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CS-6700 12/30 with CN-7801 and RD-7801?

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CS-6700 12/30 with CN-7801 and RD-7801?

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Old 09-10-14, 11:23 AM
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CS-6700 12/30 with CN-7801 and RD-7801?

Guys,

I have D/A 7800 set up on my bike. I was wondering if I can run a newer Ultegra CS-6700 12/30 with the existing D/A 7800 chain and rear der. I wanted a lower gearing than my current CS-7800 12/27. If this works, I only need to get a new cassette and a chain.

I know the other option would be using a SRAM PG-1070 12/32 with a long cage D/A 7800 rear der. People seem to have good results from this combo. I will need to buy a new rear der if I were to go with this route.

Thank you!

AX
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Old 09-10-14, 11:32 AM
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My friend's DA 7800 RD is loud as sin on the 27t he has, no matter how we tune the RD. I believe 27 is the max on that edition so going all the way out to 30 I would imagine is impossible.
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Old 09-10-14, 11:35 AM
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+1. You might be able to get a 28t to work, but that's probably about it.
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Old 09-10-14, 03:20 PM
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I use the 12-30 cassette with a D/A 7800 rd. It depends on your derailleur hanger configuration. BTW, the short cage and long cage (GS) rds both handle the same size large cog. The GS just wraps more chain for a triple.
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Old 09-10-14, 05:48 PM
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Originally Posted by dtrain
+1. You might be able to get a 28t to work, but that's probably about it.
I have race two bikes with RD-7800s, and the 28t works well, though the jockey wheel is damn near riding on the cog even with the B screw all the way in - on both bikes.
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Old 09-10-14, 07:20 PM
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Will the 7800 shifters work with a short cage 6700 RD? If so, I have the 12-30T working fine on three different bikes with the short cage RD.
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Old 09-10-14, 08:53 PM
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Originally Posted by fstshrk
Will the 7800 shifters work with a short cage 6700 RD? If so, I have the 12-30T working fine on three different bikes with the short cage RD.
They should. One of my race bikes has 6700 shifters, the other has 5700. The RD-7800 works fine on both, so I'd think that's pretty good indication that 7800 shifters would work fine with an RD-6700.
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Old 09-10-14, 09:47 PM
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The 6700 RD is a later design and specifically rated to handle 30t (per Shimano). The 7800 and 6700 RD's were only rated to 27t. The 10 speed shifters and derailleurs should be interchangeable.
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Old 09-11-14, 09:16 AM
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I have DA 7800 with RD 7700
It runs with a CS-6700 12-30 but is loud in 30. Shifts into it just fine
Also loud with my usual 12-27 cassette in 27. I think the RD is rated for 25 max!

The Shimano RDs have quite a bit of wiggle room.
I imagine the newer RD 5700A and 6700A, which are rated for 30, will actually fit 32 or even 34.
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