Many fleet operators still maintain that truck tires represent the second (to fuel) largest operating expense in their budget.
This “truism” seems pretty amazing, considering the tremendous advances made in radial tire technology that have led to longer treadlife (original and retread), improved casing durability and much better resistance to injury. And it is surprising, given that new-tire prices aren’t much different from levels paid in the 1970s.
But this alleged fact is also key to understanding why the most knowledgeable and diligent maintenance managers spend considerable time and effort in refining programs for optimum tire selection and maintenance. When changes in their tire programs do occur, they tend to be evolutionary since the consequences of missteps can be very large.
Most commercial tire dealers appreciate the differences between consumer and commercial markets. One of the most distinguishing is that many but certainly not all consumer purchases are impulse based, or are at least decisions influenced by third-party information sources, such as buff magazines or advertising programs.
Commercial customers, however, tend to take much smaller steps before committing to changes in brands or even tread patterns. Most tend to understand that even small changes in tire selection, usage requirements or equipment configurations can affect overall lifecycle tire costs. Still, they are not likely to embrace change quickly.
The fact is tires play key roles in the performance of many types of rolling stock, regardless of equipment type and operating conditions. Tires are the only physical connection transmitting driving, braking and cornering forces between the vehicle and the roadway.
The Racing Parallel
Any pneumatic-tire-shod vehicle also relies on its tires as a major component affecting overall handling. This is most obvious in racecar applications, and especially on dirt-track sprint cars.
Paul Lauritzen, operations manager of dirt-track racing for Goodyear, says that many tire designers consider dirt-track cars to be the most pure, blood-and-guts application, one that clearly defines the relationship between vehicle handling and tractive capabilities and tire design variables. There is, therefore, considerable transfer of the lessons learned and technology developed on dirt tracks to other race tire and car applications.
Seasoned drivers in a variety of racing series consider high-winged sprint cars to be the pinnacle of driver control and chassis setup. These methanol-fueled, solid axle, torsion bar-suspended racers develop 800 hp-plus but weigh only about 1,200 pounds. They are push started and use in-out (direct drive) boxes instead of transmissions.
A typical sprint car competing in the World of Outlaws (WoO) series (www.worldofoutlawsracing.com) requires at least three different tire sizes and a fourth in reserve for stagger adjustments. Consequently, there are also three different wheel sizes and at least three inflation pressure settings.
Front tires are typically sized at 26.5×8.0-15 fitted to 8- to 9-inch wheel widths. Right rears are 33.0×17.0-15 fitted to 17- to 18-inch wheel widths, and left rears are commonly 29.0×14.5-15 fitted to 14- to 15-inch wheels.
Differentials are non-existent, and all driving torque is delivered through splined spools that are, in reality, permanently locked axles. The diameter difference between the left and right drive tires creates a “stagger” (defined as a difference in rolling diameter) that causes the car to turn left under acceleration. This is handy because dirt-track races are really one long left-hand turn.
Short, sticky (high adhesion) tracks call for setups of up to 17 inches of stagger, while longer, slicker tracks typically use 8- to 10-inch stagger combinations.
Track speeds and banking also affect this combination. The ultimate goal for the driver is to accelerate constantly through both straight and curved portions of the track, using only small throttle setting adjustments to control rear axle slide (oversteer), fine tuning the direction of travel for passing maneuvers or avoiding collisions.
In a WoO race, the cars rarely travel straight ahead. Instead, they are in constant oversteer or drift. Second, they are scary fast. Most cars accelerate sufficiently to lift the front tires, thereby losing conventional steering control when exiting turns two and four of short and mid-size oval tracks.
Pressures and Variables
Tire pressures are also critical to sprint-car handling. Typical inflation specs are unique to each of the four wheel positions and range from approximately 12 psi in the right front and 10 psi in the left front, to 8 to 8.5 psi in the right rear and from 4 to 4.5 psi in the left rear.
Pressure bleeders are normally installed in both rear tires to ensure that inflation stays constant as heat buildup, tire cavity expansion and track temperatures rise or fall. No inner tires or tubes are used in this series, so a tire pressure loss is completely disabling. Two components used rarely, if ever, during a WoO race: brakes and left front tires. Cars have finished, even won, races without the benefit of either.
In the world of sprint cars, tire combinations, suspension setups and a host of other controlled variables may be changed on any given hot summer evening in search of an all-important win. Sometimes, a team will walk closer to the edge just because they “feel lucky” that evening.
Track conditions top layer moisture content, compaction and underlayment hardness are examined by probing with screwdrivers before making final chassis setups for feature races. Gas shock absorbers on each of the chassis corners can be individually adjusted by the driver as track conditions change during a race.
Why go on about dirt-track racing? Well, perhaps to reiterate the obvious: Fleet customers don’t have the luxury of racecar-type, trial-and-error experimentation or even on-the-fly adjustments in modern commercial vehicle operations. Their businesses can ill-afford component failure that leads to a “DNF.”
These are key reasons why fleet customers seem so slow in making changes in vehicle components like tires or in maintenance preferences. Like racecar drivers, they fear that the slightest change will drop them to the back of the pack or, worse, leave them spinning out into the proverbial wall.
Decisions about tire/wheel selection, maintenance and servicing can have important effects on the ultimate success of any trucking operation. You, in effect, have to be your fleet customers’ crew chief and pit crew, applying your knowledge and the right products and service to control their tire budgets.
Wise choices about the components that comprise any fleet’s second-most significant operating expense can surely make a staggering difference hopefully in the right direction.