Why S5 Owners Move to Carbon Ceramic Brakes
The B9 S5 is a daily car with a 3.0-liter turbo V6 and all-wheel drive that makes it easy to carry real speed into a corner without thinking about it. That's exactly the problem. The factory front brakes are sized for a comfortable commuter that occasionally gets driven hard, not a car that regularly gets driven hard on the way home from work.
Owners who come to us about this conversion are usually chasing the same thing: a pedal that doesn't go soft on the third or fourth hard stop down a canyon road, and a front end that turns in without feeling like it's dragging two heavy discs around with it. Neither complaint shows up on a spec sheet. Both show up the first time you push the car.
What wasn't working
- Pedal firms up less predictably after repeated hard stops on a fast road
- Front-axle weight sits right where it hurts turn-in response most
- Factory rotors streak and rust behind open-spoke wheels after a wet week parked
- Brake dust cakes the front wheels faster than the rears
What owners want instead
- A firmer, more repeatable pedal under real driving, not track abuse
- Less unsprung mass up front without giving up daily comfort
- Wheels that stay clean for weeks, not days
- A brake package that looks the part behind a 20-inch wheel
The Build: What's On This S5
| Item | This build |
|---|---|
| Vehicle | Audi S5 (B9) |
| Front caliper | AP Racing Radi-CAL II CP8521 fixed six-piston, supplied with this kit |
| Front rotor | 393mm STOPFLEX carbon ceramic disc |
| Rear hardware | Factory single-piston caliper and electronic parking brake 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 carbon ceramic brake conversion |
Read this before you order
This is a caliper-and-rotor conversion, not a rotor-only swap onto your factory front caliper. The AP Racing caliper supplied with this kit and the 393mm STOPFLEX rotor typically need 20-inch wheels for clearance. If you want to keep your factory front calipers and stock wheels, a rotor-only carbon ceramic path is the better starting point — ask us before you buy either way.
What the STOPFLEX Carbon Ceramic Upgrade Changes
Every part of this build answers one of the two complaints from the last section: too much weight at the front corners, or a pedal that doesn't hold up under repeated hard use. Here's how the pieces work together on a car this size and this heavy in front.
| STOPFLEX feature | Why it matters on the S5 B9 | What you notice |
|---|---|---|
| Carbon ceramic rotor, about half the weight of steel | The S5's turbo V6 and all-wheel-drive hardware already load the front axle heavily; rotating mass at the rotor makes that worse. | The front feels less burdened turning in, and steering response settles quicker after a bump. |
| High-temperature stability, holding roughly 0.3μ at 900°C | A heavy AWD coupe builds serious heat on a long descent or a string of on-ramp-to-off-ramp hard stops. | The pedal doesn't go long and soft on the fourth or fifth hard stop the way an overworked iron rotor can. |
| Fixed six-piston caliper geometry | A stiffer caliper body flexes less under load than the factory floating design, so clamping stays even across the pad. | A firmer, more consistent pedal that doesn't move around as you lean on it. |
| Rust-free rotor surface | S5 owners who park outside deal with flash rust on factory rotors after every rain. | Clean rotor faces behind the wheel, week after week, with no orange ring after a wash. |
| Low-dust ceramic pad compound | Front pads on an AWD car with this much torque wear the wheel face fast under stock hardware. | Noticeably less black film on the front wheels between washes. |
| Long street-service life, roughly 250,000–300,000 km off-track | A big-brake conversion is a real up-front spend, so the payoff has to show up over years of ownership, not one track day. | You're replacing pads on a normal service schedule, not rotors. |
What gets better
- Lighter front corners, so the nose feels less loaded on turn-in
- Firmer, more repeatable pedal under hard, repeated braking
- More thermal margin on a long grade or a fast back road
- Cleaner wheels between washes with STOPFLEX pads
- Rotors that don't rust and hold up for years of street use
What to confirm first
- Wheel size and inner barrel clearance — plan on 20-inch wheels
- Whether you want this full caliper-and-rotor conversion or a rotor-only carbon ceramic path that keeps your factory front caliper
- How far to take the rear axle — matching rotors and pads while keeping the factory rear caliper and parking brake
- Pad compound for your actual mix of commuting and spirited driving
The up-front cost of a conversion like this is real, but it's worth weighing against how long a carbon ceramic rotor actually lasts compared to replacing iron rotors every couple years — our carbon ceramic brakes price and cost guide walks through that math. 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 carbon ceramic brake collection.
Fitment & Installation
The caliper bracket in this kit is machined to the S5's actual steering knuckle geometry, not pulled from a generic six-piston catalog fit. That matters more than it sounds like it should: a bracket that's a couple millimeters off center doesn't just look wrong, it loads one side of the pad more than the other, and you'll eat through that pad unevenly long before it's actually worn out. That's the expensive detail a generic kit skips and a bespoke one doesn't.
The first thing we ask for is your wheel's spoke profile and inner barrel diameter, not just the size printed on the sticker — two 20-inch wheels from different manufacturers can clear this caliper very differently. Nine times out of ten, the sticking point on a front conversion like this isn't the caliper itself, it's whether the bracket geometry we machine actually clears the spoke sitting right behind it.
On install day, the factory front caliper and rotor come off, the new bracket goes on to the knuckle, the AP Racing caliper and 393mm STOPFLEX rotor go on next, and everything gets torqued to spec before the car goes anywhere. Fresh pads and rotors need a proper bedding cycle — a set of moderate stops from speed, cooling in between, before you lean on the brakes hard.
- Vehicle and confirmation of B9 chassis / model year
- Wheel diameter, offset, and spoke profile at the inner barrel
- Current front caliper — factory or already upgraded
- Front-only scope, or front and rear together
- How the car actually gets driven day to day
Give the rotors and pads a proper bedding-in cycle before you drive them hard, and give the new setup a few hundred miles before you judge it. We'd rather turn down a fitment we haven't confirmed than ship a bracket that binds against your wheel, so send the details in before the order, not after.
What Changes After the Upgrade
We don't have an instrumented before-and-after for this specific car, and you should be skeptical of anyone who quotes you an exact stopping-distance number on a street build without a test sheet to back it up. What we can talk about honestly is what a fixed six-piston caliper and a carbon ceramic rotor are built to do, and what most owners in this position notice.
| Situation | Factory setup | After the STOPFLEX + AP Racing upgrade |
|---|---|---|
| Repeated hard stops on a mountain road | Pedal can start to feel long and soft by the fourth or fifth stop | Pedal travel stays consistent stop after stop |
| Turn-in response on a twisty road | Front feels slightly heavier to change direction | Nose feels lighter and quicker to settle |
| Wheel cleanliness after a week of driving | Visible dust film on the front wheels | Noticeably less buildup with STOPFLEX pads |
| Rotor condition after a rainy week parked | Light surface rust on the front rotor face | No rust — carbon ceramic doesn't flash-rust |
| Long-term brake service cost | Iron rotors typically replaced every couple of years of hard use | One rotor set built to outlast several iron replacements in street use |
None of this replaces a real instrumented test. What we're confident in is the mechanism: a stiffer caliper clamps more evenly, a carbon ceramic disc resists fade at higher temperatures, and less rotating mass at the front axle changes how the car turns in. That's the honest version — no invented lap times, no made-up stopping-distance figure. Owners who've made this switch on other S5s tell us the pedal feel is the thing they notice first, more than any number we could print here.
Build Gallery
Audi S5 B9 Carbon Ceramic Brake Questions
Is a carbon ceramic brake upgrade worth it on a daily-driven Audi S5 B9?
If you're chasing a lighter front end, a firmer pedal under repeated hard stops, and cleaner wheels, yes. If your S5 never sees a back road or a mountain grade, the factory front brakes already do the job and this becomes a want, not a need.
Why upgrade to an AP Racing caliper instead of keeping the factory Audi S5 front brakes?
The factory floating caliper is fine for normal commuting, but it flexes more under sustained hard braking than a fixed six-piston design. Paired with a 393mm STOPFLEX carbon ceramic rotor, the AP Racing caliper supplied with this kit clamps more evenly and holds pedal feel deeper into repeated stops.
What wheel size do I need for the S5 B9 393mm carbon ceramic brake kit?
Plan on 20-inch wheels. The caliper and 393mm rotor package needs enough inner barrel clearance that most factory 19-inch wheels won't work without checking spoke profile first, so confirm your exact wheel before ordering.
Do carbon ceramic brakes make more dust on an Audi S5?
Less, not more. Paired with STOPFLEX's low-dust ceramic pad compound, the wheels stay noticeably cleaner between washes than they do on the factory setup, and the rotor face itself won't rust or streak.
Can the Audi S5 B9 rear brakes be upgraded to match the front carbon ceramic setup?
Yes, with matching rotors and pads on the rear axle. Most owners keep the factory rear caliper in place since the electronic parking brake integration makes a full rear caliper swap a bigger job than most street builds need.
