According to Wayne Jackson, president of International Tire Repair Solutions, proprietary materials and techniques used in some systems for repairing off-highway tires could potentially place 40 percent of tires thrown on the scrap pile—with injuries considered too severe for treatment—back into service. A proper repair can restore the integrity of a valuable carcass, he says, yielding the potential to run the tire to retread—or a second retread.
“A vital and too often overlooked factor in off-road tire management is repairability,” says Jackson. “The recent shortage of all sizes of off-road tires has spawned a whole new interest in quality repair methods and materials for these giant tires. There’s no silver bullet for salvaging damaged tires—you have to be sensible and knowledgeable—but you can recover a lot of tires.”
Depending on the capabilities of the specific repair system, says Jackson, repair of large sections of a tire (aptly called “section repairs”) potentially can be performed on any area of the tire except in close proximity to the bead bundle. Section-repair “patches” have historically been made of nylon or polyester cords embedded in rubber, he says, but recent developments have added new dimensions to the mix, including DuPont Kevlar and proprietary patches that include replacement steel cables.
Says Heinz Haischt, general manager of Vulcan-Vulcap Industries, which builds tire-repair systems, “Section repairing is often the only way to keep millions of dollars of equipment running until such time as new tires are available.” Here’s a step-by-step look at section repair (scroll to the bottom of the web page.)
Tires in short supply
As Jackson and Haischt indicated, the increasing awareness of major repair as a life-extending measure for off-road tires is due in part to equipment owners needing to keep machines working while tires are in short supply.
“The off-road tire supply is very serious,” says Gary Nash, vice president of OTR [off-the-road] tires for Yokohama Tire Corp., “and I anticipate that it may go on for some time. Basically all tire sizes have heavy backorders, but large and extra-large sizes, both radial and bias, seem to be particularly affected. Demand from BRIC countries [Brazil, Russia, India and China] and other global areas has applied extreme pressure on North American suppliers.”
According to Bruce Besancon, director of marketing, Michelin Earthmover Tires, the company has seen the demand for its earthmover tires increase by more than 20 percent between 2009 and 2011.
“Increases in demand have been across the board,” says Besancon. “Demand is high, and raw material prices, which have risen to historic highs in the last few years, remain a key factor in pricing.”
Bill Porterfield, western region OTR-tire sales manager for Titan International, encourages fleets to regularly inspect their vehicles’ tires in order to project wear rates and to determine six months out when replacements might be needed. The present backlog for tire orders, he says, is at four months or more.
Tire applications and modifications
Extending tire life to mitigate the effect of shortages might mean refocusing on the fundamentals, including tire selection; maintenance; vehicle operation; site maintenance; tire tracking; and failure analysis.
“First,” says Steve White, business segment manager, Michelin Earthmover Tires, “fleets should make sure the right tire is purchased for the application. Long cycles—where greater distances are covered, or where high speeds can occur—might require a tire with less tread depth or special rubber compounds to enable staying within a certain operating temperature range.”
On the other hand, says White, operations using traction-type tires on loaders and graders at sites having no real traction issues might do better with a tire having more tread depth, which will last longer and more than offset the added cost. If tire protection is a primary concern, he says, then an even deeper tread might be of value, remembering, of course, he cautions, that more tire weight can mean increased fuel consumption.
Titan’s Porterfield also suggests assessing a machine’s present configuration when choosing replacement tires, taking stock of possible modifications—sideboards, body liners, bucket reinforcing or larger replacement buckets—that might call for a tire stronger than the original.
And, of course, most off-highway-tire users running transport vehicles—rigid-frame and articulated haul trucks, scrapers, or load-and-carry loaders—know that abiding by a tire’s ton-miles-per-hour (TMPH) rating is critical for tire life and safety. Depending on a transport tire’s specific design, it can go only so far, only so fast, carrying a given load, at a specific pressure if it is to maintain temperature equilibrium.
Exceed the limitations, and the heat generated by the abuse will cause inevitable consequences, either immediate (tire fires or blowouts) or delayed, such as carcass damage that disqualifies the tire for retread. Tires are unforgiving when overheated; their “heat-history” memory can’t be erased. Before replacing tires, make sure the tire dealer understands any changes or proposed changes in haul roads or production schedules that could affect TMPH ratings.
Off-road tire maintenance
At the top of the tire-maintenance list is air pressure—first, establishing the correct pressure for the tire in its operating situation, then regularly checking pressure (the more often, the better) and recording readings to identify any developing trends.
“Some mining operations are checking pressure at every fueling stop and marking the pressure on the tire with a crayon,” says Porterfield. “If there’s a significant change at the next stop, the wheel is pulled from service to determine the cause. The results are amazing; these tires are routinely running to 80-percent wear-out rates.”
Regarding wear-out rates, Porterfield advises fleet managers not to think they’re doing themselves a favor by running tires until the tread is hardly visible. He recommends pulling tires when 12 to 20 percent of the tread remains, because going beyond that, he says, risks damaging the transitional layer of soft rubber between the casing and tread rubber. The result is a tire more difficult to retread. Yokohama’s Nash adds sobering economics to potentially jeopardizing a tire’s retreadability, noting that the retread value of some tires can approach 75 percent of their purchase price.
As a bit of practical advice, Porterfield cautions that haulers with dual wheels should have the extension hose from the inboard tire’s valve properly attached to the outer wheel to prevent it from flopping around and causing air loss. Also on the subject of dual wheels, Yokohama’s Nash says that mating dual tires is critical, because when tires are not properly mated, one will carry more than its share and wear prematurely. Mating dual tires is always a serious concern, says Nash, but becomes more acute in times of shortage, because an exact match might be more difficult to find
Finally, basic tire maintenance should include serious consideration of repair. Repairing cuts and cracks in radial tires is especially important, because these injuries allow water to enter and rust steel belts, eventually causing materials to delaminate. The industry’s rule of thumb is that investing 10 to 12 percent of a tire’s original cost in a section repair is economically feasible.
Extending tire life
Loading/Hauling: If loading equipment consistently places off-centered loads in trucks, these lopsided loads cause extreme tire stress on the heavy side, especially through corners, so posting speed limits in turns might be a practical idea. Keep rocks off the haul road, because rocks that lodge in tread grooves can work into the under-tread and belt layer, a process known as “stone drill.” Tires with “stone rejectors” (small rubber pads at the base of tread grooves) help mitigate this problem.
Informed Operators: Operators who understand the basics of tire care—proper air pressure, observing TMPH limits, avoiding haul-road rocks, and adjusting speed in sharp turns or on downhill runs with heavy loads—can be a valuable asset in extending tire life, says Michelin’s White.
Tire Tracking: Most tire manufacturers have proprietary tracking programs—usually administered by the tire dealer—that involve periodic inspection to record a tire’s condition and to initiate timely repair. These programs provide cost-per-hour figures for tires, as well as projected replacement intervals, thus potentially assisting fleet owners with overall tire management.
Ken George, an OTR tire consultant, has developed what he calls “a practical, user-friendly, interactive tire-tracking website” that allows fleet owners and their tire dealers to “coordinate tire needs.” The goal of this free-of-charge program, says George, is to bring “true preventive maintenance” to the off-road, radial-tire industry.
Scrap-tire Analysis: Most tire manufacturers and their dealers are competent at assisting fleet owners sort through scrap-tire piles to identify out-of-service causes. Discoloration in the bead area, for instance, could indicate excessive heat from under inflation or high speeds; repetitive cuts in scraper tires might result from improper pushing techniques; damaged tires that originate at the same wheel position on haul trucks could indicate a haul-road fault; and separation of material in casings could be an indicator of using a rubber compound not optimally suited to the application.
It would seem, then, that tire life might be legitimately extended fundamental-by-fundamental.