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I have Shimano Deore RD M591 Rear Derailleur (http://www.jensonusa.com/Shimano-Deore-M591-9-SPD-Rear-Derailleur) that I am having trouble dialing in shifting when used with Tiagra 4700 2x10 STI shifters (http://www.chainreactioncycles.com/us/en/shimano-tiagra-4700-2x10-speed-sti-shifter-set/rp-prod137777) and a SLX 11-36t 10 speed cassette. I was working off of the general hypothesis that a 9 speed mountain derailleur would have the same pull ratio as the 10 speed STI shifters. I can adjust shifting to work as needed for the first 3 highest gears, but then when I shift beyond that towards the "easier" rear cogs it is consistently skipping over a cog (from 3rd to 5th for example). This continues up to the 10th cog, shifting two gears for every one click of the shifter. If I adjust cable tension so shifting is smooth in the middle or low end of the gear range, it is then not accurate at the high end of the gear range.

My goal was to extend my climbing gear range as much as possible so I could take my winter/cyclocross frame and turn it into a gravel bike capable of climbing some steep Vermont dirt roads.

Any thoughts or ideas appreciated. Thanks!

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    I remember an answer about one version of Tiagra having a weird cable pull. I know it was @nathan knutson who provided the info. I'll have a look for it. – Argenti Apparatus Jun 7 '18 at 15:16
  • That was super helpful, I have been assuming my issue was derailleur based but I just did some research on the 4700 shifters and found this out. – JSpin Jun 7 '18 at 15:33
  • "Exception is Shimano Tiagra 4700 10 speed road RD – it has the same shift ratio as Shimano road 11 speed RDs, so it will work only with Tiagra 4700 shifters and Shimano 11 speed road shifters." – JSpin Jun 7 '18 at 15:33
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I was working off of the general hypothesis that a 9 speed mountain derailleur would have the same pull ratio as the 10 speed STI shifters.

That's true, except for Tiagra 4700, which rather inexplicably uses the 11 speed pull ratio.

See https://bicycles.stackexchange.com/a/52277/24228

Presently there are two different 10-speed Tiagra generations, 4600 and 4700. (So the STI from one is ST-4600 and the other is ST-4700, etc). 4600 uses the same classic actuation ratio that all pre-11-speed Shimano road groups used other than first generation Dura-Ace. 4700, however, is an oddball group. It's 10-speed but uses the new 11-speed actuation ratio

  • I wonder if it is possible that a 10 speed slx derailleur I have around will work then? I plant to try that next. – JSpin Jun 7 '18 at 17:05
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According to this video despite the claimed 32t cog max, the RD-4700-GS can handle a 10 speed 11-36 without any extra tricks or issues. So you can just get get on of these.

Alternatively, because ST-4700 have the same pull ratio as Shimano 11 speed road groups, you can also use any 11 speed rear derailleur that can handle 11-36, like RD-5800-GS or ST-R8000-GS. Of course none of these are rated as 11-36 compatible, but still work. For example, here's a video of RD-8000-GS working with 11-40 cassette.

If you want, you can even get an 11 speed Shimano MTB rear derailleur and Wolftooth Tanpan which, converts the pull ratio between two systems. JTek Shiftmate can probably do this too.

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