AP Racing World Radi-CALโข 4-Piston Front Caliper Pair
Part Numbers: CP8530-4S0R2 (Right Hand) & CP8530-5S0R2 (Left Hand)
This part combination forms a complete, symmetrical front axle set of genuine AP Racing World Radi-CALโข (Generation 1) 4-piston calipers. Finished in high-temperature Gloss Red, this matched pair is the industry benchmark for premium street-legal Big Brake Kits (BBK), engineered for high-performance street cars and track-day builds.
Understanding the Left/Right Configuration
While both calipers share identical premium internals and construction, they are strictly side-specific due to their asymmetrical design and fluid dynamics:
CP8530-4S0R2 (Right Hand, Leading): Mounted on the driver's side (or right-hand side) of the vehicle, positioned on the front/forward facing side of the brake rotor.
CP8530-5S0R2 (Left Hand, Leading): Mounted on the passenger's side (or left-hand side) of the vehicle, positioned on the front/forward facing side of the brake rotor.
โ ๏ธ Critical Fitment Note: AP Racing utilizes differential piston bores (staggered sizes: ร38.1mm leading and ร41.3mm trailing). The calipers must not be swapped side-to-side. During installation, ensure the brake rotor rotates into the smaller piston first, then the larger piston. This directional engineering completely eliminates uneven pad wear (pad tapering).
Axle Kit Technical Specifications
Specification
Data per Caliper
Caliper Type
Opposed 4-Piston (Forged 2-Piece Aluminium Body)
Piston Diameters
ร38.1mm (x2) & ร41.3mm (x2)
Total Piston Area
49.56 cmยฒ
Caliper Finish
Gloss Red PTFE Coating with White AP Racing Logo
Seal Configuration
S0 Spec: Fitted with full rubber boot-type dirt seals
Compatible Rotor Diameters
ร330.0mm up to ร400.0mm
Compatible Rotor Thickness
32.0mm
Mounting Type
Radial Mount (195.0mm mounting centres)
Caliper Weight
3.35 kg (7.38 lbs) excluding brake pads
Matching Brake Pad
CP6600D55 pad family (16.75mm thickness)
Fluid Thread Port
M10 x 1.0
๐ Performance & Engineering Advantages
Patented Radi-CALโข Topology: By shedding dead weight and restructuring the caliper using Finite Element Analysis (FEA), AP Racing created an organic, non-symmetrical body. It delivers unparalleled resistance to dynamic caliper flex under extreme loads, giving the driver a rock-solid, incredibly linear pedal response.
Low-Maintenance Street Integration (S0 Spec): Unlike pure motorsport calipers that require frequent rebuilds, the S0 specification features advanced internal rubber dirt seals. These boots shield the pistons from road salt, grime, and moisture, preventing piston seizure and ensuring everyday reliability.
Highly Versatile Wheel Clearance: Thanks to the slim profile and optimized structural sculpt of the Radi-CAL body, this 4-piston setup maximizes wheel barrel clearance (X-Factor). It allows massive stopping power to fit under a broad range of 17-inch (sport application) and 18-inch+ performance wheels.
Compatible Vehicles- (UNIVERSAL STREET PERFORMANCE CALIPERS)
These calipers are a perfect front-axle upgrade for performance hot hatches, sports sedans, and iconic JDM tuning cars:
Euro Hot Hatches & Sedans:
Volkswagen: Golf GTI / Golf R (MK5, MK6, MK7, MK8)
๐ง 2. The Ideal Big Brake Kit Setup (What's the Setup?)
To install these calipers onto a car, you will need a complete Big Brake Kit (BBK) configuration consisting of the following parts:
Wheel Size: Requires 18-inch wheels or larger (some high-clearance 17-inch motorsport wheels may fit) to clear the outer profile of the caliper.
Brake Rotors: The absolute sweet spot is a 355mm diameter x 32mm thickness two-piece floating rotor. (The caliper can accommodate sizes from 330mm up to 380mm x 32mm).
Custom Mounting Brackets (Dogbones): You will need a pair of model-specific metal brackets to bolt these radial-mount calipers securely to your car's wheel hubs/spindles.
Brake Pads: Uses the CP6600D55 pad shape. Popular compound choices include Ferodo DS2500 for mixed street/track use, or Hawk HPS 5.0 for aggressive street driving.
Brake Lines: A pair of stainless steel braided brake lines with an M10 x 1.0 banjo bolt fitting to ensure crisp pedal response.
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