In the mid-1990s, the term tire management became a common phrase made popular by commentators on NASCAR television broadcasts. The term was first used in a Circle Track magazine article as part of a series I wrote while serving as the magazine’s editor. At that time the basic premise related to the driver and how tires were being managed during a race or qualifying. In the 20 years that have passed since that article appeared, the term has expanded to cover all aspects of the use and care of race tires on and off the racetrack. Since tires are the only link between the track surface and the car, they are critically important. And how the team and especially the driver manage those important components is major key to success.
The original idea behind “tire management” related to how the driver cared for the tires and manipulated the tires for maximum traction. And while the off-track care and use of tires leading up to this is really important, what the driver does in the cockpit with the controls on the track is still the most important element.
Getting Heat in the Tires
Tires need heat to make traction, but not too much. On a warm-up or pace lap or after a caution period, getting heat into the tires is an important task for the driver, but maybe not as important as you might think. Heat builds up quickly in a tire, obviously depending upon the ambient conditions and tire rubber compound. Here is a reality: How often have you seen drivers approach the limit of the first corner of a race or restart? Not often. Most everyone brakes at the same braking point as for a hot lap even though vehicles are usually somewhat slower. This gives the tires a good chance to get up to temperature. Most tires are at optimum traction when temperatures at the contact patch are between 160 degree and 220 degrees Fahrenheit. Really soft rain tires need much less heat and are easily overheated. But it is still important to heat tires on warm-up laps. And to clean debris from the tread surfaces.
The basic rule of thumb is abrupt steering motions side to side are primarily for tire cleaning. Hard braking puts more heat into the front tires quickly while acceleration will heat the rear tires on rear drivers. Lower-powered front drivers benefit more from braking hard than acceleration. High-horsepower rear drivers need a little wheel spin prior to the start to get some beneficial heat in the tread surface. Cleaning may be the more important of the two criteria, because abrupt steering inputs will put heat in the tires also, just not as quickly as hard braking and acceleration.
The driver is the master of the controls and, therefore, assuming a good setup — which is never a good assumption — the master of traction. While the vehicle design and the tire parameters play a role as does the setup of the car, the use of the controls is the major factor.
The Controls: Steering
Every time the steering wheel is turned, lateral weight transfer takes place. Vertical load on the tire contact patches changes and that causes traction to change. Since traction is proportional to vertical load on a tire, when weight transfers onto a tire and off another tire, the relative traction changes. This can alter the handling balance from understeer to oversteer for example, or vice versa.
For example, if the driver initiates left steering input, weight transfers to the right side tires. If this is done with no brake or throttle input changes, then the handling balance will remain as it was. But if the driver adds a braking or throttle input, then there is also front-to-rear weight transfer. Then the handling balance will be altered slightly. This can cause an improvement in balance, or make it worse. Lifting off the throttle in a high-speed turn is good example. If the car feels a little loose, or the driver simply panics and lifts off the throttle abruptly, the reduced traction at the rear will make the situation worse, and often cause a spin. Conversely, braking entering a corner can improve traction at turn-in and improve overall traction.
An additional issue with steering is how quickly the wheel is turned. Good tire management requires that the driver be precise with steering. It takes a finite amount of time for the tire contact patches to reach the optimum slip angle in a corner. The tighter the turn, the longer it takes, and the more the driver must turn the steering. But if the driver turns the steering wheel too quickly, optimum steering lock is reached before optimum slip angles at the tire contact patches. This creates a vague feel in the steering, causing the steering input to feel like it is too little, so the driver adds steering input. By the time the tire slip angles catch up, they are larger than necessary, the tires are scrubbing to some degree, heat is building up more than necessary and tire tread wear accelerates.
Ideally, the tire contact patch slip angle reaches the maximum at the same instant that the driver has turned the steering wheel as much as is needed to negotiate the corner. Easier said than done. While the driver turning too much may be as fast as the driver nailing the correct steering input, the driver turning too much will not be as fast after five or 10 laps. That driver’s tires will begin to “go off” sooner, slow down some and wear faster. Doing this is an art form. To do it perfectly, or nearly so lap after lap is what separates great drivers from good drivers. Good drivers can drive at the limits of tire traction lap after lap. Great drivers drive at the limits of traction at smaller slip angles, saving the tires for longer runs and not overheating them to the detriment of tire traction.
Referring again to a previous Speed News article, the traction circle theory and the characteristics of tires and traction dictate that maximum traction occurs at a given slip angle when cornering. Traction increases up to that maximum slip angle, then drops off as slip angles exceed optimum. If you plot this on a graph, it looks like a bell curve. The slope at the top of the curve is gentle, meaning that the maximum traction area of the curve is a section not a point. Where absolute traction may max out at around 6 degrees of slip angle, very near maximum traction actually occurs between 4.5 and 5.5 degrees. The driver consistently turning at 4.5 degrees is not going any faster than the driver at 5.5 degrees, but the tires are being better managed by the driver at 4.5 degrees. Less scrub, less heat, less wear! And the driver at 4.5 degrees of slip angle has a little traction left in the bank. By pushing when necessary to 5 degrees of slip angle, that driver can go a little faster for a turn or a lap or to make a pass. Truly great drivers do this routinely.
Brakes and Throttle
As we have seen above, using the brake or throttle while cornering can have a very real effect on traction at each tire, which in turn affects the handling balance of the car. How and when the controls are used is very important. Using any control too abruptly can cause problems. The more abrupt, the bigger the problem becomes. Too hard and fast on the throttle can induce wheel-spin, especially exiting slow corners in a front driver. Wheel-spin causes a reduction in traction, overheats the tires and accelerates tread wear. A quick, stabbing application of the brakes can cause lock up. This damages tires worst case, and will overheat the tread, which accelerates wear. But it also can cause an abrupt change in weight distribution. In a straight line, as long as brake bias is set correctly, this change in weight distribution is not a problem. But if you are turning while braking, any change in weight transfer can upset the handling balance, scrub off critical speed, accelerate tire wear or even cause a spin or crash.
On the other hand, the brake and throttle can be great tools for perfecting handling balance while turning. This is one way to compensate for tire wear or changing fuel loads. It takes practice to become proficient. You change traction at each tire by altering the load on each tire. Braking and turning puts more weight on the outside front tire, takes weight off the inside rear tire. Used properly, this can reduce corner entry understeer. At corner exit, the correct amount of throttle application can increase drive off a turn, reduce oversteer or increase understeer. Of course, the optimum line is also crucial to make this work.
If you ever have the opportunity to practice on a skid pad, you can easily and quickly learn how your car responds to braking while cornering and using the throttle while cornering. Try turning the steering a set amount (this can be done on a long, constant radius corner also), the accelerate hard but hold the steering wheel steady. Observe the path change, then lift off the throttle (which is like braking because weight is being transferred) and again observe how the attitude and path of the vehicle changes.
If you are at the limit of traction when you do this, you should find that increased throttle application will cause the car to widen its radius, which is basic understeer. Weight off the front on onto the rear changes handling balance by changing traction. When you lift off the throttle, the opposite occurs and the car will now oversteer. You can actually steer the car by manipulating the throttle. In fact, once the car is set into the turn, or circle of the skid pad, the fastest way around is to hold the steering wheel at a steady angle while altering the path by changing throttle position. When I was doing a lot of car, tire and suspension testing, I spent a lot of time on the skid pad. This was my secret to setting very fast times around the 100-foot-radius skid pad.
Another way to manage is tires is using cockpit controls not found on most club level race cars, but they are worth mentioning. Brake bias and adjustable antiroll bars are two such items. Practice using these controls to aid in tire management as fuel loads diminish and traction degrades during the course of an event.
“The tires went off on lap 15!” There two primary causes of accelerated tire wear. First, the car setup can be off. Second, is overdriving the tires, which causes excessive heat. This element falls totally on how the driver uses the controls. We’ve discussed the issues: turning the steering wheel as little as possible to hold your line, gentle brake and throttle applications. Here is one simple example.
I was driving the last stint of a three-hour enduro in a low-powered front-drive car several years ago at Willow Springs International Raceway in California. Turn 2 is a long, sweeping right hander, slightly uphill and pretty fast. The first driver went through a set of front tires about 5 laps before we planned a pit stop midway through the race. That meant I had to figure out how to conserve tires without losing ground to the car behind us. The left front was basically gone, blistered and about ready to blow. The vibration was what warned the first driver to pit early or risk a crash. Much of the wear on the left front came from Turn 2.
The first driver’s lap times were good, consistent and left us in a good position. I have hundreds of laps at Willow, which certainly helped my situation. After a couple of laps, I changed my line in Turn 2 slightly, but more importantly, I used the throttle to steer the car. By lifting for an instant, then returning to full throttle, I was able to reduce steering lock considerably and actually run lap times a couple of tenths quicker. But mostly, this kept the left front tire from chunking and blistering. By the end of the hour-and-45-minute stint, the tires were done, but in decent condition. The key was using as little steering as possible and manipulating weight transfer and tire load by using the throttle. This allowed the left front tire to survive, increase the wear on the right front and was an important lesson in tire management. In fact, it was this long-ago race that got me thinking about tire management well before that article in Circle Track magazine.
Give some thought to how you can manage tires for optimum performance. Then make a special effort to practice tire management on a skid pad or track. It only takes a few minutes or a few laps to really learn what you can do to better manage your tires.
Dyson Racing posted this video on YouTube, and it demonstrates many of the same points made in this story.