- [Narrator] All four wheelers, after having been driven
for 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 comes
from the frictional force between the tire and the road. The outer wheels will have
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 tire
is 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 it's 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 a
wheel alignment point of view, this is the toe-out condition. This means that if you set
the wheels in 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 car's
straight line stability, steering wheel returnability,
and cornering capability. Your support at Patreon.com
is invaluable to us. And, please, don't forget to
subscribe to Learn Engineering. Thank you.
