Tires grip the road primarily through a process involving the deformation of the rubber tread and a phenomenon called hysteresis.
Understanding Tire Grip
The grip between a tire and the road surface is a complex interaction, but a significant part of it comes from the tire's ability to conform to the road's texture, even at a microscopic level.
The Role of Tread Deformation and Hysteresis
When a tire rolls, the tread blocks constantly encounter the road surface. As a tread block makes contact, it presses against the irregularities (bumps and dips) of the road. This causes the rubber to momentarily deform or change shape around these features.
According to the provided reference:
Therefore, as the tread block strikes a bump in the road, it deforms, but due to the hysteresis of rubber it does not immediately return back to its original shape. This asymmetrical deformation of the rubber generates a reaction force which opposes slippage – in other words it generates a friction force (grip).
Let's break down this process:
- Deformation: The flexible rubber tread molds itself into the tiny textures and bumps on the road surface.
- Hysteresis: This is a property of rubber where the energy absorbed during deformation is not immediately and fully released when the deformation force is removed. Think of it like squeezing a stress ball – it doesn't instantly spring back to perfect shape; there's a slight delay and energy loss.
- Asymmetrical Deformation: As the tire rolls over a bump, the front edge of the tread block is deformed by hitting the bump. As the block passes over the bump, the back edge is still interacting, but the deformation isn't symmetrical around the bump's peak due to the tire's motion and the rubber's hysteresis. The rubber resists springing back immediately as it rides off the bump.
- Generating Grip: This "sticky" or delayed recovery action creates a force opposing the relative motion (or potential slippage) between the tire and the road. This opposing force is what we experience as grip or friction. The energy lost due to hysteresis is essentially converted into this friction force.
In Simple Terms
Imagine pressing a piece of very soft, slightly sticky chewing gum onto a rough surface and then trying to slide it. The gum conforms to the surface, and its reluctance to instantly pull away from every tiny bump and crevice as you slide creates resistance. Tire grip works on a similar principle, but with the high-tech rubber compounds used in tires.
Factors Influencing This Grip
While the reference highlights deformation and hysteresis, the effectiveness of this grip mechanism is influenced by:
- Rubber Compound: The specific properties of the rubber mix greatly affect its hysteresis and ability to deform and recover.
- Road Surface Texture: Rougher surfaces allow for more mechanical keying and deformation of the tread.
- Temperature: Rubber properties change with temperature, affecting hysteresis.
Ultimately, the complex interaction between the tire's designed properties and the road surface allows for the crucial friction needed for driving actions like accelerating, braking, and turning.
