Trends In Treads
These days, fleets can select tire systems that range from the relatively simple to the very sophisticated.
Truck tires have come a long way. Not so long ago, you had to deal with tire tubes and bias ply tires. With the advent of radial tires, so many more things became possible. Tires are built better in a number of different ways and last longer. And the changes keep coming – many of them in the tread itself.
Evan Lockridge
Contributing Editor
One notable thing that’s happened to truck tire treads in recent years is changes in thickness. Some are getting thicker, while others are getting a bit thinner.
“Ten or 12 years ago, the average tread depth (on drive tires) was 22/32 or 24/32, and now they have gone all the way to 32/32,” says Peggy Fisher of Fleet Tire Consulting. This, she says, has helped fleets increase their removal miles on drive tires from 250,000 miles to as much as 350,000 on tandem-axle tractors.
The same cannot be said for tread depths on steer tires, according to William Forsch, manager of original equipment with Yokohama. “The standard used to be 19/32, and now some people are sampling as low as 18/32 to 16/32,” he says. The slightly thinner treads reduce the chance of irregular wear.
Also helping steer tires last longer, and in part increasing removal miles on drive tires, have been improvements in rubber compounds. Yokohama, like many other tire makers, has developed compounds that have less rolling resistance, resist chipping and cutting and are more resistant to heat.
Fisher says rubber compounds also have become far more application-specific. “For instance, if you’ve got a truck doing regional applications that includes both over-the-road and local work, there are specific tires meant for those applications, and they are compounded and have tread designs specifically for those applications so they get the most mileage. We didn’t have those before, and they are a new development in the last 10 years.”
Wider treads are another change. “Tire manufacturers are creating wider tread patterns because more rubber tends to allow the tire to wear at a slower rate,” Forsch said. “That’s allowed a pickup of 20% to 25% higher mileage.”
Perhaps the most revolutionary trend of recent years – now spread across the entire industry – is what’s called the decoupling groove or defensive groove. This is a groove that is molded into the outside shoulder ribs of tires to reduce or eliminate irregular wear. As its name implies, it decouples the tread area from the shoulder of the tire.
“As a tire rolls down the road, you have the bumping and mechanical jostling of the vehicle and its reaction to all of the irregularities in the road surface, which causes the tires to be under constant compression,” says Michael Burroughes, product manager for Michelin. “This decoupling groove helps disassociate the tread area from most of those forces that would be transmitted to it through the sidewall. So it really acts as a bit of a shock absorber.”
With all of these changes, you have to wonder what’s next on the horizon for commercial tire treads. If one of the latest announcements is any indication, the changes will be subtle but just as important when it comes to performance.
During this year’s Mid-America Trucking Show, Michelin unveiled the XDN2 drive tire with multi-dimensional sipes. Sipes are generally straight edged or slightly waved cuts across the block of rubber in a tire to help the tire grip the road better.
“Traditionally, sipes have had a very important role on steer and trailer tires, which are essentially tires that run in free rolling positions,” says Burroughes. But they have been very difficult to deal with in drive axle tires. The way the sipes interact with the mechanical forces of torque has been a very limiting factor.
What makes this siping system so different, Burroughes explains, is there are so many of them on a single tire – 1,300 in all. Other factors include how the sipes are shaped, how deep they run and how they work.
“As the tire comes through its contact area with the road surface, the sipe edge along the top of the tread provides the lateral edge that gives the gripping contact,” Burroughes says. “But as the tire and rubber compress under the weight of the vehicle and the load, the three-dimensional aspect allows it to lock together and gives it the mechanical performance of a solid piece of rubber.”
The benefit, he says, is more even wear, plus better performance in a variety of weather conditions.
In addition, Burroughes notes the sipes on the XDN2 go down almost as deep as the tread, whereas most disappear at about 11/32 of tread life.
While it may not be as radical a change as the one from bias-ply to radial tires, this and other tread trends are examples of how tires are continually evolving to provide better performance and durability.
