In the world of brakes, the day of the drum is done, even though the drum brakes of today are more efficient than the discs of the 70s. There aren’t many (if any) automakers that still use drums on the front wheels, where more efficient disc brakes are usually employed to do the lion’s share of braking. Want to learn more about current technologies and developments in braking systems? Visit our download centre for more articles, whitepapers and interviews: http://bit.ly/braking-articles

1. Automotive Braking: Materials and Development
The nectar of internal combustive invention is generally milked from the dangerous swagger
of pace, not the pedestrian commute to curtail it.
It often seems braking technology is acceleration's unwelcome side project, attracting scant
concern from automotive engineers who appear infinitely more interested in the rakish
transfer of sheer horse power to physical momentum. And who could blame them? Speed is
Elvis, after all, and braking is for squares, man.
One only has to examine the development of the technology involved in these diametric
endeavours to understand where the historical impetus of automotive R&D lay. In the
zealous quest for speed, stopping is apparently an afterthought, as if life's dowdy, fastidious
administrator stubbornly tugged the automotive manufacturers' sleeve and tiresomely
asked: "I know you don't care if you die in a squealing high-speed crash, but what about me
and the kids?!"
(This would, I imagine, inspire a Doh! moment Homer Simpson could justly pursue to
copyright litigation. Thereafter the sheepish gearheads would reluctantly shoehorn in a
couple of extra seats and, muttering, bolt on a brake or two.)
As the technology that drove cars to go faster progressed, advances dwindled from great
lunges to micrometric increments: refinement sharpens the cutting edge that shaves itself
ever thinner. Especially in motor sports, where mere hundredths of a second can so easily
describe first place from, well, death. By comparison, brake technology advanced inversely,
with little change occurring in the early days of motoring to increasingly rapid improvements
over the last thirty or forty years. One only has to drive a sports car from the 50s or 60s into
a corner at anything approaching an athletic velocity to experience the difference between
then and now: every bodily orifice startlingly puckers uncontrollably the first time you stamp
on the relatively useless brake pedal. This vigorous full-body alarm viscerally demonstrates
how urgently brake systems have evolved in more recent years.
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2. Ye Olde Drum Brakes
In the world of brakes, the day of the drum is done, even though the drum brakes of today
are more efficient than the discs of the 70s. There aren’t many (if any) automakers that still
use drums on the front wheels, where more efficient disc brakes are usually employed to do
the lion’s share of braking. The main reason they are still used on rear wheels is a result of
cost: drum brakes are much cheaper and easier to implement as a parking brake (rear discs
require a separate parking brake facility to be installed). Although cheaper to produce, their
main failing is their comparatively inadequate heat dissipation, which is essentially what
brakes are designed to do: convert kinetic energy into heat energy and disperse it as
efficiently as possible.
Discs
In order to aid heat dissipation, disc designs have for years incorporated cross-drilled holes
(increasing surface area), especially in performance designs where regular replacement due
to wear isn't such an issue, and have moved from being solid cast iron units with opposing
contact surfaces to two relatively thin contact discs separated by fins or vanes (often still a
single piece of cast iron). This allows air to flow magnanimously around the unit, vastly
increasing the cooling efficiency.
Racing Discs
Racing applications often include slotting the contact surface, where shallow channels are
machined into the disc at an angle to the direction of motion that aid in removal of debris,
gas and water. This technique is not often used for road cars as the wear on the pads is
obviously quite rapid. Air ducting is often introduced (usually to the underside of the car) to
channel airflow to the centre of the disc in further effort to increase cooling, as is the
addition of dedicated electric brake disc fans.
Brake Pads
A brake pad's effectiveness is measured by the dynamic friction coefficient " ", which is the
ratio of the friction force compared to the force pressing the two surfaces together. Most
standard automobile brake pads range from 0.35 to 0.42, while high performance brake
systems can reach up to 0.62. The best materials have a coefficient that remains fairly
constant as temperatures change. If the material's coefficient changes too much when hot or
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IQPC GmbH | Friedrichstr. 94 | D-10117 Berlin, Germany
t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de
Visit IQPC for a portfolio of topic-related events, congresses, seminars and conferences: www.iqpc.de

3. cold, the brakes may fade or grab: both undesirable results when either travelling at speed
and/or sipping a hot cup of coffee.
The dissipating of heat, therefore, is the primary impetus behind brake development, both in
design and materials technology. The main evolution has been in brake pad and disc
materials and configurations, primarily driven by the racing industry, where efficiency
translates directly into dollars.
The higher the coefficient of dynamic friction rating for the material, the better brake pad it
makes, which led to asbestos being used extensively for decades, largely because of its
toughness and heat-resistant properties. As the health dangers of asbestos dust became
apparent, however, aramid began to replace it; a synthetic fibre asbestos substitute often
used in ballistic body armour. Kevlar or fibreglass can also be used.
Composites
Composite brake pads generally consist of a material, such as aramid, infused with copper
or iron fibres/dust to provide increased heat dissipation and increased friction for greater
braking power. This does tend to make braking louder, however, and is more abrasive on
iron discs.
Want to learn more about current technologies
and developments in braking systems?
Visit our download centre for more articles, whitepapers and interviews:
http://bit.ly/braking-articles
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IQPC GmbH | Friedrichstr. 94 | D-10117 Berlin, Germany
t: +49 (0) 30 2091 3330 | f: +49 (0) 30 2091 3263 | e: eq@iqpc.de | w: www.iqpc.de
Visit IQPC for a portfolio of topic-related events, congresses, seminars and conferences: www.iqpc.de