Issue link: http://read.dmtmag.com/i/34944
If you’re accustomed to hauling 80,000 pounds most of the time and you run few empty miles, choose pressure for the heaviest loads. Many operators follow a standard of 100 psi in all tires. What is the proper pressure? That may be adequate for steers, but it will make the drive and trailer tires overinflated by as much as 15 psi with a normal configuration of two tractor axles and two trailer axles, says Walt Weller, sales vice president at CMA, maker of Double Coin tires. Overinflation is “the lesser of two evils compared to underinflation,” he says. Walenga recommends 110 psi for steers on a truck with a setback axle and a 12,000-lb. steer axle rating. “At 105, you’re technically underinflated,” he says. “For the steer axle you don’t have any leeway. You need the maximum pressure to make sure you’re carrying 12,000 pounds” effectively. Under a full load, drive and trailer tires could be 50% Tires within 5 psi of the recommended pressure. 20psi One out of 14 tires underinflated by at least that amount. 20% Dual-tire assemblies with pressures differing more than 5 psi. adequately inflated to about 75 psi, says Roger Stansbie, a director of truck tire engineering at Continental Tires, but most carriers and operators keep pressures much higher than that for better traction and to avoid letting pressures go too low. Also, inflate both tires in dual pairs in the drive and trailer positions at the same pressure. To facilitate checking the pressure for duals, make sure the tires are mounted so the valve stem is at the 12 o’clock position on one of the tires and at 6 o’clock on the other, so as not to block access to the inner stem, Walenga says. If you don’t have that alignment, you’re less likely to make the effort to check the inside tire for pressure. “Slowly the inside tire will lose air – a pound or two every month,” he says, “and soon you will have irregular wear.” Altitude and ambient temperature affect pressure. For every 1,000 feet of elevation, pressure will vary 0.5 psi, which isn’t considered significant. Temperature variations are a different story. Every 10 degrees Fahrenheit change in temperature will result in an approximate 2-psi rise. All tire manufacturers publish load/inflation tables and booklets with recommended inflation pressure by load. Another source is the Tire and Rim Association’s annual guidebook – visit www.us-tra.org to order. When owner-operator Kurt Grote switched to wide single tires, he installed an automatic monitoring system to do the job. Ideal pressure varies with the weight you’re hauling. AUTOMATIC PRESSURE MONITORING Kurt Grote moved to an automatic inflation monitoring system when he moved to using wide single tires in place of his dual drives because he wanted to know if he was in danger of tire failure. “That would give me time to shut down on the shoulder or a safe place to get the work done,” Grote says. “The system I have now has already saved me two tires and two rims. That’s around $2,500.” Grote bought his first automatic system in 2008 when he switched to super single tires. Last June he updated to a Doran 360 HD system for $750. A screen in his cab allows him to monitor his tires, which he checks each morning. The system alerts him if inflation pressure drops 12 percent below a set level in any of his tractor tires. “I urge drivers with singles [to get a pressure monitoring system], because once they go down, you’re down,” he says. Jim Samocki, general manager of Doran Manufacturing, says the wireless system includes the in-cab monitor and sensors mounted on the tire valve stems. The operator programs the desired pressure for each tire. The system provides audible and visual alerts if the pressure drops 12.5 percent or 25 percent below the set pressure. In addition, a FastLeak alert is triggered when the pressure falls 2.8 psi in less than 12 seconds, he says. The system can be installed in less than an hour, including connecting the display power wire into a 12-volt power source or hard-wiring into the truck’s electrical system, Samocki says. The sensors are projected to have a 3- to 5-year battery life and can be transferred when you change tires. PressurePro, a competing system that has been in the market for 12 years, also provides 12.5 percent and 25 percent low-pressure alerts, along with two high-pressure alerts to warn of high temperatures, says Duane Sprague, president of L&S Safety Solutions, a PressurePro distributor. Sensors attached to valve stems automatically send alert settings every time tire pressures are changed, without requiring the operator to program the pressures. Sensors have a 7-year battery life. The cost is $743 for a 10-wheel tractor, including sensors, monitor and external antenna. 32 OVERDRIVE JULY 2011 Courtesy of Kurt Grote Proper infl ation