350Z and G35
370Z and G37
Charger, Challenger, Magnum, 300C
Cobalt and HHR
Contour and Cougar
Corvette C5, Z06
Corvette C6, Z06
Countryman by MINI
Impala SS 94-96
Lightning, Harley F150 93-95 & 99-04
SHO, Flex, Explorer, MKS 2010+
Subaru WRX 08-13
Subaru WRX 99-05
Super Duty 05-12
Super Duty 13-
Super Duty 99-04
Leg- the amount of pressure placed on the brake pedal.
Master Cylinder Diameter- The bore size of the mc. If unsure use 1.00" as the default.
Front/Rear Line Pressure- This is the hydraulic pressure (un boosted) generated by Leg input based on the MC bore and a common 6:66 pedal ratio. For the rear the pressure is un restricted or non-proportioned. Different vehicles may limit this pressure by various proportioning devices so final pressure can be less- which then reduces rear rotor torque.
Front/Rear Piston diameter 1- The diameter of the first (or only if single pot caliper) piston fitted to the caliper.
Piston 2- The second piston on one side of a caliper.
Piston 3- The third piston on one side of a caliper.
Piston 4- The fourth piston on one side of a caliper.
Note: multi piston calipers express their values using one HALF of the caliper body. This accounts for the floating aspect of the single piston caliper. A six pot caliper would be 1.625/1.125/1.125" for example. True clamping force would be double that but also double the single piston of a floating caliper taking into account the 'pull' of the outer pad to the rotor surface. Using total area (all six for example) would require you double that of the floating caliper also- thus the net result is the same whichever way you do it.
*Total Front/Rear Piston Area- the total area value of the piston(s) expressed in square inches. See note above.
Front/Rear Pad Cf- the coefficient value of the brake pad. If not sure; use .40 for street pads, .48 for street performance pads, and .60 for racing pads as a rough guide.
Front/Rear rotor diameter- Expressed in inches, the total OD of the rotor.
**Pad Radial Height- This is the height of the pad friction material. Viewed from operating position it may appear as width. Most FRONT production pads will be about 2.0-2.5" and aftermarket or race pads fit to alternate calipers about 1.75 to 1.875" depending upon caliper requirements . Use 1.875" if unsure. REAR production pads are generally in the 1.500" range. Aftermarket calipers may range from 1.625 to 1.875".
Front/Rear Rotor Torque- the value of torque expressed in inch pounds.
Percentage of Front Bias- this is the net front bias of your vehicle.
While Bias is important, you can also see the cause and effect of other elements of your proposed changes. The calculator will demonstrate how a change in piston size can effect the required LEG input to get the Rotor Torque desired. Rotor Torque is the real value one must watch as it is the work being performed. Should you choose to run much less piston area you can calculate the required increase in Leg necessary to generate the same final value. This often provides a much 'firmer' pedal feel but will also need far more Leg to generate the same Rotor Torque. On the other hand you may wish to see what a smaller MC will do in the same instance to boost Rotor Toque. Rotor OD and pad Cf can also effect the amount of pressure required for the final torque value.
Why does my bias percentage shown not represent the rotor torque values to the same percent? The bias calculator expresses final bias as tire torque at the ground. By default the calculator assumes the same size tire is used front and rear. When rotor torque is expressed it is yet again a ratio of the tire in which it is functioning. The final bias is then calculated at the tire relative to those calculations. Changing the size of the tire from one end of the car to the other will effect tire torque just as changing rotor size does to rotor torque.
There are many variables which can be used to alter the final results. When shopping BBKs suppliers should be willing to give you the data here openly. If not you may want to ask why the information to make an educated decision is not afforded you. Don't be surprised if many of the sales people know nothing of this so you may have to ask for someone who does. To compare the options it helps to know the base information about your vehicle. This can often be found in the service manual and sometimes by asking on a forum if someone has compiled the data for you.
Some folks have questioned the results using this calculator. The format makes some basic assumptions; pedal ratio, pad radius etc and computes tire torque behind the scenes... The intent of the tool is to compare cause and effect more than establishing definative values. If you have questions about this calculator please feel free to contact me.
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