Wide singles: Then and now

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Paul Richards is editor of Commercial Carrier Journal. E-mail [email protected] or call (610) 993-9430.

Some 15 years ago, when wide or “super” single tire manufacturers sought to replace dual-tire assemblies with their products, we reported on the pros and cons of going single.

With the relatively recent introduction of Michelin’s X-One series, over-the-road, wide single tire, one might wonder: Are singles’ benefits still there? Have their drawbacks been overcome? Will they score this time around?

Wide singles were desirable for fleets looking to save weight and increase payload. They weighed less than the duals they replaced, and that’s true of the X-One, according to Randy Clark, Michelin’s vice president, marketing. “The X-One can reduce overall weight by up to 990 pounds, when used in both drive and trailer positions,” he says.

Improved fuel economy was another touted benefit, and that still seems plausible. A wide single tire has a smaller footprint than a pair of duals, and there are only two sidewalls at work. So there’s less material to flex, hence less rolling resistance.

And, unless the tires in a dual assembly are perfectly matched – in size, inflation pressure and degree of tread wear – their loaded radii will differ. In that case, one tire wants to travel farther per revolution than the other. The tires fight each other, consuming tread and fuel. Obviously, that can’t happen with wide singles. The X-One, says Michelin, can improve fuel economy by 5 to 10 percent.

Yet another plus for X-Ones: as with the old super singles, there are fewer tires to mount, dismount, inspect and rotate, which reduces maintenance downtime.

Years ago, single life had its advantages, but it wasn’t worry-free. A major consideration was tire trouble on the road. If a wide single blew on a single-drive-axle tractor, you had problems. If one failed on a tandem, an operator could possibly limp to the nearest truck stop or garage, but it was unlikely that the facility would stock a replacement.

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“The technology just wasn’t there back then,” explains Don Pella, linehaul segment manager for Michelin. “The X-One uses “InfiniCoil technology, which is a belt construction that runs perpendicular to the radial ply. This amounts to about a quarter mile of extra steel. It adds stability and acts as extra armor against road hazards.

“Also, we now have 500 points of service, so the tires are not difficult to find,” Pella says. “And, since they ride on wheels that are compatible with standard hubs, and since the tires come in standard overall diameters, you can simply unbolt an X-One and replace it with a pair of duals, if needed.”

Another concern with super singles was roll stability. When duals are replaced with wide singles, and wheel offset is not changed, an axle’s track is narrowed, and the danger of rollover increases. Although offset wheels were available, they were scarce. And they changed wheel bearing loading, so it was feared that they would decrease bearing life.

“The X-One uses wheels with a two-inch offset for roll stability,” says Pella. “And we’ve had no reports of bearing-life degradation.”

Finally, a single’s smaller footprint applies more unit pressure to road surfaces, and a few states actually put restrictions on their use. But “the X-One was designed to be in strict compliance with all federal and state requirements,” notes Pella. “You can run them virtually anywhere.”

So, almost two years after its introduction, is the X-One delivering on Michelin’s promises? “We’ve been evaluating them for about a year,” a Western, 500-vehicle fleet manager confides. “It’s all good…performance, service, availability…I have no issues. We’re in the process of retrofitting the entire fleet.”

All things considered, the X-One appears to be much better thought-out than the old super single. Its improvements in design, compatibility and availability should enable weight-conscious fleets to trim down and carry more payload – without the hassles of single life in the ’80s.