delingren

I'm replacing a 9-speed cassette and the shifter, but keeping the RD. I wonder if the RD (Shimano Deore XT) would be compatible with a 10-speed drive train. My understanding is that the pull ratio is 1.7 on both so it should work. If that's the case, I might as well go with a 10 speed system since there seems to be more choices out there.

Thanks.

ljsense

I'm pretty sure the 10 speed Shimano mountain bike derailleurs went to 1.2 instead of 1.7.

Frustrating, sorry -- but I could be wrong. I thought that they changed the pull with DynaSis or whatever their BS marketing portmanteau is for "not backward compatible."

delingren

Arhhh, right. It looks like DynaSis is 1.2. Although their 10 speed road is still 1.7. Thanks.

Dave Mayer

Old Shimano road (10 speed and earlier) was 1.67.

Exception: Tiagra 10 speed has the same actuation ratio as 11-speed . Which is not 1.4 as indicated by some on this Forum. I measured: it is closer to 1.5.

philbob57

Does the pull ratio dictate the shifters or the rear der?

delingren

Pull ratio is determined by the derailleur.
Shifter determines how much cable to pull per click.
Combined, they determine how much the derailleur arm moves, which should match the spacing between cogs.

The derailleur doesn't know "speeds". The shifter knows "speeds", which is its number of clicks.

delingren

Right, 10 speed road shifters have a 1.67 pull ratio. But I'm looking for a flat bar shifter.
Even at 1.5, I guess Tiagra is still too far from 1.67, which is what I need. So I guess I'll just try to find a 9 speed cassette and a 9 speed shifter.

Kapusta

All 9 speed shimano RDs (road and MTB) will work with Shimano 10 Speed road shifters (except Tiagra) to shift a 10 speed cassette.

9 speed Shimano RDs (road and MTB) will NOT work with Shimano 10 speed MTB shifters to shift a 10 speed cassette.

So, your 9 speed XT RD will work with a 10 speed shifter and cassette IF it is a Shimano ROAD shifter (except Tiagra).

If this is for a flat bar, you need to get a flat bar 10 speed road shifters that is either shimano (but not Tiagra) or made to work with shimano.

And you are in luck because microshift makes exactly that:

https://www.jensonusa.com/Microshift...-Road-Shifters

I use these with an XT 9sp RD to shift a 10 sp cassette. Works perfectly.

Koyote

Here's a related question, since you seem to know what you are talking about: Will a Shimano 10sp RD work with an otherwise 9sp system (brifters and cassette)?

delingren

Road RD, yes (except Tiagra 4700). MTB RD, no.
Derailleurs don’t know speeds. They only know cable pull ratio.

bwilli88 

Shimano makes a nice Ultegra level set of flat bar shifters and brake levers

Kapusta

I don't think I know any more about this than a lot of other folks who are commenting here (some of whom probably know even more), I think I may have just answered the OPs question more succinctly.

As to your question....If it is a ROAD 10 sp RD then I would assume it would work.... but I have not actually tried it.... and you know what they say about "assume". Though I am not sure what the benefit over a 9 speed RD would be.

Usually the reason one is using a 8 or 9 sp MTB RD with a 10 sp Road shifter is in order to make use of the larger cog capacity of the MTB RD. For example, if you have a 10 speed Road shifter, but want to run a cassette with a 36t large cog, 10 sp Road RDs won't clear it, and 10 sp MTB RDs (which would clear it) are not compatible with 10 sp Road shifters.

Why the hell Shimano could not just keep their Road and MTB shifters and RDs cross-compatible is utterly beyond me. It has given many people big headaches.

Koyote

The advantage, which is slight, is that the 9sp RD is 105, and the 10sp RD that I have sitting around is Dura-Ace.

Kapusta

Well, that is certainly enough of an advantage that I would at least want to try it. And I am pretty sure it will work, and this would confirm that. Let us know how it goes.