Fleet Management News & Business Info | Commercial Carrier Journal
Issue link: http://read.dmtmag.com/i/319866
62 COMMERCIAL CARRIER JOURNAL | JUNE 2014 EQUIPMENT: LOW-ROLLING-RESISTANCE TIRES resistance, rolling resistance increases with speed," Estupinan says. Part of a tire's rolling resistance is its aero- dynamic resistance as it moves. Even though rolling resistance doesn't increase as fast as air resistance with an increase in speed, rolling resistance is present – and a major factor – at lower speeds. Just as with air resistance, the actual amount of rolling resistance is influenced by many factors, including load, speed, inflation pressure, tread pattern and tire de - sign. "Although fuel economy has a greater impact in high-speed long-haul operations, it plays a role even in high-load on-off oper- ations," Estupinan says. Rick Phillips, senior director of commercial and over-the-road sales for Yokohama Tire, says different products have different tread depths for a reason. Depending on the application, steer tires can go from 16 ⁄32- to 23 ⁄32-inch, drive tires can be from 22 ⁄32- to 32 ⁄32-inch, and trailer tires can go from 11 ⁄32- to 17 ⁄32-inch. "Everything else being even, the tire with less tread depth is typically more fuel-effi- cient," Phillips says. A deep tread tire will have more rolling resistance when it is new than it will when it's half worn; that's why tires don't hit their fuel economy "sweet spot" until experiencing some road wear. As a tire rolls, there is less "squirm" with a shallow tread-depth tire than with a deep tread tire, Phillips says. "The more squirm a tire has, the more horsepower is required from the engine to overcome its rolling resistance," he says. Deep treads tend to deform and squirm more and generate more heat than shallow treads as the tire rolls on the highway, Estu - pinan says. "A shallow-tread tire, like a trailer tire, typically has lower rolling resistance than a deeper drive pattern with blocks and lugs," he says. "Another advantage of a shallow tread is that the initiation and expansion of irregular wear are less likely to occur as results of the reduced squirm." Changing the equation While shallower tread depths equate to better fuel economy, it's only natural for fleet managers to wonder about the impact these new designs have on tire life. Tire manu - facturers such as Michelin are aware of this inherent tradeoff and are using modern technology to counter it, Jones says. "The key is the different compounding and silicate makeups that each manufac - turer has developed to enhance tire life," he says. "The goal for all of us is to develop a more durable longer-lasting material to build tires with and deliver both low rolling resistance and longer life. Tires are not perfect products by a long shot. It's a process of continuous improvement for us. We are constantly trying to improve our tires to get the lowest rolling resistance we possibly can without sacrificing performance and safety." Guy Walenga, director of commercial products engineering for Bridgestone Amer - icas, says the fuel savings from low-roll- ing-resistance tires are real, and fleets must keep that in mind and learn a new formula for calculating tire costs. "I hear fleet managers say today that by giving up tread wear, their cost per mile will go up," Walenga says. "They're right, but if their fuel economy has gone up, they're making money. Fleets that are buying fuel-efficient tires know tire costs are going up, and they also know that at the end of the year, their overall MPG number has in - creased from 6 or 7 percent or more. They're WHERE DO TIRES FIT IN FUEL ECONOMY? Tire rolling resistance is the third-biggest factor affecting a vehicle's fuel econo- my, says Rick Phillips, senior director of commercial and over-the-road tires for Yokohama Tire. For a typical Class 8 tractor at normal operating conditions, here's where $1 worth of fuel goes: r is wasted by engine inefficiency. r is consumed by aerodynamic drag. r is consumed by overcoming tire rolling resistance (average values vary according to tread type). r by steer position r by trailer position rby drive position r is consumed by the load. r is consumed by the drivetrain. A tire underinflated by 10 percent can result in a 20 percent loss in fuel economy, so even if a fleet does everything right, re- searches all of its options and chooses to run fuel-efficient tires, it won't realize any benefit if it fails to keep them properly inflated. A technician for San Bernardino, Calif.-based Bear Trucking checks a Yokohama tire. As a tire rolls, there is less "squirm" with a shallow tread-depth tire than with a deep tread tire.