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Originally Posted by Dean
If all 4 wheels lock, you are at the limits of the brakes, not the tires necesarily. This is where people get confused. If instead of locking, the brakes continued to apply even greater decelerating force without locking the pad to rotor contact, you would not actualy reach the limits of the tires until the tires started to substantially slip while still rotating. Unfortunately, this is often closely followed by brake lockup because the reduced torque from the tire/road loss of friction shifts the balance and the pad/rotor interface locks.
I'm not saying any particular brake system is not capabe of reaching the limits of a given tire prior to locking, only to change focus from the brakes to the tires and get you to think about how limitations in the brake system could be percieved as using all the tire's traction when it may not be. The equations for all of this are way out of my league.
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Dean,
I think I have to disagree with some of what you said. If a tire locks up, by definition the caliper has applied more braking torque, and hence more force opposite the direction of tire rotation, than the tire was capable of developing for its given (instantaneous) normal force and coefficient of friction with the road surface. Take a given tire with a given downforce, section of road, and coefficient of friction of 1.0 which locks up at a braking torque of 1000lb*ft. If you strap a different tire on the car with a coefficient of friction of 2.0 on that section of road, and apply the exact same braking torque of 1000lb*ft, the wheel will now not lock up; it will now take 2000lb*ft to lock up the wheel. I think this pretty much defines being deceleration-limited by the tires, not the brakes.
I think maybe what you were trying to say was more concerning how effective a braking system (and operator) is at modulating force near the limit of what the tire can produce?