Understeer and Oversteer

These are the commonly used terms which all car guys must have come across. But do you know the factors which affect understeer and oversteer. From the name of both terms, the meaning of both is quite clear; understeer meaning you will have to steer more in order to make the turn, and oversteer meaning your slight rotation of steering wheel can make the turn for you. Let’s know what affects your steering sensitivity.

Now, we used the word sensitivity but understeering and oversteering are lot more than just sensitivity of steering. On a turn, if your car is in too much understeer then it may be impossible for you to take turn on high speed. You see how much it can affect your driving.

Now you should not come to conclusion that oversteering is a good thing. Oversteering can cause you problem when on a high traffic straight road you just bump into Mr. Smith’s car because you just wanted to get into mid lane but your slight rotation in steering made your car turn more. So oversteering can be dangerous too. But don’t worry, both can be controlled after we know what affects your steering sensitivity.

Let’s get into some technicals to know this in a good way. The value of both is usually measured using understeer gradient ‘K’. Positive value of K means understeer ans negative value of K means oversteer.

First of all, a general (steady-state) value of steering (rotation of steering wheel) is calculated by making the car turn at low speed which is called as Ackerman steering. Then as the speed of vehicle at turn is increased, push of vehicle on outer tires (lateral acceleration) is increased. To make the turn if you need a higher value of steering i.e., difference between required steering and ackerman steering is positive; the value of K comes out to be positive and it is called as understeering.

Similarly while increasing speed, if difference between required steering and ackerman steering is positive then the value of K comes out to be negative and it is called as oversteering.

In understeering, outer front wheel run at higher slip angle while in oversteering, it is the opposite.

Different things which affect understeering and oversteering include suspension, anti-roll bars, weight distribution. In the next post, we’ll know what are anti-roll bars and how they affect understeering and oversteering.

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