Brake coefficients of friction

[Homemade WRX]

I have been looking around and asking around about finding the coefficient of friction between two materials...i.e. brake pad and rotor and no one has been able to come with a formula for me, but only generic values for generic pads and rotors.

I was wondering if any of the brakes guys on here had a formula?
thanks, Micah

[Marshall Grice]

I'm kind of confused. What type of formula are you looking for?

[B]

There is not formula... yes the coefficent of friction is pressure sensitive.. but only slightly and thus can be ignored... Just take the Cf that they give u and multiply it by the effective braking diameter of the rotor... for a worn pad this is the average of the outer and inner diameter of the swept area because the pressure gradient counteracts the velocity gradient.

[Homemade WRX]

ok, so the Cf of the rotor is basically doesn't matter?...reason I ask is when talking with wilwood about the Cf's they say that is of the pad material alone...now cast iron, steel and aluminum have a difference in Cf and that will effect the total Cf between the pad and rotor, which is what should be used to calculate braking torque/force

[ben]

http://www.apracing.com/car/brakepad/performance.htm

It does depend on the disc material. I assume the numbers in the list on the AP site are for cast iron discs.

I always used 0.4 in my calcs.

Ben

[Buckingham]

Some compounds may also have a temperature dependant coefficient, which may cause a lack of performance if the brakes aren't sized correctly. This can usually be ignored in your calculations.

Ballpark numbers will usually suffice, since most braking calculations are will always only get ballpark answers as it is usually assumed that the driver's pedal force is constant, which it is not.

Additionally, if you use the same pad front and rear, any error will wash out with regard to designing your brake balance.

[Homemade WRX]

I guess I will calculate it for .4 and the heat isn't that big of an issue being the pads I'm looking at are very consistent across the heat range...