Changing Chain length to suit Rear Mech

[MGDriver]

I'm after a bit of advice; I'm currently using a Shimano Alivio rear mech, a friend has given me his old (nearly new really ) Deore XT rear mech, I have noticed that the small chain wheels are smaller on the XT mech than the Alivio, does this mean I will have to shorten the chain slightly? or will it make no real difference?

[fredmundo]

Hi MG, do you mean the arm with the sprockets attached too or do you mean the actual sprockets?

If it's just the sprockets then I'd not bother. if the arm is shorter and you use a triple ring up front then you may find you will need to definitely shorten it, probably a bit more than you think, and then also be careful with your gear discipline too.

[MGDriver]

Thanks for your reply fredmundo.

It's just the 'Jockey Wheels' are a smaller diameter, the Rear mech is a 'Long Cage' version and therefore still the same length as my current one, and should be suitable for a triple ring set-up.

My thoughts are the same as yours; as it's just the Jockey Wheels, I'll leave it as it is for now, I'll report back if I needed to make any adjustments, or it caused any problems

[steve_sordy]

There are several methods to determine the correct chain length; try this one:

Put the chain over the biggest ring and largest sprocket, with the chain running through the jockey wheels as normal. The derailleur cage should be pointing forward and at about 45 degrees to the horizontal. If the cage is pointing straight down, then you will probably be able to remove a couple of links. Try nipping the chain together to see what happens to the cage angle.

If you have a full suss bike, then do the assessment with the rear suspension fully compressed. (Either let the air out or ask a heavy friend to assist).

If the chain is too slack, you will have an increased risk of the following:
# Chain coming off.
# Chain rattling on the chainstay.
# Chainsuck.

Happy fettling!