NASHVILLE, Tenn. – Wide-base single tires are often called “super singles” for a good reason. Goodyear may have trademarked the phrase for its own products – and Michelin was the first to bring these wider tires to market – but the product category as a whole offers a number of “super” promises.
The combination of lighter wheel ends and fewer flexing sidewalls can improve fuel economy by 2-5%, and the tires are expected to play a role in helping some truck manufacturers meet 2014 standards for lower greenhouse gas emissions.
“The fuel savings is real. It’s big dollars,” said CR England maintenance head Greg Kitchen, during a presentation for the American Trucking Associations’ Technology & Maintenance Council.
The potential advantages are not limited to fuel economy. The products end the worries about mismatching dual tires, a known cause of premature tread wear, and the designs can save 1,272 lbs when coupled with aluminum wheels across a tractor-trailer. Wider tires also make it easier to move dollies around fleet yards, and this could prevent back injuries, said Peggy Fisher, president of TireStamp.
“The ride is better,” she added, likening the experience to riding on bias tires, and describing how the wider versions will not fall into the ruts on a highway.
Most of the designs officially known as Low Profile Metric Wide Base Radial Tires come in the form of 445/50R22.5 sizes rated at 10,200 lbs at 120 psi, but some buyers opt for the 455/55R22.5 designs rated at 11,000 lbs.
Still, despite their promise, wide-base designs represent a mere 5% of the tire market.
CR England has actually put its related tire program on hold because of challenges with retreading. When using the wide-base tires on tractors, the fleet lost eight traditional casings which could otherwise be retreaded for use on trailers. And while traditional tires could be retreaded three times, the fleet questioned how many times the wider casings could be reused.
The fleet has also been reluctant to mount wide-base tires on trailers because that’s where most of its on-road tire failures occur.
If a wide-base tire blows out, the truck cannot limp home, and the wheels are usually damaged in the process. “They’re very susceptible to irregular wear if they’re over-inflated or under-inflated,” Fisher added. Then there’s the additional cost. “The cost of one wide base tire is more than two dual tires. These are expensive tires, and the wheels are expensive, too.”
Of course, that’s if the tires can be found: “Availability can still be a problem, depending where you are.”
Then there are unique maintenance needs to consider.
A negative camber or flexing axle can cause the shoulder to wear prematurely, and the latter might be a bigger issue for those hauling higher weights, said Guy Walenga, director of engineering for Bridgestone Americas. Those who find both shoulders wearing away are likely over-inflating the tires, while excessive wear on the inside shoulder usually involves a negative camber angle.
Shops also need to take the care to properly seat the brake drum on its pilots. And operating pressures can differ when the tires are compared to traditional sizes. This means checking load/inflation tables before reaching for a compressor.
“Fleets can achieve the best overall wear on wide-base trailer tires with consistent inflation pressure maintenance, trailer alignment, proper bearing preset, and when possible, tire orientation,” Walenga said. “When spec’ing trailers, incorporate wider axles and zero-offset wheels at a minimum, and confirm that the axles do not start out with any negative camber. Operate trailers at the maximum load as often as possible. Lightly loaded trailers contribute to free-rolling wear,” he added.
The shift could affect the choice of a fleet’s retreading shops as well. “Do they have the right equipment, and are they following the right process?” asked Ed Steck, director of franchise business services for Michelin Retread Technologies. “With short cuts, you’re going to end up with problems out on the road.”
The shop’s probes should be 12.1 inches long, about double the length of a probe used for traditional tire sizes, to reach from one shoulder to the other. Otherwise punctures in the shoulder could be missed. Rotation speeds also need to be slowed, and buffing should not begin until pressures are running between 18 and 22 psi. Those who are too quick on the trigger will expose steel. And an expandable rim of 14.5 inches rather than 13-3/8 inches will be needed.
“Tread table rollers should be completely cleaned before each build series,” Steck added, noting how this will keep the tires from picking up contaminants from the rollers.
The impact of wide-base tire choices is not limited to tires, either.
The tires can be run in three different outsets, explained Al Cohn, director, new business development and product support at Pressure Systems International. A two-inch outset will have a 92-inch total width, 1.13” will have a 90.4” width, and 0” will have an 88.2” width. “There’s a big, big difference in the scenarios,” Cohn said. Those who simply swap standard dual wheels with a single wheel can alter the stresses in the bearing’s spindle and hub. The bigger the outset, the higher the loads on the outer bearing. This can reduce bearing life and wear the spindle.
Parallel systems use a larger outer bearing to resist the increased stress, Cohn added. “The wider axles, together with the wide-base, zero-offset wheels, will avoid bearing issues.” And housings will need to be thick enough to counter the increased bending caused by outset wheels.
But each bearing supplier will set its own standards for bearing geometry and profiles. Timken says there will be little difference in bearing life between duals and wide base tires, regardless of zero-inch or two-inch outsets. Meritor, meanwhile, reports excessive spindle wear with two-inch outsets. Dana has not seen any difference.
“There is a big, big factor in reducing bearing life when you mix cones and cups,” Cohn added, noting how Timken and Meritor have quantified this at 80%. “Never mix cups and cones.”
He also cautions against jumping for a cheap source of offshore bearings. The hardness of a trailer’s spindle ends, and the quality of steel in the bearing, will make a difference.
There are plenty of hard decisions to be made.
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