NASHVILLE, Tenn.—Truck tires are failing at a faster rate than four years ago, according to an analysis of roadside tire debris conducted last summer by a trucking and tire industry task force. The study results appear to bear out concerns expressed in 1995 that allowing trucks to operate at higher speeds would lead to an increased rate of failure of both new and retreaded truck tires. Twenty-two states now permit trucks to operate at 70 mph or more, and 17 others post 65 mph speed limits.
The overwhelming reason for truck tire failures, however—low tire pressures resulting from inadequate maintenance—did not change, said Dave Laubie, director of engineering for Bridgestone/Firestone Inc.
However, higher speeds do accelerate tire wear and casing fatigue, said Mr. Laubie, who presented the task force's findings at the annual meeting of The Maintenance Council of the American Trucking Associations, March 15-19 in Nashville.
Unusual circumstances—such as the searing heat wave that blanketed most of the U.S. last summer—cloud the impact of the study's results, and influenced the task force principals to go ahead with a study of the problem in a series of controlled tests this summer. (See story below.)
The adverse effects of running tires underinflated was listed by the task force as the cause for 86 percent of the 1,407 failed truck-tire remnants it analyzed.
Nonetheless, manufacturing-related problems were identified as the probable cause of 8 percent of the failures analyzed—up from about 5 percent in 1995—with repair-related causes being cited for another 6 percent—down from roughly 9 percent in 1995.
The amount of failed truck tire debris collected along 13 stretches of interstate highway in July and August 1998 was 28 percent greater than that collected from along the same highway segments in July 1995, according to the report.
The percentage increase in the amount of debris collected was more than twice that of the comparable gains in the number of trucks and trailers registered and trucking mileage driven over the same time period, task force data show.
The task force examined only tread segments of at least 3 feet in length in order to be able to analyze them accurately for the cause of failure, Mr. Laubie said.
Retreaded tires accounted for nearly 85 percent of the tire debris collected, both in 1995 and in 1998, the task force data show. At the same time, the number of remnants from new tires was up 59 percent over 1995, while debris from retreads was up 23 percent.
While the ratio of retreads monitored is measurably higher than their estimated 50- to 60-percent share of tires in operation, the discrepancy can be explained in part because the retread/new-tire ratio on trailers—where tire maintenance is the poorest—is acknowledged to be considerably higher, perhaps as high as three out of every four tires.
Reinforcing this conclusion is the fact that 70 percent of the tire treads analyzed were rib patterns, used overwhelmingly on trailers.
Among its conclusions, the task force determined 21 percent of the tire pieces they examined came from tires worn down to a point where they should already have been removed for retread evaluation (less than 7/32nds-inch tread depth).
Tire industry representatives say about 75 to 85 percent of fleets use retreads, which account for about 60 percent of the truck tire replacement market annually. Factoring in new truck and trailer sales, though, brings the share down closer to 50-50.
The task force also examined 242 remnants of light truck tires (up 28 percent) and 551 pieces of passenger car tires (up 17 percent).
The 13 stretches of highway monitored were in nine states—Alabama, Arizona, Nevada, New Jersey, North Carolina, Ohio, Oregon, South Carolina and Texas—and were approximately 100 miles in length each.
Highlighting the effects of the record-setting heat last summer were the results from Texas and Nevada, where the amount of debris collected was up 466 and 283 percent, respectively.
Task force participants included Bandag Inc., Bridgestone/Firestone Inc., Continental General Tire, Goodyear, Hawkinson Cos., Hercules Tire & Rubber Co., Michelin North America, Oliver Rubber Co., Teknor Apex Co., the Tire Retread Information Bureau and Yokohama Tire Corp.