KART TYRE TEMPERATURES AND PYROMETERS
"Knowing the operating graph associated with the temperatures of your set of tyres is essential to getting the most from your kart"
The temperatures expressed in degrees centigrade are shown on the y-axis, while the friction coefficient is shown on the x-axis. 3 colours can be seen in the area of the graph: blue indicates the range of temperatures below the optimal range, therefore temperatures too low for maximum grip/friction; green, between 75°C and 90°C, indicates where the rubber reaches its highest grip/friction standards; red, once the critical threshold of 95° is exceeded, indicates where a drop in performance occurs which is accentuated gradually with an increase in temperature.
Tyres are the only point of contact between the kart and the track: using them to the fullest can really make a difference in trying to achieve the best performance. To do this, it is necessary to identify elements (the feelings of drivers, the experience of the technicians, the empirical measurements, etc.) to search for any problems and, above all, to then resolve them. One of these elements is the analysis of the temperatures of the tyres, a vast topic in which a multitude of factors come into play. A few examples? The choice of the right pyrometer, suited to your needs, or the use of the correct method of collecting and reading the available data. Working on this field can be worth several tenths in terms of lap time. This is why we asked Pascal Cardinale, owner of Prisma Electronics, (a company specialised in the production of digital pressure gauges, pyrometers and chronometers for the motorsport industry), to guide us, with advice and clarifications, in regard to tyre temperatures for karting.
1 Why it is so important to monitor the temperature of tyres?
Temperatures are the litmus test of the tyre pressures and set-ups of a kart: knowing them can help a lot about understanding your vehicle and preparing it for tests or racing. Each tyre, taking into account the manufacturer and compound, has an operating temperature range in which the rubber generates its highest standards in terms of durability and performance. Knowing the operating graph associated with the temperatures of your set of tyres is essential to getting the most from your kart. All temperatures below and above this range, in addition to affecting the structure of the tyre, by decreasing the level of grip with respect to the asphalt, negatively affect performance and prevent you from racing or working optimally. For example, an increase, even of just 5°C in tyre temperatures beyond the ideal range of use generates a sudden loss of grip. At that moment it will be impossible to lower the temperatures simply by changing your driving style: if you are involved in a test, you will have to stop and change the set-up or the initial pressures; if you are racing, however, the final result will be compromised. The difference between throwing away a set of tyres and making the most of them is therefore the result of careful analysis of their temperatures.
2 How do you know the correct operating temperature of tyres?
Each manufacturer and each compound have different optimal operating temperatures, which is why it is sensitive data that must be provided by the manufacturer. In my experience, a range that is almost always universally valid is from 95°C to 85°C. It must be clarified that we are talking about a range since each part of the tyre is subject to different temperatures, so to analyse the condition of a tyre the temperature should be measured in 3 specific points on the tread: internal (T1), central (T2) and external ( T3). Since karts don’t have a suspension, the traction generated by the engine tends to cause the axle to flex. This movement affects the inner part of the rear tyres, which are most stressed in that area. The same also happens on the front axle, where the camber angle tends to stress the inner side of the tyres more. This is why temperatures should be increasingly higher towards the inside of the rubber. To summarise in purely indicative terms, a tyre that works optimally should have a T1 at 95°C, T2 at 90°C and a T3 at 85°C: temperatures, therefore, within the right operating range and which show a linear decrease from the innermost to the outermost point.
3 Are there also visual indicators that can tell us that the operating temperatures of the tyres are lower or higher than the optimal values?
If you do not have a pyrometer available, you will have to rely heavily on sight and touch to understand how the tyres are working. Let's start with clearly identifiable visual examples. Tyres with operating temperatures well below the optimal values will tend to slide a lot when cornering. This sliding is due to the lack of the right grip and generates many small tears on the carcass (so-called "graining"). In this situation, not only will the tread be damaged, but it will be really difficult, if not impossible, to reach the right temperatures. Temperatures well above the optimal ones will instead lead to "blistering", i.e. the detachment of parts of rubber from the tread due to the appearance of air bubbles, due to high temperatures inside the tyre. Unlike graining, there is no way back from blistering, since it will not only be the performance that will be compromised, but also the life-cycle of the tyre itself, which will suffer serious structural and irreversible damage. Even hand contact can help to understand how your tyres are working and especially if they show uniform degradation. For example, a depression in the central tread band may occur: this phenomenon occurs more when the rubber is inflated with very low pressures or when the rubber does not have a particularly rigid structure. This will lead the two shoulders of the tyre to be at optimal temperature levels, unlike the centre which, not reaching the temperature, will degrade more, creating a depression. An example of temperatures associated with this phenomenon can be: internal (T1) 93°C, central (T2) 89°C and external (T3) 91°C, therefore a non-optimal range. The opposite case is represented by the appearance of a central hump on the tread; in this case the phenomenon is generated by excessively high operating pressures and by a structure of a tyre that is not sufficiently rigid. This could lead to a high degradation of the side shoulders which, despite the central band being at the right temperature, exceed the recommended range and will wear out much faster. In this case we could have the following indicative temperatures values: T1 100°C, T2 90°C, T3 95°C.
Example of rubber with a central depression. The shoulders of the tyre, having reached the temperature, show a uniform degradation while the central band has undergone a greater degradation than the rest of the tyre.
4 What affects tyre temperatures the most?
Tyres are the only point of contact between the kart and the track, so they are very sensitive to the situation in which they operate. I would say that the main factors affecting their performance are the air temperature and that of the asphalt. Asphalt, in particular, is the component to be taken into consideration: low surface temperatures, in fact, can lead to tyre slippage resulting in graining, while very high temperatures can lead to blistering. In addition to the temperatures, another element to keep in mind is the condition of the track: a very worn track or an asphalt that is too new will not be able to ensure a high grip and this will make it more difficult to reach the right temperature range. Vice versa, a new and fairly rubberized track will have high standards in terms of grip, so it will be easier to reach the right temperatures, but also to exceed them if the right precautions are not taken in terms of cold tyre pressures.
5 Is temperature monitoring important for everyone in the karting world? Are there differences between beginners, practitioners and experts?
Beginners and common practitioners can limit themselves to monitoring hot tyre pressure, which usually is around 0.95 bar, to get information about the correct functioning of their tyres. Let's say that a tyre that works correctly in relation to the right pressure will have far fewer problems related to temperatures. Experts, especially those who need to get the most out of their karts, should instead take the analysis of tyre temperatures very seriously. Having said that, it is the curiosity of the individual and the need to solve a problem in terms of performance that can lead to wanting to use a pyrometer for measuring temperatures. As previously mentioned, pressure can tell us that the tyre is working correctly, but it is still an overall datum of the tyre. It could be the case that, even with the right working pressure of the tyres, tears are created on the tread or an uneven degradation occurs which could lead to the requirement of carrying out different analyses. To proceed with these analyses, you need to collect more information: and this is where the pyrometer comes into play, because the main information for proceeding with further analyses can only be collected by using an instrument for measuring temperatures.
Temperatures are the language used by tires to communicate fundamental information about: pressures, set-ups and problems relating to the Kart.
6 Can you give us an example of a problem with the tyres solved using a pyrometer?
A striking example happened to me two summers ago: on a day with high ambient temperatures and with a track around 40°C, I noticed that the left rear of my kart tended to slide a lot in support, so that it was not possible to achieve the right grip. Therefore, I measured the tyre pressure, but I realised that for all four tyres the data obtained was in line with that provided by the manufacturer of that set of tyres. At that point I checked the temperatures and it emerged that the average temperature on the tread of the tyre in question (rear left) was around 115°C, a figure not due to either the set-up or the cold pressure settings, since all the tyres were working in the right temperature range. Therefore, the only variable, was the presence of the XXL size radiator, which on such a hot day conveyed too hot air flows on the tyre tread which, precisely because of the high surface covered by the large radiator, was not hit by fresh air like the other tyres. Once the problem was identified, it was much easier to find a solution: reduce the size of the radiator, so as to allow better cooling of the rear left tyre. Without the use of the pyrometer, I probably would never have found the problem and its solution, or before finding both I would have spent much more time.
