Shimano GRX RD-RX812 11-speed rear derailleur for single chainring - IRDRX812

The GRX RD-RX812Shimano is a mechanical rear derailleur specifically designed for 1x11-speed gravel drivetrains. It combines the reliability of the ‘ Shimano ’ system with a design tailored to the specific demands of gravel riding, where changes in terrain and vibrations can put the drivetrain under considerable strain.

Intended for single-chainring set-ups, the RD-RX812 accommodates a maximum sprocket of 42 teeth and a minimum sprocket of 40 teeth in the cassette. Shimano specifies a total capacity of 31 teeth.

Its main advantage is its SHIMANO SHADOW RD+ chain stabiliser system . This limits chain movement on rough terrain and reduces the risk of chain chatter or derailment. The stabiliser features an ON/OFF switch, allowing you to adjust its operation to suit riding conditions.

The RD-RX812 is also fitted with a chain tension suitable for gravel riding. Shimano thus prioritises chain stability whilst maintaining smooth and precise gear changes.

Compatible with current Shimano road shifters designed for this drivetrain, this derailleur enables you to build a versatile gravel drivetrain based on a wide cassette and a single front chainring.

Key features of the Shimano GRX RD-RX812

• Shimano GRX rear derailleur.
• 11-speed drivetrain.
• Specifically designed for 1x11 single-chainring setups.
• SHIMANO SHADOW RD+ technology .
• Chain stabiliser with ON/OFF switch.
• Compatible with cassettes up to 42 teeth.
• Maximum sprocket: 42 teeth.
• Minimum sprocket: 40 teeth.
• Top sprocket: 11 teeth.
• Total capacity: 31 teeth.
• Clutch tension suitable for gravel riding.
• Rollers fitted with bearings.
• Compatible with adapted Shimano DUAL CONTROL road groupset components.
• Integrated cable tension adjustment.
• Conventional or Direct Mount installation depending on frame configuration.
• Claimed average weight: 267 g.

A derailleur designed for 1x11 gravel riding

The choice of a single chainring is particularly appealing for gravel riding. It simplifies the drivetrain by eliminating the front derailleur and allows the rider to focus on a single gear-shifting control.

The RD-RX812 is specifically designed with this philosophy in mind. Shimano pairs it in particular with GRX 1x11 set-ups using a wide cassette such as 11-40T or 11-42T and a front chainring with 40 or 42 teeth, depending on the configuration.

This design offers a simple and robust drivetrain, particularly suited to rides that alternate between tarmac, forest tracks, trails and technical sections.

SHIMANO SHADOW RD+ technology

The SHIMANO SHADOW RD+ system is one of the key components of the RD-RX812.

Its chain stabiliser reduces unwanted chain movement when the bike is riding over rough terrain. The aim is to achieve a quieter drivetrain and greater chain stability.

Shimano It also allows you to switch the stabiliser on or off using a switch on the derailleur. The system can thus be adapted to riding conditions: the stabiliser can be switched on over rough terrain or switched off when conditions are smoother.

For gravel riding, this feature is particularly useful, as the bike can go from a perfectly tarmac-surfaced road to a heavily rutted track within a few kilometres.

Which cassette should be used with the RD-RX812?

The RD-RX812 is designed to work with a cassette whose largest sprocket has between 40 and 42 teeth, with Shimano specifying a maximum of 42 teeth.

An 11-42T cassette offers a wide gear range and allows you to use a gear ratio that’s low enough for steep climbs and rough trails.

For a more rolling gravel ride, an 11-40T cassette can also be a good option, with slightly different gear ratios.

The choice of front chainring should be based on the terrain and the level of versatility required.

Compatibility and fitting

The RD-RX812 is a mechanical rear derailleur operated by a shift lever and a cable.

It is designed for Shimano DUAL CONTROL road-type shifters compatible with the relevant GRX drivetrain. Shimano also indicates compatibility with Direct Mount systems depending on the configuration.

Before installation, it is important to check:

• the number of gears: 11;
• the configuration: 1x11;
• the cassette capacity;
• shifter compatibility;
• the compatibility of the frame and derailleur hanger.

Our workshop tip: if you’re looking for a highly versatile setup, pairing it with an 11-42T cassette gives you a low gear ratio that’s ideal for climbs. However, choose the front chainring teeth carefully to find the right balance for your riding style.

Please also take care not to confuse the mechanical RD-RX812 with the RD-RX817 Di2: both belong to the GRX 1x11 family, but their operation and control systems differ. Shimano identifies the RX812 as the mechanical version and the RX817 as the Di2 version.

Technical specifications