TUCSON, Ariz.—It's difficult to get a perspective about the immensity of giant earthmoving equipment. In huge open pit mines, like the one outside Tucson—where copper and molybdenum, an ore used in steel alloys, are unearthed—the huge haul trucks, graders and loaders look like Tonka toys. From a distance.
That is, until you get next to them.
Then you find yourself staring upwards, like a child, at machines two stories tall, rolling on tires 12-feet high. And suddenly you feel like you've been cast in the latest Hollywood sci-fi movie where one of these gargantuan beasts demolishes a city block in a single swipe.
These are vehicles that, depending on size, can haul payloads of up to 360 tons or scoop 75 metric tons of earth in one pass.
Attendees at the Tire Association of North America's Off-the-Road Conference in Tucson Feb. 18 saw first-hand how big and powerful these machines are during a demonstration at Caterpillar Inc.'s Tinaja Hills Training Center and later at the nearby Phelps Dodge Sierrita Inc. pit, a working mine.
Like a well-orchestrated Disney production, Caterpillar showcased its earthmovers to 200-plus TANA dealer and tire supplier visitors at the center, located on 6,250 acres of Sonoran desert about 45 minutes from Tucson.
Watching from bleachers, dealers saw haul trucks, loaders and graders put on a synchronized display of their ability to move and haul dirt. Just as one piece of equipment completed its performance, another would begin like clockwork.
When the show was over, dealers were able to get a closer look at the mammoth equipment, some of which boast tires priced at as much as $50,000 each.
Then it was off to the Phelps Dodge Sierrita mine where dealers donned hardhats to peer over a fenced ledge at the equipment working below in a 1,400-ft.-deep pit.
Phelps Dodge operates a fleet of 23 trucks at the mine, including the Caterpillar 793, a 240-ton hauler, and the 797, the world's largest truck with a 360-ton payload.
As befits its behemoth status, the 797 also features the world's largest tire, size 55/80R63 E-4, which stands nearly as tall as a city bus.
Phelps Dodge has operated the mine since 1957 and produces 250 million pounds of copper and 22 million pounds of molybdenum annually.
Purcell Tire & Rubber Co., based in Potosi, Mo., provides tire service to the mine, including repairing and retreading of the giant OTR tires.
Just as the tires themselves are huge and expensive, so is the cost to retread them.
For Caterpillar's largest loader, the 994D, a new radial tire, size 50/80R57, might sell for $35,000, said Juanita Purcell of Purcell Tire. Retreaded versions cost about half as much and use about 6,000 pounds of tread rubber.
That's enough tread rubber to retread more than 270 medium truck tires.