Car Wheel and Steering Mechanics

Basics of Wheel and Steering Mechanics

Centripetal force is center seeking force which is always directed towards the center of a circular path and act at right angles to the direction of motion along a circular path.

Centrifugal force  is an apparent force in a certain situation that a body appears to be acted upon by a force while there is no force acting on the body, For example consider a situation inside a car we have a cup placed on the left side of dashboard ,the vehicle is moving in a straight road and cup will remain there since the cup is also traveling in straight line ,it will remain in straight line until an external force is applied to change its direction of motion as we know in this situation we are not disturbing the cup . Suppose we take a right turn and the car wheels turns due to centripetal force which act as an external force to change the direction of car and this force is produced from the frictional energy on the contact area of car tires. But the cup which was moving in a straight line cannot change its direction since there is no external force available, the friction between the cup and dashboard is not enough to resist the change in direction so to conserve the universal law the cup moves in such a way to the right side that it will appear to continue its straight line path this fictitious force or apparent force is centrifugal force. 

Caster Angle Basics

On a Trolley the steering pivot is ahead of the wheel and as soon as the trolley moves the wheel cannot help but follow, On a car the steering pivot is near the wheel center but the castering effect can be achieved if the steering pivot is tilted backwards. If an imaginary line is drawn through the steering pivot to the road meets the ground ahead of center of Tyre contact called patch area, the small amount of resulting camber is sufficient to provide steering that automatically self centers.

Camber angle

If the steering pivot is vertically along side a wheel it is subjected to considerable stress , Cambering the wheel and putting the contact area under the pivot relieves much of this stress.

In order to understand the point of camber, you need to know a little bit about weight transfer. You’re flying into a tight right hander in your Racing Car.. The body of the car has inertia and wants to keep going straight. This causes the car to roll to the left, during the right turn. This roll also increases the amount of weight on the left tires, while decreasing the amount of weight on the right side. The basic idea behind camber is this: keep as much of the tire, touching the pavement throughout the whole track. As your car leans left, both tires lean left as well. Let’s say you have zero camber. Your alignment would look something like this:

Then, as you turn right into a corner, the body of the car rolls to the left, and the tires roll as well. As a result, both tires now have a smaller contact patch and therefore less grip.

If you aligned your car with an appropriate amount of camber, the outside tire would actually gain contact patch, and therefore gain grip, during weight transfer.

As the left tire rolls, it loses camber and the tire’s contact patch gets larger. Remember that it’s this tire, the outside tire, that has the most weight on it and therefore has the potential for the most grip. The inside tire will still lose contact patch during the weight transfer, but it’s less crucial as it has far less weight on it.

Toe in and Toe out :

Toe In / Toe Out describes the angle of the front (or rear) tires when viewed from above. If the front of the tires angles in (or towards the chassis), that is Toe In. If the front of the tires angles out (or away from the chassis), that is Toe Out. 

Adding Toe In will decrease steering into a corner, but add steering out of a corner during acceleration. Toe In will also stabilize the car under acceleration. Toe Out will increase steering into a corner, but cause the car to wander a little on the straights and in bumpy sections. It is not normally suggested that you use more than 1deg of Toe In or Toe Out.
Toe in is suitable for straight drives because the wheels will straighten itself under acceleration . In case of front wheel drives there is a chance of Under steering toe out will compensate this under steering.  
Steering Angle Basics:

Velocity at the center contact area of wheel should be zero so that there will not be any slippage between the stationary road and the wheel at the contact point. In order to achieve zero velocity at moving point the transitional velocity should cancel the bottom rotational velocity. they should act in opposite directions on straight line. 

In the above situation velocities doesn't cancel each other and the wheel will skid.

 To have proper turning without skid ,perpendicular lines drawn from front wheels should meet the rear wheel axis at a common point , for that the angles turned by right and left front wheels are not the same .If they are same then they will not meet the rear wheel axis at a common point.

Under steer
Under steer, is the tendency of a vehicle to continue in a straight line when the wheels are turned. Under steer is the natural handling characteristic of front wheel drive  for several reasons
• The majority of vehicle weight is carried over the front wheels
• The front wheels must drive the car, brake and steer

In case of excessive speed and hard braking will lock the front wheels , it is common in front wheel drive since the front wheel has to accelerate and turn at the same time. During understeer condition if we turn the steering more it will increase steering lock and increase slip angle thus the amount of area of contact Tyre makes with road is reduced . If we suddenly reduce the throttle it will transfer the car weight to front axle making the rear side light and car will spin (Lift of oversteer). Easing the throttle or brake pedal we can manage under steer. To reduce under steer we have to fit wider tyres, decrease ride height, increase camber and having good tyres.

 

Over Steer : Over-steer refers to the back end of a car coming loose, usually quite suddenly. If corrected poorly, over steer will most likely result in a spin.

In rear wheel drive cars, over steer is generally caused by a lack of traction at the rear, coupled by a turn of the front wheels or uneven application of power to the rear wheels. Many things can cause over steer, but slippery conditions, jerky steering wheel movements and inappropriate braking are usually the root cause.

Putting on lower gears while car is at high speed can lock rear wheels since the rear wheels cannot track the selected speed achieved by front wheels intended with that gear position and the rear end will lose traction. Pull the hand brake suddenly will also oversteer. As car oversteers and spin we have to counter steer and gradually decrease the throttle. Dont lift the throttle suddenly.