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At the heart of the modern automobile
brake system is a disc rotor which rotates
with the wheel. Working with the rotor is
the caliper, which when the brake is applied,
tries to "grab" and thereby stop the rotor.
The efficiency of the system depends on a
few basic factors:
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- The ability of the caliper to apply enough clamping force to overcome the rotating rotor.
- The ability of the caliper pads to maintain adequate friction properties even with the heat
generated by continuous application of pressure from the caliper.
- The ability of the rotor to absorb and dissipate the heat.
- AND the necessary traction from the tires to allow the brake system to be effective.
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The distance from the center of the rotor to its edge (radius) can be thought of as a lever and
the caliper in effect pulls on the lever to slow the vehicle. The bigger the rotor, the longer the
lever. The longer the lever the more effective the caliper. It is easy to understand then that
larger rotors increase braking capacity. If the rotor is also well ventilated, its ability to dissipate
heat is improved, allowing the caliper pads to operate at a lower temperature and endure the
torture to which they are subjected.
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Brake Pads
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Different pad compounds offer different
friction coefficients and the ability to work
well at certain temperature ranges. Most
often a compromise is reached between
friction coefficient and the ability of the
compound to operate at the expected
temperatures, as a result, a variety of
compounds are available to work in
different heat ranges depending on the
intended use of the vehicle. The higher
the friction coefficient of the pad
compound, the more grip it has on the
rotor, making the brakes more effective.
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If we increase the area of the caliper pistons by increasing their diameter, the caliper will apply
more clamping force to the pads and rotor, further increasing the braking capacity of the
vehicle. Because the hydraulic pressure is constant throughout the system when the brake is
applied, the more caliper pistons we add, the more pressure there is exerted by the caliper.
More pressure or clamping power is more effective in preventing rotation of the rotor.
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In the event that the brake system is used to full capacity even with all of the improvements
and the rotor pads are overheated, they will give off gas as a
result of the bonding agents in the pad lining beginning to burn. The expanding
gas from the pad ("out gassing") form a cushion between the pad and the rotor
and braking effectiveness decreases rapidly. This condition is referred to as
"brake fade".
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When we drill holes through the rotor from one surface to the other and cut slots into the
surfaces of the rotor, we provide channels through which the expanding gasses can escape,
increasing the brake efficiency a step further.
(For a more detailed discussion on the merits of drilling and slotting see
To Drill or not To Drill.
The rotor must have the necessary mass to absorb the heat generated by applications of the
brakes, in effect it is a "heat sink". After the initial temperature "spike" from a hard brake
application, the rotor must be able to cool or dissipate the heat ready for the next application.
Many methods of cooling have been tried, even water cooling, but most often rotors are air
cooled. Increasing the surface
area of a given mass allows more contact with the cooling air and so speeds the dissipation of
heat.
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The most common cooling design is referred to as a
ventilated rotor and most often is a sandwich of the
two pad friction surfaces separated by fins. Separating
the friction surfaces and adding cooling fins increases
the overall cooling area of the rotor.
This allows air to circulate between the hot friction
surfaces and around the cooling fins, sucking away the
heat. There are designs with more and less fins,
staggered fin placement, posts instead of fins, curved
fins etc. etc. The most common high performance
designs have curved fins or vanes. This design makes
the rotor into an impeller pump which actually forces
air through itself for super cooling. Cross drilling of the
rotor increases ventilation and can be a factor in
cooling efficiency as well as dealing with pad out
gassing.
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A consideration sometimes overlooked is the overall rigidity of the various components of the
brake system. If a component flexes or yields under the pressure to which it is subjected, it
limits the maximum pressure in the system. Rubber brake flex hoses are known to expand
under pressure, some calipers flex under pressure, a poorly designed brake pedal can flex,
causing an overall drop in system efficiency. Flexing of components creates a mushy, not
solid, feel to the pedal, usually requiring greater pedal travel to achieve a given force at the
calipers. Removing flex from the system can make a marked improvement in brake function.
The first choice for improvement is typically the flex hoses as most other system flex problems
are more difficult to solve for the average enthusiast.
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All the brake improvements in the world are not going to help if
there is no traction available between the wheel and road.
Ultimately, your tires will determine how well your car stops. A
brake system of given efficiency will be most effective with the
smallest possible diameter tire. In the same way that the larger
rotor offers the caliper a longer lever, the smallest diameter tire
offers the vehicle a smaller lever. While different (smaller) wheel
and tire diameters are frequently an option for racers, most street
vehicles are limited to near standard tire diameters for a variety of
reasons.
Fortunately the trend in recent years toward larger diameter rims
and low profile tires has opened up many options in the area of
big brakes. In many cases, increasing rotor diameter will require
an increase in rim diameter to make room for the rotor.
Fortunately, low profile tires keep the outside diameter the same
or near the same as the original equipment so increasing the rim
diameter usually has no ill effect on braking. Conversely, modern
low profile tires are typically of a higher traction rating (or at least
high traction ratings are available) which will aid braking.
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Most often, vehicle manufacturers provide adequate, not excellent brakes on their production
vehicles. It is safe to say we don't get what we don't pay for. More expensive vehicles tend to
have better brake systems than the less expensive ones for obvious reasons, though this is not
always true. What is true is that almost all of them can be improved and that's our business.
The various brake systems we supply provide some or all of the improvements listed above.
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High Performance Brake Pads
Probably the least expensive, single most effective upgrade one can perform is a brake
pad upgrade. This is an area where one definitely does NOT fit all. There are as many
pad compounds as manufacturers of pads and each has its particular niche. For the sake
of simplicity, we have broken pads in three basic categories; High Performance Street,
High Performance Street / Race combination and Race Only. Street pads have to be able
to work well at low to moderate temperatures because street vehicles are driven cold and
under normal circumstances don't generate high temperatures. Usually in this category,
the pads work well cold and their effectiveness decreases as their temperatures increase
until breakdown of the compound bonding agents cause brake fade. Repeated hard brake
applications as in most types of racing will quickly overheat these pads making them
useless.
Combination pads usually incorporate some degree of compromise to incorporate this
flexibility of use. For the street they have to work well enough at low temperatures to be
safe and must also be competitively functional at moderately high temperatures under
racing conditions. These pads usually increase in effectiveness as they heat up through
their upper operating range then fade with overheating. They usually don't work as well
cold as a street pad and they don't work as well in the upper temperatures as would a
racing pad, the trade off for an "all around" pad. There are many circumstances where
these are the best pad for the application.
Race only pads do not work cold, period. Do not use race only pads on a street vehicle
thinking "If they are for racing they must be great pads". You will be in for a huge
surprise the first time you go to stop at a street light and sail right through the
intersection as though you had just hit the gas! They do not work cold and must be
warmed up before they are at all useful and in most circumstances require certain driver
skills to optimize their use. If you have a "race only" vehicle, we can supply a number of
race compounds for the different types of track you may encounter.
We can supply Porterfield pads for street use on most production vehicles. They also
have pads for high performance street and for racing on production vehicles and some
racing calipers including Wilwood. We carry a full range of Wilwood pads for use with
Wilwood calipers for both street an race.
All in all, we can supply the right pad for your application or applications if your vehicle is
multi purpose. Sometimes a simple pad change can make the difference between poor
brakes and reasonably good brakes. If you would like an inexpensive brake
improvement, our recommendation would be a pad upgrade.
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Cross Drilled and Slotted Rotors
These rotor surface treatments do not automatically guarantee
a shorter stopping distance, but can. As mentioned, cross
drilling and slotting is useful when the pads become
sufficiently hot to emit gas. Without an escape route, the gas is
trapped between the pad and rotor and actually prevent the
pad applying pressure to the rotor (brake fade). For the most
part and within the working heat range of the pad, slotting
and drilling prevent this from occurring. The extra capacity
afforded by these surface treatments can mean the difference
between being able to make those last few stops driving down
a mount road or not. They offer that extra capacity for sports
drivers and an extra margin of safety for everyone for a very
small investment.
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We always recommend slotting on the surface of drilled
rotors as it has a tendency to keep the pad surface clean
and free from glazing. While the irregularity of the rotor
surface does not necessarily improve friction, it does help
maintain a high friction coefficient as a result of the constant
cleaning action of the slots as they wipe the rotor, allowing
more consistent (non deteriorating) performance between
pad changes.
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Steel braided Teflon flex hoses are popular and for good cause. These hoses are stronger and
in most cases provide the driver with a more firm pedal as compared to the standard rubber
type hoses which can swell under pressure. This situation can be aggravated by heat, both
radiant (from the rotor) and conductive (from the brake fluid). The stainless steel and Teflon
both handle heat very well and tend to maintain a constant cross section under these
conditions. Braided hoses are a very worthwhile upgrade and perfectly compliment good pads
and rotors.
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Big Rotor Kits for Use with Standard Calipers
Frequently, it is possible to increase the rotor diameter and efficiency without major changes
to the brake system. Depending upon the availability of a compatible rotor to work with the
original equipment caliper, we provide a larger diameter rotor and caliper relocation bracket.
This combination makes it possible to see huge brake efficiency improvements without the
huge investment. We usually can supply these kits with rotor diameters varying from 11" to
13".
Big Rotor and Multi Piston Caliper Systems
These systems are the ultimate upgrade. We combine rotors from 11" to 14" in diameter and
up to 1.38" (35mm) thick with calipers from 2 to 6 pistons of various volumes, piston sizes
and configurations. Most of our systems utilize the high quality race proven Wilwood calipers
and high performance rotors. For applications with two piece rotors we use equipment from a
variety of vendors, all hand picked for quality and durability. Most of these are purpose built to
our specification, though we do rely on Wilwood Engineering for the huge variety of top
quality two piece rotors they provide.
Every system is engineered to exacting specifications for trouble free high performance abuse.
Systems are complete and include all necessary components, including master cylinder
upgrades where necessary, hoses, any special fittings, hardware and instructions. We include
specific pads for your intended us and can provide a variety for your various uses as necessary.
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Revolution Brake LLC
280 E. Hersey St. Ste. 2
Ashland, OR 97520
PH.541.201.8596
FAX.541.708.5248
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