Tire makers soon may see a new proposed safety and performance standard for commercial truck tires, including possible testing requirements for truck retreads, a top government official said.
However, at the 22nd Annual Clemson Tire Industry Conference where that news was dispensed, Bridgestone/Fire- stone reported on a survey that shows truck tires can last for up to 15 years and five retreads, if cared for properly. Using pure nitrogen instead of ambient air for inflation can extend their service life even further, according to other speakers at the March 15-17 meeting at Hilton Head Island, S.C.
The Transportation Recall Enhancement, Accountability and Documentation Act mandates an upgrade of truck tire testing standards, just as it did for passenger tire standards, according to Keith Brewer. He is director of the Office of Crash Avoidance Standards at the National Highway Traffic Safety Administration.
The first safety standards for passenger and truck tires were issued in 1968. A final revamping of auto tire testing came down from the agency in 2003, although it since has been revised.
NHTSA is looking at the results of its tests involving 180 new truck tires and 220 truck retreads to determine what the truck tire testing proposal should contain, Brewer said. He left little doubt that such a proposal will contain a high-speed test. "The current truck tire standard has no high-speed test at all," he said.
No time line
Truck retreads never had to meet any federal standards to date, and it still isn´t certain if they will be included in the proposed rule, according to Brewer. However, he said all retreads easily pass current truck tire performance standards, but their failure rate increases sharply under more stringent testing.
To conduct its survey on commercial truck tire performance, BFS asked tire dealers and truck fleets to collect unserviceable truck tires for the company´s inspection, said Guy J. Walenga, BFS engineering manager for North American commercial products.
A total of 10,291 tires were gathered between 2000 and 2005, of which more than 75 percent were size LP22.5, Wa-lenga said. Some 19 manufacturers were represented in the survey; six had at least 250 tires in the sample. All the tires were made between 1990 and 2005, the vast majority between 1995 and 2000.
A significant number of the tires had been involved in line or regional hauling, according to Walenga.
"These tires spent a lot of time in service, and that´s the key," he said. Most of the tires had been retreaded at least once, and a minority three, four or even five times.
Ozone cracking in the sidewall-a natural part of aging for any tire-is a factor BFS paid close attention to in the survey, Walenga said. If a crack reached at least 2/32 of an inch in depth, cracking was considered a factor in the tire´s failure.
Safety, financial gains
Over the five years of the survey, the sample tires demonstrated that fleet owners have been paying increasingly greater attention to proper inflation, and this has had both safety and financial benefits, Walenga said. "Because you take care of safety issues, you have lower costs per tire."
Generally speaking, the surveyed tires had a useful life of 10 to 15 years and are durable enough to accept multiple retreads and repairs, Walenga said. "Commercial tires are designed properly for the purpose they´re made for," he said.
Commercial tires will last even longer when inflated by a nitrogen compressor, according to David J. Connaughton, strategic account manager for Parker Hannifin Corp.´s Filtration and Separation Division.
Unlike ambient air with its oxidizing effect, nitrogen is dry and inert, and will not react with rubber, Connaughton said. It permeates rubber three times more slowly than oxygen, allowing tires to hold their inflation pressures longer, and because of its dryness it also improves the accuracy of tire pressure monitoring systems.
"With nitrogen you have fewer road failures, better retreadability and longer tire life," he said. "One of our fleet customers went from about 30 blowouts every summer to three."
Connaughton estimated nitrogen-inflated tires enjoy about a 10-percent improvement in service life and safety over tires inflated with air.