They're called "double-wide," "super-wide," "wide-base singles," anything but "super singles." That's a Goodyear trademark for oversized conventional section tires.
We're looking at the ones that are no taller than conventional rubber, but twice as wide. They sit on 14-inch wide 22.5-inch rims. Two companies make them. Michelin calls theirs "X-One." Bridgestone's are named "Greatec."
Both brands' tires are Load Range L, meaning they can each support 10,000 pounds at a minimum inflation pressure of 115 psi. Recommended maximum load is 10,200 pounds at 120 psi, with a maximum speed of 75 mph. When running fully loaded, with 34,000 pounds on each tandem, you can run within manufacturers' recommendations (8,500 pounds per axle-end) at 100 psi, but you should never, ever go below that. These wide tires are extra sensitive to air pressure.
Both companies make specialized drive and trailer tires. Michelin's X-One tires have Infini-Coil construction, with more than one-quarter of a mile of steel cable wound circumferentially around the tire. Bridgestone's Greatec tires use special "Waved Belt" design that allows controlled distortion to keep the tread flat to the road and reduce tire wear.
Pros and Cons
The fact that these tires can be interchanged with readily available sizes is a great safety feature. These tires are not yet in widespread distribution, so rather than waiting for the exact tire to be delivered, you can replace them with dual low profile 22.5s if you need to get under way fast.
Product availability is just one issue about these wide tires. Others are their sensitivity to low air pressure, their greater susceptibility to curb damage, the lack of "limp home" capability with only one tire per wheel-end, and the fact that you need to be a Paul Bunyan to pick up an assembly.
Retreadability is still an unknown. Both brands provide pre-molded treads for retreading at their own shops, and Bandag can retread the Bridgestones. The question is, how many treads is each casing good for? The makers promise at least one, but that, as always, is provided the casing has not been abused.
With these possible negatives, why should anyone consider these tires? Because the benefits outweigh the risks-for the right operation. The primary benefits are weight savings and increased fuel economy. Secondary, but still important benefits, are ride quality and, when applicable, improved stability. And a full set of four costs less than eight standard tires and rims.
While each wide tire assembly weighs significantly more than each half of a dual, the entire wheel and tire assembly weighs less per axle end. Switching from 16 duals on steel wheels to eight wide-base tires on aluminum wheels saves more than 1,200 pounds. Converting from aluminum wheels still saves almost 600 pounds.
A major factor in improving fuel economy is by reducing rolling resistance. When tire sidewalls flex, energy is consumed, contributing to rolling resistance. With half the sidewalls eliminated compared with duals, fuel economy will improve from one to five percent, all other factors being constant. Greater savings will be found closer to 55 mph, with benefits diminishing as speeds approach the tires' 75 mph limit.
These tires place enough tread on the road to be legal in all states that limit loads per-inch-of-tread-width. Because there is no gap between two duals, the inner edges of the tires are further outboard, so engineers have more room to lower tanks and bulk hoppers. The resulting lower center of gravity improves stability.
How They Ride
Finally, ride quality is improved. I heard that from a number of drivers, but I had to find out for myself before writing about these tires. At the Mid-America Trucking Show, Michelin arranged a test drive in a Volvo 780 fully equipped with their X-Ones. Then Bridgestone and Peterbilt made a Greatec-equipped test rig available at Denton, Texas.
In Louisville, I couldn't get fully up to speed, nor could I find rutted roads to shake down the X-Ones, but I did manage a few quick stability tests. Every time I had the opportunity, I tried lane change maneuvers to stress the tires. They performed perfectly, regardless of speed, providing stability and traction as good as any duals. If anything, recovery was improved.
In Texas, Peterbilt provided two almost-identical 387s to drive around North Texas and the grounds of the Texas Motor Speedway. One Pete had Bridgestone's standard duals and the other was shod with Greatecs. I was able to put them through a little more torture than the X-Ones, but only because of logistics. No reflection on either tire.
In every test, the Greatec excelled compared to the duals. I did lane changes at speeds from 40 to 70 mph, ran on rutted roads, experienced some stretches of blacktop so worn they were essentially gravel roads. The Greatecs gripped the pavement better, smoothed out the ruts, riding over the tops for a stable, controlled, comfortable ride that equaled or surpassed any with duals.
Are these tires for you? No, if you don't meet all the qualifications. But a resounding "yes" if you do.
Do you or your fleet run lanes where there are a number of service shops for your preferred tire?
You'll want to be sure the tire you choose is at your preferred tire shop.
Do you practice good tire maintenance? Do your trailers have tire pressure warning or maintenance systems? Do you pull bulk loads or "gross-out" so weight is a factor?
If so, you can get better fuel mileage, more payload, greater stability and a more comfortable ride with super-wide, double-wide, extra-wide tires. Just don't call them "super singles."
