Why this 991 got the conversion
The 991 is one of the easiest 911s to drive quickly, which is exactly why its factory brakes get worked hard. A car that flatters the driver on a mountain road or a track day also invites more repeated hard braking than most owners plan for, and iron rotors start to tell on you after the third or fourth stop from real speed — the pedal gets longer, the bite softens, and the confidence you had on lap one is gone by lap four.
Owners who bring a 991 in for this kind of conversion are usually chasing one of two things: a pedal that doesn't fade when the car finally gets used the way it was built to be used, or a set of wheels that stop needing a scrub every weekend from iron brake dust. Carbon ceramic brakes solve both at once, which is why this is one of the more common upgrades we see on this chassis.
What wasn't working
- Pedal travel creeping longer after repeated hard stops on a descent or a track session.
- Iron rotor dust caking the face of open-spoke wheels within days.
- Surface rust forming on the rotor faces after the car sits through a rainy stretch.
- Extra unsprung mass at the front corners making the chassis feel slower to settle over broken pavement.
What owners want instead
- A pedal that feels the same on the last hard stop as it did on the first.
- Wheels that stay clean for weeks, not days.
- Rotors that don't need babying after a car wash or a wet week in the garage.
- Lighter rotating mass that makes the car feel as sharp as the chassis actually is.
Build sheet: what's on the car
| Component | STOPFLEX specification |
|---|---|
| Vehicle | Porsche 911 (991) |
| Front calipers | Akebono 10-piston fixed calipers, supplied with this kit |
| Front rotors | STOPFLEX C/SiC carbon ceramic, 410 x 36 mm |
| Rear calipers | Brembo 4-piston fixed calipers, supplied with this kit |
| Rear rotors | STOPFLEX C/SiC carbon ceramic, 400 x 28 mm |
| Pad compound | STOPFLEX ceramic street and track compound |
| Axle scope | Full front and rear carbon ceramic conversion |
| Wheel target | 20-inch, pending clearance confirmation |
Read this before you order
This is a caliper-and-disc conversion, not a rotor-only swap — the factory front caliper comes off and a wide 10-piston Akebono unit goes on in its place. The Akebono and Brembo calipers here are supplied as part of this kit; they are not the 991's factory hardware, and the discs paired with them are STOPFLEX carbon ceramic rotors, not a caliper maker's own disc. Clearing a 20-inch wheel depends on inner-barrel diameter and spoke shape around that larger front caliper, not just rotor size, so that check has to happen before the parts ship.
Why this specific setup
A 991 doesn't need a bigger rotor because the car is slow to stop — it needs one because the car is easy to get moving fast enough that stopping repeatedly becomes the hard part. Every choice in this build traces back to that: more piston area to spread clamp force, more rotor mass to soak up heat, and a rotor material that keeps working after the iron equivalent has already started to give up.
| STOPFLEX feature | Why it matters on a 991 | What you notice |
|---|---|---|
| C/SiC carbon ceramic friction matrix | Iron starts to heat-soak well before this material does — testing shows rotor surface friction holding around 0.3μ even at 900°C. | A pedal that stays firm and short through a long descent or a full track session instead of going long on the fourth or fifth hard stop. |
| Roughly half the weight of an equivalent steel rotor | Every pound cut here is unsprung and rotating mass at the corner where a sports car feels it most. | Quicker turn-in and a front end that settles faster over mid-corner bumps. |
| Continuous-fiber disc construction | Long continuous carbon fiber carries load across the whole rotor body, rather than relying on short chopped strands, which matters through repeated heat cycles. | A disc built to take the abuse of a driven weekend without the structural fatigue an iron rotor eventually shows. |
| Rust-free rotor surface | A 991 parked between drives, especially through a wet season, is exactly the scenario where iron rotors flash-rust on the face. | Clean rotor faces behind the wheel with no orange ring after a rain or a car wash. |
| CCB-specific ceramic pad compound | A pad built for this rotor material, stable to about 750°C with roughly 0.44 average friction, keeps bite consistent instead of glazing under heat. | Low visible dust day to day and predictable bite whether the car is cold in traffic or hot after a canyon run. |
| Bespoke per-vehicle engineering | The bracket, hat offset, and pad shape are machined to this exact chassis rather than adapted from a generic catalog part. | A kit that bolts to the 991 as designed, without shimming or improvising at install. |
What gets better
- Pedal firmness holds through repeated hard braking instead of degrading.
- Lighter front and rear corners for sharper handling response.
- Cold-morning bite stays close to normal with the correct pad.
- Wheels stay visibly cleaner for weeks between washes.
What to confirm first
- Exact 991 variant, model year, and factory brake option fitted.
- 20-inch wheel inner-barrel diameter and spoke clearance around the front caliper.
- Whether the car sees track days, and how often, to size the pad correctly.
- That both axles are being converted together, since this build is front and rear.
Carbon ceramic brakes cost more up front than an iron rotor set, but a rotor engineered for a 250,000 to 300,000 km street life changes the math over the life of the car — our carbon ceramic brakes price and cost guide breaks that down in more detail. If you're not sure your car matches the spec shown here, send us your wheel and variant details and we'll confirm Porsche 911 (991) fitment before you order through our Porsche carbon ceramic brakes collection.
Fitment and installation
The first thing we ask for on a build like this isn't a photo of the wheel — it's a photo of the steering knuckle. The caliper bracket in this kit is machined to match that exact knuckle, so the 10-piston Akebono front caliper and the Brembo rear caliper bolt on with no cutting, no drilling, and no adapting a bracket that was designed for a different chassis.
On a rotor-only order, hat offset gets matched to the factory disc so the new rotor lands exactly where the OEM caliper already sits. Get that wrong by even a couple of millimeters and pad contact goes off-center, which shows up as uneven wear and, eventually, a pulsing pedal — it's not something you shim away after the fact, which is why we machine it to the vehicle rather than guess from a catalog fitment chart.
The install itself follows a standard sequence: the factory front caliper and rotor come off, the new bracket and Akebono caliper go on, the rear gets the same treatment with the Brembo caliper and 400mm rotor, and everything gets torqued to spec before the car moves an inch. From there, the pads need a proper bedding cycle — a handful of moderate stops that build heat gradually — before you ask the brakes to do anything close to their real job.
- Confirm exact 991 variant, chassis code, and model year.
- Confirm factory brake package currently fitted.
- Send wheel diameter, inner-barrel width, and spoke profile.
- Confirm current front and rear caliper setup.
- Tell us how the car is actually driven — street, occasional track, or both.
Give the pads a full bedding cycle before any hard use — a series of moderate stops from moderate speed, no full-ABS panic stops, letting the rotors cool between runs. Skipping this step is the single most common reason a correctly installed carbon ceramic setup feels underwhelming on its first drive.
What changes after the upgrade
We don't publish an instrumented stopping-distance number for this build, and you should be skeptical of anyone who hands you one without a test sheet behind it. What we can describe honestly is how this class of setup tends to behave in the situations that actually expose a brake's limits.
| Situation | Factory setup | After the STOPFLEX conversion |
|---|---|---|
| Repeated hard stops on a descent or track session | Pedal travel tends to lengthen and bite softens as heat builds. | Bite and pedal travel stay close to consistent stop after stop. |
| First cold stop on a winter morning | Normal cold bite, as expected of iron. | Close to normal bite with the correct STOPFLEX pad, with a touch more margin recommended on the very coldest mornings. |
| Wheel cleanliness after a week of driving | Visible iron dust builds up within days. | Dust stays noticeably lower for weeks between washes. |
| Steering response over broken pavement | Extra unsprung mass at each front corner. | Lighter corners typically feel quicker to settle. |
| Rotor appearance after a rainy week parked | Iron rotors flash-rust on the face. | Carbon ceramic rotors stay rust-free. |
This build was not put through instrumented testing, and we're not going to pretend otherwise. What we're comfortable standing behind is the engineering behind each part of the spec — the piston count, the rotor mass, the pad compound — and how that combination is designed to behave under real, repeated braking on a car like the 991.
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FAQ
Why upgrade a 911 991 to a 10-piston Akebono caliper instead of keeping the factory front caliper?
Ten pistons spread clamp force across a larger pad and the bigger 410mm STOPFLEX rotor, which keeps heat distributed evenly instead of concentrated in a few hot spots. On repeated hard stops that translates into a pedal that stays consistent from the first stop to the tenth.
Do carbon ceramic brakes actually change how a 911 991 feels to drive?
They can. A STOPFLEX carbon ceramic rotor weighs roughly half of the same-size steel disc, so unsprung and rotating mass drops at every corner. Owners typically notice quicker turn-in and a car that settles faster over rough pavement, not a stopwatch number.
Are carbon ceramic brakes reliable for daily street driving on a 911, or only for track days?
With the correct STOPFLEX pad, cold bite stays close to normal on the first stop of a winter morning and dust stays very low, so the car is fine as a daily driver. The same setup carries the thermal capacity to handle a track day without a pad or fluid change.
Will 410mm front and 400mm rear carbon ceramic rotors clear a 20-inch wheel on a 991?
This build is sized around 20-inch wheels, but rotor diameter is only half the check. The wide 10-piston front caliper also has to clear the wheel's inner barrel and spoke profile, so that has to be confirmed against your specific wheel before ordering.
How long do STOPFLEX carbon ceramic rotors last on a street-driven Porsche 911?
Left off the track, a STOPFLEX carbon ceramic rotor set is engineered for a street-service life in the range of 250,000 to 300,000 km, well beyond a typical iron rotor. Real mileage still depends on pad choice, driving style, and how often the car sees a track.
