The need for traction at the steer and drive positions is self-evident. While deeper treads here are an advantage, steering and torque inputs to tires at these positions can help curb irregular wear - barring any external problems. There are few external forces acting on a trailer tire, so deeper treads on trailer tires tend to promote irregular wear, and once it starts, it's impossible to stop.
Take Goodyear's G316 LHT trailer tire, for example. Goodyear's commercial tire marketing and communications manager, Tim Miller, describes it - in jest - as a "half-worn" steer tire.
"It's not a lower quality or lower performing casing. It's the same as a steer tire in most regards, but it starts with just 12/32 of tread as opposed to 16/32 or 18/32 on a steer tire," he says. "When you start with a shallower tread on the trailer, you get a longer-wearing tire, because the shallower tread is more stable and less prone to squirming. If you start with deep treads at the trailer position, you wind up with noisy, ugly-looking tires that wear faster."
For many fleets, however, irregular wear on trailer tires is not a worry, Bridgestone tells us. "Either it's not a problem, or if it is, they don't worry about it."
Even without the torque and steering inputs, trailer tires are subject to external forces that can cause problems, like lateral scuffing caused by crosswinds or misalignment, curb damage, etc.
Trailer tires are often designed with various defense mechanisms built in to mitigate these kinds of wear and damage, such as the Defense Grooves and Equalizer Rib found on the Bridgestone R195F. Bridgestone says these features are self-sacrificing by design in order to preserve the integrity of the rest of the tread.
Ultimately, what you want to do is get every possible mile out of every 32nd of tread on the tire - without risking the integrity of the casing in the final few 32nds, says Michelin's product marketing manager, Don Baldwin.
"The shallower the tread, the less able it is to protect against penetration," he says. "You can take a tire down to the point where the tread life is maximized, but if you push too far you can damage the casing, and that could hurt the ROI on your tire program. We recommend not taking the tread much below 4/32. The casing still has some protection there."
You can take your chances with thin-treaded trailer tires - they are, after all, more efficient at that stage of life. But a potentially valuable casing hangs in the balance. A couple of thousand more miles of tread life, or zero value for wrecked casing. It's a roll of the dice.
James Mason, maintenance director for bulk cement hauler McConnell and Sons, of Little Rock, Ark., says he has found the silver bullet for trailer tire protection: Goodyear's Dura-Seal Technology. He's less concerned about casing penetration today, because he knows the self-sealing feature of Dura-Seal will prevent air loss in holes up to 1/4-inch in diameter.
"We had a problem with debris picked up on jobsites, and used to see 10-15 flat tires per month," Mason says. "Some of those tires were repairable; many were not, and those were good casings destroyed by running them soft or flat."
Some trailers may not get to maintenance facilities for months at a time, especially when they are dropping at customer yards. A tire can lose up to 5 psi over a month all on its own - through osmosis. If there's a slow leak, it'll be even worse. When a driver pulls a soft tire down the road, it's a death sentence for that tire. Automatic inflation systems can earn their keep here in these cases.
According to Al Cohn, director of new market development and engineering support for the Meritor Tire Inflation System by PSI, a slow-leaking puncture in the tread is the number one reason for tire-related road-service calls.
"If you don't lose the tire altogether, fuel economy will certainly be compromised," Cohn says. "Fuel economy can drop by 2-3 percent if tires are running at reduced air pressure." And if a service call is warranted, you've probably crucified the casing, too.
"There are financial gains from auto inflation systems beyond improved fuel economy, like extended tread life, and the better prevention of blowouts due to incorrect tire pressure," says Steve Slesinski, director of product management for the Commercial Vehicle Products Group of Dana Holding Corp. "In any event, the paybacks are substantial when you compare the benefits of a tire management system to using nothing at all."
You can throw your old skins back to the trailer in hope of getting a few thousand miles more before decommissioning them and hope for the best, or you can manage the risk, get the miles, and preserve casing value, too.
From the August 2010 issue of Heavy Duty Trucking.