The wear demons don't discriminate between standard and wide-base single tires. With a few exceptions, the kinds of irregular wear that standard tires exhibit will appear on wide-base singles, too.

In a recent fleet survey done by the American Trucking Associations' Technology & Maintenance Council, managers reported nothing exceptional with wide singles in free-rolling positions, though many noted that some wide singles seemed more susceptible to certain types of wear under certain conditions.

Misalignment and low inflation pressures are the most common culprits, noted Guy Walenga, Bridgestone's director of engineering for commercial products, at a tire seminar last summer. "The wear associated with pressure variations and alignment is consistent with dual tires, but it can be exacerbated on the wide-base singles," he said.

One type of wear associated with wide-base singles - inside shoulder wear, especially on trailers - is getting a lot of attention. While it's fairly common on the inner tire of a dual assembly on trailers, it hasn't been viewed as a big problem.

"Fleets usually don't use premium tires on trailers, or they run out steer and drive tires back there until they are retreaded, so fleets have not been overly concerned about inside shoulder wear on dual tires," says Doug Jones, Michelin's customer engineering support manager. "It's a different situation now that fleets are using wide-base singles on trailers. The cost of the tire is a factor. When the inside shoulder wear shows up, it creates a lot of consternation."

The causes of inside shoulder wear are generally the same across the two types of tire: axle misalignment, load-induced camber, low inflation pressure, and in some cases, neglect.

"We've looked at a number of things, but we all know that trailers are often not properly aligned, tire pressures are low and all of that," says Jones. "What we have found is that if a fleet is diligent with tire pressures, and the trailers are properly aligned, inside shoulder wear on wide-base singles is minimal. In some instances they don't even see it."

Why some fleets have problems and others do not remains a pressing question. The tire makers are looking into it now, and TMC has convened a task force to get to the root of the problem.