help: medium or long cage x9 rear D

danK said:

Which do I need?
I'm running an xt compact crankset and an xt cassette, but forget which on:

If it's the 34, I want the long?
If it's the 32, I want the medium?
Or am I mistaken?

I'm at work and can't remember which I have, hence the general inquiry.
Thanks.

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cage length is determined by your crank and cassette. you take the difference of crank teeth and add those to the difference of cassette teeth to come up with a total capacity. different caged deraillers have different capacities. the medium cage X-0 has a capacity of 37 teeth, while the long cage has a capacity of 45 teeth. so if you have a 22-32-44 crank and 11-32 cassette, that is a capacity of (44-22) 22 + (32-11) 21 = 43 teeth, thus you would need the long cage derailler, as that combination of crank and cassette would exceed the capacity of the medium cage RD.

i believe the only size the X-9 comes in is long cage. but even if it did have a medium cage version, you would want a long cage for both of those cassettes (assuming 11-32 and 11-34 and that you have a 22-32-44 crank).