Big Rig Basics

Rolling Along

Regular tire inspections go a long way in cutting tire costs and staying out of trouble with the DOT

Tires are the second largest expense in running a truck, after fuel. Inspecting them carefully will tell you how well the truck’s suspension and steering systems — and you — are taking care of them and help you head off a lot of expensive repairs. Frequent inspections also will allow you to replace or retread them before they wear enough to get into trouble safety-wise.

1.  First, measure tread depth to determine how worn each tire is. For each tire, hold the body of the gauge in one hand, then pull the stem all the way out of the gauge body.

2.  Rest the gauge on the tire with the stem down in one of the grooves and the flange flat on the tread surface on either side of the groove. Gently push down on the body of the gauge until it touches the tread on either side.

3.  Without disturbing the stem, remove the gauge and read the number sitting right above the edge of the gauge body. Note that there are scales for both mm and 32nds of an inch. The 32nds of an inch is the one to read. The bare minimum for drive and trailer tires in roadside inspections is 2/32, and 4/32 is the minimum for steer tires. Replacing or retreading earlier helps prevent damage to the casing as well as reducing on-road failures.

4.  Repeat for the two steer tires, all eight drive tires and, if you have a trailer, all eight trailer tires.

5.  Part of daily inspection is a pressure check. You can normally read the recommended pressure off the sidewall. Always check tire pressure when cold — before starting out.

6.  Fully inflated tires run cooler, last much longer and use less fuel. Remove the valve stem cap, then force the pressure gauge snugly over the valve stem. Read the gauge after it has settled out, ensuring your gauge is tight enough on the stem to eliminate leakage.

7.  Observe the tread for irregular wear. Underinflation causes wear at the outsides of the tread, while overinflation causes wear at the center. Wear on one side comes from camber-a bent axle. Bald spots normally mean a balance problem. Look also for signs of cracking from a botched repair, as shown in the illustration.

8.  Run your hand over the tread to feel for uneven wear-feathered edges with the outside lower or higher than the inside. Wear of this type normally means the toe-in is incorrect, so the wheels point inward or outward rather than being straight ahead. The drawing shows how the front wheels will look when toed in.

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9.  Incorrect toe-in is corrected by having the wheel alignment set on a rack like the one shown here. Lasers are used to line up the wheels perfectly. The steer axle’s toe-in, caster and camber should be checked and, if necessary, set first. Then the drive axles must be aligned to the front axle, and the trailer axles to the tractor axles. The front axle needs the most attention, but the entire rig should be aligned periodically.

10.  Inspect for poor repairs. Here, an improper repair is causing a rope plug to be forced out of the tire. Leaks must be repaired with the tire off the truck, and the inner liner which keeps moisture out of the casing must be sealed, which was not done here.

Truckers News thanks Wilmer Martin, an instructor at Universal Technical Institute in Exton, Pa., for his help with this article and Norman Norville, education manager at the facility, for arranging for the school’s assistance.


Required tools: Tire tread depth gauge, tire pressure gauge and high-pressure air supply

Level of difficulty: 5 (on a scale of 5-10)

Time required: 45 minutes


Retreaded tires are definitely the way to go on all but the front axle if you want to keep tire costs down. Cliff Downing says he is going to retread a number of his casings the next time he needs tires. “New tires are just too expensive,” he says.

A tire casing is a durable piece of equipment and, like an engine block, is designed to be re-used when a fast-wearing part, in this case the tread, means it can no longer be used. You just need to keep your tires aired up to minimize heat damage, and make sure they are properly repaired when road damage affects them. This means taking the tire off the rim and sealing the inner liner and using a vulcanizing process to repair them where necessary.

Go to a good retreader with a production line type of shop, well-trained technicians and where every casing is thoroughly inspected, preferably with X-ray and magnetic technology. A good retread shop will repair a slightly damaged casing after a thorough inspection, will offer a guarantee and will be happy to give you references to call to check on the quality of their retread process. Re-using your casings twice will cut your tire costs by 20% or more and help the environment.

Big Rig Basics Tip

Cliff Downing of MAC Trucking is leased to Fremont Contract Carriers and drives an International. He says a pressure check of your tires is “part of a pre-trip inspection. And doing it helps keep you out of trouble. … Imagine the consequences if one of your tires blew because of low pressure and it caused an accident that killed someone. You could end up in jail!”

He says if your tires are in good shape and the weather is stable, you may even be able to go as long as a week without airing them up. But checking them frequently with a good gauge, not by merely thumping them, is “just common sense.”

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