When you’re building a serious big brake kit, the caliper isn’t just “the thing that holds the pads.” It’s the control valve for everything you feel through the pedal: bite, modulation, consistency, and the ability to stay stable when temperatures climb.
That’s exactly why we use the AP Racing Pro5000R CP9660 in our XC3 big brake kits, it’s a forged, two-piece, 6-piston caliper built around AP Racing’s asymmetric design concept for stiffness and dynamic performance.
And if you’re buying the calipers on their own, we stock them in two finishes:
- Anodised: CP9660-2S4L (RH) / CP9660-3S4L (LH)
- Electroless Nickel (ENP): CP9660-2S4LN (RH) / CP9660-3S4LN (LH)
The problem: big power and big grip overwhelm average brakes
Even on fast road cars, once you increase tyre, aero, and speed, the braking system gets asked to do more than “stop the car”:
- hold pedal feel through repeated high-energy stops
- resist knockback and long pedal on rough circuits/kerbs
- keep pads stable and consistent at high temp
- maintain stiffness so caliper flex doesn’t become “spongey feel”
If you’re putting together a proper big brake kit, you want a caliper that’s designed to take that punishment by default, not one that’s “good enough” until it isn’t.
Why the AP Racing CP9660 is a standout caliper
The CP9660 sits in AP Racing’s Pro 5000 R range and is built around a “radical asymmetric design concept” with a forged, two-piece aluminium alloy body aimed at increased stiffness and superior dynamic performance.
Key engineering features (the stuff that matters on track):
- Radial mount: 180.0mm centres with 42.0mm offset
- Stainless steel pistons + high temperature seals
- 4lb anti-knockback springs fitted (helps reduce long pedal from knockback)
- Stainless wear plates (durability where pads slide/locate)
This is the kind of spec list that translates directly into driver confidence, especially when you start pushing longer sessions and higher speeds.
CP9660 sizing and compatibility (disc and pad basics)
The CP9660 is designed around a very common “proper BBK” window:
- Disc diameter: 356mm min to 380mm max
- Disc thickness: 32mm min to 36mm max
- Pad family: CP3905D54 (pad area 77.4cm², 18.0mm thick)
- Piston sizes: 27.0 / 31.8 / 38.1mm (differential bore layout) with ~50cm² total area
If you’re matching calipers to bells, brackets, and discs, these numbers are exactly why the CP9660 is such a reliable “known quantity” for big brake kit design.
Anodised vs Nickel finish: which should you choose?
Both are the same core caliper. The difference is surface treatment, and it’s mostly about long-term appearance, corrosion resistance, and how you want the caliper to look behind the wheel.
Anodised finish (CP9660-2S4L / 3S4L)
- Classic motorsport look
- Tough and clean
- Great if you want an OE+ performance aesthetic
Electroless Nickel (ENP) finish (CP9660-2S4LN / 3S4LN)
- The “standout” finish — bright, high-end, and very resistant to looking tired
- Ideal for show-level builds that still see track use
Why we use CP9660 calipers in XC3 big brake kits
A big brake kit should be more than just expensive parts. It should be a matched system that delivers:
- repeatable pedal feel
- predictable bite and modulation
- stable performance as temps rise
- a rigid platform for pad control
The CP9660 gives us a proven, motorsport-developed caliper that fits the disc sizes we want to run, supports full-depth pad shapes, and includes key details like anti-knockback springs and stainless hardware interfaces that matter when the car is driven hard.
Who the CP9660 is for
- Track day and fast road cars that want a genuine motorsport caliper
- Heavy, high-speed platforms that cook standard brakes quickly
- Builds moving to 356–380mm discs in a proper big brake kit setup
Quick FAQ
Do these calipers come as a pair?
Yes a handed pair (LH + RH) in either anodised or nickel finish, or can be purchased individually
What pads fit CP9660?
The correct pad family is CP3905D54.
What Rotors does CP9660 suit?
356–380mm diameter and 32–36mm thickness.
Shop the calipers (or choose them as part of an XC3 Big Brake Kit)
- XC3 Engineering Big Brake Kits - View
- AP Racing Pro5000R CP9660 (Anodised) - View
- AP Racing Pro5000R CP9660 (Nickel / ENP) – View
If you want these calipers as part of a complete package, our XC3 big brake kits are designed around proven component matching, so you get performance you can lean on, not just parts that look good on paper.