Tires can make a staggering difference: race car tires provide insights into truck tire...

Many fleet operators maintain that truck tires represent the second-largest equipment expense. Considering the tremendous advances in radial tires, which have led to longer tread life, improved casing durability, better resistance to injury--and costs that aren't much different from the 1980s--this

Regardless of equipment type and operating conditions, tires play key roles in the performance of many vehicles Tires are the only physical connection transmitting driving, braking and cornering forces between the vehicle and the road. Any pneumatic-tire-shod vehicle also relies on its tires for overall handling. This is most obvious in racecar applications-specifically in dirt track sprint car applications.

Paul Lauritzen, operations manager of dirt track racing for The Goodyear tire & Rubber Co., says that many tire designers consider sprints to be the most pure, blood-and-guts application in defining relationships between vehicle handling and tractive capabilities versus tire design variables. There is much to be learned, and technology developed, on dirt tracks.

A number of seasoned drivers consider winged sprint cars to be the pinnacle showcase of driver control and chassis setup. These methanol-fueled, solid axle, torsion bar suspended racers develop 800-plus horsepower and weigh approximately 1,200 pounds. They are push started and utilize in-out (direct drive) boxes instead of transmissions.

A typical sprint car competing in the World of Outlaws (WOO) series has at least three different tire sizes, with a fourth in reserve for stagger adjustments; three different rim sizes; and at least three inflation pressure settings. Front tires are typically sized at 26.5X8.0-15 fitted to eight- to nine-inch rim widths. Right rears are 33.0 X 17.0-15 fitted to 17- to 18-inch rim widths and left rears are commonly 29.0 X 14.5-15 fitted to 15-to 15-inch rims.

Differentials are non-existent and all driving torque is delivered through splined spools that are permanently locked axles. The diameter difference between the left and right drive tires creates a "stagger," defined as a difference in rolling diameter, causing the car to turn left under acceleration. Short, sticky (high adhesion) tracks call for set ups of up to 17 inches of stagger, while longer, slicker tracks typically use eight- to 10-inch stagger combinations. Track speeds and banking also affect this combination, with the ultimate goat being constant acceleration through both straight and curved portions of the track, using only small throttle setting adjustments to control rear axle slide, fine tuning the direction of travel for passing maneuvers or avoiding collisions. Two common observations are that the cars rarely travel straight ahead, but instead are in constant over-steer, or drifting. Secondly, they are fast! Most cars can accelerate sufficiently to lift the front tires, thereby losing conventional steering control when exiting turns two and four of short and mid-sized oval tracks.

Tire pressures are critical. Typical inflation specs are unique to each four wheel position and range from approximately 12 psi in the right front, 10 psi in the left front, to eight to 8.5 psi in the right rear, and from four to 4.5 psi in the left rear. Pres-sure bleeders are normally installed in both rear tires to ensure constant inflation as heat build-up, tire cavity expansion and track temperatures rise or fall. No inner tires or tubes are used in this series, so tire pressure loss is completely disabling. Two components used rarely, if ever, are brakes and left front tires. Cars have finished, even won races, without either.

We don't have the luxury of racecar-type experimentation in trucking operations. However, choices about tire/wheel selection, maintenance and servicing can have equally important effects on the ultimate success, of a trucking operation. It is our intent to bring pertinent tire/wheel related items to your attention, so that you can make more informed choices. Inhouse knowledge, reliable industry resources, and good tire personnel training programs are key ingredients in controlling tire budgets.

In the final analysis, wise choices about the components that comprise your second-most significant equipment operating expense can surely make a staggering difference--hopefully in the right direction.