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.”

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