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Two Cx bikes need lower gearing (Shimano 10sp)

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Two Cx bikes need lower gearing (Shimano 10sp)

Old 01-26-15, 10:55 AM
  #1  
SEAtrain
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Two Cx bikes need lower gearing (Shimano 10sp)

I'm currently working on two different 10-sp cx bikes which need lower gearing. I'd like some input on my choices and options, please. Both bikes are "gravel bikes" used on paved, gravel and rough rock roads with steep climbs. Both are over-geared on the climbs. Whatever I end up doing, it needs to work reliably.

Current setup:
Chainwheel: 46x34T
Cassette: 28-11T
Rear Derailleur: Shimano 105 (approx. 2.3" pulley C-C) and Shimano Ultegra (approx. 2.1" pulley C-C)
Lever: Shimano 105 and Shimano Ultegra

New Parts:
Cassette: Shimano XT CS-M771 11-32 or, perhaps, 11-34
Rear Derailleur: Shimano XT M772 (Med Cage)
Chains: Shimano Ultegra 10-sp

Is this certain to work well assuming proper installation? Is there another route I should consider? I originally selected a XT-M786 rear derailleur but found a thread which states that I need a 9speed derailleur. I'm not sure how to get the specs to confirm one way or another.
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Old 01-26-15, 11:18 AM
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Originally Posted by SEAtrain View Post
I'm currently working on two different 10-sp cx bikes which need lower gearing. I'd like some input on my choices and options, please. Both bikes are "gravel bikes" used on paved, gravel and rough rock roads with steep climbs. Both are over-geared on the climbs. Whatever I end up doing, it needs to work reliably.

Current setup:
Chainwheel: 46x34T
Cassette: 28-11T
Rear Derailleur: Shimano 105 (approx. 2.3" pulley C-C) and Shimano Ultegra (approx. 2.1" pulley C-C)
Lever: Shimano 105 and Shimano Ultegra

New Parts:
Cassette: Shimano XT CS-M771 11-32 or, perhaps, 11-34
Rear Derailleur: Shimano XT M772 (Med Cage)
Chains: Shimano Ultegra 10-sp

Is this certain to work well assuming proper installation? Is there another route I should consider? I originally selected a XT-M786 rear derailleur but found a thread which states that I need a 9speed derailleur. I'm not sure how to get the specs to confirm one way or another.
The M771 is the correct derailer and will work with your 10 speed. The M786 is a Dynasys that will not work with road shifters. Before you purchase the XT, however you could try to use the 105 derailer with a 32 tooth low gear. If it doesn't work, you can always get the XT.
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Old 01-26-15, 11:32 AM
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Depending on what 105 RD you have, it could go up to 32. The RD-5701 with the longer cage is approved to 32T with a double crank up front. It could probably be pushed to 34.

The big issue I see with your setup is that you're going to be using 10 speed shifters with a 9 speed derailleur. That may just not work. Everyone I know who mixes road brifters with mountain derailleurs are using 9-speed brifters, with a 9 speed mountain derailleur and cassette.
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Old 01-26-15, 12:17 PM
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Your 10 speed shifters will work fine with the 9 speed RD. I prefer the older style ones that have a barrel adjuster. The T661 is nice. Avoid any that say Shadow or low- normal, IMO.
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Old 01-26-15, 01:01 PM
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Your medium cage has exactly the required tooth capacity with the 11-34 you are looking at - 35 teeth. You should be good to go.
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Old 01-26-15, 01:37 PM
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Originally Posted by dr_lha View Post
The big issue I see with your setup is that you're going to be using 10 speed shifters with a 9 speed derailleur. That may just not work. Everyone I know who mixes road brifters with mountain derailleurs are using 9-speed brifters, with a 9 speed mountain derailleur and cassette.
I have a 9-speed Ultegra (RD-6503) rear derailleur I've used with a 10-speed shifter and chain for thousands of miles and it works perfectly. Absolutely no reason a 9-speed MTB rear derailleur wouldn't be just as satisfactory.
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Old 01-26-15, 01:40 PM
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Originally Posted by HillRider View Post
I have a 9-speed Ultegra (RD-6503) rear derailleur I've used with a 10-speed shifter and chain for thousands of miles and it works perfectly. Absolutely no reason a 9-speed MTB rear derailleur wouldn't be just as satisfactory.
Good to know. I couldn't think of any real good reason it shouldn't work, but I've had issues mixing and matching components before. It only takes a minor mismatch for your shifting to be a pain-in-the-butt after all.
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Old 01-26-15, 01:49 PM
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It's been well documented and discussed in multiple cycling forums about the successful use of Shimano 9-speed MTB rear derailleurs with Shimano 10-speed shifters.

As for personal experience; I've set up my wife's road bike exactly that way: Shimano 6603 triple shifters/crank/front derailleur and Shimamo XT 9-speed rear derailleur and an 11-34 cassette. It's worked perfectly for over 10,000 miles.
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Old 01-26-15, 08:07 PM
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You can use this power calculator along with Sheldon's gear calculator to estimate if you're going to need a 32 or 34 rear sprocket. The difference between 28 to 32 is double the difference of 32 to 34.

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Old 01-27-15, 07:32 PM
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Originally Posted by SEAtrain View Post
I'm not sure how to get the specs
https://productinfo.shimano.com/specifications.html

MTB > Rear Derailleur > Submit
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