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What matters more: matching rear derailleur to shifters or cassette?

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What matters more: matching rear derailleur to shifters or cassette?

Old 06-11-15, 07:09 PM
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What matters more: matching rear derailleur to shifters or cassette?

So I recently got a nice thirdhand 2009 Fuji Touring with nearly all stock parts, but many of the parts were just worn to the ground and beyond. I've fixed the major issues (brakes), and I'm finally tackling the cassette and chain (which is stretched so badly I can't shift into my third/largest gear up front).

Of course, I couldn't do this without getting sucked into the dangerous, addicting, bottomless vortex that begins with "I need to replace my 9 speed cassette, and this 10 speed is on sale" and leads to "so these are the parts I need for a custom bike build"...you know how it goes.

Eventually, swayed by the opportunities I had at hand (namely, a 105 10spd 11-28 on sale, and a hand-me-down set of Dura Ace bar end shifters ), I've settled on taking my [Shimano Tiagra shifters and FD, SRAM PG950 9spd 11-32 cassette, Deore RD, 30/42/52 Truvativ Touro crankset] current set up and turning it into a 3x10 set up with the 105 cassette and the DA bar enders.

My question is: what matters more, matching the RD with the cassette, or matching the RD with the shifters? I've seen Sheldon's page on DA compatibility, and since he says "Any 10 speed Shifter except Shadow" can be used with "Any 1997 or later Shimano Rear Derailer; Or: Any S.I.S. Rear Derailer except pre-1997 Dura-Ace and XTR Shadow series", I'm guessing that I should worry more about matching the RD with the cassette, but I am unsure how his reasons for the compatibility, the part about cable travel, will affect any of the set up, especially with the way bar end shifters work (which I don't really know how they differ from STI shifters).

Given all that, should I get a 105 RD to match my cassette, or are there any advantages to getting a Deore or XTR rear mech over a road one, or any other tips/concerns you guys can think of?

Thanks!
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Old 06-11-15, 07:28 PM
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Deore and XTR are mountain bike parts (I think), so are not compatible with road parts (I think) .... different cable pull or such. So go all road parts.
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Old 06-11-15, 07:29 PM
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Unless you were mixing Shimano shifters and SRAM rear derailleur or vise versa, it most likely doesn't matter...the rear derailleur will do what the shifters an cassette tell it to.
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Old 06-11-15, 07:33 PM
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Originally Posted by Homebrew01
Deore and XTR are mountain bike parts (I think), so are not compatible with road parts (I think) .... different cable pull or such. So go all road parts.
An mtb rear derailleur will work fine with road bike shifters.

Im using Dura Ace 9 speed bar end shifters with XT rear derailleur an it works perfect. If I were you I'd just avoid the shadow stuff altogether since it seems to be much more finniky than non shadow derailleurs.

Last edited by Wolf Dust; 06-11-15 at 07:47 PM.
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Old 06-11-15, 07:56 PM
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Shimano 10-speed mountain bike rear derailleurs are not compatible with road bike shifters, 9-speed mtn. RD's are.
In general Mountain bike and road bike front derailleurs and shifters are not cross compatible, but with certain modifications they can be.
Indexed shifters need to have the same number of speeds as the number of cassette cogs.
There is a lot of compatibility across the Shimano line, but there are also some serious incompatibilities. Your questions and choices need to be specific. And although Sheldon Brown's (RIP) advice is monumental, some of it is no longer applicable.
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Old 06-11-15, 07:59 PM
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Originally Posted by Homebrew01
Deore and XTR are mountain bike parts (I think), so are not compatible with road parts (I think) .... different cable pull or such. So go all road parts.
Deore, XTR, and other mountain bike cassettes are compatible with Shimano road shifters, but not necessarily with all rear derailleurs.

Here is a link to helpful (or confusing) information about shifting and gearing compatibilities: https://en.wikibooks.org/wiki/Bicycle...ing_Dimensions

Last edited by Al1943; 06-11-15 at 08:04 PM.
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Old 06-11-15, 09:33 PM
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Originally Posted by RideForWind
Given all that, should I get a 105 RD to match my cassette, or are there any advantages to getting a Deore or XTR rear mech over a road one, or any other tips/concerns you guys can think of?
A 105 rear derailleur might not work with your 11-32 cassette- some people claim it can be done by finessing the B-screw adjustment, but this sounds too finicky for my tastes. You need a "MTB" rear derailleur to work reliably.

However, as you've found, 10-speed MTB (aka "Dyna-Sys") rear derailleurs are not compatible with "road" shifters, either bar-end or brifter.

The way around this is to use a 9-speed MTB rear derailleur. When used with 10-speed road shifters, they will index across a 10-speed cassette.
https://www.universalcycles.com/shop...6&category=691
https://www.universalcycles.com/shop...4&category=691
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Old 06-11-15, 10:03 PM
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Originally Posted by Wolf Dust
Unless you were mixing Shimano shifters and SRAM rear derailleur or vise versa, it most likely doesn't matter...the rear derailleur will do what the shifters an cassette tell it to.
Nope, sticking to all Shimano; saving getting to know the SRAM system for a dedicated road bike :rollseyes: That's good to know! (And makes sense, I guess the RD itself can't move independently...haha)

Originally Posted by Al1943
Shimano 10-speed mountain bike rear derailleurs are not compatible with road bike shifters, 9-speed mtn. RD's are.
In general Mountain bike and road bike front derailleurs and shifters are not cross compatible, but with certain modifications they can be.
Indexed shifters need to have the same number of speeds as the number of cassette cogs.
There is a lot of compatibility across the Shimano line, but there are also some serious incompatibilities. Your questions and choices need to be specific. And although Sheldon Brown's (RIP) advice is monumental, some of it is no longer applicable.
Well, I'm not sure what the differences between mountain bike derailleurs and road bike ones are, nor the purpose of those differences/lack thereof. Anyone want to give me a rundown?

Originally Posted by Al1943
Deore, XTR, and other mountain bike cassettes are compatible with Shimano road shifters, but not necessarily with all rear derailleurs.

Here is a link to helpful (or confusing) information about shifting and gearing compatibilities: Bicycles/Maintenance and Repair/Gear-changing Dimensions - Wikibooks, open books for an open world
Thanks for the link! Dumb question: Do I have to measure all those specs...? Haha it just seems like I haven't seen any cable pull lengths or chainring spacing numbers on the specs of any websites or the boxes of parts...
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Old 06-11-15, 10:08 PM
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Originally Posted by Jeff Wills
A 105 rear derailleur might not work with your 11-32 cassette- some people claim it can be done by finessing the B-screw adjustment, but this sounds too finicky for my tastes. You need a "MTB" rear derailleur to work reliably.

However, as you've found, 10-speed MTB (aka "Dyna-Sys") rear derailleurs are not compatible with "road" shifters, either bar-end or brifter.

The way around this is to use a 9-speed MTB rear derailleur. When used with 10-speed road shifters, they will index across a 10-speed cassette.
https://www.universalcycles.com/shop...6&category=691
https://www.universalcycles.com/shop...4&category=691
https://www.universalcycles.com/shop...0&category=691
Thanks Jeff! I'm actually preparing to overhaul with Dura Ace 10 spd bar-end shifters, and a 105 10spd 11-28t cassette, so that shouldn't be a problem, but if I have to replace my current cassette and chain only for some reason (e.g.: my chain finally throws in the towel), that's very useful to know. How is it that 9-spd MTB RDs can index across 10-spd cassettes, though?
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Old 06-11-15, 10:25 PM
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Originally Posted by RideForWind
How is it that 9-spd MTB RDs can index across 10-spd cassettes, though?
Because Shimano generally used the same pull ratio -- the amount of derailleur movement per unit of cable pull -- for indexed rear derailleurs, whether road or mountain, until the "Dyna-Sys" 10-speed mountain derailleurs came out. And because derailleurs don't do indexing -- they just go wherever the shifter tells them. The indexing is in the shifter.
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Old 06-12-15, 08:08 PM
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Originally Posted by SkyDog75
Because Shimano generally used the same pull ratio -- the amount of derailleur movement per unit of cable pull -- for indexed rear derailleurs, whether road or mountain, until the "Dyna-Sys" 10-speed mountain derailleurs came out. And because derailleurs don't do indexing -- they just go wherever the shifter tells them. The indexing is in the shifter.
Precisely. With a couple exceptions, Shimano has used the same cable-pull-to-derailleur-movement ratio since they began making "SIS" derailleurs and shifters. Those exceptions are pre-9-speed Dura-Ace and 10-speed MTB "Dyna-Sys" systems. I once built a bike with a Shimano derailleur from the '00's, and shifter from the '90's, and a 7-speed hub from the '80's. They were all happy together.

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