Art of tire design
We’ve been doing PR in the tire sector for more than a decade. We’ve always found tires to be interesting, so wanted to find the true story behind designing commercial tires. We interviewed the folks at Cooper Tire and learned a great deal…as did the many readers who saw the piece in trade journals… Take a look
Today’s commercial truck tires are are rolling pieces of sophistication. They are the vessels that carry the payload on a tractor and trailer, so 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,” said 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 the second highest operating cost after fuel, miles to removal and fuel economy – balanced by a competitive price – is what can keep fleets making money. Providing our customers with a low cost of ownership is what Cooper is all about.”
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,” said 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. “And, like 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 said. “And for the most part, you get what you pay for.”
In defining the tiers, Mosier said that the lower the tier, typically the lower the performance -- fewer miles to removal, for example. A tier 4 tire might show up sporadically in the U.S. market for example, then disappear. And, there are a lot of players. There are more than 250 different brands of drive tires listed on the SmartWay website – the vast majority in the lowest tier. “The buyers of these tires are looking for rubber to put on the road – not high mileage, retreadability or other metrics,” explained 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 long miles to removal, better fuel economy, and are engineered for multiple retreads. 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.”
When looking at a passenger tire versus commercial truck tire, Mosier said each has its own performance challenges for engineers. “With a passenger tire, consumers are looking for handling, low road noise, and mileage in the 30,000 to 80,000 mile range. With commercial truck tires, it’s those attributes plus casing integrity. Some fleets, with diligent tire maintenance practices, get more than 400,000 miles on drive tires. Consumers driving sports cars are looking for high performance tires – traction and braking are paramount – so the tread has to grip the road. And, that means sacrifices in other areas, like mileage. Conversely, some fleets, especially in Canada, look for tires that have better traction, to handle snow and ice conditions. They too will give up fuel economy for specific performance.”
According to Mosier, long haul and regional operations each pose different challenges and that’s why wear (miles to removal) can vary greatly. “The trick – or the art in what we do – is in balancing the performance attributes of the tire,” he said. “The first 5 miles and the last 5 miles of a trip wear out a tire faster than the 500 miles in-between. Stopping, starting, and scrubbing tires (turning) are what wear away the tread and it can impact uniform wear. So, as a tire designer, we have to figure out a way to resist those forces in order to make a better tire. Anyone can build a tire to go straight for 500 miles…and have good wear. But to get top performance you have to offset the forces that eat up a tire, or cause it to come out of service due to irregular wear. That’s the challenge.”
Also challenging tire designers are the different wheel positions. Steer tires are considered the most important as they typically carry maximum loads and are very sensitive to tire pressure. “And, they’re constantly turning and scrubbing, and can be impacted by alignment issues,” said Mosier. “It’s why there is so much emphasis at Cooper in engineering a tire that can withstand all the forces that come into play. We’ve seen changes over the last 10- to 15 years as well. In the past, the typical width of a steer tire was 8-1/2 inches – now it’s 9-inches. What this has done has given a bigger footprint to spread weight. And new compounds have made that tread roll easier over the road – our new Cooper PRO Series LHS steer tire, for example, exceeds SmartWay rolling resistance standards by 15%. That’s a huge improvement. We continue to push the envelope to improve performance for our customers.”
According to Mosier, commercial tires are evolving at a rapid pace. “Compounds continue to change and the mixes keep improving,” he said. “The use of new raw materials and formulations allow us as tire designers to expand performance so that improvements can be made in rolling resistance while maintaining, or improving, 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,” Mosier said. “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 said it’s an exciting time to be a tire designer. “We have so much technology and research at our fingertips,” he said. “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.”