Car tires are more important than many people give them credit for being. They are literally your link with the road. The most dangerous place for you to be is out of or in poor contact with the road. In this predicament you are not able to have any input into your course of direction and that is a bad thing when you are going 60 plus miles per hour with no way to avoid crashing into something. Friction is what we are going for and there are some things that you have control of and some things that you don't in this area. You are responsible for your own and anyone else's life in the car you are driving and so you had better be sure that you have taken all the measures that you can to prevent a problem.

Now the contact of the road has several factors as already mentioned. The majority of the friction comes from the contact of rubber of the tire 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 so naturally more weight equals more friction between the road and your car tires. 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. Anyway rubber and concrete naturally have a lot of friction.

Air pressure in tires will change the properties of the rubber by stretching it so that if a tire is overfilled it can decrease the amount of friction. There is also less surface area in this case. Anyway so you have rubber tires and concrete roads what more can you be responsible for? Well tread for one. How does tread affect the ability of car tires to make contact with the road? Well now we have to talk about outside factors that affect the surface of the road, namely weather. Water and snow and mud decrease the amount of friction by filling the natural grooves and not allowing contact between rubber and road.

So how does tread help in this situation. Well tread is actually good because of the grooves in the tread of your car tires. The grooves allow the material no matter what it is to have a place to go other than between the rubber of the tire and the road. This decreases the "hydroplaning" effect that you get with all the different natural elements that can make driving conditions bad. So the moral of the story is to make sure that you always have good tires with lots of tread on your vehicle in order to maximize the ability of your car to grip the road and therefore provide you with control over the vehicle that allows you to slow down and steer to avoid problems.