There is no doubt that radial tires have left an indelible footprint on the construction industry and other off-road market segments, such as mining and quarry operations.
In fact, the construction of that footprint is what separates radials from bias-ply tires and, say tire manufacturers, improves traction, stability, handling, tire life and puncture resistance, accomplishing it all while running cooler. Radials improve fuel economy as well, a fact supported by data from on-highway passenger vehicle use. Yet showing fuel efficiency in off-road applications is harder to nail down, given the myriad working environments and types of equipment that compose the off-road market.
"We don't even put the fuel thing out there," says Keith Rowell, corporate accounts technical support manager, Bridgestone/Firestone Off Road Division. "But we do put the cooler running, longer lasting, better wearing and longer tire life benefits out there."
One way the earthmover radial tire differs from bias-ply tires is that steel belts, rather than fabric, are used for the cord material.
Radials are constructed in two parts. First, a single layer of rubber-coated steel cables arches from one bead to the other to form the tire casing. Second, numerous rubber-coated steel belts are placed in the crown, under the tread, to form a strong stabilizing unit.
"Rather than laying the steel cord as a bias, we lay it radically, which means it goes from the bead straight around to the other bead," says Michael Reich, quarry account manager for Michelin. "You have that one layer that is strong enough to support the weight of the vehicle by itself. It has the strength to carry the load. But in addition, we also put steel belts around the tread area, or the crown facing. We put multiple layers of steel cord, one on top of the other, which does two things: One, it helps protect the tire from debris that can cut or damage it and, two, it adds stability to the footprint."
The sidewall and the tread formation function separately, Reich says. There is a flat footprint for the tread that sits squarely on the ground. The casing itself has the ability to deform separately from the tread.
Tires generally last twice as long because there's not much tread squirm. This also makes the tread last longer.
Bias-ply tires, by comparison, are made of rubber-coated plies, usually nylon, placed on top of each other at about 30- or 45-degree angles. The plies are then wrapped around the bead wires, which anchor the tire to the rim, to form the casing, or air chamber. The plies are then covered with more rubber to form the tread pattern. "You continue to put more plies in until you get the desired strength for the load you have to carry," Reich says.
"Radials give better stability for machine handling and traction," says Tim Good, off-road global accounts manager for Goodyear Tire & Rubber. "A radial with its footprint provides more net-to-gross. You're utilizing more tread face for traction, so you're getting more deliverable torque to the ground with less spin."
Also, he says, radials have a wider footprint and many times they will "engulf or walk over an object." That helps stop cuts, bruises and flats.
Scott Sloan, vice president of engineering and technical services at Titan Tire, says, "generally speaking, radial construction benefits include improved tread wear. This is attributable to the tread and body of the tire working independently of each other, which allows less movement of the tread surface as it contacts the ground rolling through the footprint." For the same reason, he says, rolling resistance is less "and equates to improved fuel efficiency."
Radial design contributes significantly to equipment uptime and availability, according to tire makers, since radials run cooler, carry heavier loads over longer distances at faster speeds, and are harder to puncture.
"You don't have downtime due to tire issues that you would have with bias ply tires," says Goodyear's Good. "If the machine runs over a rock, for instance, a bias tire won't give, so it has a tendency to fail. A radial tire, by comparison, engulfs the object. Radials also have steel belts, rather than fabric belts, to protect against failure."
Radials also give machine operators a smoother ride. "You don't have as many issues with jarring or back problems," Good says. "At the end of the day there is less operator fatigue with radials."
There is also protection for the machine itself, according to Bridgestone's Rowell. "Most equipment doesn't have suspension systems for a comfortable ride," he says. "They may have shock absorbers on some, such as haul trucks, but your loaders and graders don't have any suspension system whatsoever. They use the spring rate of the tire as the ride comfort for the machine."
The spring rate on a radial is about 4 percent that of a bias ply tire, according to Rowell. "If a properly inflated bias tire, under proper load and speed, has a 6-percent deflection in the sidewall, a radial will have 10 percent," he says. "The better spring rate cuts down on damage to the equipment. When you have less vibration in the sidewalls, you take up some of the shock, and that takes some of the stress out of the frame and other equipment components."
Michelin's Reich concurs. "Because radials last longer, typically you'll cut the amount of servicing in half," he says. "The tire will last twice as long, so you don't replace it that often. Since a contractor doesn't know what he's going to be into next week, radials are more flexible because they are much more resistant to downtime due to cutting. That's the main thing, from a profitability standpoint.
"If a fleet manager sees a tire wearing out, he can schedule around it," he says. "What costs contractors money is when he's working on a deadline and, right in the middle of some project, the machine goes down with a flat. That's a tremendous headache, and it happens a lot."
Although a large share of the off-road market has embraced radials, there are still hurdles.
For one thing, radials cost more than bias-ply tires. "Cost is always an issue, absolutely," says Bridgestone's Rowell. "Quarry managers want to know what will it cost today, not sometime down the road. We have accumulated numerous data that show radials save money, last longer, produce less machine downtime, and that they can carry greater loads than a bias tire. If you're moving more material at less downtime, then you're going to have a higher product output."
But, in some cases, it's still a selling job. Return on investment varies greatly due to application and work environment, says Rowell. "It depends on each individual quarry, and the only way you can tell is by tracking each individual tire. Every tire, regardless of who manufactures it, has its own identification number. If you don't have a software-management system to track tires, you won't ever know what your ROI is or which tire is the best tire to run."
Titan's Sloan says cost justification is "the big question," and it depends on each operation. "If the operation is more continuous, has long distances for travel, an argument for the more expensive radial tire could be made, especially with mounting fuel prices," he says. "If it's a stop-and-go application in rough terrain, it would be difficult to justify. Really, it boils down to what the operator or owner is comfortable with."
Another issue, according to Good at Goodyear, is that, initially, operators complained about "the feel."
"Right now, if you have a machine with bias tires and you put radials on it, you'll still feel the difference," he says. But once operators adjust to radials, he says, "they won't go back."
Although radial technology is well advanced, key developments and trends are emerging in tire design and product improvement.
Bridgestone, for example, continues to expand its rubber compounds, says Rowell. "We're looking at more ways to use synthetic materials. Rubber is becoming scarce. Rubber tree plants can only be grown about five degrees above or below the equator. That's pretty limited. Another reason for exploring more synthetic material is oil dependency, which is a problem."
Tread pattern is yet another key development area, he says. "The only reason for a tread pattern is to cut down through adverse conditions — slop, mud, rain — to reach a hard surface to give traction," he says. "How that tire disperses matter such as rain or snow depends on the tread pattern. The tread has to be self-cleaning to get rid of debris it picks up, such as stones. We're continually looking for better tread patterns that gives traction in adverse conditions."
Another trend is toward a wider tire, such as the Goodyear 65 Series used on articulated trucks and loaders, says Good. "This gives you even better traction and stability," he says. "As customer demands change, the tires also have to change to run cooler."
Reich says the most recent development at Michelin is the introduction of the "first ever" radial skid-steer tires. "They offer some pretty amazing tread wear," he says. "If you think about it, a skid-steer is designed to wear the tire out. With a radial, the advantage is dramatic, cost-justifiable life spans; plus it offers tremendous savings by reducing downtime due to flats."
Sloan says Titan is currently working on new tire designs for loaders, articulated dump trucks, and logger skidders. "These new designs could potentially have a diametric cost impact — that is a cost reduction — while improving the performance for equipment manufacturers and end-users," he says.
Reich agrees. "Manufacturers are working to develop radials with higher treadwear and higher protection against damage while maintaining, or even increasing, the speed capability of tires, especially on haul trucks," he says. "We should see continued developments that make vehicles more productive. We're trying to take it to the next level of giving better tire protection, better life, while at least maintaining the load capacity and the speed necessary to deliver the product. We see that as being key to the marketplace."