understeer

In cars, a problem that can occur when steering. When you turn the wheel, it doesn't seem the car is turning enough -- intuition tells you the car should be turning more than it is. One way to think about it is as follows: say you're driving a car around a bend, and you draw the arc of the curve. If your front wheels are not tangential to the arc, and indeed they are angled towards the centre of curvature of the arc, then you have understeer. It means that you have to turn more to end up where you would usually be.

Usually, unudersteer is caused when the front wheels have less traction then the back wheels. This could be because the front tyres are more worn, because there is more weight on the back, or several other reasons.

It's only really a problem for race drivers. In most cases, it's not a problem in normal circumstances, unless it's extreme, as it will limit your ability to get out of dangerous situations etc.

It's also important to know that, in an understeer situation, the correct thing to do is unwind the steering wheel. What's happening is that the front tires are turned more than they should be, and are being dragged across the ground straight, rather than turning the car. To regain grip, unwind the wheel, then do the turn again, this time more gently.

Usually understeer refers to the case where you are skidding the front tires. That's extreme understeer, it can be caused by braking hard, accelerating hard, turning too suddenly as aiken says or other traction issues.

However understeer is actually any situation where the metal of the front wheels is turned more than the car is turning. Due to normal distortion of the tyre wall during cornering that doesn't necessarily mean that the tyre is skidding.

Modern cars commonly have relatively stiff front suspension spring rates. This causes progressive understeer which is generally believed to be safer for most drivers. Understeer is also affected by tyre pressures, weight distribution of the car and suspension geometries. Additionally, cars will understeer more downhill due to weight transfer. High performance cars generally understeer less and may even allow you to adjust it.