Shimano has introduced a new component series, the GRX, the “world’s first dedicated family of gravel/adventure components built for both fast riding and assured capability on loose surfaces”.
GRX offers RX800, RX600 or RX400-series components with 1×11, 2×11 and 2×10 drivetrains and mechanical and Di2 electronic shifting options, allowing riders to “tailor their mixed surface riding experience and explore beyond their usual limits to pursue a wide range of terrain”.
These components employ Shimano’s drivetrain technologies from both the road and mountain bike side to deliver the “hallmark shifting precision and stability for which the company is known”.
The GRX cranksets are built for tackling different riding terrains and riding styles, all coming with a +2.5mm chainline for increased tyre and frame clearance. GRX single ring cranksets offer the simplicity of shifting only on the rear cassette (options include RX800/600 40T chainrings or the RX800 42T chainrings) and are delivered with Shimano’s Dynamic Chain Engagement tooth profile on the front chainring to offer increased chain retention over bumpy ground. The GRX double chainring RX810 crankset employs a 17-tooth gap which, at 48-31T, is the company’s widest-ever gear ratio, it has said. Together with the additional RX600-11/10 46-30T options, the double cranksets give big enough gear ratios for tackling the steepest climbs and pinning the steepest descents.
Complementing the cranksets, the Di2 (FD-RX815) or mechanical (FD-RX810/RX400) front derailleurs are built with 2.5mm more outbound clearance for wider tires (up to 42mm) to cope with riding on rough roads. This means GRX front derailleurs must be combined with Shimano GRX +2.5mm cranksets. Both RX800-series mechanical and Di2 front derailleurs are built to accommodate Shimano’s widest 17T front chainring 48-31T gear ratio whilst the FD-RX400 10-speed derailleur accommodates the 16T chainrings found on the RX600 46-30T 10-speed cranksets. Shimano Di2 FD’s can be adjusted using Shimano’s simple and integrated controls whilst mechanical FDs bring a light front shifting feeling with an ergonomic power curve, toggle link construction for more cable routing options and an integrated cable tension bolt for precise and easy adjustments.
Adopting the technology introduced in 2018’s RX rear derailleur, the GRX Di2 RDs (RD-RX815/RX817) or mechanical RDs (RD-RX810/RX812/RX400) are designed for silent, smooth and reliable shifting on rough terrain with a chain stabilising system known as Shadow RD+ to manage ‘chain chatter’, minimise unnecessary derailleur arm movement and provide uninterrupted shifting performance. GRX comes with the choice of four derailleurs depending on the cassette and gear shifting operation chosen.
Riders using an Ultegra, 105 or Tiagra level 11-30/34T cassette will need to use the short cage Di2 RD-RX815 or mechanical RD-RX810 rear derailleur, whilst riders choosing a Deore XT, SLX or Deore level 11-40/42 cassette will need to use the longer cage Di2 RD-RX817 or mechanical RD-RX812 RD, both of which come with a pull ratio similar to Shimano’s road derailleurs.
GRX shifting comes courtesy of dedicated gravel-specific ergonomic levers (Di2: ST-RX815 or mechanical: ST-RX810/RX600/RX400, ST-RX810-LA) featuring curved brake lever profiles and an anti-slip textured finish which can be gripped with assurance over rough terrain. The ST-RX815 also features an 18mm higher axis point.
To integrate the use of dropper posts in gravel riding, Shimano has created the GRX mechanical ST-RX810-LA left hydraulic disc brake lever that, when used with a 1×11 drivetrain, can control a dropper post whilst also keeping the cockpit tidy. The integrated cable pulling system has a 9mm lever throw to operate dropper posts with cable heads at the shift lever. Shimano GRX also includes 1×11-specific RX800 and RX600-series left side hydraulic disc brake levers with no dropper or shift internals, including the 1×11 Di2 left-hand lever (ST-RX15), which comes with three buttons (two side buttons and a hood top button) for operating ancillary functions such as lights or third-party computers.
One variant of the RX800-series brake levers (ST-RX815) offers Servo Wave technology coming from Shimano’s mountain bike brakes. This provides a stronger braking feeling with greater modulation options for ‘more aggressive’ riding. An additional braking option comes with an inline hydraulic sub-brake lever (BL-RX812-L/R) which connects to the main hydraulic line running to the front and/or the rear caliper. The sub-brake lever is designed to be mounted on the handlebar next to the stem offering options for braking when riding with hands on the tops.
To complete the experience, Shimano has two gravel/adventure-inspired 12mm E-thru axle wheelsets (WH-RX570-TL-F12/R12). The 700c or 650b (non-boost) tubeless-ready wheelsets offer an optimal balance between weight, stiffness and gravel durability, bringing a wider 21.6mm inner rim width (comparable with MTB XC wheels) and an off-set rim height of 22mm.