2022 marks the 70th anniversary of the debut of disk brakes on automobiles in a meaningful way. The disc brake supplanted drum brakes which, while completely adequate for everyday driving, were not up to the job as cars got more powerful.
The secret of disc brakes' superior performance is owed to their ability to better dissipate heat. The result is less performance degradation or "brake fade" due to heat buildup than their predecessors. Plus, they offer more “feel” for the driver who can be more precise when applying them.
After overhearing a recent conversation about the first use of disc brakes in cars, I did what I do, which is to commence an impromptu research project. I discovered a few facts that helped me understand the roundabout path by which disc brakes ended up on being on nearly every modern automobile.
Fact 1: Disc brakes and drum brakes were both patented in 1902. Carl Benz is credited with inventing the automobile in 1886. The original braking system for early cars was the spoon brake, already a 200-year-old invention at that time. (It was the braking system on horse-drawn carts and buggies.) First utilized on these carts, it was a simple, mechanical lever, with a block that exerted a frictional force on the rim.
In 1889, American inventor Elmer Sperry invented disc brakes for use on an electric car prototype he was working on. A fellow named Frederick Lanchester of the Lanchester Motor Company filed a patent for disc brakes in 1902. Lanchester’s early choice of brake pad material was copper, which was too soft to work well, so they never caught on. In 1907, British inventor Herbert Frood invented a better brake pad using asbestos, which was the material of choice until the 1980s.
Coincidentally in 1902, French inventor and industrialist Louis Renault filed a patent for drum brakes. However, Maybach was known to have used them as early as 1900 and failed to pursue a patent.
Fact 2: Drum brakes were initially the clear winner. Once pneumatic tires replaced wooden and metal wheels, the spoon brake was finished. Renault’s drum brakes quickly became the standard across Europe and America.
They worked superbly in the early days of the car, when speeds were still not high. The enclosed system of the drum brake was its biggest advantage, protecting the pad and drum from exposure to the elements, and preventing water and dirt from fouling them -- an important consideration when many roads were still primitive.
The early drum brake systems used mechanical pressure from the driver. As vehicle speeds increased, so did the need for leg strength! The hydraulic brake system was invented by Malcolm Loughead in 1918, but it was not used commercially until 1929, when a Duesenberg was outfitted with them on all four wheels. Hydraulic systems multiplied the force exerted by the driver, which was needed for safety as cars increased in both speed and mass.
Fact 3: Dunlop Rubber Co. revived disc brakes for planes. For whatever reason, everyone seemed to either forget about or completely dismiss disc brakes. That was until Dunlop started experimenting with them on aircraft during WWII. Dunlop was already a leading tire manufacturer, but in the 1930s the company supported the war effort by creating control systems for Spitfires and other allied aircraft.
This work led to experimentation with disc brakes with the Royal Air Force. Once the war concluded, Dunlop filed a patent for the new design in 1946. As Dunlop was already a fixture in the automobile industry, this gave them a big head start, and they began work on a disc brake suitable for cars.
Fact 4: Jaguar pioneered the disc brake in the C-Type. Jaguar was enjoying success in racing with the XK120 and C-Type, but the faster speeds were revealing the weakness of drum brakes. Dunlop and Jaguar began collaborating in late 1951, to experiment with a new braking system under the direction of Dunlop’s Harry Hodkinson, an RAF test pilot who had worked with Dunlop during the war.
In early 1952, the first C-Type (XKC 001) was built with Dunlop disc brakes. They tested the car at an old RAF base with test driver Norman Dewis behind the wheel. With Le Mans in mind, they showed that the innovation of disc brakes was superior to drums at arresting cars at the end of the Mulsanne straight.
Fact 5: Stirling Moss was the first driver to race -- and win -- with disc brakes. Stirling Moss was absolutely essential to the development of this innovative technology. As Dunlop’s Harry Hodkinson said, “Moss was a real professional. He was always prepared to help and encourage by coping with experimental equipment, and he would always make the most of it.”
Moss pushed Jaguar to allow him to use disc brakes at the 1952 Goodwood Handicap Easter Meetings on April 14, 1952. Moss drove the car (XKC-003) to a fine fourth place, recording the fastest lap along the way.
On June 29, 1952, Moss took a C-Type (XKC-005) to victory in Reims, marking the first race won by a car fitted with disc brakes. Following the race, Dunlop engineers learned that the pads would not have lasted for an entire 24-hour race. Since changing them would take too much time, they compensated by making the pads thicker so that they would endure the test of Le Mans. They demonstrated that in the 1953 race which saw Jaguar C-Types finish 1-2 on the debut of disc brakes at Le Mans!
Fact 6: The Citroen DS was the first mass-produced car to use disc brakes. While Jaguar was the first major manufacturer to adopt disc brakes, they were utilized exclusively for race cars until 1958 when introduced in the Mark I saloons.
Citroen beat them to the punch about production cars when they introduced them in the DS in 1955. The avant-garde DS featured front-wheel drive, an advanced hydropneumatic suspension, and disc brakes -- a technological tour de force. It is interesting to note that the disc brakes in the DS were in-board brakes rather than the more common position within the rim of the wheels themselves.
Fact 7: The GT40 Mk IV could change brake rotors in 60 seconds. As noted above, Dunlop and Jaguar were able to solve the issue of brake wear by making the brake pads thicker. By the mid-1960s, brakes were being pushed to the absolute limit, and none more than those on the Ford GT40 that reached a top speed of 223 mph on the Mulsanne, and reached 1,650 degrees Fahrenheit. To be competitive, brakes needed to be changed mid-race at Le Mans.
While Shelby American's Phil Remington was credited with the invention in Ford vs. Ferrari, that isn't entirely correct. The innovation of quick-change pads was the brainchild of Remington, the quick-change rotors were actually developed by John Holman of Holman-Moody Racing. No longer would it take 20-30 minutes to refresh the brakes, but rather only a minute, which meant it could be done in the same amount of time as refueling. (Whatever you do, do not forget your asbestos gloves!)
Disc brakes have transformed the safety and performance of automobiles. Now modern advances for disc brakes are continuing this progression with new materials like carbon and ceramic discs, improved ventilation and cooling, and electronic systems like ABS.
Not bad for a technology that sat completely dormant for the first 50 years of the automobile, only to be rediscovered by a tire company!