Important information regarding "brake bias" or "brake
A brake system is designed to change the forces acting on
the car; the obvious observation is that it decelerates the car as
a single mass. However, this is a simplistic view that does
not take into account other factors such as the car's front-to-rear
weight bias and more importantly, the shift in weight bias that
happens under braking, and in turn most importantly, what effect
that weight shift has on the suspension. A car's stability in
any direction is only as good as the connection between the tires
and road surface, and a sudden upset (such as excessive unloading
of the rear wheels) can upset this stability. The goal of a
good brake system is to maintain this balance.
Vehicle manufacturers take the vehicle dynamics into account when
designing the original brake system, and adjust the size of the
various components. These components include rotor
diameter, caliper piston size, caliper piston quantity, pad
dimensions, and even pad friction index (which varies by
compound). Some original equipment systems utilize different
types of pads front and rear to adjust bias as much as 15% instead
of modifying the mechanical components.
Aftermarket performance brake manufacturers should take all of
those factors into account when applying their components.
They must also analyze whether their pre-made components
(specifically caliper piston size) are too large or too small, and
whether this affects bias or is inappropriate for the car's
In a front-only kit, having pistons that are the
wrong size for correct bias with the original rear brakes can
affect vehicle stability under braking and lengthen stopping
In a four-wheel kit, having pistons that are not
matched properly for the specific car's weight bias and suspension
setup can also affect vehicle stability and stopping distances.
Pistons that are too large for the original
hydraulic system can result in a soft or mushy brake pedal,
inconsistent brake response (first pedal push soft, second firm),
and difficulty in modulating or controlling the brake
UUC analyzes all of these factors during the
development of our performance brake packages. Our brake kits
are all vehicle-specific, and will even vary between two models
that would otherwise seem to be identical. For example, all
of our front-only kits are specifically tailored to provide ideal
brake bias with the original rears - this means that the "ideal"
kit for a 330i is very different than for a 323i due to different
original-equipment rear brakes and their specific hydraulic
The result is that every fitment has the "ideal brake bias"
when using the UUC-specified brake package, with every car having
firm pedal, shortest stopping distances, and normalized pad
For advanced users, brake bias can be easily adjusted
to compensate for unique suspension setups, tire size changes,
specific track requirements, or driver preference using "brake pad
By selecting different pads front and rear, bias can be
shifted forward or rearward as desired. Wilwood (and other
pad manufacturers such as Cobalt Friction) publishes the
coefficient of friction for each of their compounds (expressed as
"Cf" or the Greek letter "m", as in "0.64m").
Wilwood goes one step further and provides data on the effect that
temperature has on the friction coefficient, which simplifies the
tuning for the actual operating temperature range of the
brakes. Cf is directly related to brake pad effectiveness,
i.e. brake torque generated:
WILWOOD TRACK / RACE COMPOUNDS
WILWOOD STREET COMPOUNDS
What about "brake bias" or "brake balance"?
There are currently no