A nose heavy car will understeer while a tail heavy car will over steer. Toyota MR2s, Acura NSXs, and early Porches are know for this tail happy dynamic. To explain it, think of the car a pendulum with the front of the car hanging from the ceiling. If the rear of the car is heavy, then the car will tend to rotate easily about the front axis. Think of it as a string with a weight on the end of it. If the front of the car is heavy, then the car will resist rotation about its front axis. Think of a string with no weight attached. An easy way to check this out is with a hammer. Take the hammer by the handle and hold if horzontal to the floor. It will tend to rotate downward quite easily. Now take the opposite end of it and do the same thing. It will be easier to hold it horizontal. When a car goes into a turn at speed the car is rotating around the center between the front wheels. If the force produced by this change in accelerationis greater that the frictional force of the rear, tires then the car spins out. If the car is balanced to the rear this lateral force can easily overcome the frictional force of the tire. The frictional force is the weight on the tire multiplied by the coefficient of friction. The coefficient is variable depending on the type of tire, the road, temperature, etc and is always less than 1. Hope this helps.