The Art of Tire Design

The Art of Tire Design

Today’s commercial truck tires are rolling pieces of sophistication. Because they carry the weight of tractors/trailers loaded with logs and timber products the importance of their construction and foundation (the casing), can’t be understated.

“Other than tires for the aerospace industry, commercial truck tires have arguably the toughest job in the tire business,” says Phil Mosier, Cooper Tire’s manager of commercial tire development. “It’s why we dedicate so much engineering time to ensure our tires perform safely and productively. From a productivity standpoint, since tires are such a high operating cost, miles to removal and durability – balanced by a competitive price — are what can help loggers keep costs down. Providing our customers with a low-cost of ownership is what Cooper is all about.”

Phil MosierPhil Mosier, Cooper Tire manager (center), says it’s an exciting time to be a tire designer. “We have so much technology and research at our fingertips."

High-Tech Tires

So what makes tires so high-tech? On the surface, they’re black and round and look pretty much the same. “Commercial truck tire manufacturers all primarily use natural rubber for heat resistance and durability,” says Mosier. “As a comparison, the automotive tires you drive on generally consist of more synthetic rubber than natural rubber. And truck tires all use carbon black to some degree as a primary ingredient in the chemistry of the tire. But that’s where the similarities end.”

According to Mosier, some commercial tire brands are well known and have been around for generations — proving their performance on North American roads. Others are less known with limited distribution. “As with any product, you have varying degrees of quality and expectations — in the tire world you have up to four tiers of quality and pricing,” he says. “And for the most part, you get what you pay for.”

A tier 4 tire might show up sporadically in the U.S. market for example, then disappear. And there are a lot of players. “The buyers of these tires are looking for rubber to put on the road – not high mileage, retreadability, or other metrics,” explains Mosier. “They’re low-priced tires with casings that typically don’t hold up to multiple retreads. When you move up to tier 2 and tier 1 tires, you find a huge quality improvement, and casings with a 4-belt package. These tires give you better overall performance and are engineered for multiple retreads.”

He adds, “One way to sum up the quality variant is to look at the tire manufacturer’s warranty. The better it is, the higher the quality. A tire manufacturer knows better than anyone else how its tires will perform. At Cooper, for example, we track performance data — it’s why we’re able to offer an industry-leading warranty program.”

Phil MosierPhil Mosier (left) says that traction design elements need to carry all the way through to the bottom of the tread, so you don’t have to pull the tires prematurely due to lack of grip.

Balancing Act

According to Mosier, tires used in logging applications are tough and unique for three key reasons. “The casing durability is first and foremost,” he says. “Trucks are off road, driven to and from the job site over sharp rock and sticks, branches, and other debris. The casing has to be durable enough to resist cuts and punctures associated with this type of work.”

Next is traction. Many work sites might be only one or two miles off the main paved highway, while others are many miles into the woods. Those roads are rough and often muddy, and if a truck gets stuck in the back woods, they risk holding up the transportation process for the entire operation. The last thing a driver wants is to be stuck with a load of timber, so heavy lugs with good traction is a must.

Lastly, while traction is needed off the road, the truck is running on paved highways the majority of the time. For this reason, the tires also need to be designed to resist the irregular wear often seen in over-the-road applications, such as heel-toe and cupping or scalloped wear.

“The trick – or the art in what we do – is in balancing the performance attributes of the tire,” Mosier says. “We know tires on log trucks take a pounding. As a tire designer, we have to figure out a way to resist off-road challenges, coupled with highway forces, in order to make a better tire. That’s the challenge.”

Added Challenges to Design

Also challenging for tire designers are the different wheel positions. With drive tires you need a combination of deep tread depth matched with traction. “Since tread wear is faster, we need to go with deeper tread depth – the Cooper Severe Series MSD for example has 32/32nds of tread. To protect against tire squirm, the tread lugs are interconnected with triangular shaped tie-bars. That’s an important performance enhancer over conventional tires. Since the tie-bars are narrower at the peak while widening out toward the groove bottom, it gives a larger ‘void’ area for off-road capabilities while the interconnecting lugs help reduce irregular tire wear over-the-road.”

What’s more, Mosier says traction design elements need to carry all the way through to the bottom of the tread, so you don’t have to pull the tires prematurely due to lack of grip. Tires are also now wider. “In the past, the typical width of a drive tire was 8 1/2 inches – now it’s more than 9 inches. What this has done has given a bigger footprint to spread weight, and that helps improve tire longevity.”

Evolution

According to Mosier, commercial tires are evolving at a rapid pace. “Compounds continue to change, and the mixes keep improving. The use of new raw materials and formulations allows us as tire designers to expand performance so that improvements can be made in durability — chunk and tread tear resistance — plus in treadwear and traction.”

Another component in continued tire quality improvement is in the manufacturing process. To be considered a top tire manufacturer, tires coming off the line need to be uniform. “And that means the specs and tolerances are very tight,” says Mosier. “For top tire brands, if the tires don’t meet spec, they’re rejected. And top brands, like Cooper, use x-ray and uniformity machines to inspect every tire coming off the line. Manufacturing commercial tires has come a long way. These improvements mean tires from the leading brands have better uniformity, which translates to longer, more even wear.”

All told, Mosier says it’s an exciting time to be a tire designer. “We have so much technology and research at our fingertips. We have chemists with PhDs who uncover new ways to perfect compounding, and we have new ways to design and test our tires to ensure top performance. There is so much opportunity in the commercial tire space — it’s exhilarating to come to work every day to see what we can accomplish.”

 

TimberWest November/December 2013
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