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Discussion Starter · #1 ·
Hi guys

I'm going through the process of building up a new gravel bike. As for gearing, I intend to run a 50/34 compact chainset with a 11-speed 11-36 cassette. I have some dura ace sti levers laying around from an older project and intend to use them on this build. Is it possible to combine them with shimano mtb derailleurs such as an XT and XT disc brake calipers as the frame has postmount brake mounts? Or are there other options to make a 11-36 cassette work with a road derailleur.

Thank you all in advance!
 

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I wanted to do something similar to my Sequoia, it has a 105 group on it. I ride it off road quite a bit and it has terrible chain slap from the RD. I was looking to put an XT RD with clutch on it and was told by my LBS that the road group shifter/brake levers are not compatible with MTB RD. Didn't make sense to me but that is what I was told.
 

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... I was looking to put an XT RD with clutch on it and was told by my LBS that the road group shifter0brake levers are not compatible with MTB RD. Didn't make sense to me but that is what I was told.
Incompatibility between shifters and rear derailleurs stems from differences between how much cable a shifter pulls to move between gears compared to how much cable a particular rear derailleur needs to move between gears. This depends on the details of the design of the shifter and of the derailleur and can differ between models, speeds, mtb vs road, brands, etc. There are pull converters that can correct for a mismatch as linked to in post #2.

Here's an article that talks about this specifically. It's a little dated as it does not have any 12 speed stuff.

Science Behind the Magic | Drivetrain Compatibility - Art's SLO Cyclery
 

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The longer cage Shimano road 11 speed rear derailers will shift that cassette no problem. I've run that combo with both Ultegra and 105 mechs and it's been fine.
 

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Discussion Starter · #6 ·
Thank you guys a lot for your inputs. Until now I didn't bother much about bike tech as long as my bikes just worked, so this subject is still a bit confusing to me.
Thank you Lone Ranger for your explanations regarding cable pull, this helped clarifying the matter a lot.
Does anyone of you have experience with pull converters such as the "Tanpan" or others? Do they work reliably?
@SteveF: As far as I know, Shimano long cage derailleurs officialy only support cassettes up to 11-34 cogs. Is there no problem with chain slap and/or wear when exceeding this limit?
 

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Does anyone of you have experience with pull converters such as the "Tanpan" or others? Do they work reliably?
Working nicely since Sept 2018 so far.
11-40 11 spd cassette.
Now running the Zee 10spd mech with XT Cage instead of the RAD cage with no issues.
Very smooth shifting with the clutch on or off.
 

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@SteveF: As far as I know, Shimano long cage derailleurs officialy only support cassettes up to 11-34 cogs. Is there no problem with chain slap and/or wear when exceeding this limit?
Not at all, it worked every bit as well as you'd expect Shimano to. 2 teeth is a pretty tiny change in overall diameter, and Shimano's official limits are conservative. I've seen you-tube vids of guys using as big as a 40 tooth cog with these derailers.
 

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Discussion Starter · #9 ·
Well, that's excellent news @SteveF, in this case I'll try my luck with a Ultegra long cage derailleur if 11-36 is no problem.
Thank you @NordieBoy, for your explanations regarding the "Tanpan", sounds like a valid option if find myself in need for some even smaller gears in the future.

Just for clarification - am I right that Shimano hydraulic disc calipers can be mixed and matched even between different mtb and road groups?
 

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The Tanpan just lets you run a MTB clutched rear mech in an otherwise road ecosystem, they came out way before clutched road mechs were available and are slightly cheaper than a new rear mech.
I went with the 11spd 11-40 MTB cassette as all my wheels are MTB and can't mount an 11 speed road cassette.
A 32t low would have been fine for my riding.

My RS685's are using what looks exactly like the Deore calipers on another of my bikes.

I got the RS685's 2nd hand. I think the previous owner could never get the braking working smoothly. He'd obviously gone to a bike shop and ordered road disc pads which were way too small to fit correctly in the MTB style calipers.
Every time you put the brakes on, there was a CLUNK from each end as the pads rotated on the pin toward the front of the caliper and whacked the caliper body.
His loss, my gain :)
 
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