How To Set Racecar Tyre Pressures
You’ve done your testing. Done the maths. You know the cold tyre pressures you need to get the perfect hot pressures on track. You’re ready.
Using your favourite and trusty tyre pressure gauge you set your cold pressures. Head out on track. Run your session. The car feels ok but not great. Back in the pits you discover your hot pressures are way off.
What is going on and what can you do about it? Read on…
Why Your Tyre Pressures Are Off
The fun (and frustration!!!) of our sport is in its complexity. There could be any number of reasons, inside and outside of your control, that mean your hot tyre pressures were not where you expected them:
- a change in weather or track temperature,
- a different driving style,
- more or less moisture within the air in your tyres,
- that damper setting change you made,
- … you disappearing further down the “it could be this too” rabbit hole!
Or maybe its:
- because your cold pressures were not set correctly to start with – even though you are convinced they were!
If you get the procedure for setting your racing car tyre pressures wrong it can mean any work you have done in determining your ideal on track tyre pressures is wasted.
Having experienced some odd and inconsistent tyre pressure behaviour over the years, I developed a little theory I call “sloshy air”.
Imagine for a second what is happening within your tyre when you are adjusting your tyre pressures. Whatever inert gas (air / dry air / nitrogen) you are using, when you add or remove it from the tyre the gas tends to “slosh about a bit” within the tyre. A bit like water in a bucket.
Your pressure gauge takes its reading but as a snap shot in time. With the air “moving about in the tyre”, the pressure reading you get will be slightly different depending on when you check.
You can actually read the tyre pressure twice (without bleeding) and get a big difference. Sometimes I’ve seen a 1 psi difference – and the second time it was higher!
For consistent and accurate readings you want to take your pressures when the air in the tyre is stabilised.
What Are The Best Racecar Tyre Pressures?
If have not seen it, I wrote this article on how to set your tyre pressures right every time so perhaps have a scan if you are not familiar with the challenge (it has a handy calculator too.)
In summary, you can only set tyre pressures when they are notionally cold and you are in the pits. On the track, the tyres warm up and the pressure goes up.
For best performance, the hot pressures are what matters. The article shows you a method for setting cold tyre pressures so that you can reliably control what the hot pressures will be on track, and, therefore, better control your performance.
It is quite a bit of work to do properly. You, therefore, do not want to waste that effort by not actually setting the cold tyre pressures to the values you intended.
So, assuming your tyres are already nicely mounted on rims and using your suitably calibrated digital tyre pressure gauge, here is a …
6 Step Procedure For Setting Racecar Tyre Pressures
The approach simply involves adding pressure to the tyres, to a little over your cold target, and then slowly bleeding the tyre down to your cold target pressures.
It goes like this:
- Pressure to cold target +2 psi
- Bleed a bit
- Wait (Count to 5)
- Bleed a bit
- Wait (Count to 5)
- Final bleed to cold target
Do This And Always Start From A Known Baseline
If the pressures are set reliably, you are starting from a known baseline each time.
You can then more robustly start to determine your hot pressures using mine or your own approach to that.
Yes it is a detailed (arguably OCD style) approach to adopt. But it is easy.
With tyre pressures being so critical, this a simple procedure will ensure you are always setting your tyre pressures as accurately as possible.
Enjoyed this? Check out these other articles:
Want to take the guesswork out of setting your tyre pressures? Try this article including a free calculator: https://www.yourdatadriven.com/how-to-set-your-racing-car-tyre-pressures-perfectly-every-time/
Wondering what the tyres are actually doing? This article should help your visualisation:https://www.yourdatadriven.com/tyre-slip-angle-explained/