This blog is about the mechanism that has kept providing “automobiles” the right direction since ages. Yes, I am talking about “Steering”. We all know what a steering is , but let me take you through a much more elaborated dimension, and it’s gonna be fun indeed !

The basic definition of a steering system can be stated as , the mechanism which is used to turn a vehicle in a desired path. In the early 18th century , there were ‘Horse-carriages’ with large open wheels. Basically, any vehicle is steered by turning the front wheels, and it was the same way with those horse-carriages. This type of steering mechanism involved a single pivot in the center of the front axles, however both the axles were fixed. But it had some disadvantages; it was only ideal for very low speeds and the maneuverability was also proved to be very ineffective.

As a solution to this , Rudolf Ackermann patented a design which was nearly close to an ideal steering design. That was named as an “Ackermann Geometry” for steering. It had two different pivots for the two front wheels with different slip angles for both the wheels. There is another effective steering geometry known as the “Anti-Ackermaan Geometry” used for high speed vehicles for efficient cornerings. Steering geometries will be discussed in another blog soon.

How does it work?

In the cars today, a Rack & Pinion Assembly is used to transfer the motion from the steering wheel to the front wheels of the car.

When the steering wheel is turned, the pinion(2) gets rotated upon the rack(3) and the circular motion gets converted into linear motion. The motion is then transferred from the rack to the tie rods(4). The tie rod further transfers the motion to the knuckle and the wheel is turned accordingly.


Scrub Radius of a vehicle can be explained very easily. Consider you are viewing the left front wheel assembly in the front view.

Now, extend the kingpin axis (steering axis) and the axis from the center of the contact patch of the tyre hypothetically. They will intersect at a point at the road and after extending it further after the intersection point we will obtain a length between the two line at the road surface. That length or radius is known as scrub radius. It can be Positive, Negative, and Zero.

Concurrently, KPIA is basically inclining the kingpin axis or the steering axis ,in order to reduce the scrub radius in order to improve high-speed maneuverability.

In motorsports, it becomes very necessary to corner your car without skidding off the track, maintaining your car’s speed. This is why , choosing the correct steering geometry, scrub radius , and KPIA is necessary in high-speed vehicles dynamics.


                                     BY - SHUBHODEEP CHAKRABORTY

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