Car tyres are literally your link with the road. The most dangerous place for you is to have poor contact with the road. Friction is what we are going for and the majority of it comes from the contact of rubber of the tyre with the concrete or asphalt of the road. The action of gravity on the mass of your car is the only thing that is causing this contact and more weight equals more friction between the road and your car tyres. A good thing but can turn against you in the form of inertia after the friction has been overcome say after you’ve locked up the brakes, now inertia is greater with a heavier vehicle and takes more in the way of friction to stop it.

Air pressure in tyres will change the properties of the rubber by stretching it so that if a tyre is overfilled it can decrease the amount of friction. There is also less surface area in this case. Outside factors also affect the surface of the road, namely weather. Water and mud (snow in other countries) decrease the amount of friction by filling the natural grooves and not allowing contact between rubber and road. That’s why we have a tread and every tread on your tyre has grooves. The grooves allow the material no matter what it is to have a place to go other than between the rubber of the tyre and the road. This decreases the ‘hydroplaning’ effect that you get with all the different natural elements that can make driving conditions bad.