Many haul roads also have berms on the sides of the road. "Berms can prevent proper drainage, creating pooling on the road surface," says Best. "We see some sites where parts of the berm have been pushed back every couple hundred feet to allow for draining off the side of the road. Drivers should be cautioned to the openings in the berm to avoid running into them."
Keep grades to a minimum
Steep grades will reduce tire life. "Steeper grades can cause the tires to slip, and slippage reduces tire life," says Best. "So the lower the grade, the better."
The grades can change loading on the tires. "Hauling on steep grades causes a load to shift to the front or the rear of the vehicle, depending on which direction you are hauling the load," says Tolman. "If you are hauling the load down, you should pay special attention to the air pressure adjustment of the front tires and set them according to operating conditions. This compensation should be done only after consulting with your tire manufacturer representative to ensure the proper air pressure setting. When designing haul roads, try to avoid grades higher than 8% to reduce the effect of load transfer."
Good agrees, adding, "It is best to limit grades between 5% and 8% for improved tire traction and fuel economy. If steep grades are unavoidable, weather conditions will dictate when equipment may operate. Heavy downpours or snow on steep grades cause tire slip with corresponding rapid wear, loss of traction and possible safety issues."
Think through the curves
Tight curves should be avoided because they create additional wear on the tires. "If the work area is tight and can't be expanded, we recommend the operators lower speeds going through the curves to prevent excess load transfer on the tires," says Best. "But definitely, a larger radius curve allows the truck to run at a higher speed within the tire manufacturer recommendations, and helps reduce the load transfer on the tires."
Banking the corners can compensate for the curve radius and take stress off the tires. "If the roads are sloped or banked appropriately, it can greatly aid the turning radius of the vehicles," says Tolman.
It essentially boils down to using the laws of physics to your advantage. "Basically, the idea is that the truck can run through the curve at full speed, just like on a race track" says Best. "Elevate one side of the track and the load transfer isn't as great."
On a flat curve, more load is transferred to the outside of the tire. "It could be really bad if it is all transferred to the right front tire in a left curve," says Best. "You just add that much more overload condition to the tire. The load transfer will heat up the tire faster over time and create the opportunity for premature failure. If you run over a rock with that tire, it is more susceptible to damage."
Keep it clean
"Smooth roads and well-maintained loading and dump areas will yield positive returns," says Good. Consider data from hard-rock mine sites. "It is not unusual for 45% of the tires to be removed for cuts, 29% for impacts, 7% for worn treads and 18% for other conditions. If you can eliminate half of your cuts and impacts, tires removed for worn treads actually increase to 44%, and have a major impact on overall tire cost.
"Unfortunately, a cut or impact can lead to tire removal when it is 1% worn or 90% worn," he continues. "These early hazard failures are particularly costly, due to equipment downtime for tire repair or a search for a replacement."
Much of the damage occurs in load and dump areas. ""Usually, 80% of the rock cuts happen in dumping or loading areas," says Best.
Excessive speed contributes to the problem. "By slowing down before entering loading and dumping areas, operators can avoid spillage from road undulations that result in excess tire deflections," says Good.
"In the dump areas, when you slow down as you approach, you can make a wider radius turn, which reduces spillage and the possibility of riding on the shoulders of the tires," says Tolman. "This reduces the wear and tear and prolongs their life."
By approaching at a slower speed, you are also better able to navigate rocks or debris in the area. "At this point, it is very important not to damage the tires.," Tolman states. "The tires have been working very hard to carry the load and have probably reached their maximum temperature, making them more susceptible to damage."