You made it to your first track day. It is something you have been waiting to do for a long time, and you finally pulled the trigger, pre-registered for an HPDE event and are at the track. Congratulations! Before the big day, you took the time to wash your car so it will look shiny and fast as you drive around the race course. You find a place in the paddock to park next to another HPDE driver who looks like she has been to the track a few times. Her car has a few track map stickers on the rear window. The two of you exchange pleasantries and start to talk about where the driver’s meeting will be held and then she asks, “What tire pressures are you running?”

You pause for a moment, because the fact of the matter is you don’t know what your pressures are. You know that you have tires and they have air in them, otherwise your pesky tire-pressure monitoring system would have lit up the dashboard like a Christmas tree. But, you don’t know exactly what the tire pressures are and that could be a problem for high performance driving.

Baseline

By opening your driver’s door, you will find a tire loading and information decal. It is a Federal Motor Vehicle Safety Standard that this label is placed on your vehicle by the manufacturer, so I assure you that you can find it.

The good news is the information about what your HPDE tire pressure should be (at a minimum) is stuck to your car inside the driver’s door. Open your door and check the decal to determine what the manufacturer recommends for each tire. In the case of a Ford Fiesta ST, the front and rear pressures are different: 39 p.s.i. front; 36 p.s.i. rear. A general recommendation for track days/HPDE is that tire pressures should be — at an absolute minimum — what the manufacturer recommends on the tire loading and information decal, and should be between two to five pounds above that minimum for each tire. The reason for this is your car is going to be driven aggressively around the track, and for safety reasons NASA does not want you to have a tire come off the bead of the rim because you don’t have enough air pressure inside the tire.

Visual Inspection

The scuff marks on this sidewall are not from bad parallel parking where somebody hit a curb. These tires were run hard at a track day where there was insufficient air pressure in the tire, and the tire rolled over, allowing the sidewall to come into contact with the track surface. Luckily the tire didn’t come off the rim.

Owning a good tire-pressure gauge is a great tool to have with you at an HPDE event. You will find that tires are the most important thing to improving a vehicle’s performance. Knowing what the tire pressure is exactly is important to help you make decisions to raise or lower the tire pressure. I use a digital gauge that has a memory in it to keep track of tire pressures before and after a track session. But you don’t need a super fancy digital tire gauge to do the job. A much less expensive analog gauge works just as well.

This combination tire gauge/pyrometer with memory is super cool, but really not necessary. For HPDE you just need a tire gauge that provides air pressure readings.

It is best to plan ahead and arrive at the track with the correct pressures in your tires, but if you need a few pounds of air you can usually find a tire shop at the track or somebody with an air tank that will be kind enough to help you add a few pounds of air in your tires. After you make your first runs around the track it is crucial to take a look at your sidewalls and see what kind of rollover you are getting. If the tire wear is rolling over right to the edge of the tread blocks on the tire, that is good. If you are rolling over onto the sidewall, you will want to add tire pressure. Start with a 3 pound increase. If your tire isn’t rolling over at all toward the edge you can consider lowing your pressures 2 pounds. When you check your pressures after a track session, they will naturally be higher in pressure due to warm air expanding in the tire. Remember the tire pressures listed on your door jamb are for cold tire pressures. The increase is OK and normal.

This Yokohama Advan A502 tire shows perfect rollover onto the edge of the tread blocks. You can see the tire rolled right to the edge but not beyond, indicating the perfect tire pressure.

Pyrometer Adjustments

Another tool for making adjustments to tire pressure, besides visually inspecting the sidewall rollover and using a tire gauge, is a pyrometer. A pyrometer is simply a thermometer for a tire. You jam a small probe into the tire to measure the heat within the rubber. This measurement is done at three different locations along the tire — outboard, middle, inboard — of the lateral tire tread. Looking at the difference in those temperatures along the tire can help indicate if you have too much or too little air pressure, or if you need to make an alignment change to the car.

A tire pyrometer is simply a meat thermometer for a rubber tire. Jam in the probe and get a temperature. You can see the outboard of this Yokohama tire is at 140 degrees, on a 74 degree day, after a spirited track session.

When using a tire pyrometer, it helps to know what to do with the information. A basic guideline is that if the middle of the tire is hotter than the inboard and outboard of the tire then the tire is ballooning because it has too much pressure inside it. If you find that type of heat data I would lower the tire pressure in that tire. Conversely, if the outboard and inboard of the tire are warmer than the middle of the tire I would add tire pressure.

Here is a chart to detail what pressure adjustments to make based on straight line testing using a pyrometer on a tire.

Once you have tire pressures adjusted for straight line speed based on the chart above, you can begin to drive the car aggressively through a number of corners and then use the pyrometer again to determine if your alignment can use some adjustment. If you have an extreme tire temperature difference — more than 30 degrees — between the inboard and middle of the tire versus the outboard portion of the tire that may mean you need to add more negative camber at an alignment shop. Your tire pressure may be just fine. The outboard heat may be a function of suspension geometry and not tire pressure.

Camber is an alignment term referencing how much a tire leans in or away from your car. As a car leans through a corner camber can assist, or harm, the tires’ ability to be flat on the racing surface. This lack of flatness causes different heat patterns in the tire.

Alignment

If the outboard edges of your tires are running warmer than the rest of the tire, that is a natural thing for street car tires to do at an HPDE event. It is simply a function of the vehicle leaning through the curves, which means the outboard of the tire is doing more of the work through the corners. To try and get more surface area of the tire to help with those cornering forces, you can add negative camber to your alignment. It depends on the vehicle, but these adjustments usually aren’t terribly difficult to make.

We use a Smart Camber tool to measure how much negative camber our car has before and after an adjustment. This stock Ford Fiesta ST has 0.7 degrees of negative camber. Dedicated track cars run between 2.5 to 3.5 degrees of negative camber.

By collecting tire data using a pyrometer and a tire gauge, you may decide you do want to make an alignment change. You may not have the tools or know-how to do it at the track, but you can take the data you gleaned from your time at HPDE and have the car given a performance alignment at a shop before you come back for another HPDE. Chances are you will be back. Track days are addictive.

Stick It

We use a pyrometer every time a car comes off the track to see what the tires are dealing with. It isn’t a complicated process. Simply stick the tire, wait a few seconds to get a consistent reading and then move to the next part of the tire. Three measurements per tire, four tires, means you should have 12 data points after every session.

When it comes to tire pressures for HPDE, start with safety first, ensure your car has at least what the manufacturer mandates and then I would suggest going up from there to start. Inspect your outer edges of your tires after every session. Use your tire gauge to make minor adjustments. Use a pyrometer to fine-tune your pressures for optimal performance. And most importantly have fun on track!

Image courtesy of Rob Krider

6 COMMENTS

  1. I use a different approach. Start at manufacturer’s recommendations. Then monitor your car during the session. If it starts to understeer or plow thru corners or if you tires start to feel “greasy” during the session, you have too much air in your tires. Drop the pressure by 3 lbs when you come in. Continue to drop by 1 lb increments thereafter until you can drive the entire session w/o feeling understeer. Also keep in mind time of day makes a difference due to ambient and track temps increase during the day, so you will be chasing the proper pressure all day. Generally you figure out the ideal pressures when the tires are hot and then you adjust accordingly to that pressure.

    • Hopefully no one in HPDE (with an instructor) skips the important observational and technically true tips from the article!

  2. There really is no answer for ‘what pressure should I run’.

    In my car there is actually a process in the Owners Manual for starting and target temps. But that assumes you are running the OEM tire. Once you change the compound or the size, it’s back to a guessing game. I do think the rest of the article talking about the tire temp zones is great advice that will help you make your tires last as long as possible.

  3. For HPDE: The advice is right on for HPDE. But you are correct, modified equipment comes with specific recommendations because of tire compound and designs including sidewall rigidity, changes in tire sizing to name a few. But the techniques listed wrt to camber, temperature, and observation are time tested and true across the spectrum!

  4. All great data, but I have found that if I run recommended pressure in Michelin PSS they shed large chunks. If I start below recommended such that when warm they are approaching the recommended press I get much better results. The new Michelin PS4s seem to have enough sidewalk stiffness to avoid rolling onto the shoulder with this process.

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