The build: what's on this S5
| Item | This build |
|---|---|
| Vehicle | Audi S5 (B9) |
| Front caliper | AP Racing Radi-CAL II CP8521 six-piston |
| Front rotor | 393mm STOPFLEX carbon ceramic |
| Rear hardware | Factory single-piston caliper retained |
| Pads | STOPFLEX low-dust ceramic compound |
| Front-axle weight saving | Approximately 16 kg (35 lb) |
| Wheel requirement | 20-inch wheels typical for clearance |
| Axle scope | Front big brake conversion |
Read this before you order
This is a custom front big brake kit, not a bolt-on rotor swap for the factory calipers. The AP Racing CP8521 caliper and 393mm rotor package typically needs 20-inch wheels for clearance. If you want to keep your factory front calipers and original wheels, an OE-replacement carbon ceramic rotor path is the better starting point.
What the upgrade actually changes
| STOPFLEX + AP Racing feature | Why it matters on the S5 B9 | What you notice |
|---|---|---|
| Carbon ceramic rotor, about half the weight of steel | The S5 carries real mass over the front axle, so rotating weight at the nose is exactly where it hurts handling most. | The front feels lighter and more willing on turn-in, and the steering is a touch quicker to settle. |
| 393mm rotor with high thermal headroom | A heavy, powerful coupe builds heat fast on a long mountain descent or repeated high-speed stops. | The pedal stays consistent deeper into hard use instead of going long and soft. |
| AP Racing Radi-CAL fixed six-piston caliper | Floating calipers flex more under load; a stiff fixed body clamps the pad more evenly. | A firmer, more repeatable pedal you can lean on when the pace picks up. |
| High-temp friction (around 0.3μ at 900°C) | Friction that fades with heat is what turns a strong street brake into a scary one on a back road. | Bite that holds up when the rotors are hot, not just on the first stop. |
| Low-dust pads and rust-free rotors | Daily S5 owners hate black wheels and rusty rotor faces after a rainy week parked. | Cleaner wheels between washes and rotor edges that don't bloom orange. |
| Long street lifespan (about 250,000–300,000 km off-track) | Big brake kits scare people on running cost; carbon ceramic flips that math for street cars. | You replace pads, not rotors, for a very long time. |
What gets better
- Lighter front corners, so the nose feels less burdened on turn-in
- Firmer, more repeatable pedal under hard, repeated braking
- More thermal margin on long descents and fast roads
- Very low brake dust with STOPFLEX pads, so wheels stay cleaner
- Rotors that don't rust and last a long time in street use
What to confirm first
- Wheel size and inner barrel clearance — plan on 20-inch wheels
- Whether you want the full AP Racing conversion or an OE-style rotor upgrade that keeps the factory caliper
- How far you want to take the rear: matching rotors and pads while keeping the factory rear caliper and EPB
- Pad compound choice for your mix of street versus spirited driving
If you're not sure your car matches the spec shown here, send us your details and we'll confirm Audi S5 B9 fitment before you order through our Audi CCB collection.
Build gallery
Audi S5 B9 CCB questions
Why go AP Racing over the factory Audi S5 B9 brakes?
The factory front setup is fine for normal road use, but the AP Racing Radi-CAL CP8521 is a fixed six-piston front caliper built for harder duty. Here it cuts front-axle weight, gives a firmer and more repeatable pedal, and pairs correctly with the 393mm STOPFLEX carbon ceramic rotor.
Will this 393mm front kit clear factory 19-inch wheels?
Plan on 20-inch wheels for proper caliper and rotor clearance. Some 19-inch wheels with generous inner barrel clearance can work, but you should always confirm fitment before you order.
How do you care for STOPFLEX carbon ceramic rotors on a daily-driven S5?
It is easy. The rotors do not rust, they wear slowly in normal street use, and they respond well to regular washing with non-acidic wheel cleaner. Skip harsh chemicals and check the pads and hardware at routine service intervals.
Is an AP Racing carbon ceramic setup noisy day to day?
With the right pad compound and hardware it stays refined for street driving, but no high-performance brake is completely silent in every condition. Temperature, pad choice, and how you drive all affect occasional noise.
Can the Audi S5 B9 rear brakes be upgraded to match the front?
Yes. You can upgrade the rear with matching rotors and pads to complement the front conversion. Most owners keep the factory rear caliper because the electronic parking brake makes a full rear caliper swap more involved.
