Gravel-specific ergonomics distinguish the GRX lever shape from Shimano's road offerings in ways that become obvious after a few hours on rough surfaces. The ST-RX400 positions its brake lever pivot 18mm higher than traditional road levers, which changes the leverage angle when you're braking from the hoods or drops. That geometry translates to more natural hand positioning and less fatigue during extended descents on loose terrain where you're constantly modulating speed. The hood shape itself is taller and more supportive, designed to prevent your hands from sliding forward during impacts—a common problem with road hoods on chunky gravel.

This kit pairs the ST-RX400 lever with Shimano's BR-RX400 Flat Mount hydraulic caliper, pre-bled and connected via SM-BH90 hydraulic hose. The system arrives ready to install, with the hose cut to standard length and the mineral oil already in place. If you need to shorten the hose for your frame's routing, the J-Kit connection at the lever makes that process straightforward without requiring a full system bleed—Shimano's One Way Bleed system handles air removal with less hassle than traditional methods.

The BR-RX400 caliper uses a two-piston design with resin pads featuring IceTech cooling fins. Those aluminum fins pull heat away from the pad backing during prolonged braking, which matters on gravel descents where you might be dragging brakes for extended periods on loose surfaces. The Flat Mount interface keeps the caliper profile low and clean against the frame or fork. Pads and hardware for 140mm or 160mm rotors are included depending on which version you purchase—the rear setup typically ships with a 25mm mounting bolt for chainstay clearance, while the front includes a 160mm adapter.... Read More