cycles per second
Join Date: Oct 2003
Location: Minnesota
Bikes: Vitus Aluminum, DiamondBack Apex, Softride Powerwing 700, "Generic" Ishiwata 022, Trek OCLV 110
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It's a matter of ratios. To get the "equivalent" chainring for a cog change, multiply the gear ratio by the new cog size.
Example: 53/12*11 = 48.6
So the closest gear to a 53/12 using an 11T cog is 49/11.
To get the "equivalent" cog for a chainring change, divide the new chainring size by the gear ratio.
Example: 42/(39/23) = 24.8
So the closest gear to a 39/23 usnig a 42T chainring is 42/25
