All four-wheelers, after having been driven for a certain distance, are supposed to undergo wheel alignment. What is wheel alignment and what will happen to your car if you don’t do it? Let’s explore. At first glance, the wheels of a vehicle look as if they are perfectly straight and vertical. And this arrangement seems logical. The surprising thing is that, to improve vehicle performance, each manufacturer specifies some predefined angles to the wheels of their cars.
In these exaggerated visuals, these angles are pretty clear. We can see that there are basically three different angles associated with the wheels. Let’s first explore the importance of the camber angle. The camber angle is perfectly visible when viewed from the front of the car. This angle can be either positive or negative. A negative camber improves the cornering performance of the car. To understand how negative camber improves cornering performance, first, let us analyze how a car corners, with a zero camber angle. A centripetal force is required for the car to corner. This centripetal force comesfrom the frictional force between the tire and the road.
The outer wheels will have a higher frictional force compared to the inner wheels. The reason is simple. The outer tires will have the highest normal force during cornering. Now, let’s see what this frictional force does to the tire. You can see how the tires becoming deformed. Due to this deformation, the contact area of the wheel with the road decreases significantly. This will lead to poor frictional force. One easy way to increase this contact is to tilt the outer wheel inwards, as shown. This is exactly what negative camber is. You might ask the question ‘What happens to the inner wheel when it is tilted inwards?’ Obviously, there is a loss of some frictional force here, due to the reduced contact area. However, as we have already discussed, we want to maximize the frictional force on the outer wheels since they have the capacity to give the highest frictional force. The next important angle of an automobile is the caster angle. In the steering mechanism, the wheels turn around a steering axis.
This steering axis is never vertical in practice. The inclination of the steering axis is called the caster angle. This angle is quite critical for an automobile. You may have noticed that, after taking a turn, when you release the steering wheel, it automatically goes back to its central position. This steering wheel returnability is created by the caster angle. To understand the physics of it, please check out our detailed video on caster angles. The toe angle is the most sensitive of the three angles. When you look from above, this angle is perfectly clear. Toe-out and toe-in are illustrated here.
Ideally speaking, a zero toe angle will give minimum wear to the wheels. However, as you drive, the steering wheel undergoes minor unintentional movements. These minor steering wheel movements should not affect the straight-line motion of the car. To understand how the toe angle does it, let’s revisit the principle of steering. For perfect steering, the inner wheel should turn more than the outer wheel. If you look at it from an awheel alignment point of view, this is the toe-out condition. This means that if you set the wheels in a toe-out manner, you can achieve a perfect steering condition with just slight movements of the steering wheel. However, such a high steering response leads to safety issues as the vehicle responds even to your unintentional steering wheel movements, thus resulting in loss of straight-line stability.
Due to this reason, in passenger cars, a toe-in arrangement is always used. Toe-in provides the opposite effect. It reduces the steering responses and increases the straight line stability of the car. Usually, the toe-in has a very low angle. Each car will have an optimum set of wheel angles decided by the car manufacturer. These angles may undergo considerable variations over time, resulting in excessive tire wear. A routine wheel alignment operation is imperative for a car’s good performance as well since these angles are quite sensitive in deciding the cars straight-line stability, steering wheel returnability, and cornering capability.