Why You Need to Understand Tyre Pressure While Fine-Tuning Car Balance

Blame it on oversteer or understeer, and you are ready to be knighted as a track rat. While I do not condone pseudo-knowledge, I can’t turn a deaf ear to how often the topic gets discussed in the pits at a race track, especially from the mouths of rookies who decide to tackle the problems with the wrong approach. There are plenty of approaches that might tackle the issue, but the answer does not necessarily lie with your suspension, alignment, or even your driving technique. What if I told you the approach can be as simple as learning about tyre pressure?

We all know the importance of tyres and tyre pressures, but all my track visits have noticed how easily it is neglected. Tyre maintenance should be on the same page as your core mechanical maintenance, and there is simply no choice. I figured there is a need to say this, but tuning your tyre pressure is not all about tuning sidewall flex as it is tuning it for feel and grip. However, before you even begin with any tweaks on your tyres, there is an absolute need to understand what you want out of it.

Hot Pressure is the Key

A common sight is to see drivers do a session at the track and check tyre pressures when the tyres are hot. While cold pressure is undoubtedly a starting point, hot pressure is where all the tuning is done. Ideally, I stop checking my tyre pressures once I have hit the sweet spot for feel and feedback. But getting there is nothing short of a black art that takes a little bit of time to master. And there are a few reasons as to why that is the case.

Tyre pressures require as much attention as the roll centre and sway bars of your car. However, understanding it is much more difficult, considering the highly specific nature of tyres. Like a snowflake, every tyre differs in construction or compound. This varied construction is what makes tyre tuning more of a practical issue rather than a mathematical one. However, on any tyre, pressure affects contact patch size, slip angle tolerance, and most importantly, the contact patch.

Slip Angle Doesn’t Equal to  Drift Angle

Slip angle, unlike the common belief of being similar to drift angle, is the effective flex of the tyre under cornering forces. In more understanding terms, it is essentially the difference between steering angle and the direction of travel on a given tyre. This can be massively affected by pressure tuning.

It would be pretty difficult for me to provide a baseline figure for everyone out there, considering how it differs for every car and every tyre. Having mostly driven front-engined cars at the track, I usually begin with 30 psi cold pressure. This may differ a bit for rear-engined and mid-engined cars, which usually take staggered pressure due to their weight distribution. If this doesn’t work for you, the best solution is to clear the whiteboard and start again from the factory pressure and continue decreasing it from there.

Focus on the Feel

A set tyre pressure shouldn’t be gospel for your car. In the same breath, I would also suggest not to depend on maths so much but instead depend on the way it feels. At the end of the day, it’s only about finding the Goldilocks’ zone where the tyres agree to do the job. What works in your favour is that tyres are incredibly sensitive to pressure changes. Drivers can see notable changes in the drive with the change of a single PSI.

I would also advise drivers to only mess around with one axle at a time. If you don’t feel much difference, bring it back to the baseline and start with the other axle. In technical terms, I agree with this engineering journal piece which explains why having lower rear tyre pressure is beneficial to handling, allowing progressive breakaway and a softer sidewall and giving more room for some rotation and sensation of rotation.

Do you Need to Overinflate?

So what about overinflating than the factory-recommended pressures? Well, in my personal experience, that has never worked out well. You need to understand that the priority for car manufacturers will always be driver’s safety, and I am including performance cars in the list as well. The recommended tyre pressure is just one of the many aspects that engineers use to make the car more inert.

Summary

In my time at the track, I’ve seen how tyre pressure, often overlooked, is crucial for performance. It’s not just about mechanical adjustments but finding the right feel and grip. Hot tyre pressures post-session reveal much about car-track interaction, requiring attention to detail akin to mastering a black art. Tyre construction varies, affecting handling and necessitating personalized tuning. Starting with a basic psi and adjusting based on feel rather than strict calculations leads to the ideal balance. Remember, safety comes first, and sticking too closely or straying far from recommended pressures can have significant consequences. It’s all about hitting that perfect pressure sweet spot.