Shimano GRX RD-RX400 10-Speed Rear Derailleur

Bought to try out GRX gearing to prepare for a new bike build. Used the RX400 as it's on a rebuilt 90s Trek frame that can only fit 10-sp cassette. Was not compatible with my Microshift shifters, so had to buy Tiagra 4700s which work perfectly. Used a couple hundred miles and so far shifts smoothly with no chain drops

The derailleur itself is great. My Tiagra derailleur was worn out, so I replaced it with this one. The shifting has improved, and the clutch makes the bike much quieter over rough roads.

However, some small parts were missing. There were supposed to be a small piece of cable and, more importantly, a special washer needed for installation. Luckily, the guy at the lbs who installed the derailleur found a used one. I did not bother to contact biketiresdirect because this was the last derailleur they had. Just be aware that not everything they sell is new and complete.

The derailleur seemed to be a well-manufactured product , and I can't say it doesn't function properly with the correct shifters (perhaps MTB-style trigger or grip shifters?). However, everything I read from users and from the Shimano website suggested this could be used with road shifters, like 105, Ultegra or Dura-Ace. Unfortunately the cable pull of the shifter didn't match up correctly with that needed for the derailleur to travel properly from cog to cog, and the shifts were sloppy.

This is a great med long cage derailer. Shimano says max 36 tooth, but it seems to be working fine on a 2x system with 42 max cog. Thing to note this is shimano's new shift ratio, so grx shifters or new tiagra shifters are required, older 10speed shifters do not work.

Never quite felt like the Tiagra RD was suitable for rough gravel use (fallen chain, choppy shifting on climbs and descents). Very pleased that Shimano didn't overlook 10-speed bikes when they released their GRX components. The clutch system on the GRX RD is really amazing at reducing the chain slap (though at the expense of slightly less crisp shifting... but can always turn off the clutch for riding on smooth roads). On top of that I was able to put on a larger cassette to make climbing on gravel easier. The recommended max 11-36 cassette combined with my bike's 32/48 crankset gives me pretty much the exact range I need.