AP Racing Radi-CAL Front - 6 Piston Kit for Nissan GTR CP8521Z1000BG.CH12

AP Racing Radi-CAL Front 6-Piston Brake Kit — Nissan GT-R

The AP Racing Radi-CAL Front 6-Piston Kit (CP8521Z1000BG.CH12) is a high-performance braking upgrade intended to improve braking consistency, thermal management and pedal control on a performance car such as the Nissan GT-R.

Its engineering philosophy is straightforward: generate the required braking torque while controlling heat, maintaining stiffness and delivering predictable braking under repeated high loads. 

A six-piston caliper is only one part of that equation; rotor design, pad compound, brake fluid, tyre grip and front-to-rear brake balance are equally important.

1. Technical specifications

Verified against AP Racing’s official R35 GT-R kit specifications.

Caliper

6-piston World Radi-CAL

Forged, two-piece aluminium alloy body

Brake disc

410 × 36 mm

Ventilated, grooved rotor with 73 internal vanes

Brake pads

CP7555D70 profile

Specified kit pad: CP7555D70BX-DS25HP

Wheel compatibility

OEM wheel listed

Actual spoke and barrel clearance must still be checked

2. Why the Radi-CAL design matters

A. Caliper stiffness and pedal consistency

The Radi-CAL design concept optimises caliper structure to reduce unnecessary mass while maintaining stiffness. A rigid caliper helps keep piston movement and pad loading controlled under heavy braking.

B. Thermal management

The 410 mm ventilated rotor provides substantial thermal capacity. Its internal vanes move air through the disc to help remove heat, while the grooved faces support pad-surface cleaning and gas/debris evacuation.

C. Six-piston force distribution

Six pistons distribute hydraulic clamping force across the pad. Their different diameters are engineered to help manage pressure distribution along the pad, rather than simply maximising piston count.

These are engineering benefits, not a guarantee of a shorter stopping distance in every situation. Tyre grip, ABS calibration, road conditions and pad compound remain decisive factors.

3. What does it improve on the Nissan GT-R R35?

Performance area	Engineering advantage
Repeated hard braking	Greater thermal capacity helps resist overheating
Brake pedal control	Caliper stiffness supports consistent pad engagement
Track driving	Better suited to managing repeated high-energy braking
Brake fade resistance	Appropriate pad, fluid and cooling setup can improve resistance to fade
Unsprung mass	Radi-CAL’s lightweight design aims to reduce caliper mass

Important distinction: this is primarily a braking-system performance upgrade, not an automatic stopping-distance upgrade. 

A healthy standard brake system with suitable tyres may already stop the car close to the available tyre-grip limit during a single emergency stop.

4. Is it suitable for a modified GT-R?

• Fast road driving: Potentially worthwhile for drivers who want stronger thermal reserves and consistent pedal feel.
• Occasional track use: A compelling application, provided the pad compound, fluid and cooling are appropriate for the circuit.
• Frequent track use: The entire brake package needs to be matched to vehicle mass, speed, tyre capability and session duration.
• High-power builds: More engine power alone does not determine the required brake specification; vehicle speed, mass and braking frequency matter considerably.

Before installation, confirm wheel clearance, rotor fitment, brake-hose compatibility and front-to-rear brake balance with a qualified brake specialist.

5. Important part-number check

The official AP Racing listing identifies the black R35 GT-R kit as CP8521Z1000BG.CG12, whereas your supplied reference ends in BG.CH12. The official listing also identifies the red kit as CP8521Z1000R2.CG12.

Verdict

The AP Racing Radi-CAL CP8521 kit is a serious OEM-wheel-compatible big-brake package for the R35 GT-R, combining six-piston calipers with large 410 mm rotors. 

Its strongest proposition is repeatable braking performance, thermal capacity and controlled brake feel, rather than an unqualified promise of shorter stopping distances.

AP Racing Radi-CAL Front - 6 Piston Kit for Nissan GTR CP8521Z1000BG.CH12