What Comes Around…

At The Maintenance Council’s Summer Meeting last year, a maintenance manager for a medium-sized fleet asked if I was familiar with a new retread system from Michelin and what I thought about this “unproven” technology.

“What do you mean unproven?” I asked.

“I’ve been told it’s new and untested,” he said. “How can I be sure it’s good when it’s so new?”

You know those moments when you’d like to reach out and throttle someone? Like the mechanic who told your wife some ridiculous story as to why the car’s squealing brakes needed $1200 in repairs? This was one of those moments for me.

The mold cure system has been around almost as long as the pneumatic tire, and has been widely used to retread bias tires in both North America and Europe for decades. When the radial tire was introduced, European retreaders, led by Michelin, converted their equipment to segmented molds that accommodated radial tires. Retreaders in the U.S., however, unsuccessfully attempted to retread radial tires in the old full-circle molds they’d used for bias tires. They failed to invest in upgrading their mold cure equipment and eventually went out of business.

About this time, Bandag Inc. introduced the precure retread system. It was not all that successful at the start, but eventually the system was perfected for retreading radials.

Precure equipment was much less expensive and retreaders could equip a shop with comparatively little investment. So the precure system grew in popularity in North America (and still is the leading process for radial tires). But mold cure technology is hardly “unproven,” it’s just relatively “new” to North America’s truck tire retread market.

Now that Michelin and Goodyear have added mold cure retreading to their menu of products here (Bridgestone/Firestone offers it in the United States), you have a real choice in retreads. It’s resulting in heated market share battles-zealous attacks that haven’t been seen in this industry for years.

Mold cure restores the tire to its original profile since it is cured in a mold almost exactly the same as a new tire. There are no hinge points at the tread edge, and the footprint is the same as the new tire, rather than flat. Michelin and Bridgestone claim to use the same rubber compounds in their retread rubber as in their original tires. Therefore, fleets should expect to get the same mileage from their retreads as from the tires’ original tread. Also, the process leaves retreaded mold cure tires looking like new tires. This may be a consideration if you’ve got a lease customer who doesn’t like the appearance of precure retreads.

Produced properly, both mold cure and precure retreads are good products that can cut tire cost/mile. Don’t be afraid to try both technologies and compare their performance in your operation.

POLICY ISSUES

The important thing to realize is that maximizing tire life is less about process and more about policy. A good tire casing management strategy, for instance, sets targets for every phase of a tire’s service life-from original casing through first, second, or even third recap and ultimately to the scrap heap.

Government standards require that tires on steer axles have at least 4/32-inch of tread. All other tires must have 2/32-inch of tread. However, some fleets believe removing tires at 4/32 or 5/32 improves retreadability, and more than makes up for the loss in tread rubber and mileage.

Rotation is another element to define. Fleets normally rotate tires to: 1) get the most from the operating characteristics of a particular tire, or 2) minimize the effects of irregular wear.

Typically, the right front tires on commercial trucks wear more slowly than left fronts. And right-side tires are more susceptible to irregular wear, requiring removal despite sufficient tread depth. Hence, many fleets rotate steer tires side to side to extend mileage. Still, some steer tires wear irregularly and should be rotated to either the drive axle (if rib tires are run on drives) or to the trailer or dolly axles to use the last remaining 32nds of an inch of tread depth. Specify a tread depth at which to perform this work.

Tires spec’d for a specific application (such as open-shoulder, deep-lug drive tires) should only be rotated if irregular wear becomes apparent or if the wear rate on the tires is noticeably different from axle to axle. On tandem drive or tandem trailer axle configurations, tires on the rearward axle wear faster than those on the forward axle. To get the maximum mileage from tires in all these configurations, it makes sense to rotate the rear tires to the forward tandem and the tires on this axle to the rear tandem when there is about 4/32 difference in tread depth.

Tires designed to be rotated, such as a closed-shoulder drive tire that turns into a rib tire as it wears, should be moved from the drive axle to a trailing axle when traction diminishes. This extends tread mileage considerably. If you run this tire type, schedule this rotation.

Establish tire repair criteria. You may limit repairs to simple nail hole plugs or decide that tires with several section repairs operate well. Go with what works.

Other uses for tires should also be considered. Some fleets save the cleanest tires for over-the-road operation and put tires with more repairs in city operation. Tires that have seen better days but are not ready for the scrap pile can be used on vehicles that remain primarily in the yard.

Another factor involves how and where to run retreads. It’s common to place first retreads on drive axles, because these are the more demanding axle positions. Tires retreaded a second and third time run on trailing axles, which put less demand on casing integrity.

Set a target for casing life as well. This is influenced by scrap tire analysis results, tire manufacturer/retreader warranties, total tire/casing mileage and number of retreads, as well as number, type, and location of repairs.

Whatever your fleet’s casing management policies are, write them down and be sure maintenance personnel get a copy and follow them.