[To understand the material of this page, I assume the reader have a firm understanding of Newtonian Kinematics. Knowledge of road resistance and weight transfer is also needed in this page.]
When I was a lousy driver (Oh, I still am :(), there were couple circumstances in which I needed to brake my Protege Sedan really hard to avoid tailgating another car or running the red light. Each time there was a big cloud of smoke coming out from my front tires that smelt like burning rubber. I was thinking it was because the braking force was so powerful that it rubbed the tires really bad. It turns out there are some truth in it but it is way more complicated than I thought it was. [An interesting note is that I don't smell rubber in my S2000. I later found out it is due to the magic of Anti-lock Brake System (ABS).]
The true reason for rubber burning is that the wheels lock (ie stop rotating) and then the tires slip/skid on the road surface. This is similar to the situation when you clamp a spheric ball (e.g. basketball or a soccer ball) with two hands and then slide it across the floor without rotating the ball. You will find that it is harder to do that than rolling the ball on the floor. This is because kinetic friction is at work in the former while rolling friction is at work in the latter.
Braking is kind of like clamping the ball. There are basically two big blocks of metal close up and then clamp the wheel. As a result, the wheels slow down. There are perishable sponge-like material called brake pad to sit between the metals and the wheel to allow complete contact between the brake and the wheel. The brake pad will wear out over time. However, if you drive aggressively with lots of heavy braking then you might need to replace the brake pads more frequently than normal.
Recall from our Road Resistance Section, we know that when our tires are rolling, they are momentarily at rest relative to the ground and hence they are not subjected to the surface frictional force like static friction or kinetic friction. The resistance that acting against the motion is the rolling resistance.
First Draft: November 18th, 2000
1.0 Published: October 30th, 2003
Yee Man Chan