> How do I determine the correct chain length?
The formula I learned many years ago is easier to do than it is to describe:
Measure the distance in inches from the centre of the spindle [at the
dustcap] to the centre of the rear axle. Multiply that distance by two,
and round the product up to the next whole inch. Call this number A.
Add the number of teeth on the largest chainwheel to the number of teeth
on the largest sprocket. If that sum is odd, add one to get an even
number. Divide the resulting sum by two. If that quotient is odd, add
one to get an even number. Again divide the result by two, and call the
final quotient B.
Add the numbers A and B and one to get the chain length you need.
For example, one of my bikes has a centre-to-centre distance from the
spindle to the rear axle of 17-3/4 inches. Multiply by two and get 35.5,
so A is 36 [the next whole number].
The largest chainwheel has 53 teeth, and the largest sprocket has 28, so
their sum is 81. This is an odd number, so add one to get 82. Divide 82
by two to get 41. This is another odd number, so add one to get 42.
Divide 42 by two to get 21, so B is 21.
Adding A and B and one, I get 36 + 21 + 1 = 58 inches of chain.