# Chain Length Question

Discussion in 'Cycling Equipment' started by rickn, Jun 1, 2004.

1. ### rickn Guest

Hello:
I am in the middle of a double to triple crankset upgrade which, among
other things, includes a new rear "long" derailleur, and a new chain.
How do I determine the correct chain length?
Thanks,
Rick

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2. ### Michael Dart Guest

In news:[email protected],
rickn <rickn> typed:
> Hello:
> I am in the middle of a double to triple crankset upgrade which, among
> other things, includes a new rear "long" derailleur, and a new chain.
> How do I determine the correct chain length?
> Thanks,
> Rick

It's still measured around the big cog and big ring (not through rear
complicated with suspension but it sounds like you have a road bike. Your
original chain length should work if you aren't changing the size of the big
cog/rings. The long cage derailleur will take up the slack when you are in

Mike

3. ### Rick Onanian Guest

On Tue, 1 Jun 2004 07:07:06 -0400, rickn <rickn> wrote:
>How do I determine the correct chain length?

You want the shortest length that will run in the big-big gear
combination. Maybe add a couple links (it is easier to remove them)
in case you change your gearing in the future.
--
Rick Onanian

4. ### LioNiNoiL_a t_Ne t s c a pE_D 0 T_Ne T Guest

> 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.