.
48/16 will simplify to 3/
1. You have 1 skid patch.
If you skid ambidextrously, you can double your # of skid patches, but ONLY if it's an odd number.
Prime numbered chain rings (47, 51, etc) are good because your ratio will never simplify, and your skid patch count will simply be your rear cog number.
To the OP- just get a 17t cog like everyone says. 34 skid patches, they'll all start to run together anyway.