When choosing an AP Racing big brake kit, two calipers come up more than almost anything else: the AP Racing CP9660 and AP Racing CP9668.
Both are part of AP Racing’s Pro5000R range. Both are six-piston motorsport calipers with forged aluminium bodies, radial mounting, differential piston sizing, stainless pistons, high-temperature seals and strong pad support.
The difference is simple: CP9660 uses an 18 mm pad. CP9668 uses a 25 mm pad.
That pad thickness is what changes the use case.
The short answer
Choose CP9660 if you want a lighter, proven six-piston brake kit for fast road, track day and clubsport use.
Choose CP9668 if you want more pad depth, longer consumable life and a more endurance-focused setup for heavier cars, longer sessions or harder track use.
The CP9668 is not automatically “better”. It is the deeper-pad option.
CP9660 vs CP9668: key differences
| Feature | AP Racing CP9660 | AP Racing CP9668 |
|---|---|---|
| Caliper type | Pro5000R 6-piston | Pro5000R 6-piston |
| Mounting | Radial | Radial |
| Mounting centres | 180 mm | 180 mm |
| Piston area | 50.1 cm² | 50.1 cm² |
| Pad thickness | 18 mm | 25 mm |
| Pad family | CP3905D54 | CP3558D54 |
| Disc diameter range | 356–380 mm | 362–390 mm |
| Disc thickness range | 32–36 mm | 32–36 mm |
| Approx. caliper weight | 2.78 kg | 3.1 kg |
| Best for | Fast road / track day | Track / endurance use |
Because piston area is the same, CP9668 is not simply a “more powerful” caliper. Its main advantage is the thicker pad, which gives more usable pad material and can improve pad life during hard use.
Why choose CP9660?
The AP Racing CP9660 is an excellent choice for serious fast road, track day and clubsport cars.
It suits drivers who want:
- six-piston AP Racing performance
- strong pedal feel and modulation
- wide pad compound choice
- lower caliper weight
- compatibility with 356–380 mm discs
- a balanced setup without unnecessary endurance hardware
This is why we use the CP9660 across a range of XC3 big brake kit applications, including BMW F8X, BMW E9X, VW, Audi and Seat platforms.
It gives a strong balance of caliper stiffness, pad choice, disc compatibility and overall package size, which makes it a very effective option for serious fast road, track day and clubsport builds.
Why choose CP9668?
The AP Racing CP9668 is the deeper-pad version.
It uses a 25 mm pad, compared with the 18 mm pad in the CP9660. That makes it better suited to cars that are harder on brakes.
Choose CP9668 if:
- the car is heavier or higher powered
- you run long track sessions
- you use slicks or very high-grip tyres
- pad life is a major concern
- the car sees endurance-style use
- you want a larger custom brake package
The CP9668 makes sense when heat load, pad wear and session length justify the larger pad format.
Brake feel: will CP9668 feel stronger?
Not automatically.
Both calipers use the same piston area, so basic hydraulic output is very similar. Pedal feel depends on the full system: disc size, pad compound, brake lines, fluid, tyres, ABS calibration and caliper stiffness.
For many drivers, the pad compound will make a bigger difference to bite and feel than choosing CP9668 over CP9660.
A CP9660 with the right pad can be better than a CP9668 with the wrong pad.
Pad choice matters
Both CP9660 and CP9668 benefit from strong motorsport pad availability. That is one of the main reasons both calipers are widely used in serious brake kit packages.
The correct pad compound should be chosen around:
- vehicle weight
- tyre grip
- road vs track use
- session length
- temperature range
- required bite level
- disc life
- noise and dust tolerance
The caliper matters, but the pad compound has a major effect on how the brake kit actually feels.
The mistake to avoid
Do not assume the bigger caliper is always better.
A brake kit has to be matched to the car. Caliper size, pad depth, disc diameter, disc thickness, wheel clearance, brake balance and pad compound all matter.
A CP9668 setup may be the right choice for one car and unnecessary on another. A CP9660 setup can be the better engineered solution if it gives the right balance of performance, fitment, pad choice and weight.
Bigger is not always better. Correct is better.
Final recommendation
For most fast road, track day and clubsport builds, the AP Racing CP9660 is the better all-round choice. It gives six-piston Pro5000R performance, strong pad availability and works extremely well across XC3 big brake kit applications including BMW F8X, BMW E9X, VW, Audi and Seat.
For heavier cars, longer sessions and drivers who want increased pad life, the AP Racing CP9668 is the better option. Its 25 mm pad format gives it the durability advantage when the braking system is being worked harder for longer.
Both calipers are excellent. The right choice depends on how the car is used.
CP9660 or CP9668?
Start with the use case first.
For fast road, track day and clubsport use, the CP9660 gives an excellent balance of caliper stiffness, pad choice, package size and braking performance.
For harder, longer-duration braking where pad life and heat management become the priority, the CP9668 may be the more suitable route.
The best brake kit is not the biggest one on paper. It is the one correctly matched to the car, the driver and the job it has to do.