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Tyres are a very important feature of vehicle set up. This is because they are the only point of contact that your car has to the surface it is driving on. Therefore, all of your set up, corner balancing, driving techniques and coilover choices come down to the four contact patches with the ground through your tyres. This article will help you understand what causes tyre failure.When out on circuit, the consistent high demand from the tyres can cause them to become defective, overheat and start failing. There are some key visual signs of the tyre breaking down that can help you diagnose the reasons why the tyre is failing and help to overcome and increase the life of the tyre.
Tyre failure is often misunderstood and ruled out as a compound or a tyre pressure issue. Although these two factors do play a large part and often are the culprit, there are many other solutions that must be considered and attempted to improve the tyre performance of your car.
NOTE:
This article is designed to be used as a diagnosis and solution user guide where you can go straight to the problem you are having and resolve it quickly. Some of the solutions are the same for different problems and parts of the tyre so some repetition occurs throughout the article in places.
Graining
One of the most common tyre defects seen track side is graining. Graining represents itself as a ripple effect in the rubber like many very small tears in the surface of the rubber. It occurs when strips of rubber begin to separate and tear away from each other and then fuse back together due to the heat of the tyre. This produces a very uneven surface and damages the integrity of the compound, reducing grip specifically in corners and during braking. Graining is formed by overheating caused by friction with the road surface and is a heat that starts at the contact patch and works into the compound.
One of the most common causes of graining is oversteer or understeer where the compound is dragged in a particular direction, scrubbing the surface, overheating the compound and causing the rubber to shear and begin to grain. If you are experiencing oversteer or understeer then solve this issue first using tips in the article linked at the bottom of this article. If graining continues after understeer and oversteer has been solved then you must first look at the pattern of the grain to see if it is suspension related, geometry/set up related or pressure related.
The first check is to see if the graining pattern is consistent around the circumference of the tyre. Roll the tyre round observing the strip of graining. If the strip starts and stops this is a sign that the dampers need adjusting as the tyre is hopping and skipping around the corner. If the strip of graining also gets wider and thinner as the tyre rolls around then this is a further sign that your dampers need adjusting. Your rebound stiffness on the damper is likely too soft and is allowing the tyre to bounce instead of remaining in contact with the road surface. However, as is often the way with suspension, it can also mean that the rebound is too stiff.
A good way to determine whether the rebound damping is too stiff or too soft is to take a look at how the tread on the tyre is forming. If the front of the tread is raised, this points towards the rebound being too slow. If the back edge of the tread is raised, this hints at the rebound of the damper being too fast. Using these signs will help to remove the graining through the use of rebound alterations.
If the graining is consistent around the circumference of the tyre then this points towards geometry or tyre pressure being the culprit. Tyre pressures are the most common reason to create graining and one of the easiest to check and change. Measure your tyre pressures when hot as soon as the car comes in off circuit to ensure that they are set to the recommended pressure of the tyre manufacturer (often around 30psi).
If tyre pressures are fine and the pattern is consistent around the tyre then the issue will now lye with spring rates (coil and ARB), geometry, tyre compound or driving style. One common cause of graining is pushing a tyre too hard when cold on stiff springs. This overheats the surface of the tyre due to it not yet being malleable and causes layers to begin shearing from the compound. Even when the tyre is up to temperature, a spring that is too stiff can cause graining to occur as can an anti-roll bar that is too stiff for the set up. This is because the stiffer spring rate (coil or ARB) is providing a larger lateral load transfer rate onto the outside tyre during cornering. If the rate is too stiff it can force too much load through the tyre and overheat the compound due to it not being able to handle the forces exerted. A softer spring rate will reduce the level of grip back to a point that the tyre can handle. It seems counter-intuitive to reduce possible grip levels but if you are pushing a tyre beyond its limits it will have much less grip than with a softer spring rate installed.
If your spring rates are fine then it is best to observe which area of the tyre is suffering from graining to assess how geometry might be causing the issue.
Inside Edge
If graining is occurring on the inside edge of the tyre then the tyre compound is overheating on the inside edge. This is the most common area of the tyre to suffer from graining due to most cars running negative camber out on track. Reducing the negative camber will reduce the concentration of heat at the inside edge of the tyre and will reduce or remove the graining. However, reducing the camber might not be a beneficial alteration to the set up and should be the last thing altered if you have used this camber setting successfully before.
Outside Edge
If graining is occurring on the outside edge of the tyre then you are running too much positive camber causing the outside edge of the tyre to overheat as it is being over worked. To resolve this issue, increase the negative camber at the affected wheels.
Centre
If graining is occurring at the centre of the tyre then the most likely reason is that the tyre pressures are too high. This is causing the tyre to balloon due to over inflation when the tyre is getting warm out on track. To resolve this, check your tyre pressures immediately after coming off track and set this “hot” pressure to the same as the manufacturer recommended settings which is usually around 30psi.
If tyre pressures are fine then the issue could lye with your camber settings. In this case increase the negative camber to roll the tyre off the centre of the contact patch onto the inside edge when static. This will help the tyre engage the full surface area during cornering on most track car set ups.
Full Tyre
If the full tyre is affected then this suggests that your camber settings and tyre pressures are not the immediate culprit and would point towards driving style or tyre compound being the remaining issue.
If all of your geometry settings are okay then the graining can be due to your driving style or your choice of tyre compound for your application. It is also common for graining to occur on a tyre that hasn’t been warmed sufficiently before hard use. Therefore, make sure that you are doing warm up laps before pushing the car hard. If you have completed warm up laps first then alter your braking and throttle application styles to become smoother and more gradual in application. Pay close attention on corner exit and when setting off from the line with how the throttle is being applied and make sure the wheels are not spinning in these cases as that will overheat the compound. Also, reduce the amount of braking pressure on turn in as the two directions of forces (longitudinal and lateral) will heat the tyre and can also contribute towards graining.
If all of the above factors are not an issue then the tyre compound is most likely too soft. In this case you will have to install a firmer compound tyre or replace your soft compound tyres more frequently.
Excessive Tread Wear
Excessive tread wear is when a particular part of the tyre tread is wearing faster than the rest of the tyre. Similarly, the front wheels or rear wheels might be wearing noticeably faster than each other raising some concern as to why. Excessive tread wear represents itself visually where the depth of the tread is much less in one area of the tyre than it is in another. On a slick tyre it is less noticeable and can be seen by looking at the tyre front on to see if the tyre drops off rapidly as opposed to being relatively flat or slightly positively arced in the centre.
Depending on which area of the tyre is suffering depends on the solution to the problem.
Inside Edge
If the inside tread is wearing much faster than the rest of the tyre then there is likely to be too much negative camber present. However, the inside edge of the tyre should be wearing at the fastest rate on the majority of circuit cars due to negative camber being the most common set up. However, if the tread is wearing at a rate up to 3 times faster than the rest of the tyre then there is likely an issue.
If your camber is correct and this problem still occurs then the issue could lie with a faulty ball joint or bearing that is increasing the negative camber when out on circuit. This should feedback through the steering wheel but it is good practise to jack the car up and check for any play.
Alternatively, you might be having excessive wheel spin when setting off or on corner exit if you are applying the throttle too aggressively. In this case make sure to apply the throttle more gradually when re-applying so not to overcome the tractive capabilities of the tyre.
Outside Edge
If excessive tread wear is occurring on the outside edge of the tyre then there is too much positive camber present. To resolve this, increase the negative camber at the affected wheel. This situation is most common on standard cars with too little negative camber as they are aligned for road use which is not used to the corner loadings experienced when on track.
Centre
If excessive tread wear is present at the centre of the tyre then the first solution would be to reduce tyre pressures as the hot pressure of the tyre is higher than the manufacturer recommended settings causing the tyre to balloon. This will vastly reduce grip out on circuit too.
If the tyre pressures are set correctly with the right hot pressure then make sure that you are not spinning the wheels off the line and on corner exit when re-applying the throttle. Also, make sure that your brakes are not locking up into corners as this will flat spot the tyre and remove large sections of tyre tread. If you are locking the wheels then either adjust your brake bias away from the locking wheels or if that isn’t an option, brake earlier and more progressively into the corner.
Full Tyre
If the full tyre is wearing much faster than expected there are a few solutions. First of all, make sure that you are not spinning the wheels when setting off or on corner exit. If you are spinning the wheels then make sure to apply the throttle more gently when setting off and on corner exit when the throttle is reapplied after the apex.
Check to see if you are locking any of the brakes when approaching a corner. If this is the case then adjust your brake bias away from the locking wheels. If you do not have a brake bias available then apply the brake pedal more progressively and begin braking earlier on the circuit.
If you are not spinning or locking the wheels then it is most likely that the tyre compound you have chosen is too soft for your requirements and track conditions. In this case, select a harder compound tyre to install or simply accept that you will need more tyres to use on a track or race day.
Blistering
Tyre blistering is one of the more severe tyre issues that will cause massive loss of grip and will affect the integrity of the tyre drastically. It represents itself as chunks or strips of rubber removing from the surface of the tyre. It can look as though a peeler has been dragged deeply across the surface of the tyre or simply that chunks of rubber are missing. Blistering is caused by the compound overheating due to inner friction of the layers of the rubber. The overheating causes the bonds between the layers of compound to fail and shear off in large chunks. It is the most severe form of tyre failure and can result in a crash if it is not handled or the car is not slowed down quickly.
A common cause of tyre blistering is that the tyre compound is too soft for the conditions or that the track conditions are too hot for the tyre to handle. In these cases, a change of tyre brand or compound would be the best solution to prevent further issues with blistering. However, in many cases this is not possible as you might only have a certain tyre with you or be in a championship with a controlled tyre brand. This is the case we will look at below with some solutions on how to reduce tyre failure.
Similar to graining, a high tyre pressure can cause the tyre to heat up too much from within and start to separate the compound leading to blistering. Therefore, as a starting point make sure that your tyre pressures are all set to the manufacturers recommended settings. A good point to measure your tyre pressure is as soon as the car comes in off circuit as this is the operating pressure of the tyre. This figure needs to match the recommended operating temperature for your brand of tyre.
Severe amounts of understeer and oversteer can also lead to blistering as the tyre is being dragged across the surface, overheating the layers of rubber. If your car is suffering from oversteer or understeer then remove this first before trying to diagnose the source of the blistering. The link at the bottom of this article can help to resolve this issue.
On a car with a high amount of aerodynamic downforce, blistering is a more common problem. This is due to the high vertical forces exerted through the tyre, generating more grip but pushing the tyre past the point of adhesion due to the compound/tyre structure not being capable of managing the extreme forces. One solution to this, if your car runs a high amount of downforce, is to reduce the level of downforce acting upon the blistering axle. For example, if your rear tyres are beginning to blister then reduce downforce on the rear axle.
If you are not running a high amount of downforce or you are happy that the amount provided is manageable normally with these tyres, the issue could lye with spring rates. In a similar way to running too much aero, running stiff spring rates and anti-roll bar rates increases the amount of lateral load transfer during cornering. This increase in load transfer can over load the tyre past the point of adhesion and overwork the compound causing it to overheat and blister. If a certain axle is blistering particularly on the outside wheel for the circuit direction, you might need to reduce the spring rate slightly or the anti-roll bar rate.
Your damper compression stiffness also contributes to tyre blistering. similar to rebound stiffness with graining, it could be due to not enough compression stiffness or too much compression stiffness. Too much compression stiffness prevents the shock absorber from working efficiently with the spring rate, forcing the tyre to deform and act as a spring. This additional demand from the tyre causes the compound to overheat due to the vibrations being exerted through the tyre that the spring and damper are now not absorbing. If the compression settings are too soft for the conditions, the tyre will be loaded too quickly on corner entry, over working the compound and causing it to overheat. It should be apparent if your compression stiffness is too soft or too hard based upon the feel of the car on corner entry. If the car feels very stiff and non-compliant then it is likely too high. If the car seems to shift its mass and compress the outside wheels, the compression stiffness is likely too low.
If your suspension settings, aero and tyre pressures are all fine then your attention should turn to where on the tyre the blistering is occurring. This will help to find the correct solution.
Inside Edge
First of all, check that you are not running too much negative camber. This can happen when a car is lowered a long way, the camber gain in the standard geometry produces high amounts of negative camber affecting each wheel. You should check the temperature of the tyre compound across the width of the tyre and make sure the range from inside to outside isn’t more than about 15 degrees centigrade. It is normal for the inside edge to be most affected as most track cars run negative camber.
Outside edge
If blistering is occurring at the outside edge of the tyre then one of the most common causes is that too much positive camber is present. To resolve this, increase the negative camber at that wheel. To accurately adjust the camber to the correct position, a tyre pyrometer can be used to read the temperature of the tyre compound at different intervals across the width of the tyre. The inside edge should be roughly 10 to 15 degrees centigrade hotter than the outside edge with the centre being in the middle of that range.
Centre
If blistering is occurring at the centre of the front tyres then the first thing to check is that your tyre pressures are not too high. An over inflated tyre will balloon in the centre and lift the inside and outside edges from the surface. This means that only a thin strip of tyre is in contact with the ground and is having to handle all of the grip forces. This leads to the compound overheating and blistering. To resolve this, check your tyre pressures when they are hot after you have just come in off circuit, then set the hot pressure to the manufacture recommended setting, usually around the 30-psi mark.
It is also worth checking that your camber settings are optimised as more negative camber might be required to unload the centre of the tyre. Using a tyre pyrometer will allow you to check the temperature of the compound across the breadth of the tyre to see if the camber needs tuning.
Inside and Outside Edge
If blistering is occurring at both the outside and the inside edges then the issue most probably lies with your tyre pressures. Your tyre is likely under inflated, causing the centre of the tyre to depress under load lifting the contact patch in the centre away from the surface. This will cause extra stress and loading to the outside and inside edges of the tyre which can lead to blistering. This is one of the least common areas for blistering to occur as in these conditions it is difficult to get the heat into the compound.
Full Tyre
First of all, you can increase your wheel size to a larger diameter. This will provide a larger rolling radius for the tyre allowing the compound to cool more when it is not is contact with the road surface as the wheel turns. This provides a larger cooling cycle for the tyre and helps to prevent overheating and blistering. Likewise, installing a wider tyre will also help with heat dissipation and keep the tyre cooler as the extra width provides more contact patch to help handle the forces.
If installing larger wheels and tyres is not an option then altering your driving style can help to prevent your tyres from overheating. Start by providing more gentle steering inputs when turning into a corner. Erratic use of the steering wheel can scrub the tyre compound and overheat it to the point of blistering. Smooth steady inputs when approaching a corner are important to increase tyre life. Another driving style tip is to try and avoid large braking inputs which might cause the front wheels to lock up. A lock up puts excessive heat through the tyre and is a very common cause of tyre blistering.
If your geometry is okay then it could be that your tyres are over loaded and aren’t capable of handling the amount of force being put through them. Put your car on corner weights and check to see that your weight distribution doesn’t have too much of a variance. An obvious issue with mass would be a front to rear split of 70/30 etc. If it is, corner weight your car to shift more mass to the lighter axle. The mass can be shifted by adjusting your ride heights or by removing weight from the car such as interior items or replacing body panels with lighter materials such as carbon fibre.
Heavy braking might also be causing your front and rear wheels to lock up heading into the corner. This is because as you apply the brakes, the rear end is unloaded as the mass travels forward. The reduction in mass means that much less braking force is now required to stop the rear wheels from turning and cause a lock up. The lock up then makes the tyre scrub against the ground and can overheat. If it is done regularly enough on circuit it will overheat the compound and cause blistering. Heavy braking can also lock up the front wheels if you are applying them too heavily due to braking too late into the corner. The larger front brakes have more stopping force than the rears and can cause lock up.
Wheel spin is also a cause of tyre overheating which leads to blistering. Make sure that you are applying the throttle gently on corner exit to prevent the wheels from spinning up.
Tearing
Tyre tearing is a more extreme version of graining. Where graining is lots of small ruptures and undulations on the tyre surface, tearing is larger longer sections of tyre that have separated or torn away from each other but have fused back onto the compound and have not left the tyre. It can form the appearance of a knife being sliced across the surface a few times to form lacerations to the surface of the compound. Again, tearing is due to the heat being put through the tyre being too concentrated for the compound to cope with resulting in the breakdown of the compound.
Before we look at how to solve tearing at each individual area of the tyre, we will look at the two main types of tearing that occur; cold tearing and hot tearing.
Cold tearing is the result of the tyre being over inflated, making the contact patch too small, meaning that the temperature is staying too focused on one small area of contact patch. This causes the compound to tear. The tears will be deep into the compound and will lift up when prised. A deep tear of around 5mm plus is a cold tear and can be solved by reducing tyre pressure.
On the other hand, hot tear occurs due to an underinflated tyre. The underinflation causes the compound to overheat and melt layers of the tread away. The hot tears are identifiable by the shallow sections of tearing less than 5mm deep. Hot tear can be solved by increasing the tyre pressure.
If your pressures seem okay then it might lie with geometry and will depend upon which area of the tyre is affected. The solutions of the 3 main areas of the tyre that will be affected are below.
Inside Edge
If tearing is occurring on the inside edge of the tyre then there is likely to be too much toe present on the tearing wheel. Reduce toe angle to reduce tearing.
Outside Edge
If tearing is occurring on the outside edge of the tyre then there is likely to be too much toe present on the tearing wheel. Reduce toe angle to reduce tearing. You might also have too much positive camber so check your tyre temperatures with a pyrometer to see if more negative camber is required.
Centre
Similarly, to the inside and outside edge, tearing at the centre suggests that too much toe angle is being used. However, if it is only present in the centre then it would suggest that the tyre pressures are also too high. Therefore, start by reducing tyre pressures. If tearing continues across the breadth of the tyre then reduce the toe angle on the tearing wheel.
Excessive Pick Up
Excessive pick up is when the tyre picks up marbles of rubber from the race track resulting in a lumpy texture to the surface of the tyre as though chunks of rubber have been glued to the tyre surface. This is often a result of driving the car off the racing line picking up all the rubber that has sheared away from other tyres. However, if you have pick up after being on the racing line and on a particular part of the tyre it might be a visual sign that your geometry or set up can be altered to increase grip further. Depending on the area of the tyre affected will alter the solution as detailed below.
Inside Edge
Excessive pick up on the inside edge of the tyre suggests that too much positive camber is present as the tyre isn’t being scrubbed off on the inside edge to remove the pickup. To resolve this, increase the negative camber on the affected wheels.
Outside Edge
Excessive pick up on the outside edge of the tyre suggests that too much negative camber is present as the tyre isn’t being scrubbed off on the outside edge to remove the pickup. This is the most normal part of the tyre to have pick up on it due to negative camber angles being required for maximum cornering performance. In this case pay more attention to the handling characteristics of the vehicle and use a tyre pyrometer to measure the temperature distribution across the tyre.
Centre
If pick up is occurring in the centre of the tyre then it is a signal that your tyre pressures are too low due to the tyre caving in the centre. Check the tyre pressures and make sure you are running the manufacturer recommended pressures in the tyre.
Inside and Outside Edge
If you have excessive pick up on the inside and outside edge of the tyre then the tyre pressure is likely to be too high causing the tyre to balloon, lifting the outer edges of the tyre off the surface. Check tyre pressures and lower them to a point where the hot running pressure is the same as the recommended pressure from the manufacturer.
Whole Tyre
If the whole tyre is covered in pick up then you are probably driving off line through a sea of tyre marbles. In this case, assess your driving style and take extra care to ensure that you are on the racing line.
Blue Tyres
Blue tyres are often seen as dead tyres. This is not the case. Tyres are filled with oils and chemicals to help with keeping the compound soft and to help manage layer adhesion and heat management. When the tyre is put through a heat cycle out on circuit, the oils and chemicals react and make their way to the surface of the tyre. When heading back out on circuit, this initial layer will be scrubbed off almost immediately and the tyre will work well again. After another heat cycle the blue surface will return as more oils make their way to the surface.
Every time that you put the tyre through a full heat cycle you will lose more and more of the oils that keep the compound soft and grippy. Therefore, the tyre will begin to harden over time and will eventually become too hard and lose considerable grip. At this point the tyre will be useless. The best way to keep an eye on this is through the use of a tyre durometer which will measure the hardness of the compound. Once the tyre is outside of the manufacturer recommended tolerances it is time to install a fresh set.
Ideal Tyre Wear
So now that we know all of the possible failures of tyres, what do we want to see from a well worked, healthy tyre? The ideal wear will be even across the inner two thirds of the tyre and have a slight ripple effect to the surface. This means that the tyre has reached an optimal temperature and has produced the correct amount of distortion to maximize grip without failing. The ripples should be small and not be lifting away from the layers beneath.
This is an absolutely fantastic site! Very accurate and easy to read.