3500 Lb Trailer Axle Spindles Truck Boat Trailer Stub Axle

What is the coefficient of friction?

The coefficient of friction between pad & rotor is an indication of the amount of friction between the two surfaces. The higher the coefficient, the greater the friction. Typical passenger car pad coefficients are in the neighborhood of 0.3 to 0.4. Racing pads are in the 0.5 to 0.6 range. “Hard” pads have a lower coefficient but wear less; “soft” pads have a higher coefficient but can wear quickly. With most pads, the coefficient is temperature sensitive - which is why sometimes racers need to “warm up” the brakes before they work well, and also why most brakes will “fade” when they overheat – the coefficient of friction is reduced as the temperature rises. For more info in coefficient of friction, see section on pads.

What is sealing and retraction?

Caliper pistons are normally sealed with an O-ring that has a square cross-section. This O-ring stretches when the brakes are applied and the piston extends towards the rotor. When the pedal is released, the O-ring relaxes and retracts the piston. Because the rotor and brake pad surfaces are flat and aligned it takes very little movement to obtain pad-to-rotor clearance.