At what point does a difference in your hot tyre pressures make a real world difference to your car’s grip?
Is it 0.001 psi? 0.1 psi? 1.0 psi?
If you’ve previously read this article or own a copy of my Track Tyre Tuning Guide, then you’ll have an idea of what hot tyre pressures to be targeting for your car.
However, in practise, despite all your best efforts, it is unlikely you’ll hit your target hot tyre pressures, with pin-point accuracy, every time you go out.
And that’s ok… no-one does!
But how close do you need to get to your target hot tyre pressures for most grip?
In this article you will find an effective tolerance band you can aim for to get the most from your tyres… and why it is ok. Read on.
Why Its Hard To Hit Your Hot Tyre Pressure Targets
Simply because there are so many variables affecting the condition of your tyres during and after each run.
For example, air leakage (via valves, maybe even bead), moisture in the air, your tyres number of heat cycles, driver in-lap, driver “style”, track surface, track layout, even your spring and damper settings… the list goes on… as I’m sure you can imagine.
Frankly, once you start to look into the life of a track tyre, I think its amazing we get this stuff anywhere near!
How Grip Changes With Tyre Pressure?
Luckily with tyres – and with many things on your race car – being close to your target, is often good enough.
Take a look at this illustrative chart of tyre pressure and “grip”:
Your goal is to get your tyres in their “happy place” (phrase credit: Damian Harty). Where these happy places are depends on the tyre you are using. But in my experience all tyres show a similar trend of gaining more grip with pressure initially, plateauing a bit, then losing grip as the pressure continues to increase.
There are a few different reasons why this happens, however, in the context of this article, what it means to you is that it is fine if you don’t hit your hot tyre pressure target to within 10 decimal places…
TESTIMONIAL:
Your Track Tyre Tuning Guide reinforced information that I had, but it provided a lot more detail, and discussed how to approach things in a way that makes the results more reproducible and transferable to new situations. I have been successful in that I have found pressure settings that make my car behave as I want. I also get even tire wear and similar temperatures across the tire tread.
Dan Reese (Track day Driver)
What Hot Tyre Pressure Tolerance IS Good Enough?
From my own experience, and from discussions with other pro race engineers (hat tip: Jeff Braun), you might find these bands a useful guide:
- Within 0.5 psi (or 0.03 bar) is Good.
- Within 1.0 psi (or 0.07 bar) is OK.
- Outside 1.0 psi (or 0.07 bar) needs your attention.
For example, if your hot tyre pressure target is 29 psi (or 2 bar):
- Good is between 28.5 – 29.5 psi (1.97 – 2.03 bar)
- OK is between 28.0 – 30.0 psi (1.93 – 2.07 bar)
- No good is anything above or below the OK range.
Finding Your Target Hot Tyre Pressures For Most Grip
Again, if you’ve not read this article or own a copy of my Track Tyre Tuning Guide, take a look. The table gives you a starter for 10 based on your vehicle weight.
Using this information, you can start to iterate towards the best pressures you feel will suit your car on any given track.
You’ll now know you in about the right place when 0.5 psi either way doesn’t start to feel any different.
There is a little more going on (these are tyres we’re talking about!) but hopefully this should be enough to get you maximising your tyre grip – and minimising uneven tyre wear…
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