Trends in the medium-duty truck tire market come and go, but the drive to reduce rolling resistance levels is here to stay, according to Donn Kramer, Goodyear Tire & Rubber Co. director of marketing for commercial tires.

This extends not only to steer and trailer tires, but drive axle tires as well. That's why more drive tires are rolling off the assembly line with closed shoulder tread designs, Kramer noted.

"Open shoulder designs, which may be more attractive in terms of performance, are worse on fuel economy. There are more voids in the tread so there's less rubber in contact with the road. Also, there are generally more sipes. Those extra sipes hurt rolling resistance," Kramer said.

In addition, open shoulder designs are more susceptible to uneven wear, which reduces tread life.

Kramer said 60% of a drive tire's fuel economy is derived from tread elements. The rest is derived from other components, such as compounding.

To reduce rolling resistance, "you have to change the dynamics of the tire's lug elements, meaning they should be stiffer. The stiffer they are, the better it is for (lowering) rolling resistance. But you can't get them too stiff because that won't be as good for traction," Kramer said.

Technologies exist to inter-lock tread lugs, Kramer noted, "and that's what is happening with closed shoulder drive tires. You're trying to stiffen the lug elements as the tire rolls through its footprint."

Truck tire manufacturers also are switching to silica-based compounds, an effort driven by government-mandated fuel economy requirements.

Major Shift Looming?

Kramer said the focus on reducing rolling resistance will continue as the government pushes for more fuel-efficient commercial trucks.

In June 2010, President Barack Obama directed the U.S. Department of Transportation (DOT) and the U.S. Environmental Protection Agency (EPA) to boost the fuel efficiency of medium- and heavy-duty trucks, starting with 2014 model-year vehicles.

The DOT and EPA are developing rulemaking proposals to achieve the objective. A final rule will be issued next summer.

"If (fuel efficiency) standards similar to automobiles and light trucks go into effect for trucks at some point in the not-too-distant future, you're going to see tremendous emphasis on trying to hit (low rolling resistance) targets," Kramer said.

If fuel efficiency standards are set, original equipment truck manufacturers "will decide upon tire sizing and to a greater extent tread designs."

Don't Forget Casings (They're an important component, too)

A big part of drive tires is their casing construction and how many times a   fleet can utilize that casing by retreading it," said Chris Hoffman, manager, TBR and retread product marketing, Bridgestone Bandag Tire Solutions. "That's pretty important as fleets try to keep their total operating costs low."

All manufacturers, he said, want to design "a 'super tire' with the lowest rolling resistance and the longest tread wear, (but) there are different stresses put on a driven tire versus a free rolling tire."

As tiremakers continue to develop new drive axle tires, "over time, you're going to see changes in tread designs, you're going to see changes in compounds, and you will see changes in casing construction, too," Hoffman said.