long, Medium or short.

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May 23, 2012, 03:33:45 PM

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[damo]

Or8 chaps.

Right, is there anychance that someone could clear this up for me.

What are the difference between long, medium and short cages on rear mech. What are the different uses for them.

Layman's terms will do thanks. 

Cheers in advance.

Damo

[nunomelo77]

Every rear mech has a cage underneath it to guide the chain with using the jockey wheels. The length of this cage is important and it is generally best to stick with original length your bike came with.

For a Cross Country/All Mountain/Freeride bike, you get the choice of a medium or long cage; a medium cage doesn't hang down as low and therefore is less lightly to get damaged, however will only work if you are running a double chainring setup, which is unusual unless you have a bash ring. The reason for using a long cage is that the chain needs to be able to move a lot more with a triple chainring setup, because of the larger range of gears.

For DH bikes you will definitely need to go for a short (or super short) cage, as the cage needs to be as high as possible and the gear range is smaller and you will only use a single ring.

Always make sure that the mech can compensate for any "chain grow" through the complete suspension movement.

One other thing: SRAM derailleurs have shorter cages than Shimano's!

[mc]

How much the mech sticks down has nothing to do with what length you need. It's just a beneficial result.

The main deciding issue for the minimum length of mech you need, is chain growth.
Chaingrowth is a total of the difference between the small/large ring up front, and the smallest/largest sprocket at the back.

So for example, a twin ring set-up with a 22-32 up front, and a 11-32 on the back, the chain growth is (32-22)+(32-11) or 10 + 21 = 31, which means you need at least a medium length SRAM mech, or short Shimano.
From memory a short cage SRAM is capable of 22tooth chaingrowth, with 32 for medium, and 42 for long.

The main benefit of using the shortest mech possible, is better chain tension. The shorter the mech, the tighter the chain will be, which helps to reduce chainslap and chainsuck.