Dual Master Cylinder Bias and Torque Calculator
This calculator will produce torque results based upon projected maximum deceleration demands and allow users to build a dual master cylinder brake system with a wide variety of variables used in its design criteria. Additionally, the calculator can be used to fine tune desired brake bias based upon altering the pivot point of the balance bar in the pedal assembly thus giving an accurate picture of what true 'adjustable bias' can produce via the cockpit cable adjuster. *To use the dual MC calculator as a single bore design- set both MCs in the table to the same spec, then set the "pivot offset" value to zero. This will give the same line pressure to both axles and not favor one or the other.
The calculators requires a fair amount of data to get the desired results. In the brake bias calculator you will need the dimensions of many of the components of your current or desired brake system. This includes things such as the pedal dimensions, piston sizes, rotor diameter and brake pad coefficient of friction. The Torque table will require you to know the estimated weight of your vehicle per axle as well as an estimated 'center of gravity' as well as the desired g-force or "g" you feel your vehicle can achieve. When fully populated the tables work in tandem with one another allowing you to tune the bias calculator to achieve the goals set in and by the torque calculator.
A few opening thoughts:
1. The calculator has a default built into it to serve as a sample. In the sample vehicle we have designed a fairly reasonable 14"/13", 6/4 piston front and rear brake system with a modest .45 pad Cf and a common pedal ratio design. Note how the 68/32 brake bias is produced by fine tuning of the balance bar (+.150") so that the "required" torque per axle matches that of the "torque from left" cells. The total torque should also match relative to the leg input pressure for 100% value.
2. Use reasonable data. Don't make unreasonable assumptions that your car cannot achieve. A full 1g deceleration is possible on a vehicle with very high grip tires and optimum conditions. Most street tires will work best at perhaps a .6g target. If you can achieve more at some point it will only be relative to the amount of rotor torque and thus a bump in pedal effort to get to .8g may be minimal. Watch you "leg effort" number; the default 93lbs is huge. A more realistic value is in the 50-60lb range. Test this with a bathroom scale propped up againt a wall and find your comfort level.
3. Surface conditions. The calculator does not take into account surface conditions. We are assuming simple Mu of 1 or a clean, dry surface. Obviously you cannot achieve 1.2g deceleration on a gravel surface regardless of the tires or brakes. Again, be realistic in your input.
Differences in this calculator vs the Bias Calculator; Here the calculator will require you input much of the same data as the other, however there are some changes also. The pedal ratio will need to be calculated by supplying the measurements of the short and long portions of the brake pedal. You will need to populate the diameter of all pistons in the calipers to represent the total pressure- as opposed to 1/2 of the caliper when comparing only bias and an oe sliding/floating caliper. While bias will not change one way or the other we now want to calculate the total force produced by clamping. *If using a single or dual piston sliding/floating caliper populate the "Outboard" piston data to match that of the "Inboard" to compensate for the slide force factor.
Brake Bias Calculator
Weight Transfer Values
Required Brake Torque
After thoughts: in the example above we have a relatively high "leg" or input level. This is fine to show the relationship of these designs but the value should be closer to 60-70lbs total. To achieve that low a value and retain the total necessary rotor toque what would you do?? You'd use less leg input and either decrease the mc bores or more likely; increase the total piston area of both calipers. Give it a try and see. Or you can also put huge rotors on the car or even change the pedal ratio- all the while these changes will require you match the values in the right hand tables.
THANKS to the following and more for their contributions: Chris Harrison, Wilwood, Jake Latham, Stoptech and others who's data was used in part to create this tool.