The Big Footprint

| April 07, 2005

Those who work with their own tires will need to buy a wider inflation safety cage if converting to wide singles.

When dual tires were first developed at the beginning of the 20th century, the goal was to increase the payloads one vehicle could deliver. Today, we still put dual tires on either end of two tandem-drive or trailer axles to give a generous hauling capacity. Our sources estimated the tire weight ratings for tandem axles with duals to be from 46,270 pounds all the way up to 58,000 pounds, depending on tire size and quality.

Engineers have long dreamed of substituting “super” or “wide” single tires for dual tire arrangements. Why? Duals may make for maximum-weight hauling capacity, but they cause major maintenance worries. And it turns out, say single supporters, that substituting a single, wide tire for a set of duals not only eases maintenance, but also slashes tire and wheel weight and saves fuel. While weight ratings may not quite match those available with duals, they will more than do the job in most applications. Today, a new generation of wide single tires is tempting truckers willing to try a new technology to increase payloads, save fuel, simplify their inspections and reduce maintenance.

The biggest advantages
Wide singles first saw adoption by fleets squeezing a few more pounds of payload onto their rigs. The weight savings are undeniable, though the precise savings obviously vary with tire size and brand and wheel type.

Al Cohn, Goodyear’s technical marketing manager for commercial tires, calculated the savings when replacing 11R22.5 duals with the Goodyear super wide Marathon 445/50R22.5 tires on a 5-axle tractor-trailer: 892 pounds. Michelin America Truck Tires’ Vice President of Marketing Marc Lafierre estimated the savings as “averaging 200 pounds per axle, enabling a tractor/trailer rig to carry from 800 to 1,300 pounds more payload.”

Part of what makes the difference is a willingness to convert to four aluminum wheels from eight made of steel.

J. David Walters, manager of warranty and field service for Alcoa Wheel and Forged Products, gave precise figures for a conversion from steel wheels and duals to one size of wide singles with aluminum single wheels: 318 pounds per axle for a total savings of 1,272 pounds. If staying with steel wheels, you’d substitute eight 128-pound steel single wheels for 16 82-pound steel dual wheels. The total weight savings for the rig drops from 1,272 pounds to 816 pounds.

The other advantage claimed for wide singles is fuel economy.

“Michelin X-One single tire users are experiencing from 4 percent to 10 percent in fuel savings, depending on the configuration of the truck and what it carries,” Lafierre says. Where do the savings come from? “Going from two wheels to one per axle end not only reduces weight but also lowers rolling resistance by reducing the number of flexing sidewalls, thereby improving fuel economy.”

Cohn at Goodyear believes having “fewer flexing sidewalls” is good because, he says, “Drivers like how it feels. It gives a softer ride.” Part of this may come from “road rutting” occurring from standard duals. Wide singles don’t fit into the same, worn grooves in the road.

Goodyear’s wide singles operate at 120 psi rather than 100 psi, and the tread thickness drops from 30/32 to 25/32. Such factors tend to help fuel economy, making these tires even more desirable. “As fuel prices increase, fuel economy becomes more and more important,” Cohn says. “But fuel economy involves so many factors it’s hard to say what the increase will be. You won’t get 10 mpg instead of 7 mpg, but it will be better.” Walters listed fuel economy and weight as the two biggest reasons fleets are switching to wide singles. “Fuel mileage will improve by some percentage with super singles,” he says. “Each fleet will have to determine what that percentage is for their particular operation.”

The maintenance advantage
All experienced truckers know that one of the biggest hassles in trucking is matching the dual tires at each wheel position. Tires that are not identical initially, or that may not have been subjected to identical wear conditions, will have different diameters. This means they fight one another going down the road. Even a slight difference in inflation pressure will give the same problem. So as soon as a dual tire gets a significant leak, the pair of tires is in serious trouble.

The presence of a flat or low dual is rarely obvious to the driver right away. The result is at least a few miles of serious stress. As Walters says, “Running a flat tire for a period of time will cause damage to the flat tire through scrubbing and also transfer load onto the other tire/wheel dual. This is not good for the tires and wheels.” Lafierre says, “Running one flat dual causes the other dual to carry all of the load. It is not only dangerous – because it could cause rapid failure of the remaining tire and create a hazard to others on the highway – it is also illegal.”

But for wide singles, says Walters, “The driver has to stop when a flat occurs. This saves the tire casing.” While duals give an advantage in enabling the driver to comfortably pull off the road, that very capability delays discovery of the problem and creates almost certain damage. And, says Lafierre, “At Michelin’s test facilities, duals and X One tires were compared in passenger side blowout situations on a left hand turn at speeds up to 57 mph. Equipment used included 6 x 4 tractors with double drop deck trailers loaded with glass to 80,000 pounds. There were no adverse effects in handling, with the vehicle with X One tires coming to a completely controlled stop while turning off the road.”

Lafierre also mentioned Michelin’s “use of low resistance materials, which allows tires to run cooler during operating, since heat is a major factor in tire aging.” Cohn says Goodyear’s wide singles use a thinner tread to keep temperature under control. Cool running helps prevent blowouts from happening in the first place.

As far as routine maintenance goes, Lafierre says, “A driver or fleet maintenance person only has one tire to check for air pressure, and the valve stem is in plain sight. With duals, the inside dual rarely gets checked for air pressure, and the sidewalls and tread can hardly be seen. Drivers take more ownership because they can see the undercarriage of the vehicle for a pretrip inspection.” Of course, tire rotation becomes a much easier task, too.

Wide singles, says Cohn, “offer better brake cooling because you don’t trap air between the tires.” Walters agrees, saying, “The wheel offset also allows the brake drum to cool quicker since the drum is exposed.” Better brake cooling not only helps performance but also increases lining and drum life significantly.

But the offset of the wheel may create a problem. This tends to cock the spindle inside the bearing, subjecting it to stresses it may not have been designed for. “The disadvantage is that the 2-inch offset wheel is not recommended by axle manufacturers on type N spindles for trailers,” Walters says. “Truckers and vendors are concerned whether wheel bearings will hold up under the stress,” Cohn says. So check with component manufacturers to make sure the wheel bearings at every position will still live in spite of the offset. After a switch to wide singles, extra attention to periodic disassembly, renewal of seals and repacking is in order.

Our sources say the same tire tools and even most tire changing machines will handle the bigger tires and wheels. “Mounting a single is the same as mounting a 22.5 x 8.25 rim,” according to Walters. But, you will have to buy a larger safety cage for inflation. And Cohn estimates wheel/tire weight at “220 pounds versus 130-140,” meaning you may need to use different wheel-handling equipment. But Lafierre insists, “there have been no problems in regard to safe handling, and there are scores of fleets handling them every day.” The same wrenches can be used for changes and lugnut torque checks.

The same wheel fasteners will work well, says Walters, except with hub-piloted wheels. These are the ones centered where the wheel fits over the hub and not by the lugnuts. Here, he says, “a special capnut is recommended.”

Cohn warns that these tires work considerably harder. This is why Goodyear’s wide singles run at 120 psi rather than 100 and use thinner treads. “Air pressure is really critical,” he says. He recommends using a calibrated gauge and “checking pressure every time you do a walk-around.” At least airing them up will be easier. Cohn also believes wide singles are an ideal application for a tire inflation system.

Cost Analysis
In spite of the benefits, wide singles aren’t for everyone, Cohn says. “It’s a niche market. We haven’t even been very aggressive in marketing them so far, and we’re not convinced we should market wide singles to everybody,” he says. “They are for fleets that are especially weight and fuel-consumption sensitive.”

Dave Redfern, channel manager, O.E. and national fleets at Bridgestone/Firestone, agrees that wide singles will be primarily niche tires. “This niche will apply primarily to over-the-road/heavy/bulk haul applications that gross out before they cube out, thus gaining the ability to carry more payload,” he says.

Bridgestone/Firestone expects its Greatec tires to provide competitive mileage and casing durability. “However, there will still be some mileage shortfall on wide base tires with respect to original tread life vs. traditional dual tires.” There are also some limited service issues.

Redfern suggests using Bridgestone/Firestone’s “fuel efficient dual tire combination of M720, R195F” if the fleet’s primary reason for switching to wide singles would be fuel economy gain.

So, how do you determine if wide singles are right for you? “You’ve got to put a pencil to the problem of whether or not you should go to wide singles,” Cohn says.

Total cost of wheels and tires will be slightly lower because of the reduced parts count, including things like fewer valve stems and valves. But the miles on the tires at renewal or retread will be fewer. Cohn estimates ideal, over-the-road life at about 250,000 miles, versus 300,000 with duals. One factor here is the use of tread that’s 25/32 inch thick instead of 30/32 on Goodyear’s wide singles. So if you’ve been having trouble getting adequate tire life, this is probably not the way to go.

Also, “With normal duals, you’ll get two retreading cycles,” he says. “With wide singles, if everything is right, you’ll still get only one.”

Tire mileage varies from fleet to fleet, Alcoa’s Walters says. “My suggestion is to try a couple sets and see if the tire mileage, fuel mileage and recapping costs are justifiable in your fleet,” he says.

You’ll definitely save on fuel and be able to carry more payload with wide singles. For those fleets that can load the trailer with that extra 800-1,200 pounds and charge for it, it means extra dollars. However, those fleets running loads of more than 80,000 pounds should be aware that total tire rated capacity is higher with duals. As Cohn says, “These are not for 90,000-pound work.”

There also may be more limited availability of tires if you run in areas well away from routes heavily traveled by commercial vehicles, though this situation is improving rapidly, according to our sources. This might mean extra charges if you break down and your rig has to be towed or if you need to pay extra for a long-distance road call.

However, Michelin seems to be marketing its X-Ones aggressively, and Lafierre says, “There is good and growing availability of the tires through hundreds of Michelin dealers and travel plazas throughout North America. In addition, Michelin offers a special service for those who experience problems.”

If you spend hours inspecting your vehicle, repairing and rotating tires, and trying to match duals, the much simpler maintenance could enhance your income. And drivers will certainly like the simpler task of changing a wide single as compared with changing an inner dual.


Weighing In on Carrying Capacity
When considering wide singles, one critical question becomes whether or not it’s practical to substitute four big tires for eight smaller ones, weight-wise. Manufacturers’ views of just how suitable their wide singles are for carrying the heaviest loads differ. Al Cohn with Goodyear pegs the capacity of one of Goodyear’s wide singles, with load range L, at 10,200 pounds, giving a tandem capacity of 40,800 pounds. So even if you run extra-beefy 40,000-pound tandems, you’re home safe with four wide singles. Cohn admits, however, that, “Their rating is not quite double that of two tires, so the load factor is higher.”

Alcoa’s J. David Walters reports there are single tire and wheel setups rated for as much as 12,800 pounds, giving a rating of as much as 51,200 pounds for a tandem axle. He estimates dual tandem axle rating as maxing out at 58,000 pounds, however.

Marc Lafierre of Michelin reports, “The X One tire carries the same load as the two conventional dual tires it replaces, allowing the same 80,000-pound GCWs. The X-One tire was designed with a low aspect ratio and a very flat profile, giving the tire a larger footprint and more contact with the road. The X-One tire handles oversize loads better than duals because of the X-One’s inherent strength and wider stance.”

Walters agrees on this point. He notes that even though a wide single is narrower than two duals, the effective track of the vehicle is wider with wide-singles, ensuring stability in turns.


Who’s Got ‘Em?

  • Michelin has been the most aggressive marketer of single wides with its X-One.

  • Goodyear offers the G178SS and G286SS for special service applications. Super singles for linehaul usage, known as Goodyear Marathons, are in testing and are likely to be available early in 2005.
  • B.F. Goodrich has the ST565 series of wide singles.
  • Bridgestone has four series of its Greatec wide singles, the M711, R194, MM857, M844 F and L312.
  • Yokohama has the RY253 wide single, with a maximum speed rating of 65 mph.
  • Continental does not offer wide singles right now but has a design in fleet testing.

For further information, contact:
Bridgestone/Firestone
(866) 819-0105

Michelin U.S.
(800) 847-3435
(877-966-3911 Hotline for wide single emergency service)

Goodyear Tire and Rubber Co.
(330) 796-2121

Alcoa Wheel and Forged Products
(800) 242-9898

Continental Truck Tires USA/Canada
(704) 583-3900

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