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Old 01-24-17, 04:46 PM
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So if you're adding a new cassette, I would first make sure that the Rear Mech can handle the big chainring and big cog combo.

(Big ring - Small ring) + (big cog - small cog) = Chain wrap capacity.

You'd have to look up the specs on the mech to see if this falls within tolerance.

Then to size the chain I usually take the chain and wrap it through the FRONT mech around the big chainring, and around the big cog (NOT the rear mech) and see at which links you can join the chain (with no slack in the chain). Then count over 2 links longer (one inch) and connect the chain at that point.


Taken from Park Tools 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 above 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 teeth on the 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.

but that requires maths.

Hope this helps!
Seafris is offline