SRAM short cage derailleur for 2x9 set up

[akazan]

This set up will be used for suspesion frame.

I need help if SRAM "short cage" rear derailleur will work on a 2x9 set up suspension frame. The chainrings will be 29T and 42T and the casette has 11x34T. I'm afraid about the chain growth that it will snap the the short rear cage derailleur.

Thanks again

[Drea]

Not all suspension frames has chain growth and some has more than others. Wich frame are you talking about?

[BruceBrown]

This set up will be used for suspesion frame.

I need help if SRAM "short cage" rear derailleur will work on a 2x9 set up suspension frame. The chainrings will be 29T and 42T and the casette has 11x34T. I'm afraid about the chain growth that it will snap the the short rear cage derailleur.

Thanks again

If you run the formula with a 11-34 rear cassette, it looks like you need a SRAM medium cage as the short cage's capacity (even if we consider the manufacturers are conservative with their rating) is not enough. As mentioned, depending on your frame's suspension design - allowance for chain growth upon compression is highly suggested. I run the long cage on my 2 x 9 full suspension.

Capacity formula...

Capacity Required (T) = (BIG ring - small ring) + (BIG cog - small cog)

Using your 2 x 9 of 42/29 with an 11-34 cassette:

T = (42T - 29T) + (34T - 11T)
.. = (13T) + (23T)
.. = 36T

(42 - 29) + (34 - 11) = 36T

I believe SRAM's short cage derailleurs are rated with a 30T capacity, whereas their medium cage has a 37T capacity and the X.0 longs are up to 45T. I don't know what the new XX 10 speed medium and longs have for capacity.

BB

[ionsmuse]

I think the capacity formulas are guidelines, not rules. Chaingrowth at full travel is probably more relevant.

I've had an X9 shortie on my Leviathan, with a 14-32 and 20 and 34 rings with no worries for over a year.

[akazan]

I'm hoping to use the SRAM short cage derailleur for my DW Sultan. But to be on the safe side, i have to use a "medium cage" derailleur.

Thanks alot for all your input.

[kapusta]

This set up will be used for suspesion frame.

I need help if SRAM "short cage" rear derailleur will work on a 2x9 set up suspension frame. The chainrings will be 29T and 42T and the casette has 11x34T. I'm afraid about the chain growth that it will snap the the short rear cage derailleur.

Thanks again

Look at the sticky at the top of the drive train board.

A SRAM short will probably not work for that setup if you want all gear combos, but you won't be snapping or breaking anything if you go in the wrong combo, you will just make the chain go slack and maybe drop it.

[kapusta]

I think the capacity formulas are guidelines, not rules. Chaingrowth at full travel is probably more relevant.

I've had an X9 shortie on my Leviathan, with a 14-32 and 20 and 34 rings with no worries for over a year.

Your setup requires 4 teeth less RD capacity than his does.

[ionsmuse]

Your setup requires 4 teeth less RD capacity than his does.

Indeed. I suspect that the differences in axle path(s) make more of a difference than a bit more chain.

[jut8]

Does the formula still apply if you are wanting to run a 1x9? I was wanting to do a shimano 11-36 cassette, with a 32t front chainring.....can I run a sram short cage x.9? Or would i need to stick with an 11-34?

[ingluis]

Does the formula still apply if you are wanting to run a 1x9? I was wanting to do a shimano 11-36 cassette, with a 32t front chainring.....can I run a sram short cage x.9? Or would i need to stick with an 11-34?

For 1x9 you only need to consider the cassette to compute capacity. In your case 36-11 = 25.

[jut8]

nice, so i should be good with a short cage, i guess its a 12-36, not the 11-36, so i should be well within the limits of a short cage. thanks!

[ninth44]

nice, so i should be good with a short cage, i guess its a 12-36, not the 11-36, so i should be well within the limits of a short cage. thanks!

It's within chain wrap capacity but I don't think the x.9 short cage can handle a larger cog than a 34.

[boomn]

It's within chain wrap capacity but I don't think the x.9 short cage can handle a larger cog than a 34.

if the long or medium cage can then the short can too. They share the same body design, only the cage length differs

[jut8]

hmmm....this could be interesting. I really wanted to run that 12-36 for the 1x9 on a full suspension bike, but i guess i will have to go with 11-34 if it doesnt work.

Anyone tried this?

[ninth44]

if the long or medium cage can then the short can too. They share the same body design, only the cage length differs

Yeah, that sounds logic and you might be right. But. I'm in the hunt for a short cage rd myself and noticed that some sellers claim that 34 is the largest appropriate cog. Maybe they're just being overly cautious?
http://mikesbikes.com/product/sram-x...ge-42196-1.htm
http://rbikes.com/product/sram-x-9-r...ge-62425-1.htm

[boomn]

Yeah, that sounds logic and you might be right. But. I'm in the hunt for a short cage rd myself and noticed that some sellers claim that 34 is the largest appropriate cog.
http://mikesbikes.com/product/sram-x...ge-42196-1.htm
http://rbikes.com/product/sram-x-9-r...ge-62425-1.htm

I know I've heard from people on this forum that they don't have any problems with such a setup. Unfortunately people that run custom cassettes are rare, but I did find this post at least

[ninth44]

Great, thanks for clearing that up boomn.

[jut8]

now that i think about it, my Stumpy 29er Hardtail came with an X.0 long cage and a 12-36 cassette, and it worked fine. So if it did, do you think the short cage would be OK?