Chain Length?

We receive questions about the proper chain length quite often, this time we have received two, one from Peter who has a fairly good idea how to do it and one from Rusell who has a 21 gear MTB. Here (again) we will explain the two methods of finding the correct chain length

From Peter:

Question:

Dear Samuel,
I have a question about chain length please. How do I determine if a newly purchased chain needs to be shortened and if so by how much? Have had a think and am wondering do I set the chain on the smallest front and rear sprockets and then adjust its length so that the rear derailleur is just able to keep the correct tension? What is your advice please?
Many thanks,
Peter.

And from Rusell:

Question:
How do I work out the length of chain I need oh my 21speed MTB?

Hi Peter and Rusell.

This is a tricky question that we should all know the answer too, unless you have the bike shop fit your chain every time you need a new one. If you are fitting a new chain it is a very good idea to clean the chain and re-oil it before you go for a ride as the chain manufacturers pack the chains with protective grease that does not run so well on the gears. Its best if you clean the chain before you fit the chain to keep your hands cleaner, then once the chain is fitted and working perfectly you can oil it.

Method 1

The preferred method of fitting a chain by Shimano is that you put the chain around the large chain ring and the large sprocket, with out threading the chain through the rear derailleur, where the chain meets and then add two links and cut the chain at that point.

Method 2

Put the chain round the small chain ring and the small sprocket and through the rear derailleur, then the spring in the rear derailleur should take any slack from the chain. Buy holding one end pull the chain together until the spring of the rear derailleur takes the strain and that’s where you need to cut the chain.

There are the two methods, I hope they are a help, it makes no difference between road and MTB bikes, make sure there is enough chain for the big chain ring and sprocket and not too much for the small chain ring and the small sprocket and all should be OK.

Read more about Big Chain Ring with Big Sprocket? or The Correct Chain Length