Tire pressures are so important to racing of all types, not just karts, and we want to give you a quick guide on how tire pressures work. We are going to cover testing to find your ideal tire pressures, and how different tire pressures affect your kart’s handling. We will also have a look at how the pros handle their tire pressure settings.
There are many different variables when it comes to tire pressures. But it can be quite a simple set up element to get right. Furthermore, you can use some more advanced techniques to get more from your tires by understanding them.
Why Are Tire Pressures Important?
Kart tire pressures are so important is because your tires are the only part of the kart that touches the road. So essentially, they are what translates your actions into kart movements on the track.
Many people often mess around with their chassis setups because they are not happy with how their kart is handling. Sometimes it’s as simple as having the wrong tire pressures, so never overlook this small setup element.
Tire pressures can control how much grip your kart has and for how long. You can use different tire pressures to determine how quickly your tires heat up. This is important, and we will go in depth about it later on.
If you take a close look at what the professionals do, they take it even further by adjusting each individual tire’s pressure depending on the circuit and the weather. Most people though have a standard setup throughout all 4 tires.
Tire Pressure Basics
So, the general rule around tire pressures is that they have a specific operating window. This window is the PSI that will give your tires the perfect amount of grip. Your tires will not have the same PSI as when you started driving though (more on that in the next section).
This means that your tires have a ‘cold’ pressure reading and a ‘hot’ pressure reading. Your cold reading is when the tires are cool and have not been used yet. The hot reading is when you have just come off the circuit and your tires are hot from driving.
Your hot pressure reading will be a higher PSI than the cold pressure reading. So, let’s say that you are about to go out on track and you set your tire pressures to 10 PSI all around. After 15 laps of driving you come into the pits and the first thing you do is take a reading with your tire pressure gauge.
Now, not only will your tires be around 3 PSI higher than their cold state, you will also notice that all 4 tire pressures will give you different readings. This will be important later; it’s what professional karting drivers focus on when it comes to their tire pressures.
Generally, higher tire pressures (11 PSI and over) will give you more grip earlier on. They will heat up quicker and reach their optimum operating window much faster. This makes them ideal for qualifying runs where you won’t be driving on the limit consistently, but rather be looking for one flying lap at a time.
The disadvantage though is that these pressures will cause the tires to overheat quickly, and you will probably find them losing their grip after about 7 or 8 laps of consistently hard driving. In addition, your tires will also be wearing out faster because of the overheating.
Of course, you can’t take your tire pressures too high, otherwise the kart will become unstable because there is less tire contacting the circuit. There is also a maximum allowed PSI due to safety, which varies depending on the manufacturer.
Lower tire pressures (under 11 PSI) give you the opposite effect. These tires will take longer to heat up and reach their operating window. So, you might find that you are lacking grip for 5 to 6 laps before the tires really start to ‘switch on’.
This makes these pressures ideal for race conditions, as you will start to find your speed towards the middle and end of the race, rather than having your pace dropping off towards the end. It has to be said that driving on these cold tires at the start of a race can be difficult for beginners, so make sure you practice and get it right first.
I should add that all tire manufacturers have different operating windows, so the PSI may vary from Dunlop tires to Mojo tires. Some manufacturers have a really good spreadsheet on their website of recommended tire pressures based on temperatures and compounds.
Tire compounds also have a slight effect on the tire pressures you should run them at. In general, harder tire compounds will require higher pressures than soft compounds. Same goes for wet tires, which are run much higher than dry compound tires.
How Temperature Affects Tire Pressures
If you have done some tire pressure testing in the past, you may have noticed that your tire pressures fluctuate. This is because heat in the tires will cause the pressures to rise. This could be something as obvious as the tires being in the sun, or something as small as the ambient heat rising around the circuit.
This is important because not only will your tire pressures rise as you drive you kart (due to tires heating up from friction with the track surface) but as you progress throughout your race day, the ambient temperature around the track might change. Furthermore, the temperature of the tarmac on the racetrack will also rise as the sun shines down on the circuit.
So, if the temperatures are soaring and the day heats up, you will want to keep your tire pressures slightly lower in their cold state in order to ensure that their operating temperatures don’t become too high. Another thing to keep in mind is while sitting on the grid, your tire temperatures might rise while in the sun.
Or it might be the opposite, it might be a cold and cloudy day, and the ambient temperatures stay generally in the same cool range. You will most likely be adjusting your tire pressures based on this during the day. But there is another variable to keep in the back of your mind.
As mentioned earlier, you will need to adjust your tire pressures based on how long you are going to be running your kart for. Some sessions are shorter than others and require more of a sprint than an endurance factor.
If you need the tires to get to work quickly and give you all of their grip for a short amount of time, you will need to push your tire pressures up higher. This is ideal for qualifying and warmups where you can set your laps at your own pace and will have time to cool your tires down between laps.
If you are going into a sprint final, and you will be racing for 18 laps straight, you will want to set your tire pressures much lower than they were for qualifying. This will keep your tires in their operating window for the entirety of the race, rather than overheating and losing their grip halfway through.
Advanced Tire Pressure Settings
When it comes to the professionals, they look at the smallest possible detail in order to make up those tenths of a second that can help them to take the win. This method helps them to achieve a balanced hot pressure amongst all 4 tires, to keep their grip levels even.
As we know by now, each tire works differently on the circuit. For example, we know that the outside rear tire will be working the hardest of all the tires. So, if we have a clockwise circuit with more right turns than left turns, we know that the left rear tire will be working the hardest.
This means that the left rear tire will be generating the most heat of all 4 tires and is most likely to overheat and lose grip first. Now we can adjust our tire pressures accordingly. The left rear tire will be hottest; therefore, it will have the lowest cold pressure measurement.
The second hottest tire on the kart will be the inside rear tire. This tire will be taking the force of the left hand turns and is also part of the driven wheels, so will in general become really hot. This tire will have the second lowest tire pressure.
Next will be the left front. This is the outside tire once again, so it will be heating up more than the inside tire will be. This is going to be a slightly lower pressure than the inside front tire. But also remember that your front tires will be cooler than the rear tires, so you will want to push their pressures up slightly higher.
Finally, the right front tire will be the coldest tire on the kart. You will want to keep this tire pressure as the highest cold measurement because it needs to keep up temperature with the rest of the tires. If this tire becomes too cold you will lose your front-end grip going onto right-handed corners.
So, let’s look at this practically. You have just come off your last heat which was 15 laps. You started this heat with 10 PSI on both your rear tires and 10.5 PSI on both your front tires. Your hot pressures as you came off the track were between 12 to 13 PSI.
The tyres switched on at around lap 4 or 5 and started to overheat a bit towards the end of the race at around lap 14. The tires lasted pretty much the whole race which is great, and they didn’t take too long to heat up. You had good grip throughout the race.
Next up is the main race, which is 18 laps. But this time you want to adjust your tire pressures according to how much use you get out of them in order to balance the kart more and keep your grip levels stable. This race is also 4 laps longer, so you will need your tires to last a bit longer than the previous heat.
Remember, it’s been about an hour since you last drove, so now your tire pressures are at 10PSI due to the rising ambient heat.
These are example tire pressures we may be looking at for the next race:
- Front Right – 9.57 PSI (coldest tire, highest pressure)
- Front Left – 9.28 PSI
- Right Rear – 9.14 PSI
- Left Rear – 8.85 PSI (hottest tire, lowest pressure)
Tire Pressure Testing
As with any setup in karting, it is important to find what works for you. Your driving style will determine whether you can quickly get heat into your tires or whether your tires will overheat earlier than others.
It all depends on how smooth or aggressive your driving style is. So that is why it is important to find your tire pressures, rather than just copying from the guy next to you. Copying someone else can give you a good baseline to work with, but it might not work for you at all.
The best thing to do is to take a full day of testing just to find your ideal tire pressures that work best for you. Be sure to start the day by noting down the weather conditions and, if you can, the track temperature. Having these reference points can be useful to you in the future.
The goal for this test is not to try and set a personal best lap time, but rather to find out how your tire pressures are affecting your kart. Don’t push too hard, and try to be as consistent as possible. Try to also test different racing conditions such as qualifying laps, full race lengths etc.
Start with high tire pressures, for example 13 PSI, and try to focus on when your tires reach their optimum grip and when they start to drop off. Use your lap times to identify exactly when this happens to the tires. This is where being a consistent driver becomes extremely useful, because it will be more obvious to spot your tire conditions in your lap times.
If you know that you can set your lap times all within 0.100 of each other, you will see an obvious decline in lap times when you have cold tires at the start of the session, and when your tires are overheating at the end of the session.
Directly after coming into the pits off the circuit, take your tire pressure measurements again in order to get a hot measurement. This will give you an idea of how much your pressures rise while out on track.
With each run drop the PSI down by 1. Keep going lower with each run until you find the lowest pressures you can run on. Basically, keep taking the pressures down until your lap times become slower than the run before. Remember, it might take longer to reach fast lap times, so it doesn’t automatically mean that those pressures are slower than before. Make sure you get the tires working properly.
Once you have found that sweet spot for your cold PSI measurement (hint: it is normally around 8 and 10 PSI for most normal conditions). From there go up by half a PSI to see how that affects your lap times. From there, you can fine tune to find your ideal spot.
Write down what those tire pressures gave you. For example, on the 13 PSI run, I might have found that the tires switched on about 3 laps into my run, and then dropped off at around 7 laps. It would be useful to make a spreadsheet for this, for example:
Fastest Lap Time
Try to map this out for yourself in an easy way so that you can easily refer back to it in the future. This way when you are in the middle of a race weekend, all you need to do is check the temperature and you already know exactly what PSI you want your tires to be on.
Another tip that I learnt from my karting days is something that can be used, but is not always 100% accurate. This is more of a quick cheat rather than a full understanding. The idea is to find your tire’s optimum operating temperature and PSI as quickly as possible. So, you will set your tires all at a standard base value, let’s say 8 PSI.
Next you will take your kart out on track and drive it until you feel that it’s running at its maximum grip. In other words, the tires have reached their ideal temperature. At this point you go back into the pits and measure the hot tire pressures. From there lower the tire pressures to the optimum PSI that is recommended by the manufacturer. You will notice that all of your tires will be different because they all work different amounts on track.
Once all four are set to the same PSI on hot measurements (for example 14 PSI) you let them cool down. From there you take your cold measurements and write those down. These are then your recommended cold tire pressures.
I hope that this article has helped you to understand tire pressures more. It might sound like a lot of information, but once you have done a bit of testing and played around with your tire pressures a bit, you will find what works for you.
From there it becomes easier to adjust according to temperatures and track conditions. This is especially easier if you have a set up journal where you have all of your testing recorded.