Why Are Tyres So Important?

Monitoring your tyres when out on a track day or when racing is one of the most effective things you can do to make your car as grippy and as fast as possible with minimal effort. Your tyres are the final point of contact between your car and the ground. Therefore, they transmit a lot of information from your suspension set up and also store a lot of useful information that can be measured to help fine tune your geometry to make the tyre work more efficiently with the ground to make your car go faster with ease.

When understeer or oversteer begins to occur it can be too easy to start adjusting dampers and anti-roll bars to solve the problem when in fact a quick look at the tyres might give all the answers required to solve the problem.

What Equipment Is Required?

Two pieces of equipment will be enough to measure the tyres and gauge their performance at the track side for improvements to be made.

  • Tyre Pressure Gauge

The tyre pressure gauge is a cheap piece of equipment and an accurate digital version can be purchased for £20. It is pressed onto the tyre valve and displays the pressure within the tyre which can then be recorded and the tyres can have their readings compared against each other.

  • Tyre Temperature Pyrometer

The tyre pyrometer is a more expensive piece of equipment but can deliver information to help fine tune the grip into the car. It is a temperature probe that can be pressed into the rubber to produce the temperature across the width of the tyre stored within the rubber just below the surface. These values for all the tyres can be compared against each other to fine tune the set up. If you are a serious track day enthusiast then it would be recommended to purchase one and if you are a racer then it is highly advised to purchase one as the benefits will quickly outweigh the cost of the tool. A good tyre pyrometer can be purchased for £120.

How To Measure Tyre Pressures

The most cost effective way to measure tyre pressures is with a hand held pressure gauge as soon as the car comes in off track. When the car returns from circuit no time can be wasted getting the tyre pressures as they will immediately begin to change and drop as the tyres cool back down. Therefore it is usually best to hand the job to a friend so that as soon as the car is stopped they can press the gauge onto the tyre valves to get immediate readings. A good tip to reduce the time to collect the data is to leave the tyre valve dust cap off when out on circuit so they don’t need to be unscrewed before a reading can be taken. A pad and pen should be to hand when going round the car collecting the tyre pressures so that the results can be noted down immediately. The following notations can be written on the pad so that the pressures can be compared between different sessions or days.

  • FL = Front Left Tyre or Front Nearside Tyre
  • FR = Front Right Tyre or Front Offside Tyre
  • RL = Rear Left Tyre or Rear Nearside Tyre
  • RR = Rear Right Tyre or Rear Offside Tyre

Another way in which the tyre pressures can be recorded and monitored is by using wireless tyre pressure sensors that can be mounted to the tyre valve when out on circuit providing live figures. These sensors can be wired into a data logger for the serious racer meaning that when returning from circuit the data logged information can be viewed on a laptop to show the pressure figures for when the car was out on circuit. This is more accurate and relevant information that the hand held tyre pressure gauge as the hand held gauge is measuring pressures that have had a small amount of time to reduce due to the tyre cooling when coming into the pits. However, the cost difference is such that the hand held pressure gauge works well enough that the live pressures only need installing for a serious racer or track day enthusiast.

How To Measure Tyre Temperatures

The lowest cost option for monitoring tyre temperatures is using the tyre temperature probe. As soon as the car comes in all 4 tyres need measuring in 3 places per tyre. The places to measure are directly across the top of the tyre as soon as the car has stopped after coming off track on the outside edge, centre and inside edge of the tread surface. This needs repeating for the other 3 tyres and all of the values need recording in a table so the tyres can all be compared to each other. The table similar to below can be used to log the tyre temperature data.

Outside Edge

(Degrees C)

Centre

(Degrees C)

Inside Edge

(Degrees C)

Front Left Tyre      
Front Right Tyre
Rear Left Tyre
Rear Right Tyre

A more advanced way to measure tyre temperatures which is used in high levels of motorsport is to set up a tyre pyrometer rig which mounts a row of infra-red temperature sensors just above the surface of the tyre which record live temperature data across the width of the tyre back to a data logger. This technique is of much higher cost and complexity but is much more accurate as issues can be spotted in particular corners and sections of the circuit that might not otherwise be noticed when the tyres have cooled slightly after coming down the pit lane.

How To Adjust Tyre Pressures

Before you begin the track day or test day make sure that all your tyre pressures are set even side to side. Then head out and complete a session. Once the session is complete measure the tyre pressures at all four wheels and record them for reference. The table below shows some example figures for a car returning from a clockwise circuit.

Wheel Pressure (psi)
Front Left 38
Front Right 34
Rear Left 37
Rear Right 33

 

The aim is to now make the tyre pressures even side to side when hot. The tyre manufacturer will often provide an optimum tyre pressure where the tyre provides maximum grip as it will be a pressure where the tyre does not balloon and bulge in the centre or is not too low so that the middle of the contact patch caves in. Therefore, in this scenario we can say that the tyre manufacturer has suggested a tyre pressure of 34psi. Now we can lower the left wheel values to match 34psi and increase the right rear by 1 psi to match. This puts all of the tyre pressures when hot at an even point which means that when the tyres are working out on track, they will all be working to their optimum.

The reason certain tyres increase in pressure more than others is due to two main reasons. One is that on a clockwise circuit for example the outside (left) wheels are travelling a further distance than the inside (right ) wheels because their path around the corner is on the outside line which is a longer arc. Therefore, they are actually travelling slightly faster and doing more work, therefore generating more heat which in turn increases the tyre pressure.

The other reason, and the main reason, is that the outside wheels are the loaded wheels that will have a percentage of the vehicle mass transferred onto them during cornering. On a clockwise circuit, the outside wheels will be loaded through corners more times than the right hand wheels. Therefore, they will experience a higher increase of load and will be made to do more work than the right hand wheels which again increases the heat of the tyre and the pressure will rise more.

How To Adjust Tyre Temperatures

Once you have sent the car out on circuit and have made sure that the pressures of the tyre seem relatively even side to side and are happy that they are close to the recommended operating pressure, you can begin to fine tune the tyre using the tyre temperature probe. Send the car out for another session to get the tyres through another good heat cycle. Upon return to the pits immediately measure all 4 tyres in the 3 points mentioned in the measurement section.  Record all the values in a table so that the figures can be compared. The aim for this process is to get an relatively even temperature across the full width of each tyre with the inside edge being slightly hotter than the outside. The range of temperature from outside to inside should be between 10 and 15 degrees with the middle being in the middle of the readings. This range can be larger or smaller depending on the tyre used. Below are a few examples of results for one tyre across the width and what the results mean and the solutions.

Example 1

Outside Edge

(Degrees C)

Centre

(Degrees C)

Inside Edge

(Degrees C)

Front Left Tyre 40 65 80

 

In this example you can see the temperature of the tyre increases towards the inside edge of the tyre by a large amount. This pattern of results suggests that the car currently has too much negative camber present at that particular wheel and the solution would be to reduce the negative camber on the front left wheel which would allow the outside of the contact patch to engage with the circuit when out on track, increasing front end grip levels. The negative camber should be reduced to a point where the temperatures are within a range of 10-15 degrees from inside edge to outside edge with the inside being hotter than the outside and the centre of the tyre being somewhere close to the middle of the range.

Example 2

Outside Edge

(Degrees C)

Centre

(Degrees C)

Inside Edge

(Degrees C)

Front Left Tyre 80 72 68

 

In example 2 the opposite pattern in present where the temperatures across the tyres decrease towards the inside edge of the tyre. This means that there is too much positive camber present at the wheel and therefore would need the positive camber reducing to allow the inside edge of the tyre to engage with the circuit more, increasing grip on track. If this results occurs after you have had results similar to example 1 and made an adjustment, don’t worry as it takes a few adjustments and fine tuning to get the set up perfect.

Example 3

Outside Edge

(Degrees C)

Centre

(Degrees C)

Inside Edge

(Degrees C)

Front Left Tyre 72 80 72

In this example you can see that the temperature of the tyre is hottest in the centre of the tyre contact patch. This pattern suggests that the pressure of the tyre is too high causing the tyre to balloon slightly which is the reason for the increased temperature in the centre. The solution to this would be to reduce the tyre pressure of that particular tyre slightly until the values all read very similar temperatures. Even if you have set your pressures first to the manufacturers recommended pressure, they can still be wrong so trust the temperature values to fine tune as they are giving accurate feedback on how the tyre is working with your particular car on that particular track.

Example 4

Outside Edge

(Degrees C)

Centre

(Degrees C)

Inside Edge

(Degrees C)

Front Left Tyre 72 68 72

 

In example 4 you can see that the temperature reduces towards the centre of the tyre. This pattern of values suggests that the tyre does not have enough pressure inside it and is causing the tyre to cave in, meaning that the centre of the contact patch is not coming into contact with the track surface to its full extent. The solution to this would be to increase the tyre pressure of that particular tyre to make the values read as evenly as possible. Again, Even if you have set your pressures first to the manufacturers recommended pressure; they can still be wrong so trust the temperature values to fine tune as they are giving accurate feedback on how the tyre is working with your particular car on that particular track.

Example 5

Outside Edge

(Degrees C)

Centre

(Degrees C)

Inside Edge

(Degrees C)

Front Left Tyre 85 87 89
Front Right Tyre 72 75 82
Rear Left Tyre 72 75 82
Rear Right Tyre 71.5 74 81

In the above example all tyres have been fine-tuned individually to provide an even reading of tyre temperature across the breadth of the tyre. However, as you can see, the front left tyre has considerably higher values than the rest of the tyres. This large increase could be problematic to handling and cause understeer due to the tyre overheating past recommended operating temperature and making the car perform badly even though it has an even spread of temperature and all wheels have good tyre pressures. One of the reasons for this could be that there is too much static mass present at the wheel which means that there is always more mass on the tyre even in straight lines meaning that that particular tyre is always working harder around the full circuit, causing it to overheat. A solution to this would be to corner weight the car to get a more even mass balance across all 4 tyres which will reduce the temperatures of that tyre and improve vehicle grip.

Another solution if the static masses are all close enough to each other would be to reduce the lateral load transfer acting across the front axle. This can be achieved in a few ways all discussed in our load transfer article.

Getting Optimum Tyre Temperatures

If you have adjusted your camber and pressure settings and have achieved an relatively even temperature spread across the tyre with optimum temperature range but the temperatures still aren’t high enough to be what the manufacturer has recommended for the tyre to operate at then toe can be adjusted to increase the temperature of the tyres. Giving a wheel toe in or toe out will force the tyre to distort in a straight line, generating a slip angle and therefore making the tyre do more work, in turn increasing the temperature of the overall tyre. Therefore using toe as a fine tuning tool to perfect the tyre temperature can be done at track side and the temperature can be measured after each adjustment until the target temperature is reached. However, be careful when adjusting toe as it will also affect the handling of your car. Make sure to read our article on “How to Adjust and Tune Toe” for more information.

Using Caster to Alter Tyre Temperatures

If your tyre temperature data is suggesting that more negative camber is required on the outside front wheels but you have a front wheel drive car and  don’t want to lose traction, it is possible to adjust this using caster as well. You might also need to increase front negative camber but have run out of adjustment. Either way adjusting your caster can help.

If you increase the amount of positive caster at the front wheels, this will also increase the amount of negative camber per degree of steering on the outside loaded wheel. Therefore, in a scenario where tyre data is suggesting that more negative camber on the front wheels would be of benefit you can increase positive camber which will achieve this in the corners but will not have excessive static camber meaning that forward traction is not affected.

Finally

With a good test day done and all tyres temperatures recorded and pressures known it is often required to repeat the process particularly if you are racing at a different circuit or in different conditions, (wet and dry) until you begin to build a catalogue of data that can be called upon at each circuit so you know exactly what camber, pressure and mass settings are required on the car before turning up allowing you and the car to go your fastest straight away.

Tyre data is one of the most simple forms of data to collect with relatively cheap equipment so is highly recommended that you pay attention to the setting sand results as it is free speed and faster lap times for the sake of a few simple measurement sand adjustments.

 

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2 Comments

  1. Great article! the information provided is exactly what i was looking for.

    Quick question, have you applied this information and setup changes to karts? We all know karts setup changes can be different to cars for different effects, but a habdy guide like his would help a lot of karters with setup issues.

  2. Hi Cody,

    Thanks for the comment and we are pleased that you enjoyed the article. These set ups are focused at cars however, we are looking at doing a few focused write ups based around karts as they do behave slightly differently. Since you have shown a keen interest in it we will move it up the list of future posts.

    Thanks

    Suspension Secrets

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