Let’s say that you are driving on an icy street. You are going straight, but there is a corner coming up, so you turn your steering wheel. You turn it as you would normally, but your car just barely begins to turn.
This is called Understeer.
Basically, the term Understeer means that you have to give your car more steering input than the corner should require to get it to go around. The advantage of this is that your car is usually very stable in a straight line, but you have to work harder to get the car to turn.
For a more scientific definition, imagine that we draw a tangent line to the circle that the car is traveling around. If you have to turn the front wheels so that they are at a more aggressive angle (pointed more to center) than the tangent line, your car tends toward Understeer.
Here’s another way to think of Understeer. If you are driving around in a circle of constant radius, and you start accelerating, your front tires will be the first to lose traction, which will increase the radius of the circle.
It turns out that most automobile manufacturers build in some degree of Understeer into their cars because it is considered to be as safer tendency than Oversteer. This is because if you turn your steering wheel, and your car doesn’t turn, it is a natural instinct to slow down. Once you slow down to a speed where your tires have enough traction to go around the corner, your car will do what you are telling it to do and go around the corner.
It should also be mentioned that there are a lot of variables in play when it comes to a car’s handing, and even if you have a car that tends to Understeer, it may not do so in all cornering situations. One of the more significant variables is weight transfer from either acceleration or braking, and it will be discussed in another FAQ.