we never notice them. When one goes bad, it's a major and often costly inconvenience. We gripe about the cost of the things and what a pain they can be to maintain, but do we ever stop to think about the job they do?
A typical linehaul tire goes around about 500 times every mile. If you get 100,000 miles out of a tire, it will have been through 50 million revolutions. That's 50 million times its sidewalls have flexed and deformed. Fifty million times a 1-square-foot area of the tread has to bear a 5,000-pound load, squishing and squirming across scorching hot or freezing cold asphalt and concrete. They run pressured up to 100 psi, and they see temperatures ranging from 50 below up to 150 degrees.
Your tires are driven over curbs, rocks, and chunks of steel, and through potholes and cracks in the roads, and over grated steel bridge decks. They're torqued all to hell by today's 2,050-pounds-foot-and-beyond engines, and they're torn in all directions during hard braking.
At the end of the day, 18 square feet of rubber are all that stand between you, the pavement, and the great beyond.
If they didn't already exist and do what they do, you'd be laughed out the door if you presented such a wish list to an engineer and asked him to build you such a thing.
You couldn't have done it 30 years ago. But today, we're on the phone to the dealer if a linehaul tire doesn't go beyond 100,000 miles.
In the mid-'70s, the tire industry was riding the first wave of steel-belted radial tires. Bias ply was as good as it got up to that point, and by today's standards, that wasn't much. Two hundred dollars would buy you a tire made of rubber-coated fabric plies layered over each other at a bias and built up to a certain thickness, plus a rubber liner and an inner tube.
"You got a lightweight tire that wore very quickly," says Bridgestone Bandag's Guy Walenga, director of engineering for commercial products. "It wasn't stable. The footprint was always shaking on the ground. They weren't good for fuel economy, they weren't very durable, and they weren't good candidates for retreading because they were made of fabric."
In addition, you had a lot of parts to deal with. You had the tire, a flap or a liner, and the inner tube, and you had multi-piece wheels to put them on. The more parts you had, the harder it was to keep everything matched up, uniform, and concentric.
Tubeless tires came next. They were considered quite a leap forward - fewer parts, consistent mounting, ease of maintenance, and improved durability. If you got 75,000 miles out of one, you considered yourself lucky. They weren't very resistant to punctures or sidewall damage, and many of them died premature deaths.
Enter the Radial Tire
Then along came radial tires. Fabric-ply radials emerged first, but they weren't on the market long. Single steel body plies and steel belts added immeasurably to the strength of the casing. Performance and durability nearly doubled, along with the life of the tire. It was a little heavier than a bias tire, but rolling resistance was fraction of what it was.
"As the tire rolled, the casing deflected, by virtue of its design, but the tread wasn't really connected to it," Walenga explains. "It stayed flat, because you had steel belts above the casing and below the tread. That helped keep the tread flat on the ground - unlike the bias tire tread that squirmed all over the place."
Radial tire technology did for tires what diesel engines did for trucking. It brought performance and durability enhancements to in-service tires, better repairability, and it offered superior casings, which made retreading a more cost-effective proposition. Cradle to grave, radial tires probably went three times as far as even the best bias-ply tire could.
But tire design and manufacturing processes were still in their infancy - in the Stone Age by today's standards.
One of the key enablers in the switch from fabric to steel belts was the ability to get rubber to adhere to steel. Walenga says that was a significant achievement.
"Once we figured out how to use steel for the body ply, we put belts of steel into the tire, we took out all those layers of fabric, and we replaced them with a single steel ply," Walenga says. "One steel ply had the strength of 16 or 18 layers of fabric. It's steel cable - little wound strands of wire twisted together - and then connected from one bead to the other radially. They never touch each other, they never cross over each other, and they are all encased in rubber. That took a lot of technology back then."
And 30 years ago, few people had even seen a computer, let alone used one to design a tire.
Goodyear's Dan Harrison, a project manager in Akron, Ohio, remembers hiring on with the company 30 years ago.
"I remember when we got the first PC here at the plant," he recalls. "People used to come up and touch it. Now all the tire machines have seven or eight processors on them to do the different functions."
The biggest gain to come from computer-aided design has been the ability to design tires for very specific applications, i.e., city and regional tires versus an all-purpose tire used in urban and highway environments. That optimized tire performance and durability for each market segment, bringing greater value to a broader range of customers.
But even as tire design was becoming more sophisticated, a need remained for a rugged tire that would take its share of abuse, but was inexpensive enough to throw away when it had been beaten into submission. According to Walenga, the construction and P&D markets were the last holdouts for bias ply tires.
"Those are brutal applications." Curbs, rocks, loading dock debris, etc., just tore tires up, he says, especially the sidewalls. "Bias tires cost less than half of a radial tire, but they still took a beating. When you killed it, you threw it away. You weren't losing much. If you beat up a new radial tire like that, you lost not only the remaining tread, but with a damaged sidewall, you had no casing either. That was expensive."
The solution: sidewall protectors. The enabler: computer-aided design. Once tire manufacturers found a way to protect the sidewall, the radial made sense even in construction and P&D. Despite the worst you could throw at a tire, the casing was protected so you'd still have something worth retreading. Suddenly the radial was king. "That was the change that sealed the fate of the bias ply tire," Walenga says.
Along Comes Low-Pro
Years before wide-base singles hit the North American market, low-profile tires appeared boasting many of the same advantages that wide-base tires claim today. They were lighter, and were believed to offer less rolling resistance than standard-sidewall tires. The shorter, stiffer sidewalls on the low-pro tires proved very successful, eventually making it the best-selling tire in the over-the-road market. They remain the number one selling tire in that application today. But they had other strong selling features, too.
"The low-pros weighed less than a 90-series standard tubeless radial, and the federal excise tax charged on tires was weight based," Walenga explains. "Low-pros were lighter, so you saved money up front."
Because the tires had a lower overall diameter, trailer makers discovered that their floors could be dropped a few inches. That brought a sea change in van trailer design, making 110-inch inside height possible. The market responded favorably.
If there was a downside to the low-pro tires, it was the stiffer sidewall. Some drivers complained that they rode harder because there was less flex in the sidewall, and sidewall injuries went up a lit