Is it super to go single?
Nov 1, 2002 12:00 PM, By Rick Weber
ARE you ready for wide-base tires? Maybe there's another question: Are the companies that produce wide-base tires ready for you?
Goodyear, for example, started production two years ago on its first wide-base tire that fleets are now testing, and the company maintains its primary manufacturing at a plant in Luxembourg, its most diversified complex outside the United States.
But, as Al Cohn, Goodyear's manager of strategic initiatives and communications, notes: “We have the tires, but we couldn't convert 10,000 trailers tomorrow. You cannot force the issue on this. It's going to take several years to build this up and see what the fleets really think about this. It takes time to get some acceptance. You can show the fleets all this great data, but until they actually run a couple of trucks and test for themselves and convince themselves that this is the future, it will take a long time to get acceptance.”
Tire companies first have to change perceptions and market the wide-base tires, or super singles, to fleets willing to explore the potential advantages. For now, availability is an issue. That's much more critical with wide-base tires than it is with duals.
“If this tire goes down, you can't limp home,” Cohn says. “You're stuck out there.
“For fleets going coast-to-coast, it's going to take a lot longer for them to buy into it because of availability. You'll have to have tire banks set up all over where you travel to make sure you can get the product.”
The regional line haul fleets that have tested them are giving generally positive reports.
Since November 2001, H E Butt Grocery Company of San Antonio, Texas, operator of more than 300 HEB stores, has been testing 30 units — 10 tractors and 20 Utility refrigerated trailers — with Michelin's X-One XDA series in a drive pattern and XTA series in a trailer pattern. Although 800 miles separate the southern- and northern-most stores, the typical trip is 228 miles, and all units return home nightly. In that environment, the tires have been performing very well, according to fleet manager Xavier Olivo. HEB also operates 20 stores in Mexico; although, equipment with the wide-base tires is not sent into Mexico.
“The drivers really like them,” Olivo says.
It took some time to overcome their wariness. He says that when the tires initially were installed, the drivers' biggest concern was that they were losing their aiming point. In a dual-tire configuration, they use the outside of the trailer tires as the aiming point when backing onto a dock. That's not possible with wide-base tires, which on the HEB units are offset by an inch from the inside of the trailer.
“Once they get used to that, they really have not had any concerns,” Olivo says. “The tires seem to perform very, very well in wet weather. They're holding up good. We haven't seen any premature wear on them.”
Olivo says that although the tires are performing at a high level on trailers, he's having “some issues” with their usage on tractors because of the applications and the high-scrub environment in which HEB operates.
“The road surfaces in Houston are tough on all tires, not just wide-base singles,” he says. “Everybody knows that. In Houston, if you get one-half to two-thirds of the tire life you do in other places, you're doing good.”
He said he'd be hesitant to go beyond an extended testing stage with wide-base tires if he can't use them on both his power units and his trailers. The best approach for improved fuel economy is to run wide tires on both the tractor and trailer, and that requires a large wide-base tire population. HEB needs a long test period to build up a large supply of the tires.
“The way I run my business, my trailer tires are primarily recaps, so if I don't have enough drive tire casings to recap for trailers, I'm really going to see an increase in my tire costs,” he says.
Cohn admits retreadability is one of the major negatives. He says 80% of fleets retread in an attempt to reduce costs. Many of the fleets that are testing Goodyear's Marathon LHT tires have not reached that stage yet, and Cohn isn't sure what will develop when they do.
“Typically in line haul, you retread two times,” he says. “Can you get two retreads out of these new tires? We don't know yet. The jury's still out as far as the ability to survive multiple retreads.
“In a perfect world, you're going to reduce your costs with these tires. But we're not dealing with a perfect world. In the real world, especially with trailers, they only want to check the air once a year. We're asking them to check all the time.
“Air pressure is absolutely critical on these tires. You don't have two tires. The air is what's carrying the load. If you run low air pressure, you're going to generate a lot of heat and the tire's not going to last. Inflation is the number one issue facing fleets today. Unless you can get everyone to check air pressure using a calibrated gauge, there are going to be issues.”
To monitor tires, which might be the most sensitive component on a trailer, some fleet managers are using the Meritor Tire Inflation System by PSI. The system, made in San Antonio by PSI and marketed and serviced worldwide by ArvinMeritor, connects tires to a vehicle's compressed air supply and maintains pressure within a few pounds of a set level.
The benefits: flats, blowouts, and road-service calls are almost completely eliminated — a tire that's flat from a slow leak will be completely filled with air within a mile — tire life is appreciably extended, and the cost of the system can be recouped quickly by savings in material and labor. HEB, equipping most of its 1,400 trailers with the system, has experienced a six-month return on investment, based on the average road-service expense of $400.
Olivo says tread wear has improved by 15%, with tires remaining at the proper pressure of 100 psi on Michelin's X-Ones. Hoses and connections on the system do need to be checked, but Olivo says that is done when tires are changed every six or seven months.
Other potential negatives of wide-base tires:
Assembly size and weight. One wheel assembly with a wide-base tire weighs about 245 lb, compared to 175 lb for a standard-size tire. It's difficult for one person to pick up the wheel assembly and move it around.
Highway damage. Although a study conducted by the Virginia Polytechnic Institute and State University and published by the Reserve Board in January 2002 showed there is no significant road damage caused by wide-base tires compared to duals — Michelin marketing director Ralph Beaveridge refers to wide-base tires as “damage neutral” — a 1998 study in the United Kingdom posed questions. It concluded that the cause of surface-initiated cracking was due to horizontal tensile stresses generated by truck tires at the asphalt surface, and that wide-base tires generated the highest tensile stresses.
Stress on bearings. Dan Tilton, chief engineer for heavy-truck applications for Timken, says his studies have concluded that if a user is operating with an existing wheel-end design and simply taking off a dual and replacing it with a wide-base tire, there could be a “fairly significant reduction in the expected life of the bearing components.
“It changes the load position on the bearings,” he says. “With the duals, the load position was designed to put it in a favorable position relative to the bearings, which are somewhat centered over the two bearing rows. Those designs have been around for quite some time, and the bearings were designed in the ‘50s and ‘60s. Users wanted the ability to go from dual to single and back to dual, so the wheel-end design has not been changed to accommodate the shifting of that load line.”
He says that on the traditional wheel end for a trailer application, Timken might predict two or three million miles of bearing-fatigue life. With a wide-base tire on that same wheel end, it might be 500,000 miles.
Tilton says that if wide-base tires continue to gain acceptance in North America and are used on dual wheel-end designs, “it will require using a high-quality bearing component in the wheel end. There has been quite a bit of use of bearing components from China and other regions that aren't quite up to the level of your top-of-the-line bearing manufacturers.”
Positives outweigh negatives
The negatives, according to most of the sources contacted for this story, seem to be far outweighed by the benefits. Besides performance and driver acceptance, they potentially are:
Weight savings. On a twin-screw tractor with aluminum wheels, it's about 392 lb, and about 328 lb on trailers. Beaveridge estimates 200-250 lb per axle of weight savings or about 1,000 lb on a regular tandem trailer. “For fleets where weight is critical, this comes into play,” Cohn says.
Fuel economy. Michelin's Beaveridge says fuel savings results from reduced rolling resistance, primarily because there are only half as many tire sidewalls to absorb and waste energy. He says that when rolling resistance is lowered by 3%, fuel economy is increased by 1%, and that by switching from its most fuel-efficient drive tire, the XDA2, to the X-One XDA, and the trailer from the XT-1 to the X-One XTA, fuel efficiency would increase by approximately 5%. He says that one fleet experienced fuel savings of 10% by changing both the tractor and trailer tires.
Olivo says that while he has seen an improvement in fuel economy due to lower rolling resistance, it is somewhat lower than anticipated based on the data provided by Michelin.
“Their marketing claims are based on a test environment,” he says. “Once you put that tire into an actual day-to-day operation and the traffic you have to face in Houston, San Antonio, Austin and up I-35, sometimes it can be a bit different. We have 10 tractors and 20 trailers running these tires. When you put X-Ones on the four drive tire positions and the four trailer positions, you see an improvement in fuel mileage. A mixed combination with four drive tires and eight trailer tires or the other way around doesn't produce the best fuel economy results. But the test is a long time from being over.”
Cohn says Goodyear is not promising an increase.
“The driver has such an incredible influence,” he says. “If he's sitting there idling, you've lost all the advantage. If he's a 21-year-old driver versus a guy driving for 30 years, you'll see a huge difference. On the fuel side, it's difficult to convince a fleet manager that he's really reducing his fuel costs, even though when you run an SAE-type fuel test, it shows an improvement. Directionally, it's better. But you're not going from 6 mpg to 8 mpg. It's maybe a tenth of a mile per gallon. If you have a huge fleet and fuel is a big percentage of the cost, if you can save 2%, that's a lot.”
Stability. Some tire manufacturers say that the tires make a rig more stable because they move the vehicle track outboard by about two inches, although Goodyear's Cohn says tests (slalom maneuvers and wet braking) show performance that is nothing more than “equivalent.”
Michelin says its Infini-Coil Technology incorporates over one-quarter mile of continuous steel cable to help eliminate casing growth at operating temperatures, promoting driver comfort and vehicle stability.
Manufacturers can take advantage of the slightly narrower tire, taking a tanker with tapered sides and lowering it a few inches into the liberated space between the wheels, thus lowering the center of gravity and increasing stability. They also can increase capacity by building more trailer volume into that additional space.
Lower wheel costs. Alcoa says its aluminum wheels cost $1,040 less than the wheels for conventional duals.
Extended brake drum and lining life. Although the running assembly is cooler, Cohn says, “It's difficult to generate data on that issue. But you've got a bigger tire that still generating heat, rather than two. Directionally, you should be able to extend its life, but the numbers are anyone's guess.”
Cohn says that he sees the tires filling a “niche market” for now.
Ten years from now?
“Assuming the retreading works out, it's possible we'll see wide acceptance of these tires,” he says. “But it'll be very gradual.”
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