It takes a lot of guts to take your pride and joy out on a high-speed road course for the very first time. Risks, both imaginary and real, dart through your mind prior to turning your first lap. Will I wreck? Do I have enough brakes, tires and gas to go the entire day? Will I totally embarrass myself? All of the worries fade once you get those tires and brakes up to temperature and complete your first laps. But there comes a day--for most of us our second or third open track outing--when we start wondering why other cars and their drivers are so much faster--with equipment that may not even be as good.
Driver skill and equipment do have a lot to do with going fast, but there is one area that can help all drivers of all skill levels and equipment levels: knowing the proper way to set tire pressure.
For most of our lives, our knowledge of setting tire pressure consists of going to the service station and setting all the tires at the same safe pressure. Doing so religiously has been a motto for tire manufacturers, vehicle manufacturers and auto clubs since the first car was built. But that's the extent of the average guy's knowledge.
What most novice road racers and autocrossers don't fully realize is that a tire's temperature across its width will tell you exactly what's going on with the suspension and what the tire needs in terms of air pressure. Perhaps on an intellectual level, beginners know this, but the idea is ingrained that the science of tire pressure and car set-up is reserved for multi-million dollar racing teams wearing uniforms and toting computers. Fact is, you can have all the tools you need to shave seconds off your lap time for less than the cost of a good helmet. To fully take advantage, you'll need a high-quality tire gauge, a logbook and a decent pyrometer. That's it. The amazing improvement you can get with these items will astound you.
Like a lot of novices, this author got his first taste of road racing at one of the many driving schools held every weekend across the country at tracks everywhere. One of the benefits over a regular lapping session is the high quality of instruction given to beginners and experienced amateurs alike. This type of school emphasizes driving your own car rather than a school-maintained car, which has the added benefit of helping the car owner develop his or her tuning skills in conjunction with the driving skills. One such school put on by Mustang tuner and racer, Kenny Brown, has helped hundreds of students. Brown, the proprietor of Kenny Brown Performance in Indianapolis, IN, has built many successful racecars for World Challenge and SCCA competition, in addition to building countless customer cars for street and open track.
"Tire pressure is one of the very few things you can adjust at the track with minimal effort that will produce real results," says Brown. "Once you have a log of your tires' temperatures, that will give you better insight into how your suspension is working and how to set up your car for the next event. We teach this at every school we do and our customers are amazed when they see the results."
As you lap the track, the four tires do the work to accelerate, turn and stop the car. The amount of heat that builds up across the tread of each tire can tell you how hard each tire is working and what part of the tire is doing the most work. In a perfect world, that work is shared evenly across the tire. That's the key to getting the most out of any car whether it's a street car doing occasional track work, or a Winston Cup car carving up the esses at Watkins Glen. "Tire pressure is pretty important, obviously since TV commentators are always talking about it," says Brown. "It's a critical element in maximizing handling. You need some place to start in terms of tire pressure, whether it's your buddy or the recommendations of the tire manufacturer. It's best if you reference somebody who's done this before and then adjust from there."
You can learn the skill of tuning by means of the pyrometer at one of Kenny Brown's driving schools. Here, Kenny Brown support personnel take pyrometer readings on a student's car during a lapping session at Watkins Glen. Kenny Brown's students go away not just with improved driver skills, but with basic pyrometer tuning skills they can use on their own cars. Incredibly, that's a first for driving schools of all types.
Getting Started
The key to making tire temperature and tire pressure work for you is good record keeping. Before you start your first on-track session, or even before you leave your driveway in the morning (if you're driving to the track), establish a baseline pressure while the tires are cold. As Brown said, it could be either a manufacturer's recommendation or the advice of a more experienced driver--the important thing at this point is the accuracy and consistency of the pressure measurement. Brown told PHR: "Try to use the same tire gauge every time. If you're at the track and you've got multiple tire gauges, make sure to check them against each other. The dial type pressure gauge is preferred."
Keeping a concise log of your lapping sessions makes a big difference too. Writing pressures and temperatures on random scraps of paper is not the smart way to work since you won't be able to learn anything over the long term. We suggest you obtain logbook pages from Longacre (www.longacreracing.com) or CV Products (www.cvproducts.com). For an even better deal, you can go to the Kenny Brown website (www.kennybrown.com) and download a free logbook page to duplicate.
If you have no logbook, you can make one out of a spiral-bound notebook and jot down the starting pressure of each tire in a grid shaped like a big "+" sign. Looking down on the "plus" sign is analogous to looking down on your car from above, with the upper left quadrant representing the front left tire.
The cold starting pressure is your baseline and is the only time you will measure true pressure. Why? Because once the tires heat up, the pressure will go up. The amount of pressure after your first session may, for instance, read 40 psi, but there is actually no more air in the tire than when it was cold at 30 psi. This is similar to what happens when you go on a long road trip and you observe the pressure being higher when you arrive than when you left.
Ideally, you use temperatures to tell you if the pressure is too high or too low, then add or subtract pressure incrementally. If you start a cold tire out at 30 psi and through the course of the day you take out a total of 7.5 psi, you may actually end up with 35 psi of hot pressure. The thing to remember here is to keep track of the incremental amount of pressure you add or subtract each time you change it. This is done with a new log sheet every time you make an adjustment in the pits or the paddock area.
Whether or not you decide to record the incremental pressures changes is up to you, as long as you recheck and log the cold pressure the following day after the changes are made. The main thing to be gained by recording incremental pressure changes is that you begin to equate differences in handling with a given change in pressure.
The AccuTech No. 50640 from Longacre Racing Products is a staple of novice and amateur road racers. Its low cost ($132) and high accuracy means it pays for itself rapidly in improved tire wear and quicker lap times. The result: more smiles per lap.
Measuring Tire Temperature
Once you complete your first lapping session, you will want to use your pyrometer to record the temperature across the face of each tire--one reading for the inside, one for the middle and one for the outside. You may want to experiment with the locations you "stick" with the pyrometer's probe because the construction of the shoulder area differs slightly between manufacturers. Wherever you decide to probe the tire, consistency is key, both in terms of where you stick the tire for a reading, and how soon after you enter pit road. Ideally, tire temps are taken as soon as possible after lapping, when they are at their hottest.
Record the temperatures (there should be 12 temps each time you probe) in the quadrant grid. Each quadrant corresponds to a tire and three temperatures are recorded in each quadrant--the outside tire temps on the outside of each quadrant, the inside temps on the inside of each quadrant and the middle temps in the middle of each quadrant. You will also want to record pertinent data on each log sheet such as the track, date, time of day, session number, tire type and fuel load.
Hint: if you have a crew member who can check the tire temps on pit road after a session, your results will be far more consistent. Always follow the direction of course workers when in the pit area. Pull to the pit wall and turn your front tires away from the wall to make them easier for your crew member to stick. Also, after coming to a stop, never use the service brake or emergency brake to hold the car in place, as it will warp the rotors.
Once you have recorded your first set of baseline temperatures, you can analyze them in the paddock area as you maintain your car between sessions. You'll find more experienced drivers in the paddock who can bring knowledge to your readings and recommend changes, but even in their absence, there are easy "no-brainer" changes that will lower your lap times by seconds. Kenny Brown agrees: "Depending on the driver and the track, you can see an extra three or four seconds per lap. By adjusting the tire pressure, you're putting more tire contact patch on the ground to give you more grip. The car just feels better; it's easier to drive and that increases the fun factor."
The three circles represent the general areas where pyrometer readings should be taken (center, and 3/4 of an inch to one inch from each edge). The probe should be stuck sufficiently into the tire to measure the core temperature of the tread. Consistency in the probe points is key in evaluating incremental changes in pressure and suspension geometry.
Interpreting Tire Temperatures
You have just measured your tire temps for the first time. You've got good baseline cold temperatures recorded for each. Now it's time to get to the nitty gritty: using tire temperatures to lower your lap times. "The basic philosophy is to measure the temperature of the tire in three different places," says Brown, "the outside, the middle and the inside. By 'outside' or 'inside' we don't mean the very edge, but 3/4 of an inch to an inch in from the edge. If you don't have anything else, an infrared gun will be okay, but the quality of the data will not match the pyrometer. With an infrared, you're only measuring the surface temperature, which has the tendency to cool very quickly. With a pyrometer, you're actually sticking the probe into the tire and measuring the temperature of the rubber."
Areas that are worked harder and see more severe contact with the road will read higher. When the shape of the tire is affected negatively by the air pressure, it will be manifested as either a high or a low temperature in the center.
Brown explains it like this: "In a perfect world, with a perfect suspension and perfect tire pressure, you would see the same temperature inside, center and outside. It will vary from tire to tire--since you're asking each tire to do a different job--but it will be the same across the tire. But we don't live in a perfect world, so we need to interpret what the pyrometer tells us and adjust accordingly.
"Looking at the three temperatures, the center of the tire is your 'pressure' temperature. You typically will not see the same temperatures on the edges, but the center will split the difference with the outside edges. Example: if the outside of the tire is 160 degrees and the inside is 140, then theoretically you want the middle to be 150. If your center is higher than 150, then there's too much air and the tire is bowing the center of the tire out, in which case you want to let a little air out. If the center temperature is under 150, then pressure is too low and you'd want to put a little air in."
Simply put, the center temperature tells you which way to turn the proverbial knob. A center temp lower than the average of the edges means go up in pressure, and a center temp higher than the edge average means go down. Regardless of what your buddy's tire temps are, and regardless of what your tire pressure stands at, the center temp will tell you what the tire needs for a pressure adjustment, plain and simple. You may be tempted to do something entirely different based on intuition, but if it goes against this overriding principle, it will be the wrong move.
This analog racing tire gauge from CV Products (part No. CVAG100) costs $74.95 and reads reliably up to 100 psi. The cost is quite a bit more than your average gauge, but when you're dealing with increments of a half pound, the accuracy of the gauge is imperative.
So how much should you take out or add? That depends on how far off the center is from the average of the edges. According to Kenny Brown, "As you start to do this, work in one-pound increments. Once you get the feel of it, you can work in half-pound increments. It's just time and learning. At the end of the day, you're going to find that each of your tires has a different pressure. The reason for this is that if it's a clockwise track, you're asking the left front to work the hardest and it'll have the highest hot pressure and the highest temperatures. The right rear will have the coolest temperatures and the lowest pressure. Once you've got the car working well, let the tires cool overnight and then check the cold pressures and that will be your new cold starting pressure for each one of those tires. That way you're not starting from scratch, you just pick up where you left off and adjust for that new day."
Since most open-track driving events and schools are two days in length, you will have the opportunity to make cold pressure readings on the morning of the second day. When you take advantage of this, you will put yourself a leg up the second day of the event, and if it's a Pro Solo event, it can mean the difference between placing for a trophy and going home empty handed!
Advanced Tuning
Besides using the pyrometer to fine-tune tire pressure, it can also be helpful in diagnosing suspension deficiencies. Steep temperature gradients across the whole surface of the tire indicate that one side is being overworked while the other side is underworked. "The inside and outside temperatures tell you about the camber on the car," says Brown. "This primarily is on the front, and also on the rear with four-wheel independent suspension. If the outside of the tire is significantly hotter than the inside, that wheel needs more negative camber to try to get the contact patch bigger. If the inside is higher than the outside, then either there's too much negative camber, or there's too much toe-out. That tells you what you have to adjust for the next time."
Most novices start with street tires, such as the Goodyear GS-Cs mounted on the author's '94 Camaro. If you plan on road racing often or just want more grip (or more lifespan for your street tires!), we recommend you upgrade to a set of DOT race tires on separate rims. These Kumho V700 Victoracers measure 275/40VR17, or about 25 percent more footprint over our stock tire. Softer rubber improves grip over stock by an even greater margin.
For many cars, the ability to adjust camber at the track can be a big advantage. A popular aftermarket item for many late-model Mustangs is an adjustable caster/camber plate on the strut tower. This makes a camber change in the paddock area nearly as easy as an air pressure adjustment. None of these trick suspension pieces, however, have any prayer of meeting their full potential without a tire pyrometer.
Another phenomenon that sometimes surfaces under the scrutiny of a pyrometer is elevated rear tire temperatures. Even after optimizing pressures and camber angles, it's possible to see rear tire temps 30, 40 or even 50 degrees higher than the fronts. "If you see really high rear temperatures, you've got wheel spin coming off the corners," says Brown. "You've got too much torque, you may be in too low of a gear or you've got a rear suspension deficiency. Also, the tires and wheels in the back could be too small. The easy answer is to just go up a gear. Instead of using Second, use Third. For most people, that will typically result in a quicker lap time too."
Discovering a rear temp elevation can sometimes solve a crucial piece of the puzzle, as this author discovered in his LT1-powered Firebird. A torquey fuel-injected stroker engine with a heavy front weight bias and a relatively small rear tire caused an understeer going into the corner and oversteer on the exit. Temperature analysis finally helped solved the problem when larger rear tires and a higher gear were used.
The Longacre AccuTech
The best part about lowering your lap times with a digital pyrometer is that the results are immediate and the cost is low in comparison to more car mods. It really boils down to one thing: it's easier and cheaper to improve performance by picking the low-lying fruit first. As cheap as they are, a digital pyrometer and an accurate tire gauge should be the first things on your shopping list, not the last.
We checked out some prices on pyrometers recently and found Longacre's entry-level AccuTech unit (part No. 50640, $132) to be one of the best values out there. It's a no frills unit with basic "Hold," and "Max/Min" functions, it comes in a padded protective case, and even includes a nine-volt battery. According to Longacre's Tom Glithero, the AccuTech's basic sensor circuitry is the same as their bulkier, higher-priced pro units with printers and built-in memory, but the advantages are just as great for the novice or advanced weekend warrior. Kenny Brown put it best: "Not only will a digital pyrometer improve your lap times, but it will improve tire wear and increase the fun factor. It will pay for itself rather quickly."
PYROMETER TIPS FROM KENNY BROWN
On Fine Tuning:
"You'll need to adjust pressures a little different for every track and even from day to day because of the weather. Knowing which way to take it is simply a matter of keeping a logbook and having a reference base."
When The Car Changes Traits:
"When we start setting the car up, we'll send the driver out and the car will feel pretty good. Then about three to five laps in, the car won't feel as good--it'll get loose or have a push. If we have the luxury to bring the car in, that's when we take the temperatures and make an adjustement."
Tire Temps And Cool Down Laps:
"If you're driving a full session, on the cooldown lap the trick is to cool the car down on the straightaways but try to keep your corning at 80 percent of what you were at to keep those temperatures fresh. Once you bring it in, you get those temperatures as soon as you can when you get off the track."
On Street Tires:
"My view is that street tires are only good for your first school. Beyond that, your competency improves to where you overheat those. The first feeling is squirminess, and then chunking. The reason for that is that the rubber was not designed for the high temperature and there's just too much rubber."
Pyrometer Probe Tips:
"Protect your tip! These do break easily and sometimes they're hard to replace. Pay attention to it. Don't drop it on the ground, don't stick it in sideways and bend it once it's in the tire."