that after making a turn,

when you release the steering wheel

it will automatically return to the central position.

You will be amazed to find out

that this steering wheel return ability

is not achieved by any complicated mechanism

using springs or valves.

Instead, engineers have achieved

the return motion of the steering wheel

solely by giving the front wheels

an angle called a caster angle.

Let's discover the interesting physics

behind how providing an angle to the front wheels

makes the wheels and the steering wheel

come back to their original positions.

First, let's have a closer look

at the steering wheel mechanism.

It is clear that the rotation of the steering wheel

is transferred to the rack and pinion mechanism

which then turns both the wheels.

If you observe closely, you can see

that the wheels are turning along a particular axis.

This axis is called the steering axis.

In the current demonstration,

you can see that the steering axis is perfectly vertical.

However, this is not normally the case in practice.

In practice, the steering axis will be slightly inclined

to the vertical as shown.

This angle is called the caster angle.

You will get a clearer picture of this angle

when it is viewed from the side.

Let's watch how this steering mechanism works.

At first you might not notice much difference

from the previous mechanism.

However, when you understand

the concepts of patch area and pivot point,

you will notice a big difference.

Patch area is the area where force

is transferred to the wheels.

It is clear that the wheel is pivoted

to turn around at the meeting point

of the steering axle and road.

Let's call this meeting point the pivot point.

In the first mechanism,

the patch area is in line with the pivot point.

However, in the second case,

the patch area is way behind the pivot point.

To understand the effect of this trailing patch area,

let's study more about the forces

acting on the wheels during cornering.

Assume that your car is making a perfect circular turn

in a level plane.

To make this turn, what the car needs

is a centripetal force.

In a level plane turn, this centripetal force should come

from the frictional forces at the wheel patch area

and this fact is clear from this snapshot.

Now let's analyze in detail

what this frictional force does to the front wheels.

In the actual steering wheel geometry,

we saw that the patch area

is behind the steering axle meeting point or pivot point.

If you no longer hold the steering wheel

in this turned condition,

the effect of the centripetal force

on the wheels is obvious.

It will produce a restoring torque

and the wheels will automatically realign to the center.

Let's watch it from the top view also to get a better idea.

However, for the initial geometry

with zero caster angle,

there won't be any restoring torque

since the centripetal force passes through the pivot point.

In short, just by giving a positive caster angle

to the steering mechanism,

engineers were able to attain the restoring torque.

We salute the brilliant minds that visualized

such an ingenious idea and avoided the need

for a complex mechanism.

It is clear from these discussions

just how critical the caster angle is

for a vehicle's straight-line stability.

The caster angle is not adjustable on modern cars

but if during the wheel alignment operation

any variation is found,

due to wear and tear of the connected parts,

the issue should be fixed.

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Thank you!