Originally Posted by
Steve_sr
Hello,
Does anyone know or can point to documentation as to whether or not you can use an RX-812 (long cage) rear derailleur on their normal 2X setup. I believe that the difference in cog sizes are 34 max on the 2X and 42 max on the 1X. The difference is only 8 teeth which I would hope would be made up with the long cage rear der.
I am working on speccing a new build with a 2X GRX drive train and would like the option to provide lower gearing if needed in the future without replacving the rear der. I know that this trick would work on older Shimano drive trains but don't know about this one.
RD-R812 is not "long cage." Its cage is actually shorter than the one on RD-RX810, since due to being a "1x" derailleur, it does not need to be able to wrap as much chain.
Personally I'd probably err toward the RD-RX810 for what you're trying to do. It can tolerate a larger cassette than spec: I know multiple people running the RX400 or RX810 on their gravel bikes with an 11-40 or 11-42 cassette and a 16-tooth front difference, with pretty reasonable results.