Important information regarding "brake bias" or "brake balance"

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 hydraulic system:

  • 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 distances.

  • 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 application.

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 systems.

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 wear.

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 tuning".

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:




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