Graining and blistering are two terms used a lot in F1 when discussing the tires. They are very important concepts for the drivers and teams, and they can severely impact a driver’s race. But what are graining and blistering?
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 when bits of the tire shear off as a result of overheating, 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. Below, I dive into more details to help explain why graining and blistering are important in F1.
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 worn excessively by friction with the track surface, 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 (side to side), 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 when the tread of the tire (the outer part) heats up because of friction between tire and the track surface (usually by the tire ‘sliding’ across it), while the carcass (the inner part) does not reach the necessary operating temperature. This itself occurs for various reasons, which I’ll discuss below.
Working Through The Graining Phase
You’ll sometimes hear of drivers being able to work through this graining phase of their tires. This was a common thing at the beginning of the era of the tire war between Michelin and Bridgestone.
Due to the construction of the Michelin tires, the tread of these tires generally became less hot than that of the Bridgestone tires, which brought advantages in degradation and wear, but also resulted in the tire interior heating up less quickly.
This of course led to graining, which is triggered by the fact that the carcass of the tire is not at operating temperature, while the tread of the tire already has significantly higher surface temperatures due to friction with the asphalt. But after several laps, the carcass of the tire reached the necessary temperature, and the graining disappeared.
So, a driver must be able to bring the inside of the tire up to temperature to avoid or solve this problem. 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?
The trigger for graining is always a large temperature difference between the inside of the tire and the tread on the outside. There are various reasons this can happen. In addition to tire construction, the ambient temperature and even the way the brakes are cooled can also be reasons.
But 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. Let’s take a look at each of these issues below.
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. If this is excessive, it can cause graining.
But drivers and teams set the cars up in different ways, and some drivers ‘prefer’ some oversteer or understeer, depending on their driving style. I won’t go into the details on that here, but it’s worth being aware that understeer and oversteer, in small amounts, are not always a bad thing.
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.
The type of graining often indicates which setup problem is present. If the graining pattern occurs inconsistently on and around the tread, it is likely the tire is hopping and skipping in the corner, which suggests the dampers are the likely cause. It may also be that the strip of graining becomes wider if the damper is the cause and too soft.
If graining only occurs on the inside or the outer edge of the tire, the geometry of the suspension is the problem, and this may indicate too much positive or negative camber. Camber is the angle of the tires compared to a flat road (usually an inward tilt), when looking at a car from head on.
If the graining is even and only occurring on the outer edge of the tire, this may indicate too much camber.
If it is even across the entire tire, it may be due to low spring rates or incorrectly set anti-roll bars. However, the driver can also cause graining by pushing too hard in a setup with hard springs when the tire is not yet evenly warm. They then overheat the surface of the tires too much and the large difference between the tire interior and tread then leads to graining.
This can also happen when the tire is properly warmed up. Stiff springs or a stiff anti-roll bar can cause the tire to be overloaded, which in turn heats the tread more. Clearly there are a lot of potential causes for the engineers to analyze if their car is showing graining!
Incorrect Tire Pressures
Tire pressures are another potential cause, but one that is relatively easy to check. The tire pressure should be accurate to Pirelli’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.
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.
Note: You can learn more about how tire compound affects wear in our article on how long F1 tires last
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 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.
Tire Compound Mismatch
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.
Incorrect Tire Pressures
The tire could have been inflated to too high a pressure, generating more heat within the tire as it takes on load.
Setup Issues
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 more of the vibrations, adding to the overall stress the tire is under.
This usually happens when the dampers are too stiff and do not properly absorb the bumps and push the tire back to the road too quickly. Dampers that are too soft similarly overload the tire because the load change occurs too quickly.
Similar to graining, however, blistering can also be caused by springs or anti-roll bars that are too stiff, and the increased load transfer this causes can overload the tire, causing it to overheat. If the tires show blistering on the inner or outer shoulders, again (for the same reasons as with graining) too much positive or negative camber can be the reason.
Examples Of Graining & Blistering In F1
Red Bull In 2022/2023
If you take a closer look at graining and blistering, you’ll see that these problems often occur under unusual racing conditions. Red Bull had major problems with graining at Imola in 2022, for example. Here, the temperatures were very cool. The Red Bull is a car that brings its tires up to temperature comparatively slowly (in contrast, the Ferraris had no trouble bringing their tires up to temperature during that race).
This was evident in qualifying in Australia in 2023. Max Verstappen was only able to clinch pole position in his final run. This is because he needed more time to bring the tires into the ideal temperature window. But as with everything in F1, this is a matter of making compromises.
Cars that bring their tires up to temperature faster have an advantage in qualifying and in the first laps of the race. Cars that bring their tires up to temperature slower have a disadvantage in qualifying and in the first laps of the race, but they have an advantage in terms of tire degradation and tire wear.
Goodyear Teams In Canada
Going further back in time, in Canada in 1997, many Goodyear teams had problems with the blistering of the tires. Here, the high temperatures combined with tire compounds that were too soft were to blame.
Ferrari In 1997
If you look at Ferrari and their tire problems in 1997, and the problems of the F310B, it becomes clear that Michael Schumacher had little possibility to influence this. The F310B’s center of gravity was too high, and its fuel tank (which was changed during the season by Ross Brawn and Rory Byrne) allowed the fuel inside it to move too much. This led to major load changes, which in turn caused tire problems.
If you look at the problems with graining and blistering over the years, it becomes clear that the driver has little influence on this. Graining and blistering usually happen when temperatures are extremely cool (graining), or extremely hot (blistering), and certain characteristics of the car are what exacerbate the issues, rather than the driver.
How Can F1 Drivers Prevent Graining & 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.
Driving styles vary a lot across the grid, and there are so many tiny nuances that make them different from one another. But it’s a small factor to consider when discussing graining and blistering, as really it mostly depends on the car setup and even more so the track conditions.
Other Problems F1 Tires Face
Graining and blistering are some of the most common issues that F1 drivers face with their tires. However, there are other problems that drivers need to watch out for as they take care of their tires.
Flat Spotting
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, 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. The vibrations are uncomfortable for the driver, but they can also lead to damage on the car if they’re excessive enough.
Cold Tires
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.
Note: You can learn more about this in our article on how hot F1 tires get
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.
Final Thoughts
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.
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