AKRON—After problems with Bridgestone/Firestone tires on the Ford Explorer ignited a massive recall eight years ago, all eyes were on the passenger and light truck tire industry.
That sector, after all, was where most of the troubles occurred and became the focus of the ensuing Transportation Recall Enhancement, Accountability and Documentation Act.
But for the past four years, an ASTM International truck/bus tire test development task group has been working quietly to develop laboratory tests to effectively match the highway operating conditions for over-the-road, commercial truck tires.
The group is ready to write up two standards that might become a reference for a proposed upgraded rule for truck/bus tires currently being developed by the National Highway Traffic Safety Administration, according to Terrence Ruip, chairman of the ASTM task group and a technology adviser for tire test engineering at Goodyear.
One of the ASTM standards will cover the endurance and high-speed test the task group developed, while the other will detail a highway speed equivalency algorithm it worked out during its testing, Ruip said.
Under the TREAD Act, NHTSA was charged with reviewing and upgrading—if necessary—regulatory tests for tires.
Once NHTSA completed most of its rule making under the act for passenger and light truck tires—covered under FMVSS 109—the agency turned its attention to truck tires. It asked the ASTM to form a task group in 2004 to study truck tire performance and truck tire operating temperatures.
Ruip said he “was volunteered by Goodyear” to serve as chairman of the task group. About 40 people signed up to be members, with roughly 20 active, he said. The members include a cross-section from major tire companies, testing laboratories, auto makers and even some government observers from NHTSA.
The action plan involved studying operating temperatures of truck tires on the road and also in the lab on a road wheel. The group would then compare the temperatures and develop regression temperature models that would help members design endurance and high-speed tests.
“Our objective was to maintain equality in temperatures between the road and the lab,” Ruip said.
The task wasn't as simple as it sounded. He said the standard 67-inch diameter road wheel used in most testing labs generally worked fine for passenger and light truck tires.
But when you start putting a 42- or 44-inch truck tire up against that same road wheel, it created problems. “You're really starting to distort the footprint of the truck tire,” the 37-year Goodyear veteran said. “It's no longer the shape and pressure distribution that it was designed to have.”
To bring the test tire from the road into the lab and test it at equal conditions, something has to be adjusted—either the load, inflation or speed. Ruip and his group found that the most influential modification it could make was with the speed.
“The load and inflation will help you hold your temperatures to what they are on the road, but the speed gives you the most bang for your bucks,” he said.
Generally, the group found that if the load and inflation in the lab was the same as on the road, the speed in the lab would need to be reduced by 25 mph to maintain equivalent tire temperatures.
While at first the group concentrated on long-haul tires prevalent on 18-wheelers, by the end the members had captured temperatures for the whole range of truck tires, including bus and trash haul tires.
“We created temperature-regression models that would allow us to predict what the temperatures will be at these locations for any combination of running conditions either on the road or in the lab,” Ruip said.
The two standards the task group will write will be viewed as a standard way of testing for people who want to “talk apples to apples concerning truck tires,” with testing conducted according to the standard, he said.
Fleet owners, for example, may want to ensure the durability of the tires they purchase so they may ask potential suppliers bidding on the contract to do testing according to the ASTM standard.
The federal government, most likely NHTSA, would be another user of the standard as it works on upgrading FMVSS 119 for truck tires.
“They had asked us to form the task group because they're not set up to do this kind of work,” Ruip said, noting that NHTSA's proposed new rule for truck tires is expected to come out sometime after the first of the year.
While the agency rushed forward to address problems with passenger and light truck tires following passage of the TREAD Act, Ruip said there wasn't the same urgency with truck tires. “Truck tires are a completely different thing than passenger tires,” he said. “These things run a million miles after they've been retreaded several times. So truck tire testing and design is a lot different than passenger tires, and truck tire customers are a lot different than passenger tire customers.”
Specifically, fleet buyers are normally more discerning and have entire programs designed for truck tire maintenance. “So there's not really a truck tire performance problem,” Ruip said. “It's just that NHTSA does not want one to appear in the future.”
The task group chairman didn't know what to expect when he first got involved in the project because it was his initial experience with an ASTM project. But when he saw what was going on with some other related task groups, he realized it would be a several-year project.
He was pleased with the “abundance of cooperation” from the active members of the group along with the level of interest from the major tire companies.
Ruip also realized that such a project would have cost a great deal of money had everything been paid for at market rate, but the manpower of group members was donated as was the equipment and some of the testing. Each of the companies with members on the group also pledged a small amount of money to pay other costs.