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Please help me understand why

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Please help me understand why
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Posted: Sep 12, 2014 at 9:49 Quote
So I keep hearing it. 'You should use a medium or long cage rear derailleur for a 1x10 with an extended range 42 or 40 tooth chain-ring on you rear cassette'.

I'm a long term fan of short cage 9 speed SRAM derailleurs and I just cannot see nor understand why I need a medium or long cage 10 speed derailleur, just ugly, slow shifting and far more in harms way. As far as I can see the top cog is changing gear and the length of the upper body is the same, and that's what is doing the shifting, the cage seems to be longer or shorter to deal with shifting on the crank chain rings.

If you know why you really need a medium or long cage RD with a 42tx10 or 40tx10 please explain in technical terms, rather than hearsay.

Also I would be pleased to hear from anyone with direct personal experience of conversions, particularly SRAM vs Shimano, x9, XO, slx xt. zee, etc, how do they compare and how useable is the extra chain ring? Would I be best off with one-up components or some other brand.

ps I already run a 1x9 with a narrow wide

Posted: Sep 12, 2014 at 11:48 Quote
the medium & long cages is used to take up the extra slack in the chain when running larger cassettes. You need a longer chain when using the larger cogs, a short cage will not be able to take up enough slack to keep the chain under proper tension and you'll have a droopy chain.
I hope this is clear & helps

Posted: Sep 13, 2014 at 1:17 Quote
Sort of right, the capacity of a rear derailleur is the maximum tooth capacity (change) that it can handle, this is roughly based on the arc of movement around the top pulley centre, since there is no front chainring change to worry about then a shorter cage may work on the rear. Wide range 42 - 11 = 31 that's the tooth range you need, Shimano GS has a capacity of 35 so that would be OK, sorry don't know about the ranges on SRAM stuff

Posted: Sep 13, 2014 at 1:24 Quote
i made a custom 9 speed 11-40t setup with a short cage zee mech and an sram shifter, perfect Smile

I really do not need 10 gears and have a load of 9 speed stuff hanging about

the capacity of the RD is half the story as you also need to allow for any chain growth that your bikes suspension linkage may have.

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