Heavy Duty Trucking

DEC 2014

The Fleet Business Authority

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won't support a 13,000-pound load at 100 psi. A low-profile LRH tire will need at least 110 psi, some as much as 120 psi. Funny thing about inflation Fleets routinely over-inflate drive and trailer tires by about 33%, but they are reluctant to inflate a steer tire to its required pressure because it's north of 100 psi. "A low-pro 22.5 casing carrying 4,250 pounds requires a minimum inflation pressure of 75 psi," Beckett points out. "Yet almost everybody runs 100 psi. They are overinflat- ing by 33%, but they aren't getting center wear. If you can over inflate 16 of your 18 tires by 33% and not get any unusual wear, why can't you over inflate two steer tires by 10%?" Actually, his use of "over inflate" isn't accurate. You're inflating the tire to the recommended pressure; it's only our adherence to the arbi- trary 100 psi paradigm that leads us to believe we're over-inflating the tire. Beckett says the recommended inflation will give you the standard fuel economy. If you're 20% under- inflated, it'll cost you 1.5% in fuel economy. The other factor to consider is seepage, Decker points out. "I would never in good conscience tell a fleet to inflate drive and trailer tires to 75 psi, even though that's what the load and inflation tables call for," he says. "I know that tires pick up nails, rim and valve interfac- es leak and a certain amount of air will diffuse through the liner of the tire. We know we'll lose about 2% of our inflation pressure monthly when everything is working. At 75 psi we have no margin. I'm much more comfortable telling a fleet to inflate to 95 or 100. We are still well within the range of the tire, which with a load-range G tire would be 105 or 110, while a load-range H would be as high as 120 or 125 psi. "In the steer position, it's differ- ent, and this is where I think people Circle 152 on Reader Action Card fail to consider that a steer tire in its normal use will be loaded to 90- 95% of its load carrying capacity on a regular basis. Even if you're inflat- ing to the recommended pressure, you're leaving yourself no margin." We have thrown a lot of numbers around here. If you're a little con- fused about the pressure you should be running in your steer tires, check the load and inflation tables. You'll need to know the steer-axle weight rating of the truck, the actual loads you carry on the steer axle and the size of the tire in question. The make and model are important too, as recommended pressures do vary by manufacturer. "On steer axles, 100 psi seems to be where most fleets are comfort- able," Decker says. "I'd love to see that become 115 to 120 psi." ■ www.truckinginfo.com DECEMBER 2014 • HDT 83 Tires&Wheels Pressures of 105 psi are fine with 12,000-pound steer-axle loads, but may be 10-20 psi underinflated in 13,200-pound steer-axle loads. PHOTO: GOODYEAR

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