Proper Inflation

Max Kvidera | July 01, 2011

Overinflated or underinflated?

Overinflated tires may produce a rougher ride and handling. Jones says they are more susceptible to hydroplaning on wet surfaces. They also are more vulnerable to puncture from road debris because of their stiffness.

But don’t be too quick to bleed air from a hot tire that’s overinflated from pressure buildup, Miller says, or from a cold tire that’s running in higher ambient temperatures in summer. Heat increases inflation pressures from their cold starting levels, so deflating hot tires means you run the risk of being underinflated when the tire cools.

When a tire is underinflated, it tends to flex more, building up heat. The sidewalls begin to stress under the pressure and cables fatigue. “You can get what we call a zipper rupture,” Jones says, “when one of the cables will give and other cables will follow and push out the sidewall.”

He compares it to bending a coat hanger, which will never return to its original shape. “If a tire is severely overloaded, failure could happen in a matter of a few miles,” he says.

Occupational Safety and Health Administration regulations specify that a tire with less than 80 percent of target inflation pressure should be treated as a flat. It should be removed, examined and reinflated, if possible, in a cage to protect against an explosion, Jones says.

Walenga advises against reinflating an underinflated tire to the proper pressure and driving. “It’s a possible zipper rupture waiting to happen,” he says. Even if the tire is 10 psi below its target pressure, you should examine the tire for faults before you inflate.

Miller says a badly underinflated tire probably isn’t a retread candidate. Overdeflection, or extra heat in the tire, will show up as discoloration in the liner or even damage to the cables or cords. It could also overload the tire next to it in a dual pair and eventually cause damage to that tire as well.

Stansbie says a Continental truck stop survey found that 30 percent of tractor tires and 40 percent of trailer tires were inflated below minimum recommended levels. “The tires on average were 12 percent underinflated,” he says. “We calculated on an 80,000-lb. rig, running 120,000 miles a year, based on $4.17 a gallon and 5.5 mpg, you’re losing $1,400 a year.”


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.”