Heavy Duty Trucking

DEC 2014

The Fleet Business Authority

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know the tires are supporting close to 13,000 pounds or more. Yet, the tires on the axle at 100 psi are rated for no more than 11-5 or 11-6. If those axles are loaded, those tires could be running 1,000 or 1,500 pounds each over their rated maxi- mum." Or viewed from another angle, the tires may be underinflated by 15 to 20 psi. Load range G or H? To solve the problem, you could reduce the load on the tire or inflate it more. But reducing the load on steer tires is impractical, and the load and inflation tables for most standard and low-profile 22.5-inch tires don't allow for 13,200-pound loads. So the only remedy is a differ- ent tire: a 16-ply load range H tire inflated to 115 to 120 psi. "The axle rating or maximum allowable load for an axle is not nec- essarily the normal operating load," cautions Paul Crehan, director of product marketing at Michelin Americas Truck Tires. "Proper tire inflation pressure is dictated by the actual operating load of the vehicle and not the maximum allowable load for the vehicle. Proper steer tire selection, as well as tire inflation pressure, are linked to the specific conditions and applications of opera- tions for that vehicle." Fleets should be auditing steer axle weights anyway, given how close steer tires usually run to their maximum weight rating for a given inflation pressure. Given most fleets' reluctance to inflate beyond 100 psi, there's probably a lesson or two to be learned from that process. "The maximum load that a load range G tire can carry is 12,350 pounds," says Donn Kramer, direc- tor of product innovation at Good- year Commercial Tire Systems. "If the load is in excess of 13,000 pounds, a load range H tire inflated to 120 psi should be considered." But even a load range H tire A NEW GENERATION OF TIRE MANAGEMENT ™ www.mobileawareness.com 866-653-5036 MobileTRAQ is the most innovative TPMS ever to be designed and manufactured in the USA. Complete with a three-year warranty, this system was developed using the latest technology. Find out how MobileTRAQ can help eliminate tire failures and reduce feet maintenance costs. Circle 155 on Reader Action Card www.truckinginfo.com DECEMBER 2014 • HDT 81 Tires&Wheels I f we're talking about pushing steer tire inflation to 120 or 125 psi, can the wheels take that kind of pressure? The answer is yes. There is a maximum cold inflation pressure stamped on the rim. It's usually 120, 130 or 140 psi. Most highway tractors will have rims rated for a maxi- mum of 120 psi cold inflation pressure. Some vocational and specialty applications will have higher-rated rims. A quick look at the application guide for Alcoa's and Accuride's on- highway wheel products shows aluminum wheels are rated for 130 psi, while some steel wheels are rated at 120 psi cold inflation pressure. "When we design a wheel, we look at all the possible applications where it might see service, and then we consider all the tires that may be mounted on that wheel, and what inflation pressure they might use," says Rafael Gonzalez, director of wheel product management at Accuride. "We obviously test the wheels to make sure they are up to the pressure, and we include a safety margin as well." So you've got an H-rated tire at 120 psi and a 120 psi rim. Not much of a margin? According to Mike Beckett of MD Alignment, there's a 25-30% margin there. "Hot, the tires will be running 130-140 psi," he says. "The tires and rims are all rated at a cold inflation pressure, and the pressure rise from the heat of the tires is accounted for." But what about my wheels?

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