The Story of Disc Brakes

Motorcycle brakes were sadly, even less sophisticated as a common ' remedy' for poor brakes was to fit an 8-inch drum adapted from a mass-produced Ford car. Friction materials were secret recipes which might include such unlikely materials as horsehair, easily deteriorated by heat. The malady known as ' brake fade' is thus very old!

Riding and driving skills simply took poor brakes in stride, substituting engine braking through the traditional downshifting, aided by prudent forward planning. In those faraway days braking was a much less important component of lap time, while top speed on the longer ' natural' courses such as the Isle of Man was paramount.

Those who have heard the late Peter Ustinov's clever, extemporized ' Grand Prix of Gibraltar' recording will recall the exchange between the Italian racing team owner ' Commendatore Fanfani' and some nobody who dared ask about brakes.

'Brakes? Brakes make a car go slow, but it takes a genius to make it go fast!' That was the dominant attitude – that brakes needed no improvement because they just make you go slow. Like 'spec' racing tires today, bad brakes were 'the same for everybody'.
At first, aircraft had no need of brakes because they landed at low speed and just coasted to a stop on grassy fields. But at the Schneider Trophy air races of 1929, speeds of nearly 645km/h were achieved, and it became essential for high-speed land planes to have powerful brakes. Both Dunlop and Goodyear began work that year on disc brakes. Their potential advantage was that unlike a drum, a disc could not expand and distort away from the friction material rubbing against it. Frederick Lanchester had pioneered a disc brake in 1902 but was impractical at the time owing to poor friction materials.

Another invention of the time was the expander-tube or 'bag brake', which would be used by all large US and German aircraft of the Second World War. A full circle of friction blocks was held away from the inner surface of a drum by metal springs, and was driven outward against the drum by hydraulic inflation of a circular rubber or metal 'bag' which underlay the circle of brake blocks. Because such brakes cooled poorly they were unsuited to road vehicle use.

Goodrich in the US began development of disc brakes for aircraft in 1953, but prior to that Chrysler had offered a disc brake in 1949 and the tiny Crosley 'Hotshot' 750cc auto had featured Goodyear-Hawley disc brakes at about the same time. Aircraft disc brakes took two forms. One resembled a multi-plate clutch and it today the dominant form of aircraft brake because of the very large area swept by the many plates. It cannot be used in road vehicles because air cannot freely circulate over the brake plate surfaces. The other was the caliper-type disc brake, which because it exposes most of the disc's surface to cooling air, is the preferred type for road vehicles today.

Sudden change arrived with Jaguar's adoption of Dunlop disc brakes on its C-type sports racing car in 1953. Mercedes would famously add air brakes to their 300SLR – a flap as wide as the car which was erected hydraulically to assist its large and most elaborately finned drum brakes. No matter – the Mercedes drivers, braking as hard as they could for slow corners, were treated to the sight of the Jaguar sailing past still on full throttle, rushing in impossible deep, then braking violently once and disappearing around the corner.

Drum brakes were instantly obsolete in auto racing. Disc brake experiments with motorcycles were common in the 1950s but nothing much happened until Peter Williams made them work well on his Arter Matchless in 1968. Similar experiments were ongoing in the US, and in 1969, Honda equipped their new production CB750 four with a front caliper disc brake. Kawasaki and Suzuki gave their new 750cc two-stroke production motorcycles disc brakes in 1972. When Yamaha equipped their 1974 RD350 motorcycles with 267mm single discs, racers threw away the giant drum brakes of their TZ250s and 350s.

Today just as men of means show of the latest mobile phone or tablet-computer to another, so well-heeled vintage racers have summoned classic racing drum brake designs back into specialist production, lined with equally vintage 'green stuff' linings that can be made to squeak in proper classic style during moderate deceleration. It's the classic never ending story...
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