PRODUCT F o c u s

Sometimes, you have to make a tire specifically for the application. That’s just what Bridgestone engineers did when waste hauling fleets like BFI asked for a tire that could handle the front axle loads of trash trucks and the tough city streets they travel. And the tire also had to be made to work in the new world of refuse hauling, where trucks may never go off the road to conventional landfills. Bridgestone engineers brought together just the right mix of technologies, and the result is the new 315/80R22.5 R296 all-position rib radial. It’s been out in the field, on trash trucks, for over a year, and many users think it’s “just right” for them.

Why was the R296 needed?
For a long time, waste haulers have used on/off-highway tires on their trucks. That’s because they usually had to go to landfills once or twice a day, and landfills can be treacherous places, filled with hazards that can puncture, snag or otherwise damage tires.
In that respect, a landfill is a lot like a construction site. And since construction vehicles used them, on/off-highway tires seemed to fit refuse hauling too.

What changed?
In part, the nature of the refuse hauling business. With urban sprawl, landfills ended up being farther and farther away from urban areas.
That meant more time on the road and less off the road. Not only that, but some waste haulers stopped going to landfills altogether.

Where do they dump the trash, then?
Today, a lot of them go to “transfer stations” or indoor pit landfills. Many transfer stations are actually giant incinerators, that burn waste to produce power or heat.
The characteristic of both is that the trucks drive in on paved roads, then unload their contents onto concrete floors, where the waste is transferred to the recycling area or incinerators.
The result is that they’re spending little or no time “off the road.” And that changes their tire needs.
Picking up trash containers puts enormous loads on the forward axles of waste hauling vehicles.
How?
Typically, a tire designed for off-highway use is built to be flexible and resilient. With uneven surfaces off the highway, and with sharp objects around everywhere, the idea is to make the tire yield to rough terrain. [Editor’s Note: Please see the related story in this issue, “Technically Speaking,”]
So, typically, an on-off highway tire is built to be flexible. What you want is a tire that can “roll with the punches.” Not the best thing for an on-highway tire.
Why not?
The more flexing a tire does, the more internal heat it tends to develop. Most of the time, off-highway miles are done at very low speeds, so the extra flexing doesn’t generate that much heat.
But, put an on/off-highway tire on the interstate at high speeds, and it can develop plenty of heat. That shortens tread life, wastes fuel, and, as we all know by now, heat is the enemy of retreadability.
Tires designed for on/off-highway service often employ a split bottom belt, to increase their flexibility and power to envelop obstacles. Tires for on-highway use usually have a full bottom belt, to reduce flexing and heat.
What was the solution?
The R296 had to be built almost like a “hybrid” of an on-highway and an on/off-highway tire. While many on/off-highway tires utilize a “split” bottom belt to improve their flexibility and ability to “envelop,” rather than resist objects, engineers substituted a full bottom belt in the R296.
This makes its design, internally, at least, much like a conventional on-highway tire.

And on the outside?
Outside, the R296 still has to contend with stopping, starting, turning, maneuvering, thousands of times daily. It’s not unusual for residential waste haulers to handle 1,300 customers a day.
That’s a lot of scrubbing of tires against pavement, and not the best pavement at that. Waste haulers usually stay close to curbs to avoid obstructing streets, and this tends to be where the loose stones, gravel, debris, and other hazardous objects collect.
The answer to all this was a special tread design and tread compound.

How is the R296’s tread different?
Instead of a conventional, high-speed, on-highway compound, designed for long wear and irregular wear resistance, Bridgestone engineers chose essentially an on/off-highway compound.

But you said that this isn’t really on/off-highway service.
In many ways, it isn’t. But because of the extreme abrasiveness of the environment and the endless turning and maneuvering that trash trucks do, an on/off-highway compound, designed to resist cutting, chipping and chunking, is better for this kind of application.

What about irregular wear?
Usually, that’s not a problem. Waste hauling vehicles generally wear out tires so fast that any irregular wear patterns tend to get scrubbed away.
Many refuse haulers actually measure their tire life in “weeks” rather than in miles. [Editor’s Note: Please see the related story, “Fleet View” ]

Is there anything special about the tread design?
Yes, there is. Most fleets will put these new tires on steer axles, using retreads for the drives. So, the R296 has a 23/32nds inch tread depth – about four or five 32nds deeper than a conventional on-highway steer radial, but not quite so deep as a drive tire. This provides extra tread for longer life in this fast-wear application.

What about the pattern?
The R296 has an angled (sometimes referred to as a “zig-zag”) tread groove design and extensive siping, for enhanced traction, and special, button-like structures at the bottom of its grooves to combat stone retention.
The R296 tread pattern is designed not to capture or hold stones, and for maximum traction on wet roads.

How do those work?
Stones can work their way into a tire’s grooves and become lodged there. Over time, they are driven deeper and deeper into the grooves, and can eventually penetrate to the belts. This is called “stone drilling,” and can damage the steel cords, plus expose them to air that can cause them to rust.
And rust, like heat, can ruin a casing.
As the tire rolls in and out of its footprint, these short finger-like structures at the bottom of the grooves twist and flex, pushing against stones that may have become caught in the grooves.
The action of these “stone rejectors,” as they’re called, tends to prevent stones from getting stuck in the grooves, and actually helps push them back out again.

What did you do about the load on the tires?
That was one of the biggest challenges.
Today, it’s not unusual for a refuse hauling vehicle to have front axles rated at 18,000 to 20,000 lb., a lot more than the 12,000 lb. we see on most semi-tractors.
Typically, the tire size of these tires is 315/80R22.5, and even with a 20-ply or “L” load rating, the maximum load for that size is usually 9,000 lb. on a single assembly and 8,190 lb. in a dual configuration, both at an inflation of 130 psi.
Clearly, that’s just barely enough for an 18,000 lb. front axle, and a bit short of what’s needed for a 20,000 lb. axle.

How did you deal with that?
We re-examined the load ratings for this size and design of tire, and decided to rate the 315/80R22.5 load range L R296 at 10,000 lb. single and 9090 lb. dual, both at 130 psi, provided the tire is operated at a maximum speed of 53 mph.
Drivers must understand that failure to adhere to these restrictions will cause tires to build up excessive heat which can result in sudden tire deflation, property damage, or personal injury.

[Editor’s Note: The R296 is now available from your tire dealer in the 20 ply-rated 315/80R22.5 size.]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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PRODUCT F o c u s