How do tyres actually grip the road?
Through two mechanisms working together — adhesion and hysteresis — neither of which is what people assume, since friction between rubber and tarmac behaves nothing like the simple friction taught in school.
Adhesion. At a molecular level, rubber forms and breaks weak bonds with the road surface continuously. This dominates on smooth dry surfaces and collapses when a film of water intervenes, which is most of why wet grip is worse.
Hysteresis. Rubber is viscoelastic: it deforms around the microscopic peaks of the road surface and takes time to spring back, losing energy as heat. That energy loss is what produces resistance to sliding. This is why softer compounds grip better and wear faster, and why rolling resistance and grip trade off against each other — the same property that makes a tyre grip makes it waste fuel.
Why the simple friction model fails. School physics says friction is independent of contact area. For tyres it is not, because both mechanisms scale with real contact area — which is why a wider tyre can grip more, and why racing tyres are slick: with no water to clear, tread only reduces contact area.
What tread is actually for. Almost entirely water clearance. A tyre must displace the water in front of it through its grooves in the fraction of a second the contact patch passes. When it cannot, the tyre rides on a film of water and steering and braking effectively vanish — aquaplaning, which depends on speed, water depth, tread depth and tyre pressure.
Why temperature matters. Rubber compounds have a working temperature range. Winter tyres use compounds that stay flexible below about 7°C, where summer compounds harden and lose grip — the reason winter tyres help even on dry cold roads, not only in snow.
Why pressure matters so much. It determines the size and shape of the contact patch. Under-inflation distorts it, overheats the shoulders and raises rolling resistance; over-inflation reduces it to a narrow central strip.
The contact patch is about the size of your hand — per tyre. Everything the car does happens through four of those.