Rethinking retreads

| December 12, 2008

Regular tire pressure maintenance results in longer casing life and better fuel economy.

Would you replace an expensive shoe just because it had a worn heel or sole, or get a shoemaker to resole it and replace the heel? The same thinking applies to tires, says Harvey Brodsky, managing director of the Tire Retread Information Bureau. Like a high-quality shoe, tire casings are designed for a far longer life than the original tread, Brodsky says.

What’s the biggest reason to use retreads? Your tire costs are second only to your fuel costs, and retreading substantially cuts those costs. While a new tire will cost more than $400, a retread costs only $150, Brodsky says.

Of course, everyone has heard retread failure horror stories. Proper retreading is no simple matter, so occasionally things go wrong, especially if the job was done by one of the few “bums” in the business that Brodsky admits still exist. However, there is one simple key to avoiding retread failure, or indeed tire failure in general: the casing.

The most common myth about retreads is that roadside “alligators” are tread sections a retreader failed to attach securely. In fact, independent surveys confirm that most rubber pieces left on the road are casing failures, not tread failures, and they are as likely to come from new tires as from retreads.

The vast majority of these tire shreds contain wire, which retreaders don’t insert in the first place, says Brad Reiners, marketing communications manager at Bandag. That wire is part of the original tire maker’s casing, the inner portion that supports the load and that the tread is attached to. If you can see wire protruding, it’s a casing failure.

New tires and retreads are identical in structure. The original tire manufacturer builds up the casing out of many rubber compounds and then attaches the tread. Much the same thing occurs in “pre-cure” retreading, in which a previously molded tread section is installed on a tire casing. The only visible difference is a small seam where the new tread meets the casing. A casing that has been kept in proper condition nearly eliminates many of the causes of retreaded tire failure.

How do you care for casings? Proper inflation is by far the main thing. Underinflation and its close cousin, overloading, account for the lion’s share of tire abuse.

While thumping a tire may tell you whether it’s absolutely flat, it cannot accurately read the pressure. “It’s almost like pounding on the hood to see if your engine needs oil,” Brodsky says. “Use a gauge and check the tires when they’re cold so you get the most accurate reading.”

Running a tire even 10 to 15 pounds too low will greatly increase the flexing and heating of the casing as you drive. A tire that’s 20 pounds underinflated has been subjected to so much stress it should be removed and inspected, says Goodyear’s Pat Demianenko, North American retread business development manager. Overloading causes similar damage because it also increases the flexing of the casing.

Inflation is critical because air gives the tire its strength. Air is elastic, efficiently absorbing road shocks and rolling effects so that little heat is generated. Reduce that air pressure, and the tire flexes, generating a great deal of internal friction because rubber is far less malleable than air.

Both new and retreaded tires are put together by “vulcanization,” which uses heat to fuse the parts together with rubber-based adhesives. Vulcanization occurs at 280 to 300 degrees; run a tire when it is underinflated or overloaded, and its highway temperature approaches the vulcanization temperature. This can reverse the process that put it together, so that the tire comes apart.

The heat doesn’t affect only the vulcanized parts. Severe overheating causes the steel cords to lose their strength, too, so they begin to move out of their proper relationship to one another. The extreme result is the broken cords sprouting from alligators. The flexing has heated and softened the wire until it broke apart, as a coat hanger bent back and forth eventually will snap. And this is not easily done with the high-quality, flexible wire used to construct casings, so an alligator on the roadside likely is a relic of a severely abused tire.

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