“Tires, that is black round rubber, what is so special about that?”
Tires are the only connection between a car and the road. What ever you are doing, breaking, accelerating or steering, without a tire, that wouldn’t be working. I know that already, smart ass! Tell me something new!
Disclaimer: This is not intended to be a complete description about tires in a race car application. This is just a very basic introduction to the topic. If you are interested in more detailed information, you can find a lot of books about that topic out there, or wait for another season, where I might start to go into the details.
In the past, a wheel was just that, a wheel. Made out of wood, or even harder materials. Was that working? Yes. But was it comfortable, fast and safe? No, it wasn’t.
Thank god, someone invented the tires we know today. But what is it all about?
For the sake of simplicity, you can imagine a rim that can be bolted to the car, a tire that sits on the outside of that rim and air, that inflates the tire and pushes it against the rim, making an airtight and firm connection. As soon as your car stands on those tires, most of the time you would use four at a time, the car pushes on the tires with everything it got, and the tires, they are pushing back, all the time, every time. Due to the reason that rubber isn’t the hardest material in the world, the tire starts to deform itself under the high loads, building up a kind of a flat surface on the street. Can you imagine that? I guess so! And that is the contact patch, where the tire actually touches the surface of the road.
As soon as you start to drive the car, the tire starts to roll, it’s bolted to the axel, so there is no other option, right? But what does that mean for the tire? Yes, you are right. It means, that the tire gets constantly deformed at the lowest point where it builds up the contact patch to the road. I hope you got that one as well.
But in order to be able to accelerate, decelerate or steer the car, the tire needs to do more than just rolling around. It also needs to transfer the loads. Friction is the magical word here, right? “The tire needs to have grip!“, we all have heard that term. But what does that mean? It means that the tire doesn’t slide around, but actually can bite itself into the tarmac, transferring the loads onto the road.
Which part of the tire is responsible for that? Right, it’s the contact patch, because that’s the only thing of the tire that is in contact with the road. Makes sense.
So, if that contact patch gets bigger, you can transfer more loads? And if it gets smaller, you can transfer less loads? Is that the reason why sports cars have very wide tires? Hell yes! Good job. It is of course not as easy as that, but for today, we will try to live with that.
But is the size of the tire the only parameter that is important here? Ah, right! If there is less air in the tire, the car will deform the tire more. Air inside a closed environment? We use the term pressure to measure that. So, with less air pressure inside the tire, it get’s deformed more, which increases the contact surface to the road and therefore the grip. So far, so good.
Our tire rolls around, it has certain dimensions, a certain air pressure, looks like we are finished, right? Oh, what about the temperature? Ah, right, we all know the effect temperature has on a closed up environment, right? The temperature increases, the air pressure increases. But how does that have an effect on the tire?
Well, in order to work properly, a tire needs to have the right temperature. Depending on the material that is used, you can create hard tires, soft tires, or everything in between. We all have heard that somewhere, right? For example in formula one. So, depending on the type of your tire, the road conditions, the kind of race you are participating in and the time the tire needs to last, you can figure out the perfect temperature. Being something between 65°C and 90°C depending on what you want to do with it on the racetrack.
Ok, ok, so, my tires need to have the right temperature as well, I see. Exactly. So, depending on the temperature of the tire, the air pressure inside the tire will change. Meaning that if you start with a cold tire into your track day, and you start to heat up the tire, the air pressure increases.
But where is the connection to that all?
Air pressure low = deforming of tire increases –> larger contact surface to the road = more grip + tire heats up more quickly, but rolling resistance increases –> higher fuel consumption, lower high speed
Air pressure way too low = tire can get loose when cold and contact patch can start to decrease, due to loosing its stiffness in the middle of the contact surface, moving inwards.
Air pressure high = deforming of tire not high –> smaller contact surface to the road = lower temperature, less grip, but better rolling resistance –> better fuel consumption, higher speeds
Air pressure way too high = tire stays cold –> not much grip
Ok, so the dimensions, the temperature, the rubber mixture and the air pressure is important. What else? Ah, right! The profile of the tire. If you have a slick tire, there is no profile at all. We have all seen such a tire, right? But what is the benefit? Ah, a larger contact surface to the road, but what is the drawback? No negative profile in the surface to push the water away. Exactly! Therefore there are rain tires and slick tires and everything in between in existence.
I see. So it is actually quite complicated, that tire topic and not at all “tired“! Yes it is, and this is just an attempt to explain the basics in a very easy way. We haven’t even talked about the influence, the suspension has on the tire, because this is very important as well.
The important facts about a tire are the dimensions, the profile, the mixture of the rubber, the temperature and the air pressure. They are all somehow related to another which will demand from you, to adapt the parameters accordingly.
But what can we actually do? Well, of course it all starts with the right tire you need to buy, but generally speaking you just get what ever your budget allows or what the rules suggest and put them on your car. The main thing you can influence after that is the air pressure in a stand still, and the tire temperature due to your driving style. So, take your time, make some notes about the setup you drive, the outside temperature, the racetrack, and so on, and figure out the right numbers. Sure this takes time, but it will have a huge impact of the performance of the car.
Oh, and one more thing. Tires are more important than you think. If you need to pick one improvement for your car, always chose the tires.
See you next time!
Engineer, Motorsport Enthusiast, becoming an Entrepreneur, Author and just different