How to determine correct track tire pressures

This post needs to be updated with the lastest education from Greg Fordahl. Simplest explanation is that center temps will only tell you if you are wildly off. Then you need to work harder from there.

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This topic has come up at almost every track day I’ve been to this year. And just now I had someone in a corvette forum telling me I was wrong in my recommended hot tire pressures. So I’ve copied my post I put over there to here.

If you are running the stock tire that comes with the car, which I am. You will find that if you correctly determine hot track tire pressures using a pyrometer that the optimal pressure you get will be very close to the recommended OEM cold tire pressure. Why is that? Because the OEM tire pressure is generally set to put as much tire tread to the ground as possible. When the air in a tire heats up the tire expands slightly. That will cause the center of the tire to bow out slightly. If it the center bows out then you will not be using the outer portions of your tire to their maximum affect. You will also get uneven wear on the tire. During normal street driving a tire heats up very little. If you set to OEM cold 30 they may go up to 32 as a max. Hence you are still using the tire effectively even after they warm up.

When you take a car to the track and drive it hard. The air in the tires heats up high amount. For example if you start at cold 30. Do a 30 minute session and then come in and check your tire pressures. You will likely find that they are somewhere around 40+ on the Sport Cups. At that temperature you are riding around on the center portion of the tire.

How do you know that is happening? And how do you measure it? You use a pyrometer. A pyrometer measures heat in the tire. This is what one looks like: http://2.bp.blogspot.com/-eCo_YVSlkf…1600/50640.jpg. I prefer the needle kind for tire temps. I don’t think the infrared works as well. You take the pyrometer and measure tire temps in both outer portions of the tread and the center. So if you do that let’s say you get the following numbers: left-100 center-120 right-115. You can see that the center number is higher than both outer numbers. Than means you need to lower your tire pressure because the center is being overused. The optimal pressure will give you a center temperature which is the average if the two outer temps. If the center is lower than the average than your pressures are too low. These three temperatures can also tell you a lot about alignment but that is a whole other discussion.

The way to test this is to do a session and then come in after your last fast lap without any sort of cooldown. You don’t want the tires to cool down too much until you take the temps.

If you have a lot of track or race experience, on street tires you can feel the difference in handling of 1-2 pounds over. it is significant. On slicks you can start to feel things at even lower differences than that. Correct hot tire pressures are hugely important to going fast.

The amount that the air in your tires will heat up varies tire to tire. That means although it’s easy with a pyrometer to find the hot pressure, it takes some trial and error to find our how much air you should pull out of tire before your first session to hit your hot pressure. One way to get a goof starting point is if you’ve gotten the tire to their optimal hot pressures. Then drive the car home on that. Then next morning measure the pressures as it sits in your garage. They should have full cooled and that number gives you a good starting point. I would start out 3 pounds or so higher than that and work your way back down after each session.

One Response to “How to determine correct track tire pressures”

  1. Don says:

    Important note: Some tires heat up like crazy and your cold pressure will be way lower than your hot. I wouldn’t drop more than 5-6 pounds from OEM cold as a starting point on you first session. Then you can remove the rest after the first session. If you drop too much out to start than you need to be very careful to warm up the tires slowly.

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