Heavy Duty Trucking

DEC 2014

The Fleet Business Authority

Issue link: https://heavydutytrucking.epubxp.com/i/432752

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78 HDT • DECEMBER 2014 www.truckinginfo.com typical standard-profile 11R22.5 LRG tire needs 105 psi to get be- yond 12,000 pounds load carrying capacity. For example, Michelin's tables indicate a pair of such tires would be good for 12,350 pounds (6,175 pounds each). Low-profile 22.5-inch tires, such as a pair of 275/80R22.5 LRG, would need 110 psi (again, from Michelin's tables) to carry 12,350 pounds. (You will find minor dif- ferences when comparing load and inflation tables across the major manufacturers, but they are small, and technical in nature.) Back when they were still popu- lar, long-nose conventional steer- axle loads seldom exceeded 12,000 pounds in normal on-highway service, so 100-psi inflation pressure was adequate. Set-back steer axles shifted a larger percentage of weight forward, thus increasing steer- axle loads. And more recently, EPA emissions regulations added a bunch of emissions hardware to engines and chassis, adding another thousand pounds or so to the truck. Much of that wound up on the front axle. "Steer axle loads have increased over the years, going beyond 12,000 pounds in some cases," Decker adds. "Some manufacturers now install 13,200-pound steer axles in order to accommodate loads over 12,000 pounds. While actual steer- axle loads may not have reached that high in all cases, there are cer- tainly some situations where loads come very close to that." day. He sees a shocking number of trucks coming through his shops with low-pro 22.5 LRG tires inflat- ed to 100 psi on even 13,200-pound axles. "The heavy steer axle is there for a reason," Beckett says. "The manufacturer knows the front end of the truck is heavy, so they use an axle capable of carrying the weight. Often, those axles are loaded up to pretty close to that rating, so we The 13-2 axle adds a new dimen- sion to tire selection. In cases where the operator may not be aware of the tire rating, they may still be inflating their LRG tires to only 100 psi. If their steer-axle loads are running at or close to the axle rat- ing, the tires may be technically in run-flat condition. Mike Beckett of MD Alignment in Des Moines, Iowa, gets a close look at trucks and their tires every Tires&Wheels Watch for drivers who deflate steer tires to 90 psi thinking it will provide a smoother ride. "Even if you're inflating to the recommended pressure, you're leaving yourself no margin." – Curtis Decker, Continental Tire North America PHOTO: JIM PARK

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