There are no model-years for truck tires, no annual unveilings of all the latest and greatest new features. Instead, producing truck tires involves incremental improvement with new features, materials and designs rolled into products on an ongoing basis. Certainly the continuous improvement process is punctuated every few years by the introduction of a truly new approach to tire design, but then that new design also begins undergoing the same type of evolutionary changes to its components, materials and construction.
As a result of this constant push to improve, while truck tires are still black and round — and likely to remain so for the foreseeable future — they're really quite different than those you put on your trucks even 10 years ago. In some cases, the differences are obvious at a glance, but in many they're almost invisible, hidden inside the 17 to 23 different components that make up a truck tire.
For the fleet user, the most obvious changes are occurring in the tread and overall tire size, with the introduction of tread designs fine-tuned for ever more specific applications and renewed interest in wide base, or “super single” tires for over-the-road use.
Although the idea of using one wider tire to replace dual assemblies on drive and trailer axles enjoyed some interest in the 1980s, the concept was given new life by Michelin's introduction of the X One in 2000, a low-profile tire specifically built for over-the-road conditions.
“In a sense, it's a full turn of the wheel since Michelin introduced the dual-tire concept for trucks almost a hundred years ago,” says Michael Burroughes, Michelin NA product manager for truck tires. “The two core attributes are weight savings and decreased fuel consumption. It will never be a solution for every vehicle, but in many ways it's a disruptive technology because it challenges the status quo. Since 2000, we've seen sales double every year, and we expect growth to continue on that curve.”
REVAMPING THE PROCESS
Not only was the size a major change for truck tires, but so was the X One's construction and the process used to manufacture it. Instead of using a number of belts laid at angles in the casing, the X One uses a single metallic cable wound straight across the belts, resulting in better vehicle handling and ride, says Burroughes. The patented process was developed internally by Michelin and has resulted in a unique tire manufacturing system at its plant in Spartanburg, SC.
But even “disruptive technology” is subject to the tire industry's continuous improvement process. Although the X One is only five years old, it is already undergoing a renewal that will start with two new drive tires in the coming months.
The first, a Plus version of its X One HAD-XT, will feature wider, deeper treads for higher original tread life in high-torque OTR applications. Not only should it increase initial removal mileage by 15 to 20%, but the redesigned tread blocks will also reduce road noise and improve stone rejection, says Burroughes.
In January, Michelin will release the X One XZUS, a wide-base drive tire for high-scrub urban and regional service. With reinforced sidewalls, heavier bead design and higher capacity, it will be well suited for applications like waste collection and could eventually be used on some other vocational trucks.
Other tire makers have joined Michelin in offering OTR wide base tires or have them under consideration, but most believe actual use will be limited to a fairly narrow band of applications that “need to save weight and can turn it into revenue with extra cargo,” says Guy Walenga, engineering manager for N.A. commercial products at Bridgestone/Firestone North American Tire. “Dual tires engineered for fuel efficiency are comparable in fuel economy and still give you longer life with more removal miles.”
One area that every tire maker agrees on is the trend toward increasing tread depth on drive tires. All of the major truck-tire makers now offer drives with 30/32nds or 32/32nds treads. “It's not that easy do,” says Walenga. “Adding more rubber on the tread will give you more life, but it can cause other problems if it's not done carefully. And if you want fuel efficiency, that usually requires going below 26/32nds on the drive tread. You have to decide if you need maximum fuel economy or long original tread miles, and these days most fleets go for the miles.”
“Deeper and deeper treads (on drive tires) are definitely the trend,” says Roger Stansbie, Continental Tire's director of R&D for radial truck tires in the NAFTA market. “We're at 32/23nds now, and I'm sure we'll hit 34/32nds eventually. Am I dreaming if I say 36/32nds? The limitation will be running temperatures (with deeper treads) unless there's a major breakthrough in compounding or materials.”
Despite the apparent tread-life advantage, Stansbie isn't convinced that users really get all the benefit of those deeper treads because of irregular wear and heat build up. “And given the state of the oil industry, a renewed desire for fuel economy could put the brakes on increasing drive axle depths.”
While drives are getting deeper, when it comes to steer tire tread depth, newer casing designs and materials now mean that less is more. For example, Bridgestone/Firestone's newest premium steer tire has only 16/32nds of tread, “but it yields more miles (in original tread life) that the 18/32nd tire it replaces,” says Walanga.
Following that line of research, Toyo Tire “is seeing phenomenal on-highway mileage with 13 or 14/32nds steer tire tread depths,” says Ron Gilbert, director of sales for commercial products. “It turns out that with the right design, the shallower tread on the steer axle eliminates irregular wear.”
Tread depth isn't the only part of the tire “road interface” getting attention. Cutting tread blocks, or siping, is an old technique used to improve traction, but now it's entering a new phase with computer-aided designs.
For example, Michelin's Matrix technology allows them to cut a “three-dimensional sipe” that extends down the full depth of a tread block but is interlocking to reduce squirm that might cause irregular wear. By comparison, traditional sipes had limited depth in order to maintain the integrity of the block, says Burroughes.
“The first tire we used it on, the XDN2, is a winter drive tire with plenty of traction for wet, slippery services,” says Burroughes. “In the past, better traction compromised tread life, but with Matrix siping we found that that tire got extraordinary mileage in highway applications without sacrificing traction. Now we're carrying it over to other drive and all-position tires.”
Hand in hand with tread changes is development of new tire models targeted at ever-more-specific applications. In addition to high-torque and mileage linehaul drive tires, there are now tires intended to bring optimum performance in regional or local distribution applications. Vocational truck tires have been around for a long time, but now there are tires specifically designed for waste collection, logging and other vocations that pose their own set of special problems for tires.
“A designer can really optimize a tire to perform in a specific application, but that can bring its own set of problems,” says Stansbie. “Specific application tires tend to be more sensitive to handling conditions, which means they should only be used for their intended applications. But by the time tires reach the shop, they tend to get into all sorts of applications that weren't intended.
“For example, you can make a strong performance argument for directional tires, but do you have a workforce disciplined enough to make sure all tires are placed in the right direction?” he asks. “Dividing tires into waste haulage, true regional application and off-road makes great sense, but subdividing [applications] beyond that can introduce problems in the field.”
WHAT YOU CAN'T SEE
While changes in treads and size are immediately obvious, a radial truck tire is made up of some 17 to 23 discrete components, and most of them are invisible once the tire comes out of the manufacturing plant. Still, changes to those unseen parts, things like beads, chafers, liners and ply turnups, have been responsible for much of the most recent gains in truck-tire durability and performance.
Most tire manufacturers are reluctant to talk about internal changes in design or materials, considering it proprietary information that gives them an edge over the competition. One exception is Bridgestone/Firestone, which routinely walks its dealers through all of the recent and coming advances in its componentry.
Among the major internal changes is a new liner material that does a better job of keeping air in the tire and moisture out. “It's kind of invisible, but important,” says Walenga. “Maintaining uniform pressure in a tire improves wear, rolling resistance and overall longevity. Less permeability also keeps out moisture, which can cause deterioration of casing elements. Nitrogen does the same thing at some cost, but with this liner we get about half the performance of nitrogen with free air.”
The shape and design of the tire bead is another area that passes unnoticed by most untrained eyes, but which is about to deliver some significant improvements in truck tire ride and performance. “It's a technology developed for wide-base tires in Europe that involves a completely different bead construction,” says Walenga. It involves the turn-in ply that makes the transition from tire sidewall to bead, transferring forces between the stiff wheel and pliable wall of the casing, he explains.
“It makes that transition smoother for better road feel, which allows us to tune other casing components for the best overall durability and performance,” Walenga says. “We'll be bringing it out on out next generation of steer and on/off highway designs.”
One internal component Goodyear Tire and Rubber is willing to talk about is its new built-in puncture sealer, DuraSeal. Sitting between the liner and belt package, it will seal any puncture up to 1/4-in. in diameter, says Al Cohn, commercial tire technical marketing manager. Intended for logging, construction, landfill and other severe-service applications, it's a gel-like, solvent-free compound that seals more consistently than aftermarket liquids and can even maintain its effectiveness after retreading, according to Goodyear. “We think we'll be able to eventually extend it to P&D, emergency vehicle and other applications,” says Cohn.
It's not just what they put into a truck tire that's changing; the way they put it there is also undergoing a major evolution. As mentioned earlier, Michelin has introduced an entirely new manufacturing process for its Infinicoil, but other manufacturers have also invested heavily in plants.
THE MOVE TO AUTOMATION
While tires have involved much manual labor with hand fitment of most components, the move today is to high levels of automation. That not only improves productivity, helping keep production costs in check as raw material prices for steel and petroleum-based compounds spiral upward, but it also improves consistency between individual tires coming off production lines, explains Stansbie. “Greater consistency is important to fleets because it means they can count on getting the same initial mileage, retread life, fuel economy and so on,” he says. “Automating the process lets you avoid the fluctuations in performance.”
Like component designs, manufacturing processes are also highly protected secrets for most tire makers, but Goodyear was so proud of its new automated IMPACT system that it's gone to great lengths to explain how it works and how it improves tire performance.
In the conventional truck tire making process, rubber and other chemical ingredients are mixed in large drums and then combined with additional materials to create plies, belts, sidewalls and other components extruded into rolls. A tire builder then assembles the components into a “green tire” before it is finally cured in a press.
With IMPACT, which stands for integrated manufacturing, precision assembly, cellular technology, half of the tire's components are produced in a single continuous strip on a highly automated machine. While the older manual process could involve up to six splices for each tire, the new system requires only one.
“We rolled out IMPACT with the introduction of the G395 LHS two-and-a-half years ago,” says Cohn. “All the premium linehaul tires made at our Danville, VA, plant use IMPACT; we're also installing it in our Beacon, KS, plant.
“The consistency you get from automation means you pretty much get the same mileage from every set of tires you put on your trucks, that there's less sensitivity to the slight (operating) differences between different trucks,” he says.
While most truck tire changes are incremental, that doesn't mean there can't be much more sudden, revolutionary developments in store for the trucking industry. For example, the rising costs of raw materials could bring a move to alternative materials. Kevlar rather than steel, for example, or more petroleum-free ingredients in compounds.
It might be a stretch, but after last year's steel shortages created so many problems for tire makers, it's not inconceivable that someone might “develop airless tires that don't need the steel reinforcement to withstand air pressures,” says Stansbie.
Lower profile tires in the 45 to 55% range are much more likely, not to cut raw materials costs, but to improve truck productivity. “We're already seeing them used in Europe on trailers and drive axles to increase trailer cube capacity,” says Stansbie.
“My ‘blue-sky’ ideal, though, is a wheel and tire assembly sold as a single unit,” the researcher says. “If the tire is an integral part of the wheel, you could do away with some of the components now there to aid mounting the tire. For example, you wouldn't need a bead coil to lock it to the rim. You'd do away with handling damage and improper mounting, and might even increase the ability to maintain air pressure.”
Whether we ever see such revolutionary changes in truck tires, or the industry continues its push for continuous incremental change, “we have to keep coming back to our target — end performance,” says Walenga. “Mileage, retreadability, fuel economy — anything we change has to improve those measures of performance. Everything else is secondary.”