Determining what Tyre Pressures to use

Friday, 29 October 2010 13:37

From my experience working within a race team I quickly learnt that tyre pressures are more important than they first seem.

You may have all the best parts and equipment, but the potential that both you and the car can reach is limited if you do not take into account tyre pressures. So let’s start with the basics.

What is tyre pressure?
Tyre pressure is exactly what it appears to be, the pressure of air within the tyre. To measure this pressure an instrument called a tyre pressure gauge is needed. This piece of equipment will become your best friend in determining your optimum tyre pressures. The measurements which are used to measure tyre pressure are PSI (pounds per square inch) and BAR.

Why are tyre pressures important?
By gaining optimum tyre pressures you will provide the car with the greatest ‘contact patch’ (the area of the tyre which is in contact with the track surface). The ‘contact patch’ is where the tyre gains its grip from and the more the better in this aspect. Having under inflated tyres will result in the car not being supported by a ridge tyre and you risk bottoming out on the track. However, having over inflated tyres will result in a smaller ‘contact patch’ and therefore less grip.

Now you know the basics let’s move on to the race inspire tyre pressures. Depending on what car and what tyres you race on will depend on the final tyre pressures you use, but the basics for working them out will be the same. Find out from fellow drivers and teams in your championship or the manufacturer of the tyre you are using what they suggest the optimum hot pressure is and make your decision based on this. Most will use the same optimum hot pressure and have different starting pressures based on driving styles or car characteristics.

Finding your starting pressures will take practice and as they say practice makes perfect. My advice is go to a test day and spend time working on these pressures. Go out on track and complete a few laps to warm the tyres. Check the pressures when hot, keeping a note of them for future reference. Set them to the optimum hot pressure, allowing for a slight cooling unless you have convinced a friend to come along and take them while you sit in the car. Complete a few more laps, come in and let them cool completely. Check the pressures when the tyres are cold and you should have your starting pressures. Start the next session with these starting pressures and see how they go. You may need to tweak them slightly but the golden rule is to keep a track of all the changes you make! You do not want to find your perfect pressure and not remember how you got there. Last tip for tyre pressures, use the same tyre pressure gauge all the time as different makes may read pressures slightly different and a small different might make the difference between 1st and 2nd.

For example, take a Locost at Brands Hatch. A Locost’s optimum tyre pressure when hot is 23psi (on Yokohama A539 tyres). So if we have starting pressures of 21psi all round and find all are 23psi when hot apart from the left rear which is 24.5psi, we need to take the 1.5psi off the tyre when hot. This will affect the pressure when the tyre has cooled. When we take the pressure once cooled, we find it now being 20psi giving us the new starting pressure for the left rear. By Samantha McVey

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