Telfordsteve

The tendency of a car to oversteer is affected by several factors such as mechanical traction, aerodynamics and suspension, and driver control. The driving technique called opposite lock is meant to cope in this circumstance. Limit oversteer occurs when the rear tyres exceed the limits of their lateral traction during a cornering situation before the front tyres do, thus causing the rear of the vehicle to head towards the outside of the corner. More generally, oversteer is the condition when the slip angle of the rear tyres exceeds that of the front tires. Rear wheel drive cars are more prone to oversteer, in particular when applying power in a tight corner. This occurs because the rear tyres must handle both the lateral cornering force and engine torque. An oversteering car is alternatively referred to as 'loose' or 'tail happy.
Conversely, understeer is the condition in which the front tyres don't follow the trajectory the driver is trying to impose while taking the corner, instead following a more straight line trajectory. Understeer covers several different phenomena, in particular, there is a big difference between linear range understeer, typically between 0 and 0.4g, and limit handling understeer, which is at higher lateral accelerations, and is what racing drivers are talking about.