Next to fuel, tires represent the highest operating expense for an owner/operator. A set of 10 tires for an on-highway tractor can easily cost $3,000, so the shredded casings that line the shoulder of the road – the dreaded alligators – offer proof of lost profits.
But the same forces that allow a tread to grip the surface of the highway ensure that a tire will wear away like an eraser. And just like an eraser, a tire’s rate of wear will depend on the mistakes you make.
The following are issues to consider when caring for your investment in rubber.
Not all tires are created equal. It’s important to match the proper tread and compound to the right position and service application, says Al Cohn of Goodyear’s commercial tire business.
“Everyone wants to maximize the mileage and have great traction and have great re-treadability,” he says. But to do that, tires also need to be matched to your truck configuration, the type of roads being traveled, the weights being hauled and the speeds being driven. It doesn’t all come down to the time of year and the wheel position.
Ask any technical expert about the biggest killer of tires and under-inflation inevitably tops the list.
A linehaul tire that’s underinflated by 20 per cent will see its life shortened by 16 per cent, says Cohn.
The trick is to keep a watchful eye.
“Most (owner/operators) look at the springs and so on, and make sure there are no other leaks,” agrees Michelin’s Doug MacDonald. “Checking air pressure should be like checking oil.”
Oil costs money. Air, for the most part, is free (Yeah, yeah. Some sites will charge you to use the compressor. But have you compared the cost to a gallon of oil?)
Despite the experience you may have in thumping tires to gauge inflation, the only true indicator of air pressure is a proper tire gauge. For that matter, gauges should be calibrated and checked on a regular basis since they fall out of calibration when they’re dropped.
“You buy a gauge out of the box and the range is already plus or minus 3 psi,” Cohn says. “Each time you drop it, you don’t know (what it’s reading) … Check against a master gauge.”
Meanwhile, tire pressures should be checked once a week, and don’t forget the inside wheels on dual assemblies.
It’s equally important to check your tire pressure first thing in the morning, and not after you’ve been driving. If a tire is loaded to 100 psi during morning temperatures hovering between 7 and 8 Fahrenheit (about -14 Celsius), the air pressure will read anywhere from 110 to 115 psi after the truck spends only 30 minutes on the highway, Cohn notes.
Once tires are 20 per cent below their optimum pressure, it’s time to remove them, MacDonald adds.
“You can lose air through the valve stem,” MacDonald says of one of the common sources of leaks. And the solution can be as simple as using a hard plastic cap or metal valve cap that costs as little as a quarter.
Stay away from cheaper soft plastic caps that have no rubber grommet, he adds, noting that the threads of such varieties will break easily. They’re meant to be little more than a dust cap.
Bandag spokesman Don Schauer recommends investing in flow-though valve stems, especially for the inside tires on dual sets, making it easier to check tire pressures.
If you’re taking the time to put a gauge to the valve stem, you also have an ideal opportunity to run your hand over the tire to detect any signs of irregular wear or other damage.
A tire that has been damaged by something such as a nail should be pulled, properly patched and replaced.
“Some people put a plug in it and it’s ‘let’s go’,” Schauer admits. Yet even a 2-lb. drop in pressure will increase operating temperatures by 5 F. A typical radial tire will happily roll along the road at 150 F (66 C), but at 200 F (93 C) “rubber reversion” begins to occur and the plies of the tire begin to pull apart, he says.
Meanwhile, signs of irregular wear – ribs on the same tire that are wearing away at different rates – can indicate alignment problems.
“Toe is a very common one,” Cohen says of the alignment issue that involves steer tires that point toward the centre of the lane. The depth of an outside rib may measure a comfortable 8/32 inches when you’re checking such a tire, but each successive rib may be 1/32 inch lower than the one that precedes it.
“If you see more of the trailer in one mirror than the other, you have a problem (with the alignment of trailer axles),” adds Milt Flynn, Bridgestone’s manager of national fleet sales.
Ultimately, a gauge to check the exact depth of treads will play a key role in plans to retread a tire. Steer tires shouldn’t drop far below 8/32nds, although some fleets will move them to trailers once treads drop to 10/32nds, Cohn says. Drive tires can drop to 6/32nds before retreading.
And don’t assume that tires face equal wear across a tandem axle configuration. In a P&D operation, the difference in wear rates can be as high as 25 to 35 per cent, while linehaul vehicles can see wear rates vary by five to 10 per cent from one axle to the next, Cohn adds. The life of these tires can be extended with a simple rotation schedule.
There is an attraction to cruising 75 mph (120 km-h) down an open highway, and the option is legally available in some states. But as sure as you’re burning more fuel at the higher speeds, you’re also burning rubber.
With higher speeds come higher overall wear rates, and any irregular wear problems will only be exacerbated, says Flynn.
Remember that tires have maximum speed ratings just as they have ratings for air pressure and loads.
Above all, don’t ignore the smallest flat spots. Says Bridgestone-Firestone: “What started out as a small flat spot may grow into a severe irregular wear problem. This kind of localized damage can become a ‘seed’ of irregular wear … the flat spot can even cause irregular wear to start in a totally different place or even on a tire beside it in a dual assembly.”
And note whether an accompanying tire on a dual assembly has one. If it does, you can “clock” the two flat spots 180 degrees apart to prevent the vibration that can lead to irregular wear.
So too should you be concerned about exceeding the tire’s rated load.
While a low-scrub tire may be fine if you’re running down U.S. Interstates, a high-scrub variety will be important if you’re equipping a trailer with short spreads between the axles. The tires on a Michigan-style multi-axle trailer will virtually drag sideways whenever you turn a corner, putting more stress on the tires.
Tires matched on dual wheel ends should be relatively the same size – within 1/4 inch of each other.
“The closer the better,” Cohn says.
When it comes time to replace a tire, the use of a proper lubricant and proper mounting procedures are crucial, notes MacDonald.
“Don’t use a steel hammer to mount the tire,” he says as the first rule to follow, noting that the approach could damage the beads that contact the wheel.
“You get some air loss or air infiltration through the sidewall of the tire.”
That could lead to an oxidized casing, limiting the chance for a future retread. n
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