Big Brake Kit
XYZ Racing Hollow Front Brake Kit — Audi S4 (UFO) φ-φ (97-97) (HUB M12) (1991-1994)
SKU: XYZ-BRK-BKF-AU-21-C-FRONT
- IncludesFront axle pair (2 discs + 2 calipers)
- PositionFront
- Disc Ø330–444 mm
- Caliper pots6 / 8 / 12-pot
- Lead time10–15 working days
Fits Audi S4 (UFO) φ-φ (97-97) (HUB M12) (1991-1994)
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Caliper render for this kit:
The UrS4’s UFO braking arrangement has divided opinion since the cars left the factory. Audi’s Uni-Floating Object disc system, fitted as standard to the 1991-1994 C4 S4, was ambitious for its era, but ageing parts stocks and the system’s known sensitivity to sustained heat have left owners facing a familiar question: convert the hubs, or find a kit that works with the original architecture. The XYZ Racing front big brake kit for the Audi S4 (UFO) is built for the second path.
Engineered around the original UFO hub geometry and M12 bolt thread, this kit upgrades the front axle’s stopping capability without the hub conversion that takes the car away from its original specification. It fits as a matched pair of front calipers and two-piece floating discs across the front axle. On a platform where the 2.2-litre turbocharged five-cylinder makes genuine use of every available braking margin, that approach matters.
What this brake kit does for your 1991-1994 Audi S4 (UFO)
The hollow-vane disc addresses the heat dissipation shortfall that catches the C4 S4’s front brakes under pressure, particularly relevant given the car’s kerb weight and the way the quattro drivetrain loads the front axle under trail-braking. More efficient thermal management means more consistent pedal feel across repeat applications, replacing the gradual fade the original UFO setup became known for as temperatures built. The two-piece floating construction lets the disc expand without warping the bell, where the original UFO geometry struggled, and trims rotating and unsprung mass off the front corners. Braided lines come as part of the kit to firm up the pedal.
Three pad compounds calibrate the front axle to how the car is driven. Street is the quiet, low-dust default for road use. Sport suits the quick-road driver who still covers significant mileage. Racing is for circuit sessions where sustained hard stops are the norm. The caliper finish suits both meticulous restorations and cars built around performance above originality. Included painted colours are Red, Yellow, Gold, Black and Anodized Black at no extra cost.
About the front brake kit
The kit uses a hollow-vane disc to shed heat faster than a comparable solid disc, a meaningful advantage on the C4 S4’s weighty front end where the combined demand of quattro torque delivery and hard braking puts sustained thermal stress on the front axle. It is designed for the UFO hub mounting architecture and M12 wheel bolt thread, keeping the fitment straightforward and the installation geometry intact. The calipers are hollow-bodied as standard for strength without excess weight, with an optional Hollow Racing upgrade for repeated high-temperature cycles that drops the dust cover, is rated to 1000C and carries a two-year warranty.
Pad compound spans three grades. Beyond the included painted finishes, a Custom Color in any Pantone is available, along with premium polished-forged Titanium, Polished Gold and Polished Silver and candy Teal, Blue, Red and Orange, covering both subtle and conspicuous installations. Discs come drilled or slotted at the same price, and centre-bell upgrades, two-tone in five anodized colours or in titanium, are selectable at checkout. The kit brings the front braking capability closer to the level the AAN engine has always warranted.
Fitment for the Audi S4 (UFO) (1991-1994)
Specified for the 1991-1994 C4 platform Audi S4 in original UFO front brake configuration, with M12 hub thread. A number of C4 S4s in circulation have already had their UFO hubs replaced during previous ownership; verify your car retains the factory UFO hub arrangement before ordering. Year span is 1991 to 1994.
What buyers also search for
- Audi UrS4 front brake upgrade for cars with the original UFO hub geometry
- C4 S4 big brake kit with hollow-vane disc construction for improved heat management
- Audi S4 1991-1994 front brake kit with M12 hub bolt compatibility
- UFO-platform front brake upgrade without converting to a conventional disc layout
- UrS4 brake performance improvement for fast-road and occasional track use
Choose your pad compound and caliper finish from the options above, and we build it to your spec.
What’s in the kit
Front axle kit — supplied as a complete bolt-on assembly.
- 2×Two-piece floating discs — 330–444 mm: you pick the exact diameter with the "Disc size" option
- 2×Lightweight aluminium centre bells
- 2×Forged aluminium calipers — 6 / 8 / 12-pot
- 2×High-stiffness mounting brackets
- 2×Braided stainless steel brake lines
- 4×High-performance brake pads (1 set)
- 1×Fitting hardware & tools pack
Choosing your spec
Every kit is built to order around the choices you make above. Here is what each option actually changes, so you can spec yours with confidence.
Brake pads — Street, Sport or Racing
Every kit ships with a full set of high-performance pads; the compound is your call.
Street is the right default for fast-road driving — a strong, progressive cold bite with low noise, low dust and long disc life. Sport raises the working temperature and adds bite and fade resistance for hard road use and the occasional track day, while still behaving on a cold morning. Racing is a track compound built for sustained abuse: huge fade resistance and bite once heat is in it, at the cost of more noise and dust when cold. Match the pad to how hard you actually use the brakes — there is no benefit to a race pad that never gets up to temperature.
Caliper grade — Hollow vs Hollow Racing
Hollow is the standard caliper on every kit: a hollow-body forged caliper, lighter than a solid one, fitted with a dust cover and backed by a 5-year oil-leak warranty. For most fast-road and spirited track use it is all the caliper you need.
Hollow Racing is the track-grade upgrade. It runs the same hollow body but without a dust cover (so there is nothing to melt at sustained high temperature), uses a twin-metal piston that isolates heat travelling from the disc to the oil seal, and is rated to 1000°C. Available 286–380mm (front). Warranty is 2 years on oil leaks and 10 years on appearance. Built for professional racing and repeated track days.
Caliper colour & finish
Painted colours (Red, Yellow, Gold, Black, Anodized Black) are included at no cost. Want an exact match to your car? Custom Color (+£150) paints the calipers to any Pantone code you supply (15–20 day lead time).
Polished Forged finishes are the flagship: a forged caliper given a mirror-polished surface treatment that shifts colour with the viewing angle. Beyond the looks, the polished surface dissipates heat better, resists rust and stands up to the weather. Choose Titanium (neochrome, +£350), Polished Gold (+£300) or Polished Silver (+£250). They look their best paired with a titanium centre bell. Care: clean only with a dilute neutral cleaner or water.
Candy colours (+£200) use a deep candy-paint and polishing process for a mirror-reflection, boutique finish — pick Teal, Blue, Red or Orange (shown below right).
Centre bells
The centre bell is the CNC-machined aluminium hat that joins the disc to the hub. The standard anodized centre bell is included. The Two-tone bell (+£200) adds an anodized accent ring — choose Red, Yellow, Orange, Purple or Silver right here at checkout. The Titanium centre bell (+£500) is a forged titanium bell (bolts not included) that finishes off the polished-forged look.
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More XYZ products for the Audi S4 (UFO) φ-φ (97-97) (HUB M12) appear here as the rest of the range publishes.