To a non-racer, tires are nothing more than black rubber doughnuts requiring little maintenance other than an occasional rotation. But to the racer, tires are so much more. Tires are a racer’s direct link to the track; they give feedback to how the car is handling, are glaring indicators of what may be wrong with a suspension setup, and are a key to winning. In racing, it pays to know your tires.
To learn more about the complex world of these seemingly mundane rubber rings, Circle Track went right to source and spoke with two of racing’s major tire manufacturers: BFGoodrich and Goodyear. Matt Forthofer, tire designer for BFGoodrich, and Cal Lint, Goodyear manager of contract sales and marketing manager for NASCAR Modifieds, gave us their top tips on what every racer must know about asphalt tires. Some tips may be geared toward radials and some at bias tires, but it all aids to deepen your tire knowledge—and that can do nothing but help you win.
1. Hot Pressure Is King
“The number-one factor in any given tire’s performance is the pressure that the tire is working at on the track, or hot pressure,” explains Forthofer. “This hot pressure should be tuned within 0.5 psi of a target that was given by the tire manufacturer or determined through testing. Failure to hit that target may cause a team to chase their tail with the car setup. Try to tune the car to handle at the target pressures, then you may wish to vary the pressures slightly with changing track conditions during a race if it is long enough for pit stops. Without bleeders, keep good records of pressure build during practice so that the cold pressure can be determined for the race sets.”
2. Always Use Valve Caps to Minimize Potential Air Loss Through the Air Valve
“This is a very simple solution that a lot of people ignore,” reveals Lint. “Valve caps are a safety device that you can put on your valve to help keep the pressure in the tire. You work very hard to get your stagger and setup just right, and if you have a defective valve core, especially when you hit bumps on a track, little bits of air escape because of centrifugal force. So if you have long periods of racing, you could lose quite a bit of air, and you are left wondering why your setup has gone away.”
3. Bleeders?
“As a tire company, we hate bleeders,” Forthofer admits. “They are difficult to maintain and are a source of air leakage. It is another way that a flat tire can occur, and sometimes the leak is difficult to diagnose from a bleeder. From a racer’s standpoint, bleeders allow higher starting pressures without building up to the point of traction loss. This means the car feels better for about five laps than a tire that was started at lower pressures without bleeders. In any racing series we are involved in, we will try to outlaw bleeders. That reduces the risk of a flat while keeping the playing field level. If you are in a class that allows bleeders, then you likely have no choice but to run them, because the track position lost in those first five laps is invaluable.
Just make sure you dedicate significant time to cleaning and rebuilding those bleeders so they don’t fail.”
4. Use Only Properly Calibrated, Quality Air Pressure and Tire Temperature Gauges
Lint says, “Your tire performance is very dependent on air pressure. We found many instances where poor quality gauges and/or good gauges that are not calibrated properly will give you a difference of up to five pounds psi. So, in order to know exactly what you are doing, you have to have a properly calibrated gauge. This also applies to tire temperature gauges because the temperature information you gain will help you interpret how your car is set up.”
5. Contact Patch Area Changes Significantly With Pressure
“This is the main reason why hot pressure is so critical,” Forthofer says. “The contact patch area is roughly the load on the tire divided by the air pressure (actually about 90 percent of that, but it varies with tire construction). For instance, a tire with 500 pounds of load on it at 35 psi will have approximately 14.3 square inches of contact patch area. If we increase that pressure to 36 psi at the same load, the area becomes 13.9 square inches, which is a reduction of 2.8 percent. From this information, you would think that lower pressure is always better. That is true only until the tire does not have enough pressure in it to support a stable contact patch. Once you go below that pressure, the contact patch gets distorted and very inefficient, which causes the corner speeds to slow down. There is also the concern of sidewall flex. Going too low can be risky for the sidewalls, and the manufacturer should be consulted for the minimum pressures to prevent this.”
6. Interpret Wear Patterns for Improved Car Setup
“If you look at some tires that have been driven on, some racers are only using half of the tire, and that is not good,” Lint says. “You have to learn how to read the wear pattern so you can make the proper adjustments and get the entire tire footprint down, so you are using the whole tire for better grip and performance.”
7. Wear Affects Stagger
“Since we measure stagger on the circumference, it is greatly affected by a change in radius due to tire wear,” Forthofer says. “Right-side tires typically wear faster than left-side tires during a long run, therefore the stagger is gradually changing in a long run. Here is an example: Start off at 5/32 inch (all tires) and run a full tire stint. Let’s say the right side wears twice as fast (not uncommon). This means that the right side probably wore 4/32 inch and the left side wore 2/32 inch.
“This 2/32 difference in wear equates to 0.4-inch decrease in stagger. Now, if you change the right side only, you have a 0.8-inch increase in stagger from the end of that long run. Fuel-load and track- surface changes may overpower this during a race, but the effect is still there.”
8. Heat Cycling Makes the Tires Run Cooler
“After a tire has been scrubbed in, its chemistry changes slightly,” Forthofer says. “This usually increases the hardness and decreases the heat generation of that compound. If there is trouble with tires giving up after a long run at a particular track, scrubbing a set of tires will help them run a little cooler and wear better. They also will be a tick slower at the beginning of the run for the same reason. Toward the end of the long run, they will likely be a little faster than the sticker set. Successive heat cycles will continue this trend, and eventually the tire will become too slow to be competitive, but it will wear like iron. The number of good heat cycles in a tire varies greatly with the compounding, so unfortunately I can’t give a number for everyone’s tires.
Lint expounds on heat cycles. “Heat cycles in a tire are good and bad. If you have a tire that is too soft, you can put heat cycles in them to toughen them up a bit and be just right. When you have heat cycles, they are generally curing the rubber and make it harder and harder.
That is why when you have so many laps on a tire, the thing starts to drop down in speed because it is ‘curing up.’
“What you need to do is realize when your tires have gone through too many heat cycles. For example, if you have tried to qualify on a set of tires three or four times, maybe that is not the best thing to try and qualify the next race on. You need to get a new set of tires because you had too many heat cycles on the tires.”
9. Tune Your Camber Using Tire Temperatures
“Heat is generated on the surface of the tires as soon as you start turning, accelerating, or braking,” Forthofer says. “Your front tires see heat generation across the surface for the entire corner. This includes entry, mid-corner, and exit of a ‘classic’ corner. Generally, you want to tune the camber angle such that the temperature spread is even in the mid-corner phase. With most suspensions today, that means running a lot of static camber. This means that in the entry and exit of the corner, the tire is not at an optimal camber angle and will be heating up (for the right front) the inside shoulder.
If you don’t have the luxury of data acquisition to monitor this real time on the track, the inside of the right front and right rear should be 5-10 degrees hotter than the outside when measured in the pits. This is because that portion of the tire is being heated more throughout the corner due to the entry and exit phases, but it is optimal at the mid-corner phase because all the body roll has taken place.
“For the left-side tires, the outside shoulder should be 5-10 degrees hotter for the same reason. Some tires will need a lot of camber to make this happen (especially radials). You may get to a point where you are overstressing one sidewall with too much camber and have to compromise back to maintain the integrity of the tire. See the tire manufacturer for that recommendation. You may also want to consider increasing the camber gain if it looks like you are running too much static camber.”
10,. Good Record-Keeping Pays Off in the Long Run
“You see all kinds of methods for record-keeping,” says Lint. “Some people use a computer, and that may be the best, but you at least need a permanent notebook or other source that will contain all your tire data. That data will prove invaluable in interpreting such measurements as tire temperatures to help you improve your car’s setup.”
11. Adjust Pressure for Temperature-Crowning on Bias-Ply, but Not for Radials
“Bias-ply temperatures respond well to pressure changes in the classic sense,” Forthofer says. “If a typical bias-ply tire has 10-degree-higher temperature in the middle, dropping it a few pounds will even out those temperatures. Due to the additional constraint of the belt package on a radial tire, they will not always respond. Some designs will not change at all unless you get out of the usable pressure range of the tire. In that case, just run the recommended pressures or test to determine your own optimal pressures, and you will have to live with the temperature profile the tire gives (hopefully it is good anyway). There are some radial designs out there that will respond to pressure like a bias tire, so you will have to test to find out if you are running one of those designs, if the manufacturer doesn’t tell you up front.”
12. Understand Caster and Camber Effects on Tire Performance and Life
“This has a lot to do with using and paying attention to the information you get from your temperature gauges,” Lint says. “With camber and caster, you can obviously lean the tire one way or another and cause excessive heat, but this will cause eventual destruction of the tire if you don’t have it right. Or you can even use camber/caster if you have a cold night to generate heat to a certain point. But be careful: Going past that heat threshold will cause destruction of the tire, so you have to know where that threshold is.”
