[0:00]We've gone over in almost painful detail the rules regarding how tires could be used, but haven't yet given more than a passing glance to the mechanics of the tires themselves. In this video, we'll look at how tires wear and degrade and understand the meanings of words we hear when people talk about tires. Words like graining, heat cycles, blistering, marbles, which are not the same as laying down rubber, flat spots. To get our head around a lot of these tire phenomena, we need to get a quick understanding of what the tire is made of and how it behaves. The inside of the tire is a bunch of old gumph that keeps it all in shape and we're not too worried about that. On the outside though, is the rubber, and we're particularly interested in the part of the rubber that touches the track, called the tread. Racing tires are made of a nice soft synthetic rubber. This rubber, much like a pencil eraser, will heat up under friction. Tires heat up through the corners as there will always be some amount of sliding and lateral forces acting on the tire. Now, a lateral force is a force that acts across the direction the car is traveling, as shown here, basically 90 degrees. Bringing the tires up to working temperature is referred to as pushing them through a heat cycle. Now, as the rubber in the tread heats up and cools down, the chemical makeup of the rubber, specifically the polymers, long chains of interlaced molecules, will start to degrade. Putting heat energy through the rubber deforms it internally. Most of the rubber's composition will spring back to its original shape, but some of the chemical bonds break down or deform permanently under this heat energy. A really crude analogy would be like when you bake a cookie. The dough starts off soft and malleable, but as you continue to cook the dough, they will get tougher and tougher until the cookie is hard and brittle. F1 tires aren't exactly like this, but over time the heat will change the very nature of the rubber itself. The internal structure of the rubber will permanently change from the fresh from the packet soft and stickiness into a less grippy, less usable tire. This process is known as the tire giving up over its lifespan. Heat cycles aren't all bad though. Tires fresh out of the box often aren't ready to deliver flat-out speed straight away. Putting them through a heat cycle by doing a warm-up lap or two treats the rubber, giving it a final bake and making it just right for racing. Putting the tires through a warm-up heat cycle is known as scrubbing. You'll notice drivers often use a scrubbed tire during the race. These tires aren't worn, they've just been race prepared by putting them through a heat cycle. When the rubber is heated, it becomes more viscous. This essentially means it's a little bit more melty and malleable. When the tire rolls over the rough, hard surface of the track, the soft melty rubber squeezes into the surface texture and grips nicely. It takes a good driver to get a racing tire to a consistent temperature. If the tire overheats in such a way that the inside part of the rubber becomes hotter than the outer surface, a hot pocket of air and rubber can form and expand beneath the tread. Ultimately bursting and breaking a large chunk of the tire tread away. This is known as blistering. Blistering is a lot rarer these days as racing tire manufacturers have made better, more temperature consistent compounds. If it does happen, you can normally spot it as an anomalous blemish on the tire surface. Conversely, if the surface temperature isn't quite right, graining can occur. If the outer surface of the tire is a lot hotter than the inner rubber, it can become a lot easier for the hot melty surface of the tread to distort and wear under high cornering loads. As the car turns through a corner, particularly fast corners, there are strong lateral forces pulling on the rubber as it grips into the track. Under the right, or wrong circumstances, the rubber can deform in a sort of waves under this abrasion, and eventually these waves will deform so badly that the peaks will start to tear off. These little chunks of rubber being ripped off will be hot and sticky and will normally flick straight back onto the surface tread of the tire. And over time, the warm parts of the tread that are covered in these sticky blobs will take on a grainy texture, hence why this is known as graining. The problem with graining is that the main tread of the tire isn't making proper contact with the surface of the track anymore. The rubber in the grains isn't a good, useful rubber, like the main tire tread is, and it's much more slippery as the main point of contact. This leads to a grain tire being a much less grippy than a fresh tire. Now, not all of the little rubber chunks are thrown back onto the tire though. A lot of them are thrown completely clear of the tire and deposited onto the track. These discarded rubber deposits are known as marbles, and you'll often see them littering the edges of the racing line. From the TV cameras, they'll look like long, dark patches along the edge of the track. As with graining, running over these marbles is a lot less grippy than running the tire directly onto the track. The problem comes when there are a lot of marbles and they severely reduce the raceable part of the track. You don't want to move off the racing line and onto the marbles, which means back markers won't want to jump out of the way and overtaking becomes more of a risk. Now, having rubber on the track isn't always a bad thing. Let's not confuse marbles with just laying down rubber. As the cars drive across the track, particularly through the corners again, they will start to lay down a small amount of rubber that wears from the tire. This layer of rubber starts to build up more and more as cars go over the same line over and over again. Driving over this rubber is grippier than driving directly onto the track, and is less wearing on the tires. Think about wearing a pair of trainers or sneakers, and how much more grippy it feels on a rubber mat than straight on the pavement. This is similar. The coefficient of friction between the tire and the rubber is much higher, which makes it grippier, and the surface is smoother, so it's less wearing. You'll often see drivers purposely laying down rubber on their grid spot or in their pit box by doing a burnout. A burnout spins the tires much faster than the car actually travels, so a nice layer of rubber is scraped off and laid onto the track for a grippy getaway. Now, on the opposite end of requirements to speeding off the line, braking. Specifically, how does braking sometimes result in a flat-spotted tire? Flat spotting occurs when a car locks up under braking. Ideally, the wheel should always be rotating under braking. This means the car can still be steered a little more easily and the car can be slowed down a lot more quickly than if the tire is locked, that is, non-rotating. The maximum frictional force at the brakes is a lot stronger than the maximum frictional force between the tire and the track. We want the brake disc to keep moving through the brake pads as the brakes are applied. If the brake pads grip too strongly, the wheel will lock in place and the only braking force happening will be between the rubber and the track as it slides along the ground, and this is weaker than the force at the brakes. Not only that, but this superheats one area of the tire and it wears it away in one flat slice. This is a flat spot. A heavy flat spot will make the car judder and vibrate, as it has wrecked the nice smooth roundness of the tire. This can damage suspension, as Kimi found out in 2005, but is also a self-exaggerating injury. See, it's more difficult to rotate a tire from its flat section than it is along its roundness. The next time you break, the tire will likely slip onto its flat spot and stubbornly refuse to rotate, thus flattening it even more. Driving with a bad flat spot will make itself worse and worse every time you break, and it makes it harder to continue on those tires for long periods of time. You can spot a flat spot A from the vibrations in the car and B from a large discolored patch on the tread that flashes by as the tire rotates. So, these are some of the main elements of tire wear and tear, literally, that you'll notice during a race or session. In a later video, I'll explain some of the elements of the track itself. That's the other side of the equation.
[7:41]Hopefully, you'll understand why managing your tires is a tricky thing for a driver to do, as they need to keep the rubber in a correct temperature range or working range consistently, to make sure the rubber is heated correctly throughout and not just at the surface or core. A nice consistent temperature through the depth of the tire, not too hot, not too cold, but just right. Thanks again for watching this video. I'm nearly at 30,000 subscribers now, which is pretty amazing. I never thought that would happen. I hope this video on the elements of tire wear helps clear up some of the more technical details of often heard phrases. Next week, I'll be going over the current engine proposals for 2021. After that, I'll probably lay off tires and engines for a bit and might do a video on crashes. Again, thank you so much to my Patreons. I can honestly say that you really helped with my rent this month. It's it's been a bit of a tight time for me. Um, if you fancy becoming a patron, you can do so at the link above. I'm trying to add more exclusive content there. As for example, for this video, I've posted all the notes and sketches I made while putting this video together. See you in the next video.
