Whether you road race, autocross, run in Time Trial or HPDE, your goal is always to extract maximum performance from your car. Driving and car setup are two key elements that lead to improved performance. Both require insight, dedication and hard work. Of the two, driving is somewhat easier to understand from a learning perspective. Car setup is more difficult because racecar dynamics is a complex subject few racers understand. And unfortunately, race engineers in all of the various flavors, tend to complicate the situation, especially in the modern world of specialization.
When I was studying mechanical engineering, a wise professor made an interesting comment: “If you are a hammer, every problem looks like a nail.” His point was that to be a really good engineer, one must see the whole picture and consider all options when trying to solve problems. That allows the engineer to make the best compromises that lead to improvements.
Throughout my career, I have worked with many race engineers from shock companies, tire companies and suspension companies. Without fail, every engineer from every type of company shared a single trait: Each one wanted to “cure” a handling problem with their product. Shock guys wanted to fix every ill with shocks, tire guys with tires and spring guys with springs. But none of them looked at the big picture. What is happening to the entire platform?
I learned early on that the best way to understand what is going on with the handling of a car at — or near — the limits of tire traction is to monitor tire temperatures. The first step is to analyze the temps at each tire. By taking three readings across the surface, you can optimize that tire’s traction, meaning that the entire contact patch of the tire is working to the maximum. This is done by adjusting tire pressure and camber. Until each tire is generating the most possible traction, the overall performance will not be at its peak.
I started doing this when racing stock cars on oval tracks and it is an easy and precise way to learn about what can be done to maximize tire traction of the whole platform. You can tell if a car is understeering or oversteering in general or overall terms. You can tell if the cross weight percentage is correct from diagonal average temperatures and you also can tell if you would benefit from moving static weight around in the car (static weight distribution). What you cannot monitor is transitional handling, which happens over a very short period of time. Shock absorbers have the greatest impact on transitional handling characteristics and a good driver is the best tool for getting shock valving properly set, followed by a good data-acquisition system. Short of that, taking tire temperatures is a good way to gather data, and is a low cost data-acquisition system.
There are several ways to alter handling balance. You can change spring rates, bar rates, cross weights, suspension geometry, shock rates, roll center location, tire pressure or static weight distribution. But handling balance is only part of the story. The goal for any racing situation is get maximum traction from the tires, ideally all of the tires. Each tire is capable of making a fixed amount of traction on a given car under given track conditions. Nothing you do can cause the tires to make more traction than that limit. But how you tune the chassis and work the tire contact patches will determine how much traction you actually have available. The goal is to minimize the loss. A key way to do this is to optimize the tire’s contact patch with the track surface and optimize the load on all four contact patches relative to a given spot on the race track, corner entry, midturn or corner exit.
While not a factor for street driving, any form of motorsports competition requires the optimization of tire traction at each tire contact patch and at the highest possible level of grip from all four tires. So how do you know what’s going on? The best way is to monitor tire temperatures. Tire temperatures tell the traction tale effectively. The good news is, tire pyrometers are inexpensive, easy to use and the most important tool you can own to get a car setup dialed-in. But there are some techniques you need to know to get the best possible data. So let’s look at how best to take tire temperatures.
Taking Tire Temperatures
Here are some important tips for taking tire temperatures:
- Always take temperatures, even if the car is out only for one or two laps.
- Take temps after the event when possible.
- Record temps and pressures.
- Use a tire temperature chart.
- Take temps at three spots on each tire about 1 inch from each edge and in the middle.
- Always take temps in the same lateral spot on the tire tread.
- Always take temps in the same order on the tire (either inside or outside first, then the middle.
- Always start at the same tire.
- Always go around the car in the same direction.
- Move fast. Tires cool quickly, which results in inaccurate readings if too much time elapses. The heat also will equalize across the tire. The temperature difference decreases as time passes.
- While moving fast is important, make sure that each reading has stabilized before moving the probe to the next spot. Removing the probe from a spot too soon also can cause inaccurate readings.
- Unless you use a memory pyrometer, have one crew member record temps while the other takes the readings. If no crew member is available, the driver can record the data while sitting in the car.
- The fourth tire in the sequence will lose heat by the time the temps are taken. After you measure the fourth tire, check the first tire again so that you can see the change in temps from the first readings. This will give you an idea how hot the other tires were while the first tire was being checked. This is an important part of the procedure.
- Take tire pressures right after taking the temperatures. Go in the same order. Also record pressures just before the car goes onto the race track so that you can measure the pressure gain.
- Once in a while, check tire pressures after 5 to 10 minutes. If the pressure is higher than when the car entered the pits, the extra heat causing the pressure has come from the brakes. A long time ago, tires were known to blow out sitting in the pits due to pressure buildup from brake heat. If the pressures go up, you have a potential brake heat problem.
- The needle on the probe should be inserted into the tire tread. The heat is more stable and cools more slowly below the tread surface.
- Keep heat in the probe by holding your thumb or finger over the needle while taking the temps.
- Slide the probe over the tire tread surface when moving the probe across the tire. This keeps the probe hotter while moving it across the tire and reduces the time for the probe to get back up to peak temperature.
- A higher priced pyrometer often has a more sensitive probe, which gets up to temperature quicker.
- Using more than one pyrometer can get temps faster and give more accurate readings.
- Taking tire temperatures at different locations around the track will give you different information about what the tires are doing under different conditions of braking, cornering or accelerating. This can prove to be very helpful in solving handling problems at different points on the track.
- The driver should avoid hard braking coming into the pits (or wherever the tire temps are taken). The hard braking will put excessive heat in the front tires compared to the rear. The driver should not take a cool down lap. The tires will cool too quickly, giving false readings.
- Taking tire temperatures is a crucial link in the chassis tuning process. Be religious about taking temps and recording the appropriate information. It will come in handy.
Download this tire temperature calculator spreadsheet to the laptop you bring to the track. It has macros that calculate average temperatures and even has instructions on what to adjust based on the temperature readings.
How to Take Tire Temps with a Pyrometer
Chassis Tuning With Average Tire Temperatures
At your favorite track, you’re fast, but cannot maintain as much cornering speed as your closest competitor. He goes through midturn and the exit of the turns just a little bit faster. You’ve been monitoring tire temperatures all season, and the temps look good. All of the inside temps are just a little hotter than the outside, and the middle temps are right in between. Pressures and camber are dialed. What else can you do? You know that tire temperatures offer clues about traction at each tire contact patch, but what about comparing one tire, or pair of tires to the others? The average tire temps provide another clue you can use to find more traction. Average tire temperatures are found for each tire by adding the three temp readings together then dividing by three. In addition to the average temperature at each tire, you will want to know the average temperatures for the left side and right side, the front and the rear and the two diagonals. The goal is to get the average temps at each tire as close as possible to one another. This means that each tire is going to do as much work as possible. If one tire is much hotter, or cooler, then tuning may make your car faster. It is important to have a basic understanding of tuning the chassis, especially with tire temperatures. What average tire temperature clues can tell you is the effectiveness of static weight distribution, how cross weight is affecting the car, if the roll couple distribution is in the ball park, brake balance, how the driver is using the controls and if there may be chassis alignment problems. Always look at the individual temps because they will still tell you how well that tire contact patch is working on the track surface. Use the individual temps to tune pressures first, then camber at the front and rear.
If you run a wing and splitter, you can adjust downforce to put heat into the tires. But remember that aero changes affect high-speed corners much more than low-speed turns, so you still need the chassis balance to be as good as possible, focusing on low-speed cornering first, then using aero downforce to fine tune high-speed cornering. More downforce at one end means more vertical load on the tires which will increase traction at that end of the car.
Front-, Rear- and all-Wheel Drive
Each type of drive system will alter how you analyze tire temperatures. For example, drive wheels will always be hotter if you monitor temps at the exit of a turn. Also, most production-based cars have an unbalanced front-to-rear weight distribution, which means that the lighter end of the car never will see temps as high as the heavier end of the car. Front-drive cars are the most difficult to tune, and they usually have in the neighborhood of 60 percent front weight distribution. The first really fast front driver I drove was an IMSA International Sedan Dodge. The car was evil exiting slow corners. If you were still turning at corner exit under full throttle when the turbo boost came on, the wheel spin would cause understeer that pushed the car right off the track. The rear tire temps were much lower, so we started skid-pad testing. We found that by increasing the rear antiroll bar rate stiff enough to lift the inside rear tire just off the track surface, we had just a bit of oversteer, which helped counteract the corner-exit understeer, allowing much more throttle application. We managed to get up to 1.07 g’s of cornering force on the skid pad, an unheard of number on DOT race tires in mid-1990s. The car was the fastest of the independent entries that year, and notched a few top 10 finishes. What happens at the tire contact patch is all we really care about when trying to get the maximum traction from a race car. Nothing else really matters. Tire temperatures are the easiest and most cost-effective link you have to the action at the tire contact patch. Using the tire temperatures effectively can pay considerable dividends on the race track, and it’s worth the effort to learn what they mean and how to adjust setups accordingly.
10 Chassis Tuning Tricks Using Tire Temperatures
Your racecar is perfectly balanced through the corners. It gets into the turns quickly, and corner exit is strong, but you consistently lose two car lengths in midturn. Toe is correct. Cross weights seem right. What could cause the car to be slow in midturn? The answer is a lack of total traction.
The goal when you set up your racecar is to get maximum traction and create a good balance all the way around the racetrack. If, for some reason, maximum traction is not there, the car will not perform to its peak at some point on the racetrack. One of the most important jobs a race team does is to get the maximum traction possible out of all tires. Here are a few tricks to help you accomplish that goal.
Consider all four tires
The harder each tire works, the more traction the car will have, and the faster the car can enter, get through and exit the corners. One sign of how hard a tire is working — and therefore the tire’s traction — is the average temperature of the tire. If the average temperature is higher than the maximum temperature for your tires, that tire is working too hard. If the average temperature is lower than that of the other tires, then that tire is not doing enough work and your car will not perform as well as it could. The colder tire needs to work harder and you need to figure out how to do that. Comparing average tire temperatures can offer a wealth of information.
- The hotter end of the car is losing traction before the colder end. If the rear tire average temp is hotter than the front, the car is oversteering. If the front average is hotter, the car is understeering. This could indicate a change is needed in roll couple distribution (spring rates and/or sway bar rates).
- If one side’s average tire temperatures are hotter than the other side, more static weight on the cooler side would help. For road courses, getting as close to 50 percent left side weight (meaning that right side weight is also 50 percent) is ideal.
- Diagonal average tire temps will offer clues about cross weights for a given situation.
Look at the complete tire contact patch
Where the average tire temperature for a given tire provides a good comparison for overall traction, the individual tire temperatures at a given tire offer solid information about what is happening at each contact patch. Comparing individual tire temperatures at a given tire can tell you how to tune that tire.
- If an edge of a tire is hotter, the camber is off. If the inside edge is too hot, there is too much negative camber. If the outside edge is too hot, there is too little negative camber.
- If the middle of the tire is hotter, it means too much pressure. If the middle is cooler, it means too little pressure.
Always take tire temps
Tire temps are the only link you have to what is happening at the tire contact patch. The same is true for dirt-track cars. You need to know what is happening, so always take tire temps, even after a race.
When possible, take tire temps at different locations on the racetrack
The habit is to take tire temps in the pits. On a test day, you may be able to take tire temps at any point on the race track. This can give you important information about what the tires are doing under a variety of conditions. For example, if you measure temps coming off a corner, you will see how the tires are working at this critical point on the track. Naturally, for rear-drive cars, the rear tires should be hotter in this situation, just as the fronts should be hotter under hard braking. Keep these facts in mind when taking tire temps at various points.
- When you stop to take temps, slow down gently or too much heat will build in the front tires, unless you are measuring corner entry temps.
- When you analyze temps, take into account the point on the track at which you took them.
- Midturn setup is best when all tire temps are close to equal.
- Front temps should be hotter at corner entry, but as close to equal left to right as possible.
- Drive wheel tire temps should be equal, but hotter than fronts at corner exit.
When you take tire temps, work fast. Tire temps equalize quickly, and tires cool quickly, so fast measurements will give you better results. If you are short-handed, hand the driver a note pad and have the driver write the temps down while the crew reads them.
Always take temps the same way every time. Start at the same tire, and always start at the either the inside or outside of the tire. Take temps in the same order around the car. Keep in mind that the last temp taken will not be as accurate as the first, since the last tire will have had more time to cool and to equalize. It is a good idea to measure the first tire temp again after the last one to get an idea about how much the last tire has cooled and equalized. Also, always record pressures after temps.
Pay attention to static weight distribution
One way to get average tire temps closer together and to increase total traction is to look at the temps and compare them with static weight distribution. If a tire is more than 15 to 20 degrees cooler, that tire needs more static weight on it. More static weight on a cold tire means more dynamic weight on the same tire while cornering, and less on another tire. This will most often improve overall traction, although handling balance may need to be re-established.
Dynamic weight distribution is key
The goal is to have dynamic weight distribution as equal as possible at each tire during a corner, and more weight on the drive wheels coming off the turns. We can calculate dynamic weight distribution, and we can use load sensors to measure dynamic weight distribution, but these are difficult or expensive options. Tire temps can give us the same basic information, and allow you to make good judgments about improving setup.
Heat in the tires tells the story
If the tire has heat, it is making traction, up to the point it gets too hot. When all tires are in the optimum range of operating temperature, you are getting maximum traction. Anything less than that indicates your race car could be getting around the track faster. Here are some important facts to keep in mind:
- If any tire is overheated, it is doing too much work. A change is needed.
- If all tires are overheated, the compound may be too soft for the car and conditions.
- If front tires are overheating, it may be that the driver is using the brakes too hard while steering. Or brake bias could be too much to the front tires.
- If the drive wheel tires are overheating, the driver may be using too much throttle exiting the corners, causing wheel spin.
- If temps are too cool overall, it could be the ambient weather conditions. If it’s cold, take that into account.
- If average temps are too cold, it could be the driver. If the driver is not up to speed, temps will never get to optimum and handling problems should be nearly nonexistent. The driver needs to push the car closer to the limits of traction before any setup issue can be resolved with any clarity.
Put heat where you need it
If one tire is colder than the rest, figure out how to get more heat there. Here are some tips:
- Start with static weight distribution. Put weight on the cold tire.
- If the front or rear is colder, put more roll couple distribution (stiffer springs/bars) at that end.
- If the diagonal average temperatures are off, play with cross weights to put heat in the colder diagonal. Toe and bump steer also can be used to get heat in the inside front tire.
Memory Tire Pyrometers
The best way to take tire temperatures is with a memory pyrometer. The Longacre Deluxe Memory Pyrometer stores 10 complete sets of temps (120 total), with quick and easy recall. It also has special software that prevents accidental erasure of the readings.
Take tire temps in the preprogrammed order, or select any order you prefer. The Longacre Deluxe computes tire temp averages for temps just taken, recalled from memory, or you can even manually enter temps taken previously to compute averages. Advanced electronics stabilize your readings quickly, giving you accurate, consistent results.
The pyrometer comes with a built-in night light with automatic shutoff, fast-response coiled cord, adjustable tire probe and a carrying case. It also features a built-in four-car stopwatch with 75-lap memory for all four cars. $375.
Infrared Tire Pyrometers
The biggest advantage of an infrared pyrometer is speed. The biggest drawback is consistency. Infrared averages heat over the area within the field of view of its lens. The area the lens reads is proportional to the distance the lens is held from the heat source.
Because we need to monitor as little as one degree of temperature differential from one spot to the next on a tire, if too large an area is read, or if the area is inconsistent in size, then the data is less useful. It is critical to hold an infrared pyrometer the same distance from the tread surface every time the pyrometer is used, and it needs to be held close enough to the tread so that a spot only about one inch wide is monitored. Check the user manual to find out what distance that is with the pyrometer you own. An advantage to this type of pyrometer is that by holding the lens at the proper distance, you can get an average tire temperature for each tire very easily, but again, the distance at which it is measured must be consistent.
Finally, even though the infrared pyrometer reads temperatures very quickly, it reads the surface temp only, and the surface cools and temperature balances more quickly than the rubber below the surface. Keep these facts in mind, and decent results can be achieved with an infrared pyrometer.