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The Rubber Tire Advantage
A look at costs, service calls, tips and innovations
By Barbara Coyner
Shelling out $10,000 for a set of tires is ample cause for heartburn. But Idaho logging contractor Bob Danielson finds the price tag a bargain compared to springing for a new set of tracks.
“It’s $2,500 for one tire for my 535 Cat skidder, but it’s $30,000 to build the undercarriage on a 527 Cat. It takes two Cats to do what that skidder can do. Rubber is just faster and requires less maintenance,” says Danielson.
Loggers like Danielson figure on about two years of wear out of a set of skidder tires. He says his harvesters and forwarders go easier on rubber, with one of his 1997 forwarders still running on the same set of tires.
“Forwarders and harvesters are more slow moving, so the tires just last longer, but skidders go at higher speeds so we get about two years out of them,” he says. “Mostly we deal with the tires going flat when they get older, or maybe we get a cut in a sidewall. But tire problems are infrequent, because tires are just made better now.”
When cuts and punctures do take their toll, outfits like Les Schwab provide service calls, often getting the logger back in action in a matter of hours. St. Maries, Idaho Les Schwab shop manager, Gary Gertje, says his crew responds to about two calls per week in the summer when logging is full tilt. He adds that most operators keep spares for their machines, so the injured tire can be sent off for repairs.
Firestone’s senior project engineer Stu Miller has been at the Bridgestone/ Firestone drawing boards for 38 years, and has spent 18 years on the forestry side. In that time, he’s not only had to consider durability, but also how the tire travels over sensitive ground. “Forestry flotation tires are soft and wide with a big footprint that is environmentally friendly,” says Miller. “A 50-inch wide flotation tire has a lot of air volume, but you have to keep the air pressure fairly low, about 25 psi, to make a soft imprint on the ground. These tires have to be cut resistant, too, because they’re vulnerable to cuts and punctures. Out in the woods, you’re always running over something like stumps or sticks or rocks and those can be tough on tires.”
Cold Weather Cautions
Because logging often takes place in very cold weather, Miller cautions that minus 30 degree temperatures invite tire stiffness, which increases puncture vulnerability. He says that in those cases, operators should carry less weight. Otherwise, weather is not much of a factor in forestry tire life.
With logging machines constantly getting bigger, heavier, and stronger, Miller says that tires must do the same. In designing new tires, the company first analyzes how the tire is to be used, before researching tire compounds and tread patterns. A major product development can take up to two years to get from the drawing boards to distribution. Firestone’s test facility at Columbiana, Ohio, puts tires through rigorous paces, running tractors on tethers for hours at a time, and subjecting materials to endless stress conditions. Miller also seeks input from equipment manufacturers and conducts field tests in the woods.
Firestone designs its heavy equipment tires with cut resistant compounds in the tread and sidewalls, according to Miller. “We use very heavy gauges, and the heavier they are, the more cut resistant they are,” he says, noting that the higher the ply, the higher the load carrying capacity, so most heavy machinery tires run between 16 and 20 ply.
Below the tread are steel belts designed to stop punctures from cutting into the air chamber. The tough combination offers 12 percent improvement in cut resistance and 15 percent improvement in wear. Many of today’s tires are going tubeless, Miller adds, explaining that rubber layers inside the tire wall create an impermeable air chamber.
Miller preaches checking tire pressure as one sure fire way to get more hours out of tires, and he advises loggers to check tire pressure at the start of each work week. If tires are inflated properly, they should last the full life expectancy. If they are 10 percent under pressure, they will last only 90 percent of the expected life, and if they are 30 percent under inflation, they will last only half of the projected life.
Miller says over inflation will also decrease tire life. At 60 percent over in- flation, for example, the tire loses 75 percent of its life expectancy. Similarly, load capacity is an issue, with 40 percent overload reducing tire life by half. Such figures indicate that checking tire pressure translates into real savings over time. Miller stresses that operators should minimize tire spinning, and avoid trash buildup between the rim flange and the tire bead to get the most out of tires.
“With one tire for a skidder costing up to $3,000, and a set running between $10,000 and $12,000, loggers really need to take care of their tires and check air pressure routinely,” Miller emphasizes. “If that pressure is too low you can over-deflect and that can cost you big money.”