The interplay between friction and your tyres’ functionality on the road can’t be overstated. Friction not only propels your tyres forward, but it helps you come to a stop, accelerate, and turn.
Tyres and friction
Before touching on the physics of car tyres, it’s essential to understand how friction works. Friction does not propel a vehicle forward. Rather, friction is a force that acts against the motion. When two objects move against one another – like the road and your tyres, for example – friction builds up between the two surfaces to slow the objects or to keep them from moving entirely.
In terms of your car, this means that friction is the force that keeps your tyres from skidding across the road. That said, there are multiple types of friction. These include:
- Static friction – Friction that develops when the two objects in question are not moving against one another.
- Kinetic friction – The friction that develops when two objects are moving against one another.
You’d think, based on that explanation, that it’s kinetic friction that’s at work as you’re driving down the road. This is the case only when you’re coming to a stop, however. As you’re driving, static friction works between the still road and your tyres.
This is because, technically speaking, your tyres aren’t constantly in contact with the road. Rather, a single part of your tyre comes into contact with the road and propels itself forward. That part merely changes every millisecond or so. As such, static friction will develop between the two objects that seem – no matter how strange – to be moving in tandem with one another.
Kinetic friction and your tyres
While the friction between your tyres and the road is primarily static, it can become kinetic friction under certain circumstances. This is most often the case when there are obstacles in the road, such as water or ice. As you drive on these materials, the static force between your tyres and the road reduces, to the point where you may lose your grip on the road.
At this point, kinetic friction will take over between your wheels and the road to try and make your wheels stop spinning.
Friction versus traction
Car manufacturers and dealers don’t often use the term “friction” to describe the interplay between your tyres and the road, even though that is the force at work. Instead, you’ve probably heard the term “traction” more often. These forces are not the same things, though they are related to one another.
Friction, as mentioned, is a force that develops between your tyres and the road. You cannot see it, but you can feel and observe its impact on your driving. That said, friction can impact your entire car. Traction, specifically, describes the type of friction that develops between your tyres and the road. Without traction, your car can’t develop tyre grip with the road, and you can rapidly lose control of your car.
What goes into road grip?
So, with all of that in mind, what factors specifically contribute to your tyres’ grip on the road beneath you?
- The material your tyres are made out of
- The material the road you’re driving on is made out of
- Your tyre pressure and suspension system, both of which control how much force connects your tyres to the road
- The presence of any interfering factors, including water, snow, or spills
You can control at least two of these four factors – tyre pressure and tyre material. However, unless you can control the weather, you won’t be able to keep water or snowmelt off of the road. Similarly, without getting in touch with your local representatives, the only control you’ll have over the material of the roads you drive on will come from choosing which roads you want to take while driving.
Choosing the safest tyres for your car
When it comes to shopping for a tyre that will keep your car in touch with the road, you’ll need to take a few features into account. Tyre tread, for example, and tyre tread depth are both essential to increasing the amount of traction you have with the road. While you don’t want to go overboard while shopping, you should always try to invest in a tyre with significant tread.
In reality, of course, there is no ideally universal tyre, which will perform well in all circumstances. This is why a sports tyre, designed to operate at a higher temperature, will not work well at 10°C, whereas a universal tyre will retain its characteristics. Similarly, the numerous pleas from manufacturers to use winter tyres are not groundless.
Creating a tyre that will work in such a wide range of temperatures (from +60°C to -20°C) is simply impossible. The cut-off temperature before summer tyres lose adhesion is around 7°C. Winter tyre grip, therefore, works because winter tyres are designed to retain grip in ranges below this.