New casette so new chain...

antsmithmk

I've purchased a new cassette and have gone for a 28-12 to replace a 25-11 on my Allez.

Obviously I need a new chain at the same time but how much longer will it need to be to accommodate the 3 extra teeth? Is it as simple as 3 extra links? I have the old chain so should be easy to measure up.

Essex Rouleur

No its not just three extra links as it depends on what cassette you are fitting, but in general it tends to be 2-3 extra links.

Just buy a decent chain (they are always long enough) put the rear derailleur into the small cog and the front onto the big ring. Wrap the chain over the big ring, through the rear derailleur and pull both ends towards each other at the bottom until the rear derailleur jockey wheels line up in a straight line down from the center of the small cog. Mark the chain and remove the extra links. If when you pull the two ends of chain together whilst lining up the rear jockeys wheels, that it falls between a link then add the extra link its falling on. Its very much a visual thing getting it right.

And always make sure that the inside link of the chain is in your left hand and the outer casing of the link in your right when piecing them together ( when facing the chain from the derailleur side). This makes a stronger connection.

StillGoing

Wrap the chain around the biggest sprocket on the cassette and the big ring on the front but not through the rear derailleur. Where the chain meets, add two links to include the power link if you're going to be using one, and cut the chain. Once cut to length, then thread it through the rear derailleur.

antsmithmk

Thanks for the above....