Forces on Tire & Wheel: Steady Running, Acceleration & Deceleration

[satya430]

I have 2 doubts .

First one was to figure out how the positive and negative scrub radius will affect the dynamic toe during braking or accelerating .

Then it made me realize that to understand this I will have to analyse all the forces acting on the tire (tractive forces) . Then i read up rolling resistance , deformation of tire , hysteresis etc. . But it is not too clear , could you please explain the forces in play between the tire and the road during steady motion , acceleration and deceleration . Vector force diagrams will be of great help .

Thanks .

 

[Navin A S]

The forces acting on the tires during steady motion, acceleration and deceleration can be broken down into two components: static forces and dynamic forces. Static forces are those which act on the tire when it is stationary or when it is moving at a constant velocity. These include the weight of the car and the friction between the tire and the road surface. These forces create a static scrub radius, which is the distance from the center of the tire to the point of contact with the road surface.Dynamic forces, on the other hand, are those which act on the tire when it is accelerating or decelerating. These forces include the tractive force (the force generated by the engine to propel the vehicle forward or slow it down) and the inertial force (the force generated by the vehicle's mass as it accelerates or decelerates). The dynamic scrub radius is the distance from the center of the tire to the point of contact with the road surface when the vehicle is accelerating or decelerating.Positive scrub radius means that the center of the tire is ahead of the point of contact with the road surface. This produces a reactive force which helps to keep the front wheels in line with the direction of travel during acceleration or deceleration. Negative scrub radius, however, means that the center of the tire is behind the point of contact with the road surface. This produces a reactive force which makes the front wheels tend to turn away from the direction of travel during acceleration or deceleration, resulting in increased dynamic toe-in.Thus, a positive scrub radius will help to keep the dynamic toe-in within acceptable limits during acceleration or deceleration, while a negative scrub radius will increase the dynamic toe-in and may lead to unstable handling characteristics.