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I need suggestions from experience or a table of compatibilities in order to find a compatible rear derailleur.

And more specifically my need is for a short cage for a 20" wheel, freewheel of 7 speed and 34T max sprocket, and swift shifter from "microSHIFT" brand (7v, index, comp. Shimano Mountain)

I am aware that many the 28T max cog in the specs of many derailleurs is too conservative and they can works perfectly with 30 or 32T, specifically being 1x7 or 1x8 speeds

Note: I've already tested a Tourney RD-FT30(SS) with a link extender, a it reached the 34T but the derailleur position and tension was excessive.

  • SS: “Short Cage”
  • GS: “Medium Cage”
  • SGS: “Long Cage”
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  • One additional problem is that a 20" wheel isn't much larger than a long derailleur cage, and it can pick up a lot of dirt from the road and is exposed to damage. A link extender (hanger adapter) would make it even lower too. Just something related to think about.
    – Criggie
    Aug 9 at 11:11

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RD-TY200-SS is a current low-end one that does it. That's probably the practical answer.

RD-M952-GS is old, high-end, and somewhat sought-after, but it does meet what you're looking for. There may have been a few other similar era Shimano GS mountain models.

I'm not a master of mixing and matching Shimano rear derailleur uppers and lowers, but I've seen people do it and that could also be a practical solution for you. The idea basically is to find a mountain upper (the mounting bolt, cable attachment, and parallelogram part) that gives the 34t clearance, and then a short cage road lower that interfaces correctly with the cage pivot.

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    Officially max cog for most shimano derailleurs is 28T and a tourney short cage without parallelogram movement will have even more problems. In fact from my experience they tourney (SS) requires a extender link adapter to reach the 34T but it position and cable tension is so forced that it break with the use. Aug 9 at 8:09

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