Today's Trucking
products Brakes Tires/Wheels

AROUND AGAIN

Posted: August 1, 2014 by Rolf Lockwood

We’ve come a long way from the first pneumatic truck tires made of canvas and rubber to the sophistication of the modern low-profile radial. And retreads have come just as far from their own first days, when leather was strapped onto some otherwise dead tires to extend their lives. The
idea of curing raw rubber onto an old casing in a mold was born in the early 1920s. We’re still adding new tread to old casings, but that technology has advanced rather a lot too.

In fact, the acceptance of retreads grew steadily until the point in 1986 when it took over the replacement market for medium and heavy-duty trucks from new tires. North American truckers bought some 18.1 million retreads last year, compared to about 15.7 million new replacement tires.

Why? Cost-effectiveness. About 80% of a new tire’s cost is in its casing, so why on earth throw that away when it can be used to hold two or three new treads?

And these days there’s another compelling rationale: our natural environment can benefit from retreading. Why blot the landscape when there’s a choice to avoid it? It takes some 57 litres of oil to make the casing for a standard truck tire, so why not make those 57 litres do three or four times as much work? It takes less than 20 litres to make a retread.

Big fleets buy most of the retreads sold, but there’s no reason why owner-operators and small fleets can’t create a tire-maintenance system to make the most of a tire dollar. Retreading is just one of four elements of such a program, the others being Inflation, Inspection, and Repair.

With retreading of your original tires in mind, the object is to maintain the best possible casing so that you’ve got something to work with when retread time comes along. Abuse your casing and you can forget the retread option altogether.

Of course, the very first step is to buy the right rubber at the outset. Selecting the original-equipment tire that will do the job – and provide a useful casing for retreading afterwards – is critical. Consider key factors like casing strength (expressed as a ply rating or load range) and tread design. Purchase price is important, but cost per mile is more so.

INFLATION

Proper inflation is the cornerstone of tire maintenance generally, and a big contributor to fuel economy and safe handling as well. What’s proper?

If you’re in doubt, consult your tire manufacturer, because correct inflation depends on several design and operation factors like load and speed.

A radial tire is effectively flat, incidentally, at 85-90% of its correct inflation pressure – and there’s no way you can measure that by way of a kick or a whack with a hammer. The good old hammer won’t get you within 50 psi of an accurate reading. So your first step ought to be the purchase of a top-quality tire gauge if you don’t already have one. Buy one that can be adjusted for high or low reading.

Underinflation means hot tires because it creates abnormal deflection, and heat is the main cause of early tire failure. Bandag offers a surprising number or two that prove the point – it says a tire running at a temperature of 175°F (79°C) will last some 198,000 miles, but only 60,000 miles at 200°F (93°C).

Overinflation is just as bad because it makes the tire rigid and thus more vulnerable to cuts and snags and punctures. An overinflated tire also wears much faster.

And always use metal valve caps. They’re essential, the final seal. A plastic cap does no more than protect the threads on the valve stem, and the valve core itself is only the way to blow air in. If you’ve got metal valve caps but you still have a pressure loss, you’d better take the tire off to have a look.

IINSPECTION

Daily inspection is the first key to tire longevity, but you’ve got to follow up with a more detailed inspection at least as often as each tractor service – at 15,000 miles or so. That frequency will vary with the operation, naturally. Loggers ought to be doing careful inspections every day, for example, and short-haul trucks need a close look every few days in many cases. Long-haulers are a different matter again.

Measure tread depth in the process. Replace any tire that has less than 2/32 in. of tread (4/32 in. on steering axles) at any single spot on the tread. All worn tires should be pulled at 4/32 in. to improve retreadability. Replace duals in matched sets, preferably across the entire axle.

Then double check that the tires are matched. Diameters should be within 1/4 in. of each other on duals. Diameter should not differ by more than 1/2 in. from the left side to the right. When tires are mismatched, the taller tire does all the work and overheats.

Side-to-side mismatching on drive axles is hard on the differential. Make sure the tread widths and patterns are compatible. Mismatched treads will exhibit symptoms of brake imbalance, creating danger on wet or icy roads.

Look for flat spots caused by sliding the wheels. To reduce irregular wear, particularly diagonal wear, move the tires so that the flat spots are 180 degrees apart. Are the wheels mounted correctly? Lug nuts must be properly torqued and studs and nuts must be intact.

REPAIRS

The third element in a good tire program covers repairs, which we can divide into four basic types:

1. Rubber damage only – this is minor stuff, like a sidewall scuffed or knicked on a curb. It needs a spot repair, assuming no structural damage.
2. Nail holes – any injury with a diameter of 1/4 in. or less, assuming again no structural damage.
3. Section repairs – this is a structural repair, needed on any damage more severe than the nail hole above.
4. Bead repairs – bead damage, usually caused in mounting and dismounting, can be readily fixed if there’s no structural problem. It’s a common problem.

Experts will advise that any minor injuries – rubber damage or nail holes – should be fixed right away, as soon as they’re spotted, before they become section repairs.

How many repairs can a tire take? An unlimited number of rubber-only and nail-hole repairs, Bandag says, as long as the patches don’t touch one another. Technically, you can also do an unlimited number of section repairs, but the high cost might make the idea unattractive.

THE RIGHT NAIL-HOLE REPAIR

If you suffer a nail-hole puncture on the road and have it repaired by someone other than a tire specialist, chances are you’ll get no better than an outside-in plug. But it won’t fill the entire hole, so air will get in between the belt packages and cause belt separation. The result: a dead tire.

You might also get a patch on the inside of the tire. It will hold air in, but you’ll also get water coming in from the outside to rust the tire’s steel components. Another dead tire.

The only way to repair a nail hole, experts will tell you, is to clean out the injury – with a carbide cutting tool or a quarter-inch drill – fill the injury with rubber, and put a patch on the inside. Anything less than that is not a permanent nail-hole repair.

As long as the patches don’t touch each other, you can do as many of these repairs as you like.

Tire shops ought to have a template that will determine the size of the patch required, but it’s critical that the patch be big enough. Bigger nail-hole injuries for which a section repair is warranted will demand a special reinforced patch to act as a ‘bridge’ over the injury.

RETREADIING

If you bought quality tires in the first place and if you’ve managed to protect your casings with the first three parts of your tire program, then it remains only to select a retreader. There are different retreading processes to choose from, so you should educate yourself about them before deciding. We won’t get into their differences and relative merits here.

In any case, the most important thing to look for might be the casing-inspection method being used. A visual check is not enough. On the one hand, it might let casings sneak through that ought to be scrapped; but it might also send some to the scrap heap that could be saved with a simple repair. The best retreading outfits have some sort of mechanical testing means.

Every tire has a ‘memory’ of all the curbs and potholes it’s ever seen. The result is small separations between plies or other anomalies that can’t be detected by ‘eyeballing’. A mechanical inspection will find them and determine if there are too many for safe retreading, if they’re too big, or if they’re too close together.

If these anomalies are minor, then the tire can safely be returned to drive-axle service after retreading where it could carry a load and survive torque. The next level is a casing that can be repaired safely for trailer-axle use, and then there’s the casing that can be repaired for safe use in short-haul applications, in sand-and-gravel work, or some other such low-speed operation. The last inspection level would be outright rejection.

RETREADING CHEAPER?

Are retreads really any cheaper in the long run? If you bought quality tires in the first place, and if you’ve managed to protect your casings with the first three parts of your tire program, you’ll see the value at trade-in time.

And since you won’t be getting your own casings back, you’ll want to be reasonably sure you’re buying a well built retread. The most important thing to look for in choosing the retailer might be the casing-inspection method
they use. A visual check is not enough because it might let casings sneak through that ought to be scrapped. The best retreading outfits have some sort of mechanical testing means. Depending where you shop, you can find almost any tread pattern you want, even original-tire tread designs.
A properly retreaded tire built from a good quality casing will perform as well as any new tire. Contrary to popular belief, retreaded tires are no more prone to failure than new tires, provided they’re run and looked after properly.

TMC’s Highway Tire Debris Task Force collected and analyzed tread from 13 stretches of highway around the U.S. in 1995 and found that under-inflation was the major cause of premature tire failure, sometimes compounded by undetected cuts, punctures or other road damage.

“The proportion of retreads that were determined to have failed prematurely because they were improperly retreaded – bond failure, missed nail holes, tread ‘list’ and the like – was just 8% in the latest study,” explains tire-management consultant and TMC task force chairperson Peggy Fisher.

“Evidence of under-inflation was widespread, and if you under-inflate a tire, it will fail prematurely, regardless of whether it’s a new product or a retread.”

All this just to preserve casing value? Yes, and to extend the life of the present tire, whether virgin casings or third-generation retreads. Proper tire care will save you money. It’s a no-brainer.

And incidentally, Bandag tells us, retreads are also environmentally friendly. Tires are really petrochemical products, and it takes 22 gal of oil to make a new truck tire but only seven gal to produce a retread. Interesting, if not as compelling as the idea of more money in your jeans.

Maximizing Retreadability
1. Maintain correct inflation pressure for the load at all times.
2. Don’t exceed manufacturers’ maximum sustained speed ratings.
3. Avoid damage, especially from curbing, potholes and scuffing.
4. Keep wheels clean and corrosion-free to maintain a good air seal.
5. Mount tires carefully, using the right kind and amount of lube in the right place.
6. Follow manufacturers’ recommendations for repairs.

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