Excerpt from Chapter 7 - Advanced Street Driving Skills

When the Car Doesn't Go Where It's Pointed

When we first started driving, it seemed as if the car was always lurching forward or rearing back, and there were those really scary times when the car wouldn't even go where we pointed it. Even though we didn't know it at the time, this was our first experience with the phenomena known as oversteer and understeer.

Push the gas pedal too hard too quickly and the car will rear back, taking weight off the front wheels. Since those are the wheels that provide the car's steering, the front end of the car will become unstable and not respond as readily to movements of the steering wheel. This can be disconcerting, to say the least.

If you throw the car into a turn too quickly, it will rock towards the outside of the curve, taking weight off the opposite side of the car, upsetting your steering. If you're accelerating at the same time, then the car will be leaning back. Put the two motions together, and you have less weight on the steering wheels and less weight on the side towards the turn, meaning that one front wheel will be exerting almost no pressure on the pavement.

As you might guess, it is going to be difficult for the car to make the turn. Instead, it will continue to plow forward. We call that phenomenon "understeer." When a car understeers, instead of turning as you intended for it to do, it continues to go straight down the road. At the extreme, you'll find that you can't get the car to go around the corner. Instead, you wind up plowing off the outside of the road.

Consider the opposite phenomenon. Push the brake pedal too hard too quickly, and the car will rock forward. This takes the weight off the rear wheels and moves it onto the front wheels. If the car is in the middle of a turn, with the back wheels lifting up and losing their grip on the pavement, the car will begin to pivot on the front wheels. This also is not a good thing.

If you're going too quickly when you start to turn and then realize you're in trouble, you might instinctively try to slow down by letting off the throttle and pushing the brake pedal. What happens? The car, which is already leaning out because of the turn, then also starts leaning forward. At that point the weight of the car shifts off the inner rear wheel, which is helping the car stay stable around the corner.

With limited traction on one of the rear wheels, the rear end of the car can start to slide out towards the outside of the turn. This phenomenon is called "oversteer." When a car oversteers to an extreme, it will also slide off the road, but this time it will be the rear end that slides off first. Of course, it is possible for an excellent, experienced driver to control the oversteer by turning the front wheels the opposite direction of the skid. This has even been turned into an emerging motorsport, called drifting.

Experienced drivers simpify this oversteer-understeer thing. If the car won't turn as readily as they want it to, they say, that's understeer. On the other hand, if the car turns when they don't want it to, that's oversteer. In racing slang, a car that is understeering is said to "push." A car that consistently oversteers is said to be "loose."

To avoid all of these problems that result in the car doing what you don't want it to, the recipe is to be as smooth as possible when you use the throttle and the brakes. Instead of jamming your foot to the floor to go faster, squeeze the throttle down. Instead of slamming your foot on the brake pedal when you want to stop, roll on to the pedal, feeling it bite as you press it down. Either way, your passengers shouldn't be able to tell when you take your foot off one pedal and push down on the other.

Likewise, when you're turning into a corner, don't change direction any faster than the car can absorb the change. Feel the shift in weight balance as you turn the wheel into the corner, rather than jerking the wheel over and having the car overreact.