The Rubber Linings Playbook
A thorough tire maintenance program extends tire life, improves fuel economy

By Paul Abelson, senior technical editor

How much do you have invested in your tires? If you pull others’ trailers, it may total anywhere from $2,500 for eight recap drive tires and two new steers to almost $6,000 for 10 new premium tires. With your trailer, you can add up to $4,000 or more. You need to protect that investment.

Add to that the effect that tires have on fuel economy. The Technology and Maintenance Council states that wheels out of alignment can reduce fuel economy by more than 3 percent and dramatically shorten tire life.

When replacing tires, be sure you get the optimum tread for your needs. A shallow rib tread can reduce fuel use by 3 percent or more compared to a deep lug drive tire, but it won’t provide the traction you may need for on-off road operations. Work with your dealer to get the best balance of structure, compound and tread pattern.

When tires show wear, compare them to Recommended Practice RP 219C from the Technology and Maintenance Council (TMC). The Radial Tire Wear Conditions and Causes is a guide to analyzing causes of wear patterns. It also recommends corrective actions. Another useful document is RP 216C, Radial Tire Conditions Analysis Guide.

When properly aligned relative to the chassis and to each axle, tires run straight with minimal wear. When axles are not perpendicular to the chassis, thrust angles develop and cause tires to scrub across the pavement. With just an eighth-inch misalignment, a tire rolling 500 revolutions per mile will travel sideways more than 5 feet each mile, or almost 10 miles per year. That scrub contributes to uneven wear. Even worse, it consumes energy to wear the tire, lowering mpg.

Align all wheels, including the trailer. This means all wheels and axles are in proper alignment, not just the tractor steer tires. Axles must be perpendicular to the vehicle center line to avoid wear from thrust forces set up by wheels pointed slightly to the side. Steer tires should be checked for toe-in or toe-out, camber and caster. Toe measures where the tires are pointing when seen from above. Caster is the angle of the steering assembly kingpin with the ground, as seen from the side. Camber measures whether the tires are leaning inward or outward when seen from the front.

Each of these affects tire wear, and uneven wear cuts tire life and costs money. Establishing your own tire maintenance program is easy to do, and it will increase the use you get from your tires. If you maintain your tires well, you can have your own casings retreaded. That way, you get a retread with a known history. A good casing, kept inflated, aligned and balanced, should last two or three retread cycles, giving 500,000 miles or more total wear. Even if you don’t want to run retreads, a well-maintained casing has significant trade-in value.

It’s an important thing to keep tires properly inflated. Air under pressure is a structural part of the tire. In fact, air supports the entire truck. It’s as important as the steel belts, the radial cords or the rubber itself. They are there to contain the air.

Air pressure keeps the tire from flexing too much. Flexing generates heat inside the tire, and excessive heat ruins tires. Without enough air, flexing can heat steel tire cords past the temperature at which rubber becomes liquid. When that happens, the tire can’t hold together. That’s when pieces start to fly off.

Look at the next “gator tail” you see on the road. Chances are it has steel cords coming out. That’s not a lost tread from a recap. It’s a section of a casing that let go due to excessive heat, caused directly by low air pressure.

Proper air pressure depends on load and speed. A given tire filled to 85 psi may be safe when running empty, but it could need 100 psi to carry 80,000 pounds at 65 mph. The same tire may need 115 to 120 psi to handle 75 to 80 mph without excessive flexing. Every maker has load-speed tables for each of its tires, available from its dealers.

Tire casings become damaged when running 20 percent or more under proper load/speed inflation pressure for any sustained period. For a tire rated for its load at 100 psi at 55 mph, 20 percent under-inflation could be 96 psi at a sustained 75 mph.

Balance your tires. Much of the pavement pounding seen from loaded as well as empty trailers occurs because an imbalance wants to pull the tire off the pavement, then slam it back down as the tire rotates. Imbalance causes uneven wear.

Several devices help maintain balance with weights carried in viscous fluid, moving freely within a circular device bolted to or between wheels. Other products use granular material or fine glass beads inside the tires. The added masses automatically seek the proper position to balance the rotating assembly.

Tire pressure monitoring systems alert drivers or mechanics at each wheel end or using dashboard monitors. Inflation systems help trailer tires maintain air pressure, even after minor damage. They are well worth having.

Keep tires in a dual set matched as closely for size as possible. One-quarter inch radius difference is the recommended maximum difference, but if you can, keep tire diameters matched as close to one-eighth inch or less. Since the two tires are bolted together at the wheels, they turn the same number of revolutions per mile. Because their diameters differ, they will travel different distances resulting in scuffing and uneven wear.

At a one-quarter inch difference, the larger tire could carry 600 pounds more than the smaller. It will also wear out faster. Both will wear unevenly. Even if perfectly matched by size, inflation differences will affect wear and load. With a 15 psi difference, the higher pressure tire will carry 500 pounds more than the other. LL

Aug/Sept Digital Edition