Medium Duty: Best of Both Worlds

Some off-highway vehicles spend most of their time mucking around debris-filled construction areas or quarries while others spend most it cruising along the highway on their way to the job site, but you still need a durable, tough tire when it’s time to get dirty. So how do you build something that works for both Larry the landfill operator and Linda the landscaping supervisor?

Clearly, these are not your father’s on/off-highway tires—today’s versions have all the advantages of modern technology and years of research, giving fleets the flexibility to have it all. Yet it wasn’t that way just a decade ago, says Bridgestone Tire director of engineering for commercial products and technologies Guy Walenga, because manufacturers were simply building the wrong tire.

“We looked at maybe 80 percent off-highway, 20 percent on-highway, give or take, and we built and compounded the tire accordingly, so the rubber just didn’t stay on the tire for highway, but off the highway it was a very durable product,” he says. “Over the years, we have continued to refine what on/off-highway is, and we actually find out that in most cases, an on/off-highway tire spends maybe 80 to 90 percent of its time on improved roadways, and the other percent is off-highway—it’s not as much as we thought.

“So it’s really very little time (off-highway),” he says, “but the off-highway environment is very, very brutal, so we’ve redesigned tires to reflect more on-highway time and less off-highway, and that’s a big change. Now we’re trying to get more on-highway mileage, however we can’t give up any of the durability we put in for off-highway performance, that’s the trick. We’ve shifted to make it more ‘on-roadable’ but not reduce any of its off-highway capability.”

COMPOUND SOLUTION

On/off-highway tires look the same as your average truck tire, but there is a lot more going on inside, thanks to evolved compounds—the biggest difference in modern tires, Walenga says. And products are being analyzed, tested and upgraded all the time.

“The on/off-highway tire is kind of a tough fit,” he says. “We want a tire that’s going to run on the highway for some amount of time but be able to go off into some pretty rough territory and not get cut up and chipped up and destroyed in that off-highway service. These tires are brutalized.”

So hats off to the guys in the lab coats, who have been busy putting the new information to use.

“We’ve done a better job of finding rubber compounds that will work on the road, and we can still make them more cut and chip resistant when they go into rocky areas,” Walenga says. “The construction of the body of the tire basically remains the same; it’s still a steel body ply. We may use different cords or filaments to make it more flexible, we space those cords a lot farther apart than we do for a highway tire, so it’s a more flexible design. We have a more flexible belt package, so the steel part of the tires—the cables, their spacing, the belt spacing—that is also being tweaked over the years to make the tire more suitable for off-highway, but still even more suitable for on-highway.”

Flexibility is a good thing when a tire has to move around and over objects, as an on/off-highway often does.

“As it rolls over obstacles, you have to try to envelop them, and a steel-belted radial tire doesn’t envelop anything; it’s too stiff,” Walenga says. “So by changing the cables and the belts, spreading them out a little bit more and in some cases making a split belt—where the belt is literally in two pieces next to each other rather than one solid piece, to allow a little more flexibility in that tread—so it can envelop obstructions rather than just smack ‘em. And this makes the tire more resilient and stronger and better suited for off-highway. But, flexibility in a tread means more rapid wear—now we’re back to running on the highway with a flexible tire, and that’s what’s causing the tires to wear out faster. So, you’ve got to find that middle ground in the casing design and the belt design and still top it off with compounds to resist that scrubbing action that you’re getting from more flexible body ply and belt.”

LISTENING SESSION

As the Technology & Maintenance Council’s (TMC) Chair for the S.2 Tires and Wheels Future Truck Task Force, and Silver Spark Plug award winner, Walenga is well-connected with fleets across the country and their needs, and he says listening to them is one of the most important things he does.

“They want everything, and we’re trying to give them as much of everything as we can, and an on/off-highway tire is quite a balance: they take a whole lot more punishment,” Walenga says. “They want a drive tire, for example, that can go off-highway, won’t get bogged down in soft material—it will be able to dig itself out, won’t chip and cut up, and they won’t have to use different trucks, where they can get more highway mileage, but not give up what they could already do off the highway.”

On the other end, fleet officials need to find out exactly what kind of conditions their tires are going through, or costly mistakes can result.

“When you’re on that fine line of what’s off-highway and what’s not, some fleets will sometimes choose to use a highway tire because that’s a little less expensive, but they find that the cutting and chipping is so bad that sometimes they lose the casing,” Walenga says. “It doesn’t appear that the tire is worn out, but the cutting and chipping goes through the compound in a heartbeat, right down to the belts. You might not see it, but when you see tires in a scrap pile and start peeling away the rubber, you can see that, and that starts with wicking and moisture attacking belts, you have rust, you have a casing that’s fatigued or takes too much time and effort to buff all the rust out for a repair or retread and you lose the casings.

“So, it’s a tough choice when you’re on that fine line,” Walenga says. “‘Do I use a highway tire because it’s cheaper and just be real careful, or do I pay extra and use an on/off-highway tire and maybe give up some of my overall highway mileage, which is the bulk of the time I spend with the tire?’ Each fleet has to decide what is best for them on a cost per mile basic and where it fits into their application.”

CASING CARE

Fleets also want a tire that will not only live on-highway more and still retain off-highway properties, Walenga says, but they’ll still be able to retread.

“Retreading is just as important in this environment, if not more, than with a highway tire, because these are expensive tires, you still have the casing that is still retreadable and repairable, so these guys want to retread and get more out of their investment in that steel radial casing,” he says. “They are going off-highway, and it’s not all simply some (rough) roads or some crushed rock or few cactus you’re running over; you’re running these tires in operations where there is so much debris, you get a lot of road hazards; the tires get enough holes poked in them where they just can’t be repaired or retreaded, so the life of these tires is a little shorter, but it’s much, much more brutal.”

While other companies have had some success with self-sealing tires, Walenga says Bridgestone officials have decided to steer clear.

“It does only cover the areas in the tread that would normally be repairable if you had a puncture,” he says. “The sealant does help in so much it keeps you going, because it seals it up. But, in talking to fleets, the downside is that they have so much faith in the technology that they don’t do a really good job at inspecting their tires, and a lot of the debris that punctures the tire stays in it. And when that happens over time, even though the air is not coming out and the tire is serviceable, you tend to wick more moisture into the tire; rust attacks it, you have tires that don’t retread, that need a lot of repairs to bring them up to re-treadabililty, and a lot of times there is too much damage.”

Walenga says while the sealant serves its purpose at the moment, if you can’t convince the user to still inspect the tire, they let it go and sometimes they end up losing the casing.

“It’s just a choice, but everybody’s tires still have to be inspected, they still have to pull debris out; even in sealant tires, there is a method for pulling the debris out and doing a repair that’s considered a permanent repair for the tire,” he says.

“People are in a hurry to address or adopt technologies, especially if it helps them reduce maintenance and upkeep, but we always caution customers: don’t let the technology do all of it. It can’t; you still have to do the inspection,” he says. “The tire is still a really sophisticated envelop that holds the air, and it’s the air that holds the load, so you’re trying to keep the air inside, and if you’re not taking care of that tire, then the air doesn’t stay there and you’re stuck.”

MAINTENANCE TIPS

What are Walenga’s top tire care tips?

“No matter how many things we bring out, no matter how puncture-resistant the tires is, no matter how durable it is for off-highway work, it’s air pressure, air pressure, air pressure, air pressure,” he says. “You still get the best overall performance by maintaining the tire and the vehicle the best that you can, and maintaining the proper air pressure so the tire can flex and deflect on/off-highway like it’s designed to—these are designed to be much more flexible than their highway counterparts.”

Choosing the right tire for the right application is the first step, though.

“Get the right tire for the right application for the right wheel position, and a tire that has a good quality casing, because you should be looking right off the bat to retread,” Walenga says, going down his to-do list. “Make sure it is mounted concentrically on the wheel, so you have to have good mounting practices, lubricant on both tires beads and wheel seats and using the right tools, like a safety cage. This is just rote for a tire technician, but you have to do all these steps to make sure it’s mounted concentrically so it rolls round. Make sure your wheels are round to begin with; that you’re not using damaged wheels.”

Constant inspection and a little TLC will also go a long way.

“You still have to inspect it as often as you can, remove debris from the tire, if it has a puncture, fix the puncture, don’t just add air to it and let it go,” Walenga says. “Fix it with the proper inside-out repair, watch your air pressure and tread depths so you don’t pull the tire too late, and make sure your vehicle is aligned. This is a tough one for an off-highway vehicle because it gets a lot of knocking around; sometimes people don’t spend as much time aligning an off-highway vehicle as an on-highway vehicle, but it’s still important; people think they last forever but they don’t.

“It’s odd to see an off-highway type tire that really gets brutalized comes out of service for irregular wear—if you can find irregular wear on an on/off-highway highway tire, you’ve either got he wrong product and the wrong application or you really haven’t done an alignment on your vehicle in a while.”

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