A sharper front end for the Audi S5 B9
The Audi S5 (B9) is fast, refined, and easy to live with, but it also carries meaningful weight over the front axle. That shows up in two places drivers feel immediately: braking heat management and front-end response. This build addresses both with a custom front brake conversion built around AP Racing Radi-CAL CP8521 6-piston calipers and 393mm STOPFLEX carbon ceramic rotors.
For the right owner, this is more than a cosmetic upgrade. It is a way to reduce unsprung mass at the nose, improve pedal consistency, and bring a more deliberate, technical feel to a car that already does daily duty exceptionally well.
Fast takeaway: this article focuses on a front-axle big brake kit for the Audi S5 B9 using AP Racing 6-piston calipers and 393mm STOPFLEX carbon ceramic rotors, while retaining the factory rear caliper.
Why Audi S5 B9 owners consider this upgrade
The factory S5 braking system is competent for road use, but the car's front-heavy layout means enthusiastic driving can expose familiar compromises. A lighter, higher-capacity front package changes the way the car responds when you ask more from it.
- Less unsprung mass at the nose: STOPFLEX carbon ceramic rotors are about half the weight of same-size steel rotors, helping the S5 feel more alert on turn-in.
- Better resistance to heat buildup: repeated hard stops are where a larger 393mm carbon ceramic package starts to make sense.
- Cleaner everyday ownership: when paired with STOPFLEX pads, brake dust is kept very low compared with most conventional street setups.
- Premium finish: carbon ceramic hardware gives the wheel area a more technical, high-end look without the corrosion concerns of steel rotors.
Audi S5 B9 technical specification
| Item | Configuration |
|---|---|
| Vehicle | Audi S5 (B9) |
| Front caliper | AP Racing Radi-CAL II CP8521 6-piston |
| Front rotor | 393mm STOPFLEX carbon ceramic |
| Rear hardware | Factory single-piston caliper retained |
| Pad material | STOPFLEX low-dust ceramic compound |
| Quoted front-axle weight saving | Approximately 16 kg (35 lb) reduction |
| Wheel requirement | 20-inch wheels typical for clearance |
Compatibility note
This is a custom front big brake kit, not a simple factory-caliper rotor swap. In this application, the AP Racing Radi-CAL II CP8521 6-piston front caliper and 393mm rotor package typically requires 20-inch wheels for clearance. If you want to keep the original front calipers, an OE-replacement carbon ceramic rotor path is the better starting point.
What changes on the road
Front-end response and pedal feel
The most meaningful change is not just stopping power. It is how the S5 feels between brake release and turn-in. Reducing rotational mass at the front corners helps the car feel less burdened over the nose, and the AP Racing Radi-CAL fixed-caliper architecture gives the driver a firmer, more repeatable brake pedal when the pace rises.
Heat management
The 393mm front rotor brings far more thermal headroom than a conventional street setup. STOPFLEX rotors hold approximately 0.3μ surface friction even at 900°C, which matters on fast mountain roads, repeated high-speed stops, and any use case where a heavy, powerful coupe can overwhelm a lesser front package.
Everyday ownership
STOPFLEX carbon ceramic rotors do not rust after rain exposure, and with STOPFLEX pads they produce very little visible dust. Street-use lifespan can reach about 250,000 to 300,000 km when not used on track, which transforms how owners think about long-term brake costs.
How to plan this Audi S5 upgrade
1. Confirm wheel clearance
Start with wheel diameter and internal barrel clearance. For this 393mm AP Racing front setup, 20-inch wheels are the safe expectation unless a specific wheel has already been measured and verified.
2. Choose the front path
Decide whether you want the full AP Racing front conversion shown here or an OE-style STOPFLEX carbon ceramic rotor upgrade that retains the factory caliper architecture and original wheel fitment.
3. Decide how far to take the rear
Most owners retain the factory rear caliper and upgrade rear rotors and pads to complement the front. That preserves the electronic parking brake and keeps overall balance coherent.
Installation gallery
Audi S5 B9 carbon ceramic brake FAQ
Why choose AP Racing calipers over the factory Akebono setup on the Audi S5 B9?
The factory Akebono setup is capable for normal road use, but the AP Racing Radi-CAL front system is a more specialized fixed-caliper upgrade. In this build, it is used to reduce front-end weight, improve pedal consistency, and pair properly with the 393mm STOPFLEX carbon ceramic rotor package.
Will this 393mm front carbon ceramic brake kit fit under factory 19-inch wheels?
This application typically requires 20-inch wheels for proper caliper and rotor clearance. Some 19-inch wheels with generous internal clearance may work, but fitment should always be confirmed before ordering.
How do you maintain STOPFLEX carbon ceramic rotors on a street-driven S5?
Maintenance is straightforward. Carbon ceramic rotors do not rust, they wear slowly in normal street use, and they benefit from regular washing with non-acidic cleaners. Avoid harsh wheel chemicals and inspect pads and hardware during routine service.
Is a carbon ceramic and AP Racing brake setup noisy in daily driving?
Street behavior can remain very refined with the right pad compound and hardware, but no high-performance brake system is completely immune to occasional noise. Temperature, pad choice, and usage all affect sound levels.
Can the rear brakes on the Audi S5 B9 be upgraded to match the front?
Yes, the rear axle can be upgraded with matching rotors and pads to complement the front conversion. Most owners retain the factory rear caliper because the electronic parking brake makes a full rear caliper conversion more involved.
