November/December 2005
Need some guidance on what to look for in solid tires? This review can get you rolling.
By Jim Fowler
It’s round. It’s rubber. It’s black. So it must be a tire—but what kind of tire?
For scrap processors who operate heavy equipment such as wheel loaders and material handlers, there’s a good chance it’s a solid tire—one that can withstand maneuvering through rough surfaces peppered with jagged pieces of scrap without going flat. Granted, pneumatic tires and foam-filled tires are less expensive than solid tires, but to get a true expense picture you need to consider total cost, which includes the tires’ longevity as well as your lost production if tires go flat or fall apart.
Here, manufacturers review points to keep in mind when you’re shopping for solid tires.
First Things First
First, it’s helpful to understand that solid tires are commonly divided into two basic types based on the metal wheel at their center. The two types are:
- expanded wheel—In these tires, rubber is bonded to wheels that are generally larger in diameter than the original-equipment wheels that came on the machine; and
- pneumatic-shaped—In this case, rubber is pressed onto the original-equipment wheels of the machine or on rims similar in size to the originals.
Generally, the metal wheels are built specifically for the machinery they will be mounted on and are not interchangeable with other pieces of equipment. However, one manufacturer offers a patented adapter plate that allows one tire to fit more than one machine. “We have rubber bonded to a steel wheel,” the vendor notes. “There’s a welded ring inside the steel wheel, and our adapter plate bolts into this welded ring inside the wheel. This gives the user tremendous flexibility in changing tires from one machine to another.”
The Secret Formula
Manufacturers generally agree that the rubber compound used to make solid tires is a critical consideration. It’s no surprise, therefore, that each company’s particular formula is considered top secret.
“To simply say you use natural rubber means nothing,” asserts one tiremaker. “The advancement has been with additives that make rubber stronger. If you use a good quality natural rubber and a mediocre additive, your final product will be a mediocre tire.”
Manufacturers continually seek better rubber compounds that will make their solid tires more durable while providing a more cushioned ride for both the operator and the machine. “The major secret,” a tire rep notes, “is a compound that wears well, provides comfort, and is cut resistant.”
On the durability issue, solid tires must first be able to resist damage from sharp pieces of scrap metal that can slice, gouge, and chunk them. Toward that end, one tire producer says his company has developed “an underground, hard-rock mining compound that has incredibly high tensile strength and high tear strength.” Another states, “We’ve designed a compound that is tear resistant so that, when it comes up against steel, our tires get less chunking.”
To resist damage, a tire’s elasticity is a big factor. Thus, a manufacturer advises, “be sure to ask about the elasticity of the rubber compound. If it’s got the elasticity, it’s not going to chunk.”
Solid tires also face damage in scrapyards from fluids such as motor oil, brake fluid, transmission fluid, and hydraulic fluid. The rubber compound must be able to resist such elements. Recognizing that fact, one solid tire producer says that his company “chemically formulates a special compound for our tires used in the scrap industry that is resistant to these oils.”
While being strong enough to survive scrapyard duty, solid tires must also be soft enough to prevent operator fatigue and minimize wear on the machine. “A wheel loader has neither shocks, springs, nor rubber bushings,” a manufacturer explains. “The only suspension on a wheel loader is the tires. If you put a rock-hard tire on the loader, it’s going to cost you a lot of money to keep it running and to keep the operator out of the hospital—you’re going to lose time, so efficiency drops.”
One tiremaker says his firm balances these durability and cushioning goals by using two rubber compounds—one for wear and one for cushioning. Another says, “We use a flexible cushion compound that’s an all-ride and an all-wear formula.”
One way to check a solid tire’s softness is by asking about its durometer reading. A durometer is an instrument that measures the hardness of a material. When using such instruments, a reading of 100 is the maximum, thus the higher the reading, the harder the rubber.
Holes or No Holes?
Another important distinction between solid tire brands is whether or not they have apertures—that is, holes that extend through the tire from one sidewall to the other. While some manufacturers believe they offer significant benefits, others aren’t as convinced.
On the plus side, “apertures increase the flexibility of the tire and decrease the tire’s weight,” one vendor says. Also, he notes, as the apertures are compressed, they “pump out internal heat from the core of the tire.” Another adds that “operator comfort and machine fatigue are greatly improved with the incorporation of air holes in a softer compound of rubber. It gives a far superior ride.”
Others say that apertures help the ride a little bit, but not substantially. “We’re not sold that they give a better ride and believe the rubber compound is more important,” one tire producer states.
Then there are manufacturers firmly on the apertureless side of the fence. “There are certain applications where apertures make a lot of sense, but it doesn’t make a lot of sense to me in the scrap industry,” says one tire rep. “You don’t want a lot of voids opened up in a tire where a piece of metal can get caught and rip the rubber apart. By putting a softer compound toward the wheel in the center of the tire, you can get the ride you’re looking for without opening up all of those holes.”
Another manufacturer concurs, stating, “We don’t put holes in our tires. Go to any scrap metal yard and look at the sides of the tires. They are absolutely smashed to bits—cut up and ripped up. If you have holes in tires used in those operations, all the holes will do is catch steel bits and rip apart.”
Looking at Longevity
Two questions that all scrap operators ask when shopping for solid tires are: How long will these tires last? And which brand lasts longest?
Unfortunately, there are no definitive answers to those questions because tire longevity depends on many factors. When it comes to a tire’s physical toughness, the rubber compound is “the biggest single factor if all other conditions are the same—same driver, same application, and same machine,” one vendor says. Also, another adds, “the more rubber you have and the stronger that rubber is, the longer it’s going to wear. It comes down to physical properties.”
Some manufacturers claim that their solid tires have run up to 20,000 hours. In general, however, it’s impossible to estimate a tire’s service life because that depends on “the operator, the time of year, and the surface the tires are running on,” a vendor notes. As another recounts, “I’ve seen our tires last well over 10,000 hours, but I’ve also seen an operator spin them to the ground within 2,600 hours—and everywhere in between. It really depends on the conditions and the operator.” Yet another tiremaker concurs, asserting that “if you get a cowboy driver who is spinning the tires all day long, I don’t care what compound you have—you’re going to get a lot of premature wear on the tires.”
You also have to consider the physical characteristics of the scrap processing facility. “If it’s really a tight area and the operator has to do a lot of turning, that’s going to be a factor,” a manufacturer points out. “Also, lifting and loading into a truck rather than pushing off the floor into a hopper will affect wear, as will the type of machine on which the tires are mounted.”
Smooth Operators
Some scrap operators like solid tires with a tread pattern, others like their solid tires smooth, and both versions are readily available, though manufacturers disagree on which version is better in scrapyard applications.
In some scrap operations, vendors note, treaded tires are needed. “If a scrap dealer has a lot of mud in his yard,” one says, “he may need a tread on his tire. Though you want as few voids as possible where steel can catch and tear the rubber, we would custom-design a tread to minimize the voids but still provide traction.”
As others note, however, manufacturing tread into a tire means that you are taking rubber out of it and are providing additional surface area for cutting and chunking. “If I take a grooving gun,” explains one tiremaker, “and cut the smooth tire straight across to make a traction cut seven or eight inches deep and three inches wide, I’m losing some 25 pounds of rubber. If I put 12 or 15 of those cuts into a tire, I’ve lost 300 to 400 pounds of rubber. You take a lot of rubber out of a tire when you make a traction tire, and that impacts tire longevity.”
Another manufacturer agrees, noting that a smooth surface puts more rubber on the ground, which increases the wear surface. Also, a smooth surface eliminates tread grooves that can trap pieces of scrap metal and damage the tire. “When you start putting voids in the tire,” he says, “you create places for pieces of steel to penetrate the rubber.”
Of course, smooth tires don’t stay perfectly smooth for long in a scrapyard. The natural wear of daily scrap operations give smooth tires an unintentional tread. “As a smooth tire runs over metal in the yard,” one tire producer confirms, “the rubber is cut and forms a type of tread pattern.”
Assessing the Costs
According to some estimates, solid tires cost three to four times more than pneumatic tires and twice the cost of pneumatic foam-filled tires. But the real cost of industrial tires isn’t just about the initial price tag.
Instead, scrap processors must think about the total cost of the tires, especially the total cost per hour of operation. “You want to figure out how many inches of rubber you’re going to get on the tire, how many inches are actually wearable, and how long it’s going to last,” suggests one manufacturer. “For example, are you buying 12 inches of wearable rubber or 24 inches? With that information, you can come up with a cost per hour.”
Offering an example for foam-filled pneumatic tires, one vendor says that scrap operators could expect to spend $25,000 to $30,000 for a set of such tires for a midsized to large wheel loader. If the tires suffered major damage within, say, 10 hours after installation, the operator’s cost per hour would be enormous. “You avoid that risk with a solid tire,” the vendor states.
Another important cost-related factor is what you can do with your solid tires when they’re worn down and need replacing. Be sure to ask the various manufacturers what kind of exchange program they offer. “With solid tires,” one vendor says, “it’s critical to know what the second and third sets are going to cost you.”
On the exchange topic, another tiremaker boasts that his firm’s wheels—the metal frames in the center of solid tires—are recyclable. “Ship the used wheels back to us,” he says, “and we can put new rubber on them or provide a substantial credit for them.”
Regarding the wheels, one manufacturer recommends that scrap operators should own rather than lease their wheels. “Anyone that leases a tire is doing so for cash flow purposes and ends up paying more for their tires than they should,” he states. Also, if the processor decides to sell or trade the base machine, the leased wheels would not transfer, meaning that “you’ll have no wheel and tire assemblies on it if you lease your tires.”
Sizing Up the Situation
To accurately compare one solid tire to another, “you have to compare the total diameter, the total width, and the total depth of the rubber,” one manufacturer suggests. “Keep in mind that rubber costs more than steel and that rubber on the outside of the tire, because of its larger diameter, costs more than rubber on the inside that’s closest to the wheel.”
Also, don’t overlook that if you purchase a tire with a smaller overall diameter, the base machine will be lowered several inches and it, therefore, may not have the reach height you want. The point, a vendor states, is “you need to be sure you’re comparing apples to apples with dimensions.”
Other points to keep in mind include the tire manufacturer’s published warranty, their product availability and stocking levels, distribution centers, freight policy (one, for example, pays freight on any four tires to any one destination point in North America), and the validity of your base machine’s warranty if you install solid tires on it.
Jim Fowler is retired publisher and editorial director of Scrap.
Need some guidance on what to look for in solid tires? This review can get you rolling.