Join Date: Jul 2007
Location: Portland, OR
Bikes: Two old Schwinns, Kona Cinder Cone, Redline MonoCog, Custom (U.B.I.) Columbus Cyclocross/commuter.
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I've had really good luck with this method.
Taken from the Park Tool Website.
SIMPLE EQUATION: L = 2 (C) + F/4 + R/4 + 1
L = Chain length in inches. Round the final result to closest whole inch figure.
C = Chain stay length in inches, measure to closest 1/8”. Use chart below to find decimal measurement.
F= Number of teeth on largest front chainring.
R= Number of teeth on largest rear cog.
Example: A bike has a 42-32-22 front chainring set up. Use only the 42 for the equation. The rear cog set has 32 tooth largest cog. The bike measures 16-3/8” from the center of the rear axle to the center of the crank bolt. The decimal equivalent for 16-3/8” is 16.375 inches.
L = 2 (16.375) + 42/4 + 32/4 + 1
In the example above, this becomes 32.75 + 10.5 + 8 + 1 = 52.25 inches. Chains cannot be joined at 52.25 inches, so this length is rounded to 52 inches.
For this system, round up from 0.5. For example, a chain length figured to be 55.5 would be rounded to 56 inches.
To measure the new chain, lay it on a flat surface with the rollers and plates aligned vertically. Pull on each end to straighten out the chain. Measure from either end. Remember, you can only shorten the chain at whole inch increments. If the chain uses a master link, install it on one of the chain for purposes of measuring, and measure including the master link.