In modern F1, there is a lot of talk about tires. Getting the tires working well can be the difference between a podium and finishing outside the points. F1 drivers must understand the causes of issues like graining and blistering in order to manage their tires and extract performance.
Graining and blistering in F1 are terms that describe issues with the tires. Graining involves small tears on the tire surface, creating an uneven contact patch that lowers grip. Blistering is overheating of the tire, and this causes bits of the tire to shear off, potentially causing a tire failure.
But there is a lot more to it than that. Racing tires are an area of technology and development on their own. The chemistry and engineering in an F1 tire are intense, as the tires need to handle extreme conditions. So, let’s dive into some of the details to better understand graining and blistering.
What Is Graining In F1?
Graining can be seen in an F1 tire as little tears, like ripples, in the surface of the tire. It is when the surface of the tire is abraded by the road, and the hot compound at the contact patch begins to tear away into little ridges.
The strips of rubber in these ridges start to pull out of the body of the tire as they move laterally, and then fuse back in. This produces a graining pattern into the surface of the tire. The tire then loses grip, as the contact with the road is now with many small ridges rather than a large coherent contact patch.
The direct cause of graining in a tire is friction between the tire and the road surface, usually by the tire sliding across the track surface. This usually happens through corners and during braking. The dragging of the tire causes localized overheating at the tire surface, damaging the rubber compound and allowing the tears to begin.
You’ll often hear of drivers being able to work through this graining of their tires. Essentially, as they use the tires more and more, the graining and excess rubber on the surface of the tire wears away, and they get something like a second wind of grip. However, sometimes it’s too difficult to work through, and the driver must pit for new tires.
What Causes Graining?
There are a number of potential root causes of graining. The most common are oversteer or understeer, where the car does not turn well through a corner. But graining can also be a result of a poor suspension setup or incorrect tire pressures.
Understeer & Oversteer
With understeer, the front of the car does not turn as much into the corner as the driver is demanding – the front tires tend to slip towards the outside of the corner. With oversteer, the car turns more into the corner than desired by the driver, due to the rear tires drifting towards the outside of the corner.
Therefore, through each corner that the driver experiences either of these issues, there is some lateral dragging of the tire, while under incredible loads.
Poor Suspension Setup
Another common cause of graining is a poor suspension set up. If the graining is not uniform around the circumference of the tire, the suspension could be too soft and is allowing the tire to ‘bounce.’ Suspension that is too stiff can also cause the tire to be dragged across the road, as the suspension forces the rubber into the surface at high loads.
Incorrect Tire Pressures
Tire pressures are another potential cause, but one that is easy to check. The tire pressure should be accurate to the manufacturer’s specification when the tire is at racing temperature. If the tire pressure is too high out on the track, then the graining will be seen along the center of the tire. The higher pressure causes a smaller contact patch in the center, with more concentrated loads.
If the graining is along the inside or outside edge of the tire, then the cause could be the camber of the tire. Camber is the angle of the tires compared to a flat road (usually an inward tilt), when looking head on at a car. Again, although the camber is set in the garage, it is set in anticipation of racing conditions, to maximize the contact patch area while the car is cornering.
Wrong Tire Compound
Finally, if none of the above are the culprits, and graining is seen over the whole surface of the tire, then it is likely that the compound being used is simply too soft for track conditions. A harder compound may need to be used – if the surface of the tire is preserved, it will provide superior levels of grip for longer, compared to the graining softer tire.
What Is Blistering In F1?
Blistering of F1 tires is when chunks of the tire break away from the main body of the tire. The internal layers of the rubber start to overheat and the bonds between the layers give way, allowing pieces of the tire to fall off.
The direct reason for this is therefore overheating within the body of the tire, but practically this overheating can be caused by a range of inputs.
Blistered tires lose grip as pieces of the tire contact patch are missing and damaged. However, blistering is also particularly dangerous as the integrity of the tire itself is affected by the internal overheating. This can result in a major tire failure such as a blowout, and possibly a resulting crash.
What Causes Blistering?
Blistering of a tire can occur anywhere around a track, as it is a function of the internal temperature of the tire. Therefore, whenever the tire is rolling and flexing, such as under high downforce loads through the corners, heat is being generated within the tire.
There are a number of reasons that the heat within a tire might exceed what the tire construction is able to handle. The track temperature could be too hot for the selected tire, or conversely the chosen tire compound could be too soft for the track conditions. The tire could have been inflated to too high a pressure, generating more heat within the tire as it takes on load.
The tire absorbing load from the car’s downforce is a major contributor to internal heating. Therefore, high downforce over a particular axle can cause those tires to blister. Suspension that is too stiff can also overload the tire, forcing the tire itself to act as a shock absorbing spring, taking up some of the vibrations, adding to the overall stress the tire is under.
How Can F1 Drivers Prevent Graining And Blistering?
F1 drivers can prevent graining and blistering by warming up their tires evenly and carefully, being sure not to exceed what the tire can handle while cold. This is very difficult to get right consistently and takes expert judgement to be able to ‘feel’ what the tires can handle.
F1 tires have an ideal working temperature range, sometimes referred to as the operating window, where they have been designed to handle the expected loads and provide the maximum level of grip. Before their tires are in this range, the driver needs to avoid subjecting them to extreme loads in cornering, as they simply won’t provide enough grip and they may lose control of the car.
A driver’s unique driving style also has an effect on how heavy they are on the tires, or whether they are able to nurse them instead. Some drivers are more aggressive into corners and can introduce issues into their tires after only a few laps. A smoother, more rhythmic driving style generally translates into lower wear and stress on the tires.
Other Problems F1 Tires Face
Graining and blistering are the most common issues that F1 drivers see with their tires. However, there are other problems that drivers need to watch out for as they take care of their tires.
One of the easier problems to spot on an F1 tire is flat spotting. This is caused by a driver locking up the brakes, which is visually obvious on TV by the puff of smoke that the tires give off as they brake too hard into a corner. When the brakes lock up (by the driver applying them too hard), the wheels stop turning even though the car continues to move forward.
This forward momentum of the car simply drags the hot, soft, stationary tire across the abrasive road surface, scrubbing a section of the tire off into that plume of smoke. This creates the flat spot on the tire. As the driver continues, particularly in the slower corners, that spot on the tire surface can be seen going round and round.
This uneven surface then causes vibration at high speeds as the tire spins while being unbalanced. It also inevitably causes a lack of grip, and usually forces the driver to pit for new tires, or abandon their lap if it’s during a qualifying session.
When tires are cold, they are not in their optimum operating window and the rubber gives significantly less grip. Therefore, drivers need to tread carefully around corners on cold tires until they are up to temperature and can support higher cornering speeds and lateral forces.
Although this is not an issue with the tire itself, it is a topic of tire management that will be spoken more of in the coming seasons. Historically, F1 has used tire blankets when the cars are stationary in the pits (or on the grid before a race start) to ensure that the tires are already warm before they start turning on the track. This provides a good level of grip to the driver immediately.
But F1 is starting to restrict the use of tire blankets, forcing drivers to adapt to starting on colder tires. The reason that F1 is aiming to do away with tire blankets is that they are opposed to the sport’s current direction of cost-saving and sustainability. Tire blankets are an additional expense for the teams, and they also use a fair amount of energy.
Graining in F1 is caused by overheating of the tire surface, which creates small tears or ripples in the surface of the tire. Blistering is caused by overheating within the body of the tire, which causes the internal layers of the tire to delaminate, allowing chunks of the tire to shear off.