Brembo M4 Monobloc Radial Caliper vs Brembo GP4-RX Radial Caliper Kit

Both are Brembo 108mm radial monobloc four-piston calipers, but they are built differently. The M4 is a cast monobloc with 34mm pistons, sold as a pair, and is the simpler bolt-on upgrade for most Japanese sportbikes. The GP4-RX is a CNC-milled two-part caliper with 32mm pistons, a nickel finish and TÜV/KBA approval on many models, and it is the stronger choice for track use and riders who want street legality on paper. Owners rate both for feel and consistency; the GP4-RX is the step up in construction and finish, the M4 the easier fit.

• Choose the M4 Monobloc if you want a straightforward cast monobloc pair for a 108mm Japanese sportbike and prefer larger 34mm pistons for a softer, more progressive lever.
• Choose the GP4-RX if you want CNC-milled two-part construction, a nickel finish, TÜV/KBA approval for road use and maximum track performance.