Modern tyres are diverse in size, in construction and in application. We all understand that off-road tyres are not the sort of tyre we would want on a track day, (although I did once instruct someone in a Land Rover Defender on knobbly tyres at a Rockingham track day), but people are often surprised when their premium, high cost, sports road tyres, “ suffer”, and inevitably that question pops up again: “what pressures should I run?” I will get to that later.
The tyres seen at an average track day would roughly be 40% standard road tyres, be that budget through to premium. A further 40% would be Ultra High Performance (UHP) tyres which are performance road tyres, and the final 20% are motorsport tyres, some of which have an E mark for road approval and some, such as slick tyres, that do not. Given that all the drivers are there for roughly the same reason, what are the differences in their tyres? I will start with grip.
GRIP
Tyres must transfer all the energy from the car to the road and translate this into traction, braking and cornering forces. To do this the tyre must “grip” the road. Grip is generated in three ways, by chemical means through the compound, by the shape of the tyre through its construction and mechanically through the tread pattern. Chemical....the stickiness the tyre develops with the surface and Mechanical....the way the tyre locks into the features (stones etc.) in the surface. So, if you think of sticky tape sticking to a surface, that is chemical grip, think of a tractor tyre digging into a field, that is mechanical grip. A tyre maintaining its shape and footprint during cornering and braking is a big component in generating grip.
Road tyres in general are designed to cope with most road and weather conditions, to get you to work on a frosty morning, to the supermarket when it is raining and to Aunty Flo’s at the weekend, and it must be durable. No one is going to be happy with a road tyre that only lasts for 400 miles, no matter how great the grip is. UHP tyres, have more specialised design features to assist with performance motoring. The tread blocks will generally be larger and flex less than a standard road tyre and the carcase will be more rigid. The UHP tyre may compromise some economy and wet performance in the search for more chemical grip, whilst allowing more load and energy to be put into the tyre. Finally, we come to motorsport tyres. Here the tyre is designed for the purpose of generating the most grip through both chemical and mechanical grip. Whilst some may be road legal, they are not intended for setting the fastest time to the shops on a damp November morning. An appreciation of how compounds work will help to understand motorsport tyres.
COMPOUND
The rubber compounds used in tyre production is as varied as the intended application, they all have common factors though. Natural rubber is the base, which is essentially a series of long chain polymers in a jumble. Think of cooked spaghetti tipped out on a plate. When loaded under braking for example, these chains stretch out and return to their original state when the load is released, demonstrating an elastic property. Natural rubber is not much use in its raw state and additives are used to create the desired results. Carbon Black is added which resists UV damage from sunlight and gives the tyre its black colour, plasticisers which enable the rubber to stay pliable over time and Sulphur, which form links between those polymer chains when the rubber is cured or “vulcanised”. The type of these links within the rubber affects how the compounds behave and rubbers with different properties are used for different parts of a tyre, the sidewall that needs to flex is different from the tread rubber for instance.
To date, nobody has been able to develop a rubber compound that gives the best of all worlds (cold and wet performance on roads, long life, exceptional grip and thermal stability on track), and so we have to accept that different tyres have strengths and weaknesses, and can be compromised when pushed beyond their design expectations.
The tyres seen at an average track day would roughly be 40% standard road tyres, be that budget through to premium. A further 40% would be Ultra High Performance (UHP) tyres which are performance road tyres, and the final 20% are motorsport tyres, some of which have an E mark for road approval and some, such as slick tyres, that do not. Given that all the drivers are there for roughly the same reason, what are the differences in their tyres? I will start with grip.
GRIP
Tyres must transfer all the energy from the car to the road and translate this into traction, braking and cornering forces. To do this the tyre must “grip” the road. Grip is generated in three ways, by chemical means through the compound, by the shape of the tyre through its construction and mechanically through the tread pattern. Chemical....the stickiness the tyre develops with the surface and Mechanical....the way the tyre locks into the features (stones etc.) in the surface. So, if you think of sticky tape sticking to a surface, that is chemical grip, think of a tractor tyre digging into a field, that is mechanical grip. A tyre maintaining its shape and footprint during cornering and braking is a big component in generating grip.
Road tyres in general are designed to cope with most road and weather conditions, to get you to work on a frosty morning, to the supermarket when it is raining and to Aunty Flo’s at the weekend, and it must be durable. No one is going to be happy with a road tyre that only lasts for 400 miles, no matter how great the grip is. UHP tyres, have more specialised design features to assist with performance motoring. The tread blocks will generally be larger and flex less than a standard road tyre and the carcase will be more rigid. The UHP tyre may compromise some economy and wet performance in the search for more chemical grip, whilst allowing more load and energy to be put into the tyre. Finally, we come to motorsport tyres. Here the tyre is designed for the purpose of generating the most grip through both chemical and mechanical grip. Whilst some may be road legal, they are not intended for setting the fastest time to the shops on a damp November morning. An appreciation of how compounds work will help to understand motorsport tyres.
COMPOUND
The rubber compounds used in tyre production is as varied as the intended application, they all have common factors though. Natural rubber is the base, which is essentially a series of long chain polymers in a jumble. Think of cooked spaghetti tipped out on a plate. When loaded under braking for example, these chains stretch out and return to their original state when the load is released, demonstrating an elastic property. Natural rubber is not much use in its raw state and additives are used to create the desired results. Carbon Black is added which resists UV damage from sunlight and gives the tyre its black colour, plasticisers which enable the rubber to stay pliable over time and Sulphur, which form links between those polymer chains when the rubber is cured or “vulcanised”. The type of these links within the rubber affects how the compounds behave and rubbers with different properties are used for different parts of a tyre, the sidewall that needs to flex is different from the tread rubber for instance.
To date, nobody has been able to develop a rubber compound that gives the best of all worlds (cold and wet performance on roads, long life, exceptional grip and thermal stability on track), and so we have to accept that different tyres have strengths and weaknesses, and can be compromised when pushed beyond their design expectations.
Dandelions produce natural rubber in the form of latex, but it is thought only Bees use this latex in tyre production!
Now we have some basic understanding of tyres, let’s introduce the engine into the discussion. No race driver has ever complained of having too much power, everything else yes, but never too much power. Track drivers want power too, many of today’s road cars produce more power than F1 cars did 40 years ago. We want that power so we can accelerate more rapidly, stop more quickly and go round corners faster. All that power gets transferred to the ground through the contact of the rubber on the road. If you think of this in reverse, when you brake, you turn the energy of your car moving forward into heat and noise in the brakes. They get extremely hot, everyone loves a picture of their brake discs glowing because, well who wouldn’t? However, for the car to slow, the same amount of friction energy must be generated between the tyre and the road. We put cooling on our brakes to stop fade, we do not put cooling on our tyres to stop overheating. It is therefore important to understand that tyres have an operating window of temperature in the same way brakes do.
You may have heard of “conditioning tyres” when they are new to make them more durable. This is not “scrubbing in” or removing release agent. The principal is to warm and stretch the rubber through gentle use and break some of those sulphur bonds allowing those jumbled up polymer “spaghetti” chains to align much like uncooked spaghetti in a packet. As the rubber cools the sulphur bonds can reform and the rubber becomes tougher but no less elastic or grippy. It is not a quick process and it can take up to 48 hours to reform the bonds.
While that technical bit might have been a bit of a slog, it is relevant to the understanding of your tyre’s performance. Everything is a compromise and it is understanding those compromises that will help you.
RACE COMPOUNDS
Most people will be familiar with the terms soft, medium and hard compounds, even if you have never experienced them. In general, a soft tyre will generate the most grip and give the quickest lap time, but will wear out more quickly and may overheat if used for long distances or in warm conditions, taking it above its operating temperature and reducing the tyre’s performance. A hard compound tyre will not generate the same ultimate grip, lap times can be slower but will be more durable as they are more thermally stable than softer compounds giving more consistent lap times for longer. Medium, as the name suggests is somewhere in the middle of soft and hard. Soft, Super Soft, Medium, Hard etc. are, however, only relative measures based on the use of the tyre and are not actual measurement of tyre hardness. A soft F1 tyre will be vastly different to a soft Touring Car tyre and different again to a GT car tyre and again different to a Hill Climb tyre. This is because they have different demands, expectations and requirements placed on them. There is no point having a tyre that is a second a lap quicker over 10 laps but then wears out and loses 2 seconds a lap over the remaining laps if your races are 30 laps long.
That brings us onto operating temperatures. Heat is generated in a tyre by friction and movement of the rubber. Energy is required to flex and stretch the rubber and this internal movement results in heat, be it from the flexing of the sidewalls or stretching and compressing of the tread layer. Heat is important, particularly with race compounds as when cold and below their operating temperature, the rubber is said to be in a “glassy” state (which is sort of self-explanatory), but means that the rubber is not yet pliant enough and is not giving the chemical or mechanic grip that it should. Therefore, you see almost all race cars weaving around on the way to the grid or Dragster and Hill Climb Cars spinning wheels at a practice start.
A practical tip, you will gain more heat in a tyre on a warm up lap from accelerating and braking (if you have reasonable power) than you will from weaving side to side, although the weaving makes you look cool!
As a tyre wears, this movement of the rubber reduces, so the amount of heat generated reduces and therefore the grip level is reduced. Also there comes a point when there is not enough depth of rubber to fully engage with the features of the road surface, reducing mechanical grip. Next time someone shows a picture of a treaded tyre with no tread and says it is faster because it is like a slick you will know it is wrong.
The last piece of this puzzle is overheating. Taking the tyre above the operating temperature of the compound causes those Sulphur bonds to break down, weakening the ability for the surface rubber to hold on to the rubber below and the rubber starts to overstretch or shear off. The tyre is said to “go greasy” it slides more in the corners, braking and acceleration performance are reduced and the tyre wears more rapidly. The internal structure of the compound is breaking down. It can be a vicious circle: the more the tyre slides, the more friction, the more heat generated and so on. You have seen the races when the driver on pole gets spun on the first corner, then makes a heroic charge back though the field, only to be slow on the final laps caused by the tyres “going off” because they have been worked too hard, and if you take it too far, the tyre can blister. This is when the tread rubber becomes hot enough throughout that it can separate deeper in the tread or even at the carcase and chunks of rubber can come away.
You may have heard of “conditioning tyres” when they are new to make them more durable. This is not “scrubbing in” or removing release agent. The principal is to warm and stretch the rubber through gentle use and break some of those sulphur bonds allowing those jumbled up polymer “spaghetti” chains to align much like uncooked spaghetti in a packet. As the rubber cools the sulphur bonds can reform and the rubber becomes tougher but no less elastic or grippy. It is not a quick process and it can take up to 48 hours to reform the bonds.
While that technical bit might have been a bit of a slog, it is relevant to the understanding of your tyre’s performance. Everything is a compromise and it is understanding those compromises that will help you.
RACE COMPOUNDS
Most people will be familiar with the terms soft, medium and hard compounds, even if you have never experienced them. In general, a soft tyre will generate the most grip and give the quickest lap time, but will wear out more quickly and may overheat if used for long distances or in warm conditions, taking it above its operating temperature and reducing the tyre’s performance. A hard compound tyre will not generate the same ultimate grip, lap times can be slower but will be more durable as they are more thermally stable than softer compounds giving more consistent lap times for longer. Medium, as the name suggests is somewhere in the middle of soft and hard. Soft, Super Soft, Medium, Hard etc. are, however, only relative measures based on the use of the tyre and are not actual measurement of tyre hardness. A soft F1 tyre will be vastly different to a soft Touring Car tyre and different again to a GT car tyre and again different to a Hill Climb tyre. This is because they have different demands, expectations and requirements placed on them. There is no point having a tyre that is a second a lap quicker over 10 laps but then wears out and loses 2 seconds a lap over the remaining laps if your races are 30 laps long.
That brings us onto operating temperatures. Heat is generated in a tyre by friction and movement of the rubber. Energy is required to flex and stretch the rubber and this internal movement results in heat, be it from the flexing of the sidewalls or stretching and compressing of the tread layer. Heat is important, particularly with race compounds as when cold and below their operating temperature, the rubber is said to be in a “glassy” state (which is sort of self-explanatory), but means that the rubber is not yet pliant enough and is not giving the chemical or mechanic grip that it should. Therefore, you see almost all race cars weaving around on the way to the grid or Dragster and Hill Climb Cars spinning wheels at a practice start.
A practical tip, you will gain more heat in a tyre on a warm up lap from accelerating and braking (if you have reasonable power) than you will from weaving side to side, although the weaving makes you look cool!
As a tyre wears, this movement of the rubber reduces, so the amount of heat generated reduces and therefore the grip level is reduced. Also there comes a point when there is not enough depth of rubber to fully engage with the features of the road surface, reducing mechanical grip. Next time someone shows a picture of a treaded tyre with no tread and says it is faster because it is like a slick you will know it is wrong.
The last piece of this puzzle is overheating. Taking the tyre above the operating temperature of the compound causes those Sulphur bonds to break down, weakening the ability for the surface rubber to hold on to the rubber below and the rubber starts to overstretch or shear off. The tyre is said to “go greasy” it slides more in the corners, braking and acceleration performance are reduced and the tyre wears more rapidly. The internal structure of the compound is breaking down. It can be a vicious circle: the more the tyre slides, the more friction, the more heat generated and so on. You have seen the races when the driver on pole gets spun on the first corner, then makes a heroic charge back though the field, only to be slow on the final laps caused by the tyres “going off” because they have been worked too hard, and if you take it too far, the tyre can blister. This is when the tread rubber becomes hot enough throughout that it can separate deeper in the tread or even at the carcase and chunks of rubber can come away.
A tyre blistered and delaminating through overheating.
ROAD TYRE COMPOUNDS
Road tyre compounds are designed to operate at lower temperatures than those seen on the track. They rarely have the warmup issues of race compounds but will overheat far sooner and cannot sustain prolonged track use, particularly on heavy or powerful cars. Track day drivers should be especially cautious about this, as it’s not unusual to find that a driver has continued with their session, long after the tyres have started to move around, and discover that their tyres have suffered heavy wear.....and may no longer be road legal!
Finally, on compounds, they are not all the same. Just like cooks, manufacturers will have their own recipes, tweaks, and ingredients and just like cakes, some taste different to others and some put more expensive ingredients into them. A hill climb soft will not be the same as a touring car soft etc.
Road tyre compounds are designed to operate at lower temperatures than those seen on the track. They rarely have the warmup issues of race compounds but will overheat far sooner and cannot sustain prolonged track use, particularly on heavy or powerful cars. Track day drivers should be especially cautious about this, as it’s not unusual to find that a driver has continued with their session, long after the tyres have started to move around, and discover that their tyres have suffered heavy wear.....and may no longer be road legal!
Finally, on compounds, they are not all the same. Just like cooks, manufacturers will have their own recipes, tweaks, and ingredients and just like cakes, some taste different to others and some put more expensive ingredients into them. A hill climb soft will not be the same as a touring car soft etc.
MRF ZTR Tyre Circuit Race / Trackday 185 55 R14 80V
£132.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 215 45 R17 87W
£198.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 235 40 R17 90W
£150.00 - £210.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 235 40 R18 91W
£160.00 - £234.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 245 40 R18 93W
£254.40
Sold out
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 265 35 R18 93W
£282.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 295 30 R18 94Y
£306.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 235 35 R19 87Y
£254.40
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 205 45 R17 84W
£192.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 225 45 R15 87W
£186.00
The MRF ZTR tyre is a track focused, but road legal tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
MRF ZTR Tyre Circuit Race / Trackday 185 60 R13 80H
£114.00
The MRF ZTR tyre is a track focused, tyre used in several UK and European championships. Delivering great corner speed, excellent consistency and remarkably long life making it suitable for both sprint and endurance racing where it has enabled pole positions, fastest laps and race wins.
NOTE The 13" tyres are not currently E marked and so for circuit use only.
MRF ZTi2 Tyre Circuit Race / Trackday 205 60 R13 86H
£114.00
The MRF ZTi2 tyre is designed for dry circuit racing and track days. This intermediate pattern can be used even when the track is a little damp. The tyre gives consistent performance with sustained grip and superior handling over multiple laps.
NOTE The 13" tyres are not currently E marked and so for circuit use only.
