The Lamborghini Urus has 17.32″ brakes, currently a world record. Yes, this is not only an absolutely preposterous brake size but is also a marvel of modern engineering. This isn’t the first time a VAG product pushed the boundries of brake tech though and it certainly won’t be the last. While the Urus has a relatively tame but massive brake design, VAG has delved deep in the avant garde of the braking world.
What may be their peak of avant garde? The outer limit’s of VAG’s avant garde brake designs might be the Audi 200 20V Quattro’s front brake design which was originally designed for their S-class fighting V8 Quattro. Nicknamed the UFO rotor, the design was officially called an internal brake caliper and was produced by ATE. It was a standard disc brake system that had been inverted to have the caliper located inside of the diameter of the brake rotor. So, what on earth caused Audi to design this ridiculous looking brake rotor? Braking performance.
When Audi was developing the V8 Quattro in the late 80’s, the 17″ wheels were just about the biggest wheels you could find on a production car and even then they were few and far between. Brake rotors realistically couldn’t get far past 12″ on even the highest performance cars, the 1987 Porsche 911 came with at most an 11.1″ brake rotor which is just shy of the size of the standard brake rotor on a modern Mini Cooper. Audi wasn’t willing to put a 17″ wheel with a rock hard sidewall on their cars so they looked for a solution to their quagmire they had put themselves into. The solution was a thicker rotor that could absorb more heat and that heat absorption leads us to Audi’s UFO brake.
By placing the brake rotor inside the brake that allows that few inches of extra space to be used for more brake rotor surface area. To make this happen Audi had to make a huge wrap around hub that extends from the center of the steering knuckle to the outer edge of the brake rotor. Conveniently, this also allows the brakes to effectively have a larger heat sink that extends beyond the contact patch of the pad and fills the area up to the wheel with extra material that can absorb heat.
After ATE and Audi finished prototyping the design, Audi was able to fit a 12.2″ brake rotor behind a 15″ wheel with less than 3″ of space not dedicated to brake rotor diameter. The modern Lamborghini Urus has to run a massive 21″ wheel to fit those 17″ dinner plate rotors with twice as much space dedicated to the caliper and not allowing additional heat absorption.
Audi was able to prove the world wrong and fit a 12″ brake behind a 15″ wheel and answered a question that nobody was asking, but was it all worth it? Well, yes actually. The Audi V8 Quattro was able to stop from 60 MPH in 120 feet during it’s 1989 Motorweek review, for comparison the Lexus LS400 did it is 121 feet the next year and that was with every bit of Toyota’s vast R&D department behind it. Surely, this technology was going to change how we design brakes forever.
It did until it didn’t. While the UFO rotor made it onto the 200 Quattro, V8 Quattro and Ur S4, by 1995 brake and tire technology had advanced to make this design unnecessary. With larger wheels becoming more commonplace and lower profile tires becoming more acceptable, Audi was able to increase the size of the wheels it was fitting cars with and reverted to standard rotor designs.
Audi could have continued to utilize this design but it wasn’t without it’s issues. The biggest issue for Audi was the cost to make these. With a standard brake rotor, one size can fit multiple models across several makes, a cast for a specific diameter and hub size could be made and the PCD can be drilled to exact specifications with minimal tooling changes. With this completely different design, that wasn’t possible. Audi was responsible for the brunt of the entire cost of ATEs production for these rotors. What cost Audi an exorbitant price to make was reflected to parts costs to retail customers, while a standard brake rotor could be had for around $100 over the counter at a dealership, these were a whopping $550.
Additionally, the UFO rotors were effective but didn’t hold up well in the real world because they were very susceptible to warping. The warping wouldn’t occur during spirited driving but became a massive issue in daily use. A quick stop and holding on the brake, as one does at a stop light, would cause the rotor to develop a hot spot because half of the rotor would cool faster than the other half. As metal expands when it is warm the rotor would bend slightly where it was cooling faster, thus creating an uneven braking surface and a vibration while braking. This was extremely common and it’s almost impossible to convince owners to change their driving habits from what they were used to doing.
In a 1995 TSB, Audi advised that production was ending and, after the stock was gone, that cars be converted to standard rotors if the customer wanted official VAG parts. That was the end of the Audi UFO rotor and today the old stock is becoming harder and harder to find. Unless someone is absolutely a purist about preserving their old Audi, it’s very hard to justify keeping these strange brakes. The cars that came with these rotors are on the cusp of becoming collectible and are considered just another old car to a lot of owners. Most people with these brakes on their cars are either living with warped rotors or biting the bullet and doing the conversion. Occasionally sites like ECS Tuning offer a small stock of NOS rotors but it is rare and you’re more likely to find some being sold on the private market.
Unfortunately that’s just the cost of reinventing the wheel. It was a noble effort but a technology lost to time. The automobile world’s greatest innovators rarely see any profit from their innovation. The most innovative companies in automobile history have ended in failure. Bugatti, Citroen, Dusenberg, Bricklin, DeLorean, the list is endless. Companies like VAG and Tesla are only able to operate the way they do because of a massive amount of investment. We often give VAG a hard time here at Carbitrage because of some of their practices but we’re always willing to give credit where it is due and this is absolutely worth noting.