uploaded 10/ 11/99
The following article came out of a trip to Charlotte, No.
Carolina in September '98. A similar article appeared in Racecar
Engineering earlier in '99
Brakes on racecars have improved tremendously in the last
few years. Race teams have taken advantage of new materials and
processes but still have a way to go. Formula 1 teams have had
problems because they've tried new brake materials without enough
testing. A high coefficient of friction pad material doesn't
help if the driver can't feel what's going on well enough to
modulate braking force. I think that's what's causing the rash
of brake problems and off-course excursions.
One of my informants tells me that braking distances are so
short now in F1 that the drivers find it difficult to reduce
pedal pressure as aero downforce bleeds off with car speed. I
was told that some F1 drivers are loosening their safety belts,
locking their leg on the brake pedal, and letting the falling
deceleration of the car acting on their body mass reduce braking
I'm not sure I understand that. Isn't it a chicken/egg problem?
by Paul Haney
Modern racecars need good brakes. Constant tire development
and the aerodynamic downforce generated by racecars with wings
and underwings allow decelerations of more than 3 Gs. While the
car is slowing, aerodynamic forces decrease with the square of
the speed causing tire grip to fall off, demanding that the driver
modulate brake forces with extreme precision. 3,400-pound NASCAR
stock cars racing on relatively small tire patches are equally
demanding. Braking from 120 mph to 60 mph twice during a 20 second
lap is typical for a stock car racing on a short oval track.
The Kinetic Energy of a body is equal to one half its mass
times the square of its speed ( KE = MV2/2 ). Friction between
brake pads and brake rotors slows a racecar converting its kinetic
energy to heat.
Friction is defined by the equation Ff = CfF. The friction
force caused by one body rubbing on another at a steady speed
is the product of the coefficient of friction, a measured number,
and the force pressing the two bodies together. Friction braking
is a simple concept that becomes extremely complicated in reality.
One of those complications familiar to racers is "brake
bedding." New disc-brake pads and rotors need to go through
a specific process before they can be asked to perform reliably
and efficiently under race conditions. Rotor and friction material
manufacturers provide guidelines but most club racers and race
teams seem to develop their own routines which generally means
several laps on track alternating partial applications with cooling
periods and then ending the process with a full-hard brake application
followed by a gradual cooling. It's important that the racecar
doesn't stop when pads and rotor are hot. This can result in
uneven rotor cooling and deposition of pad material onto the
This bedding process accomplishes several tasks. It drives
off volatiles from the pads that can otherwise lubricate the
rotor/pad interface during hard braking causing the dreaded "green
fade" that can send the driver and car spinning off into
the weeds. Bedding also thermally relaxes the rotor, removes
any burrs or machining oils from the rotor, and wipes a layer
of pad material onto the rotor surface creating an almost mystical
marriage between the rotor and the brake pads. Properly done
this process insures good performance from the rotor and pads.
Bedding Eats Up Track Time
When racing was a more leisurely sport a team simply reserved
track time during a test day or early on a race weekend for bedding
brake sets and scuffing tires. As racing has become more competitive
and more dependant on entertaining fans at the track and on television,
track time has become more precious. For example, in the CART
Fedex Championship a "time certain" rule went into
effect for 1998. This rule states that all events must start
and end as listed on the event schedule. There is no possibility
for a team to regain track time lost because of the need to retrieve
a car spun off course or to remove debris caused by a crash.
As a result many teams are using pre-bedded brake pads and
rotors. Pro-System, Inc. of Cornelius, No. Carolina performs
this service. A visitor could easily miss Pro-System's building
located a short distance away from Raceparts Distribution, Inc.
(RDI), a source for racing parts for the NASCAR teams. Both buildings
lie just across a railroad track from a rural two-lane road that
used to be a main route south from Cornelius to Charlotte, now
the center of the booming NASCAR industry. Charlotte is located
about 200 miles inland from the Atlantic coast and half-way between
New York City and Miami. More than a hundred race teams and multiples
of that number of supporting businesses thrive in the Charlotte
Ashley Page runs Pro-System and is a co-owner of the business
with RDI. Page raced karts in the 1960s, a Triumph Spitfire in
Sports Car Club of America events during the 70s and worked with
GTP teams in the 80s. "We bed pads and rotors for most of
the NASCAR teams," Ashley said. "We probably supply
90% of the Winston Cup, Busch Grand National, and Craftsman Truck
teams. CART is our next-biggest market and teams in other series
do business with us also. We've had calls from a few European
teams but don't do much with them yet."
"Our business is brake system testing and development
in high-performance applications," Ashley explained. "RDI
is the sales arm of the company and Pro-System does the R&D,
engineering, and manufacturing. RDI has 26 people, we have 6.
Our NC-controlled lathes and mills give us the capability to
manufacture precision, short-run parts. We help the race teams
with their brake hardware and brake ventilation."
People in the brake industry call brake pads friction material
and they refer to cooling as ventilation.
"NASCAR Winston Cup teams race at Martinsville Speedway,
a half-mile, oval track with flat, tight-radius corners,"
Ashley explained. "Martinsville is very hard on brakes.
Four years ago the cars didn't have enough pad material to last
the race distance. It was common for a car to completely run
out of brakes before the end of the race. Lap times have improve
because of car development and better tires, and this has put
an even higher demand on the brake system. We've worked hard
with the teams to improve brake cooling and components, and we've
made progress. Lap times at Martinsville are now less than 20
seconds, and pad wear isn't a problem. They mount an in-car camera
under the car so the TV fans can see the brakes get hot and glow.
It's an old track but they keep building bigger grandstands.
More than a hundred thousand people go there on a race day. It's
an exciting place to watch a race.
At intermediate tracks like the one at Rockingham the teams
can run without brake ducting in the nose of the car and benefit
from the lower aerodynamic drag. This is the result of improved
cooling systems and better hardware from companies like Brembo
whose products we sell to the NASCAR market."
"The NASCAR teams still have brake problems and that's
where we can help them"," Ashley told me. "We
make a whole range of products: a pressure gage for setting brake
bias on dual master cylinder systems, brake tools, pedal assemblies,
brake hats for Brembo calipers, caliper mounts, mounting studs,
a brake parts kit, and a rebuild service. They can bring us their
calipers and we'll inspect them and rebuild them to factory specifications.
We try to develop parts to make their lives easier.
"You'd think that all racecars would use dual master
cylinders, but at least a third of the NASCAR teams still use
the old Ford single-piston master cylinder. With 34 races in
a season and very few weekends off they need to keep things simple,
and some teams just haven't worked with a dual system long enough
to get comfortable with it.
"Part of the problem is the pedal assembly is mounted
behind the firewall under the dash, and it's hard to get to and
difficult to maintain. We're working on a pedal assembly that
will make it easier to adjust and maintain a dual system. Teams
thrash to make the schedule, and I think more teams will switch
to a dual system when it's not such a chore to service."
The photos show the Pro-System brake dynamometer and the computer
that controls the bedding runs and records the data. More than
90% of rotors and pads sold are pre-bedded. The type and size
of rotor and pad determines the rotor speed, torque, and deceleration
rate used in a bedding sequence. During a typical run the dynamometer
spins up the rotor to the program speed. Hydraulic pressure is
applied to the caliper to maintain constant torque against an
inertia load that gives the best bedding result. At the end of
the stop the process repeats until the pads or rotors are bedded.
The sequence of stops is designed to insure that the rotor
is warmed slowly and reaches a temperature consistent with its
final use on the racecar. The components are allowed to cool
properly after the final cycle. A graph plotted by the computer
shows torque, temperature, hydraulic pressure, and rotor speed.
This graph and the summary data collected shows the operator
and the customer that the run was successful.
"We've done development work for caliper manufacturers
and for friction material manufacturers," Ashley said. "We've
tested rotors made from unique materials like aluminum and titanium.
Those customers wanted to know the critical temperatures, pad
wear, torque, and forces.
"Pro-System's brake business is growing. We'll develop
a series of tests to suit customer needs. We can use track data
furnished by the customer to develop track simulation tests.
This gives the customer information needed for further development.
When the product goes to the track it's in a more finished form
and makes the track testing more efficient. A second dyno is
under construction because of increasing demand from our customers."
Racing is an expensive sport. Track time is precious and racing
teams would rather spend that time carrying out their test program,
accumulating data, and working with their driver. If they can
install pre-bedded rotors and pads they save some of that precious
time on track.
If you have questions, contact:
19510 Zion Street
PO Box 1595
Cornelius, NC 28031, USA