Focus on Tires The Off, Off Highway Tires Revue

At a mine site, tires are a consumable, but, man, that expense can add up! Tires can form an astounding 20-25% of a haul truck’s operating costs in an open pit mine, according to George Couris, senior market manager of North America for Michelin North America Inc., based in Greenville, S.C.

Surface mines are very conscious of tire costs, and underground mines are becoming more sophisticated regarding tires, Couris says. The same is true of the manufacturers. Several recent mine tire innovations were outlined by Couris in an interview with CMJ. “It is to a mine’s advantage to take advantage of these new innovations,” he says.

Twenty years ago the choice of off-highway tires was small, but it has grown considerably, with variations in size, tread and rubber compounds for each model. Tires are being more specifically matched to the job, so they can give better performance.

There is a trend toward low-pressure tires with a lower profile, which are less susceptible to tire cuts, and which enhance handling. There are also new tread designs, such as Michelin’s XDR tires for haul trucks with a payload of 77 tonnes or more. They extend tire life by distributing the ground contact pressure more evenly across all the tread blocks, so the tread wears more slowly. Through adding more rubber and changing the tread design, these tires can give 20% longer life. For example, a site that now gets 6,000 hours of life from a tire could average 7,200 hours with the new tread designs.

Bigger tires are being manufactured for bigger trucks. The tire-makers are working closely with OEMs to develop specific tires for specific machines. “What’s helped break through the truck size barrier,” says Couris, “has been the low-pressure technology. This has enabled tire manufacturers to make tires suited to the ultra class haul trucks [>290 tonnes]. The truck is lower to the ground, and therefore has a lower centre of gravity.” The Caterpillar 797 and the Komatsu 930E-II haul trucks run on the biggest Michelin tires, the 55/80R63 and the 53/80R63, respectively. These tubeless radial tires measure nearly four metres tall and 1.5 metres wide, and can retail for up to $39,000 each.

There is a move away from bias ply toward radial tires for off-highway vehicles, following the trend in passenger car and highway truck tires. The first radial tire was developed for off-highway use in 1959, by Michelin. Now 95% of the tires used on large surface haul trucks are radial, as well as roughly 60% of the tires for all other mining equipment, both underground and on surface, according to Couris. Although more expensive to purchase, the radial tires deliver lower costs by giving two to three times the tire life of bias ply, more protection from flats and cuts, and better traction.

Underground load-haul-dumps mainly use bias ply tires, but Michelin has developed a new radial smooth tire (X Smooth Mine D2+) specifically for this equipment, that is expected to dramatically increase tire life and reduce downtime.

The latest innovative trend is the application of computer tracking technology to tire management. Several tire companies are testing systems that involve a monitoring chip imbedded in the tire and a reader on the vehicle. The systems track temperature and pressure, enabling speed or air pressure adjustments to be made before the tire fails.

What happens to all the used tires? “Tire disposal in general is still a problem,” Couris admits. “But the industry is making progress in finding ways to handle scrap tires, and a number of recycling programs are finding ways to use them. They are currently being recycled into products such as asphalt, and even park benches and parking curbs. Most tires can be retreaded as well, which cuts down on the number of scrap tires. Of course, making longer-lasting tires also helps to reduce the number of tires to be recycled.