Designer tires

This diagram shows how many belt layers and other features it takes to make up a modern heavy truck tire. Each layer has its own rubber compound to bond it together and protect it. The latest computer modeling helps engineers formulate the best possible compound for each area of a tire.

In the old days, tire makers relied on a long cycle of design and road testing to refine the final product. No longer. Engineers now simulate the shape, materials and performance in the design room before manufacturing and road testing even takes place.

“With the advent of computer-aided design techniques, tire engineers and compounders have been able to evolve the art of designing tires into a science, so the tires of today are much different from the tires of 20 years ago,” says Tim Miller, Goodyear Tire and Rubber’s director of marketing communications.

These new research and development tools enable designers to create tires that more than ever improve fuel economy, last longer and match the specific needs of different applications. For owner-operators, facing more products than ever to choose from, most with sophisticated design and characteristics, it means careful selection of tires for every position will pay big dividends.

At the major tire companies, computer-aided design, including the use of finite element analysis, has allowed designers to create tires that can do things never dreamed of in the past. Finite element analysis is a technique that allows the design of any physical object, for example an engine block or a tire casing, to be broken down into tiny segments and analyzed as to how it will react when stressed on the road.

“We have the ability to try many more options before manufacturing the first prototype,” says Don Baldwin, product manager at Michelin North America. Still, “all our tires still go through complete mechanical and field testing. You can’t just prove a design in a computer.”
Baldwin says he tests things such as the tire’s architecture, tread compound and design, and can even predict noise levels.

Miller says such attributes are especially important in long haul, where tires can make a big difference in fuel consumption.

“We have made large strides in rolling resistance without giving up removal miles,” says Guy Walenga, an engineering director with Bridgestone Bandag Tire Solutions. “There is also greater resistance to irregular wear.”

Computer hardware and software also help designers experiment with tread compounds down to the molecular level to come up with the proper characteristics for each application.

“We can optimize all the factors to balance two or three properties we want,” says Adam Willis, who works in product development for Continental Tires North America.

Bear in mind that most attributes that make tires more fuel-efficient also help them last longer. For example, reducing the flexing of the sidewall and the “hysteresis,” or how much a tread resists rolling down the road, tends to increase a tire’s life by allowing it to run cooler, Willis says.

Because a deeper tread always flexes more, another feature of fuel-efficient tires is less tread depth. Walenga gives the example of a Bridgestone drive tire with 32⁄32 tread depth and a more fuel-efficient model with 26⁄32 tread depth. For the fuel-efficient model, he says, “The design is different, the compounds in the tread and sidewalls are different, and there is a dramatic difference in rolling resistance.”

Walenga says improvements in casing design, compounding and tread design have contributed to fuel efficiency, though the biggest improvement is in rubber compounds. “There are 13 to14 different recipes in each tire, including the inner liner, the tread, the under-tread, the bead, which may have three different compounds, the sidewall, the skim stock around the steel cords, and so on,” he says.

A fuel-efficient tire’s shorter life might be a worthwhile tradeoff if the savings in fuel costs are high enough.

“With fuel at $2.25, the long-mileage tire could make up for the extra fuel cost,” Walenga says. “Now, six or eight months later, with fuel at $4.50, you need to take another look. Owner operators and small fleets might want to put on some fuel efficient drive tires so they can compare total costs and see how they look. At $2.25 you were right on the edge, but even at $4.00, you need to do some testing.

“A 5 percent reduction in rolling resistance equates to a 1 percent to 2 percent fuel savings on the highway. We see 3:1 to 4:1 ratios in dollar savings, and the EPA says it can be higher than that. So, don’t just look at tires when looking at tire costs,” Walenga says.

Baldwin says his estimates are more like 10:1. “You increase the tire budget 10 cents and you get $1 in fuel [savings],” he says. You probably fill your fuel tanks four times a week, but you replace or retread tires only once every three years.” He says he has even seen a payback for fuel-efficient tires when fuel is as cheap as $2 per gallon.

The tire experts say that the focus on the balance between tire life and fuel economy varies among trucking operators but that most pay more attention to fuel savings.

Walenga says that the amount and type of driving help determine the need for fuel-efficient tires.

“Trucks that run 120,000 to 140,000 miles per year need a fuel-efficient tire,” he says. “But in local runs where you stop and start, fuel economy is lost in acceleration and braking. The more brutal the application, the less critical rolling resistance is. A fuel-efficient tire might wear too fast.”

Baldwin says, “One of the first questions we ask is, ‘Where will you be running?’ In West Texas, you’ll have much less need for traction than in North Dakota. Some West Texas operators run trailer tires on their drive axles to save fuel. They wear faster, but they save dollars.” He says even the type of tractor you drive and the number of axles can have a bearing on choice of tread compound.

Tire specialists recommend talking with a tire sales person who understands your driving situation. Baldwin says, “Tell them how many miles you run per year and what your priorities are between renewal miles and reducing fuel costs.”

Goodyear’s Miller suggests you look at the tires the big fleets run, with the assumption that the fleets have conducted tire tests to maximize fuel efficiency and longevity. He also advises talking with other owner-operators in similar applications.

As tread wears, fuel consumption drops, Walenga says. “You still get the best benefit later in a tire’s life,” he says. “As tires wear, rolling resistance improves, and the wear rate on a new tire is faster.” Instead of getting 9,000 to 10,000 miles per 32nd, you’ll get as much as 12,000 miles per 32nd. “There is a sweet spot for fuel savings and reduced tire costs,” he says.

He suggests rotating tires for even wear to maximize your chances of reaching that sweet spot. Be careful, however, of running the tread too low and ruining the casing. One possibility, he says, would be running your casings out and then opting for a fuel economy retread design.

“You might give up some miles with a shallower tread and fuel-efficient compound, but you’ll recoup,” Walenga says. “Doing this will pay off in the long run.”

Adapting to a world of $4-plus diesel requires you to examine all aspects of your business to save money. New technology enables you to find tires that optimize fuel-efficiency and longevity with greater precision than ever.

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