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max cog of SRAM short cage RD?

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max cog of SRAM short cage RD?

Old 05-16-16, 08:50 PM
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bikebreak
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max cog of SRAM short cage RD?

I have had good luck fitting a 30t in Shimano RD7700 and 7900, about 10% over rated cog capacity.

Curious if a SRAM RD rated for 28 can also work with a 30t.


Also, since both 10 and 11 speed SRAM is 1:1 cable pull, could I use an 11 speed RD with 10 speed shifters or vice versa?

thanks!
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Old 05-16-16, 09:12 PM
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k_kibbler
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Depends. The threaded hole in the derailleur hanger needs to be low enough to mount the RD and allow adjusting the B-screw enough to leave 6~8mm between the upper pulley and the biggest cog.

You still have to think about chain wrap capacity. Short cage is usually good for about 30t of slack take-up (varies between Sram/Camp/Shim). On 11-30 & 53/39, that's 33t of slack between big-big and small-small, so you wouldn't be able to cross-chain in both directions, or risk tearing out the RD or having too much chain slack.

To your 2nd question: Yes.
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Old 05-17-16, 05:29 AM
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^ good answer.
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Old 05-17-16, 07:34 AM
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I've heard reports of a 30 working on a Sram short-cage RD. I know from personal experience that a 32 does not work. For that, you need a WiFli RD.

And as previously said, you can swap out 10- and 11-speed RDs. I've been going back and forth between a new Sram Red 10-speed short cage RD and a Force-22 Wifli RD. Since I do not have a compact crankset, I use an 11-32 cassette when I take trips to the mountains.

Last edited by topflightpro; 05-17-16 at 07:39 AM.
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Old 05-17-16, 08:35 AM
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Originally Posted by bikebreak View Post
I have had good luck fitting a 30t in Shimano RD7700 and 7900, about 10% over rated cog capacity.

Curious if a SRAM RD rated for 28 can also work with a 30t.


Also, since both 10 and 11 speed SRAM is 1:1 cable pull, could I use an 11 speed RD with 10 speed shifters or vice versa?

thanks!
I would not use a 30 tooth cog with the short cage. You risk destroying the RD. Even if you try to avoid cross chaining, it can still happen. In the large-large combination, the chain will be too short, unless you make the chain longer, in which case the chain will drag on the chain stay in the small-small. The Force WiFli is not that much. I know this all from experience - including destroying an RD.
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Old 05-17-16, 08:49 AM
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I had no trouble getting my 7800 RD to work with a 30T cog on my 80's steel bike. I decided to move that gearing to my Cannondale with SRAM Rival and there was no way any b-screw adjustment was going to get that to work. Out of curiosity I tried the Rival derailleur on the steel bike and it was closer, but not enough to clear to 30T Cog.

I ended up buying a Wolf tooth Road Link for the Cannondale and the Rival short cage now works great with 50-34 12-30T gearing, chain wrap is fine for cross chaining both ways.
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