Steer tires typically receive a lot of attention from fleets and drivers.

Certainly, these tires have a huge impact when it comes to driver comfort and road noise, but their weight-bearing abilities are more of a concern. These tires usually carry more load than any other tire on the vehicle. An individual drive or trailer tire may carry less than 4,500 lbs., while a steer tire is usually asked to carry 5,000 to 6,000 lbs.

While the steer tire has to be strong enough to carry the weight, it also has to be tough enough to handle scrubbing. “Every time the driver turns the wheel, the steer tires encounter significant lateral forces as they fight the tendency of the truck’s tandem rear axles to go straight ahead,” said Goodyear Tire & Rubber Co. “These forces are at their greatest during hard cornering or in an emergency turning maneuver.

“Side forces away from the direction of the turn cause scrubbing across the tread surface, which leads to rapid tread wear, particularly on the outer rib,” Goodyear continued. “Since drivers tend to turn more sharply to the left (sight side) rather than to the right (blind side), the right steer tire tends to get scrubbed the most.”

Setback front axles, typically 13 to 15 inches back from the standard position, are designed to improve weight distribution as well as the truck’s turning circle. But that also increases side forces on tires during turns.

Goodyear studies have shown that tires on a tractor with a 140-inch wheelbase must generate about 65% more cornering force to “slide” the tandem drive axles around a corner than steers on a 210-inch wheelbase tractor.

The setback axles also incorporate increased wheel cut angles, which add to steer tire scrubbing when turning. For many years, the standard industry wheel cut angles have been between 32 and 34 degrees. Setback axles are typically at 42 to 44 degrees. While side forces on steer tires can accelerate tread wear, higher loads on steer tires can actually help even tread wear by providing a larger, squarer footprint where the tire contacts the road surface.

“Our tests have shown that vehicles with lightly loaded steer axles (10,000 lbs. or less) are more prone to irregular steer tire wear than those with heavily loaded front ends,” Goodyear said. “With light loads, the tire’s contact area is quite long in the area of the center tread rib and much shorter toward the shoulder rib. Since the footprint is uneven, there is more scrubbing and wearing away of the shoulder rib.”

It should come as no surprise that the most frequent steer tire problem is fast shoulder wear, which can lead to cupping and early removal of the tire. Instead of running steer tires down to 6/32-inch of remaining tread and more than 100,000 miles before removal, a fleet might get only 70,000 miles out of them before the tires have to be removed for worn shoulders, while the center portion of the tread may have more than 10/32-inch of remaining tread.

Two other significant threats to steer tire performance are misalignment, which results in uneven wear, and underinflation, which causes excessive casing heat. As we all know, excessive heat reduces a tire’s retreadability or possibly leading to something far more serious: an on-road failure. Unlike a failure on one of a pair of dual tires, there is no support when a steer tire fails, and the driver may struggle to keep control of the vehicle.

“The bottom line,” said Goodyear, “is buy quality steer tires. Why compromise performance for the most important wheel position on any vehicle?”

With all the other pressures on truckers these days, the fewer worries, the better. “By investing in advances in steer tire engineering, truck operators can strike steer tires off their worry list,” the company said. “More importantly, they’ll be able to feel more confident about lowering cost per mile.”