Shimano GRX Di2 vs SRAM Force eTap AXS: Rear Derailleur

Traditionally, rear derailleurs are either road type or MTB type, and were designed quite differently to meet the different requirements.

Road rear derailleurs are small and lightweight, and have short cages to match the road cassettes. On the other hand, MTB rear derailleurs are built to be tougher and thus heavier, and they also have long cages to match the wide range MTB cassettes. Most importantly, it is equipped with a clutch to prevent chain slap and chain drop when riding on bumpy terrain.

Then, in comes gravel riding, and neither road nor MTB rear derailleurs are completely suitable. Road rear derailleurs are a bit too delicate for gravel riding, and the absence of a clutch causes the chain to bounce too much and result in chain drops. MTB rear derailleurs work a bit better, but are also not completely suitable as they are not suited for closer range cassettes.

Shimano has their GRX range of gravel rear derailleurs, while SRAM has the Force 1x series for gravel setups. Here is a comparison between the two different gravel rear derailleurs by Shimano and SRAM.

There are 4 types of gravel rear derailleurs by Shimano. Either mechanical or electronic shifting, and either front single or front double drivetrains. Pick the one that matches your setup!

GRX Rear Derailleur RD-RX815, which is for 2x11 speed gravel drivetrains, up to 34T cassette size.

Only 1 spec available for Force AXS rear derailleur. Can be used for 1x or 2x drivetrains, and also for road drivetrains.

Force AXS RD-FRC-E-D1 rear derailleur, for 1x or 2x drivetrains, and up to 36T cassette size.

Long cage on GRX rear derailleur, as it is for front double drivetrains.

Somehow the Force AXS rear derailleur is compatible to 2x drivetrains as well despite a much shorter cage.

GRX has a one-way clutch that can be switched on or off, and adjusted for clutch tension.

Force has a Orbit fluid damping clutch that does not have tension adjustment and cannot be deactivated.

GRX weighs just 287 grams, which is good considering it has a long cage and a clutch.

Force weighs 303 grams, without battery. Not too bad as well.

If the eTap battery is added to the Force rear derailleur, it is 327 grams.

GRX rear derailleur was first used on the Canyon Endurace, which was converted to a gravel bike.

Later on, the drivetrain was moved over to the Cervelo Aspero gravel bike as well, for a front double drivetrain.

Force rear derailleur is installed on the Fnhon DB12 folding bike.

Well suited to front single bikes with a wide range 10-36T cassette.

I have not ridden the Force rear derailleur off-road, since it is not installed on a gravel bike. Therefore I am unable to compare the off-road riding performance.

However, I do like the ease of setup of the wireless Force AXS rear derailleur, as well as the wide range 10-36T cassette compatibility.

The GRX rear derailleur has a clutch that can be turned off, which is useful if you are riding on smooth roads and don't need the extra chain tension. Also, you can adjust the clutch resistance if you need to, or if it wears out.

My wish is to have a GRX 12 speed gravel rear derailleur, built like the new 12 speed road rear derailleur for wireless communication with the shifters, but with a clutch for off-road riding.