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Montana Chapter, Northwest Log Truckers Cooperative |
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Beating Uneven Tire Wear
"Most of us lack instant recall on the actual wear rates of our steer, drive and trailer tires." says Russ Dagnall. chief engineer - Customer Engineering for Goodyear. "But we all know ugly irregular wear when we see it." Each axle position has its own set of uneven or irregular wear problems and its own solutions. Dagnall lists some common irregular wear problems.
Steer Tires - In the steer position, fast shoulder wear leading to cupping is the biggest irregular wear problem. The highest incidence occurs on the outside shoulder of the right steer tire because drivers make left turns tighter and faster than right turns. Steer tires may also operate under higher loads - 5.000 to 6.000 pounds than drive or trailer tires depending on whether the vehicle is loaded or unloaded. To turn the vehicle, the two steer tires must overcome the forces of the tandem drive tires that are trying to keep the vehicle traveling straight ahead This causes tremendous scrubbing forces on the outer rib of the outside steer tires in the turn. Fleets should consider purchasing steer tires designed to resist fast shoulder wear and prevent it from turning into cupping wear. Also, many fleets rotate steers from side-to-side and flip them on the wheel to keep the least worn should rib in the right outside front.
Drive tires heel/toe wear - The more extreme high/low lug wear, is the most common irregular wear problem on drive tires. Drives must supply all the driving torque that propel the vehicle down the road. This torque causes drive tire lugs to lean over slightly in the tire footprint and then to snap out of the footprint as torque exceeds the load on the tire that holds the lug in the footprint. This type of wear is most noticeable on drive tires with open should lugs and on drive tires used on long haul tractors. Long haul wear rates are slow due to lack of
sideways scrub wear encountered on tractors that do more cornering on secondary roads, city streets and parking lots. Drive tires are also lightly loaded compared to steer tires. This creates a smaller, rounder footprint shape, particularly when the vehicle is unloaded. Even a fully loaded tandem drive axle may earn just 34.000 pounds, putting only 4.250 pounds of load on each drive tire. To maximize performance, fleets should purchase open shoulder drive tires where wear rates are 10.000 miles per 32nd or less and where removal mileages are usually less than 225.000 miles.Trailer tires - The most frequent irregular wear problems for trailer tires are flat spotting and diagonal wipe. This type of uneven wear is usually started by brake skids on lightly loaded tires. Like drive tires, trailer tires on tandem axle trailers never see more than 4.250 pounds of load, even with a full tandem axle load of 34.000 pounds. With an empty trailer the load per tire is likely to be more than 1.500 pounds. These free-rolling tires are not transmitting any driving torque that could help grind away minor brake skids. The trailer tries start to help each time the small flat spot, caused by the brake skid, passes through the footprint. This causes the flat spot to grow into a diagonal wipe across the tire tread, which makes these tires extremely slow wearing. Some trailer tires in long haul service are averaging more than 20.000 miles per 32nd. For this reason fleet should consider a shallow non-skid, high solid-to-void tire with a high density of rubber in the tread pattern to resist localized flat spotting that can grow into diagonal wipe wear.
Avoid or reduce irregular tire wear by choosing the right tire for the job on each axle and by practicing good tire maintenance. Remember to educate drivers to check tires and maintain the proper air pressure.