14 Quick facts
about brakes |
Richard Oliver |
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The power generated by the
braking system of even a modest family car can exceed 500bhp (375kW),
outstripping the engine output of virtually everything on the road.
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The legendary Dunlop-developed
disc brakes that helped Jaguar to win the Le Mans 24 Hour race in 1953 were
referred to in the press of the time as "plate brakes". The term "discs"
came later.
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The first production car with
hydraulic brakes (ie using pipes and fluid rather than cables to activate
the brakes) was the 1920 Duesenberg, an American luxury car with a "straight
eight" engine. Chrysler brought the now universal feature to mass-produced
cars in 1924.
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Formula One racing is where
the most advanced brakes are found. During 1997, German driver Heinz-Harald
Frentzen recorded a force of 5.99G under braking. This is around six times
the braking performance of a conventional road car and meant that Heinz-Harald's
65kg body momentarily weighed nearly 390kg. To achieve this deceleration
he had to push the brake pedal of his Williams-Renault with a pressure of
150kg.
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Disc brake pads for a Formula
One car cost $250 each and during the course of racing and testing a team
will use around 1000 of them each season. That makes for an annual bill of
$250,000 for pads alone. Then there are rotors, calipers, fluids and other
components before you even start considering the things that make a car go
rather than stop.
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The first Holden to have disc
brakes on all four wheels was the 5 litre V6 Torana A9X of 1977. This was
quietly released to enable GMH to homologate parts required for racing. Only
500 A9X Toranas were built, including hatchback and sedan versions.
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Holden's HD model of February
1965 was the first Holden to offer the option of front-wheel disc brakes.
Originally they were dealer fitted (from Girling) and cost $30. In May 1966
disc brakes became available as a factory-fitted option at a cost of $20,
including a vacuum servo booster.
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The Spirit of America land
speed record car, which is trying to beat the supersonic record recently
set by Britain's Thrust SSC, does not have conventional brakes. The bullet
shaped, jet powered record breaker, designed to drive on a dry salt lake,
uses parachutes and an unusual sled device which is lowered against the ground
to create friction.
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The 1967 Porsche 911S was the
first production car to feature ventilated disc brake rotors. Now common,
these rotors have cooling channels running between the two friction surfaces
to give better cooling and therefore better resistance to brake fade during
heavy applications.
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The Falcon and the Commodore
models of the 1980s and early 1990s, which represent such a large percentage
of the Australian "car park", all have a hub type rotor design. This means
that the rotors are not just providing braking, but also supporting the
car.
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Modern braking components
need exceptional wear resistance, heat resistance and exceptional stopping
capabilities because - under extreme conditions - their operating temperatures
can average nearly 350 degrees Celsius.
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Harmful agents such as asbestos,
lead and cadmium have been removed from modern brake pads. Today's friction
materials are complicated mixtures of fibres, fillers, lubricants and a binder
resin. Designed for cast iron rotors, these are generally too aggressive
for lightweight alloys. Less aggressive linings have been developed for this
purpose, but practical aluminium or composite discs for everyday road cars
remain in the experimental stage.
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To improve noise suppression,
smoothness and stopping performance, the mass of disc brake rotors has increased
over recent years. The rotor for a typical Aussie "six" now weighs 12kg as
a raw casting and about 10.5kg after machining.
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Disc brake rotors were once
considered one of the simplest parts of a car to manufacture. Not any more.
With today's sophisticated electronically monitored brake systems, tolerances
need to be extraordinarily tight because the slightest shudder can confuse
the car's anti-lock braking system.
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