NHTSA: Speed limits cited for truck tire failures

By Miles Moore, Senior Washington Reporter

Editor's note: A typo in an earlier version of this story has been corrected. The tire in question is a Michelin XZA, not XZR.

WASHINGTON (April 9, 2015) — Increased highway speed limits in several states are the likely cause of the failure of several Michelin XZA tires on the steer axles of auto hauler trucks, the National Highway Traffic Safety Administration (NHTSA) said in a recently completed investigation.

NHTSA's Office of Defect Investigation (ODI) began a probe Oct. 6, 2014, of Michelin XZA 295/60/R22.5 tires manufactured in 2014.

Michelin manufactured 32,240 XZA tires of that size in 2014, the ODI said in the report it issued Feb. 27, 2015 — the day it closed the investigation.

Between them, the ODI and Michelin North America Inc. received 16 complaints about the tires, with three reported crashes.

The ODI opened its investigation based on the complaints and a police accident report about the failure of an XZA tire on the steer axle of an auto hauler, the report said. The auto hauler veered off the road and rolled over, losing some of its load. The driver was unhurt, and no other vehicles were involved, the ODI said.

Michelin XZA tires in the 295/60 size are specified as original equipment on many auto hauler trucks, according to the report. The 295/60 size has a maximum load and speed rating of 7,390 pounds and 65 mph when maintained at 130 psi cold inflation pressure and mounted on a 9-inch rim, it said.

The maximum speed can be adjusted to 75 mph when the load is limited to 7,150 pounds, according to the report. But Michelin approves only 9-inch rims, because rims of any other size compromise the integrity of the tire, the tire maker said.

Michelin had not changed the designs or material specifications for the tires, which eliminated those as possible causes for tire failure, the report said.

“The more likely explanation of failures is the increase in maximum speed limits in several states,” it said. “Currently, no truck tire is rated in excess of 81 mph (speed rating M), with the vast majority rated at 75 mph (speed rating L), yet 16 states have maximum truck speeds equal to or greater than 75 mph.

“Of those 16, four allow truck speeds of 80 mph or more,” it said.

With the help of the Pennsylvania State Police, the ODI conducted a survey of auto haulers, weighing individual steer axle tires and measuring inflation pressures, according to the report.

Fifty-five percent of the auto haulers had an overloaded tire, and 60 percent of the drivers did not know the tires' proper inflation pressures, it said.

Road hazards and misapplication of tires and rims were also factors in some of the tire failures, according to the report.

“Some fleets assumed there was a defect with the 295/60 tires and used the 275/70 instead,” it said. “Michelin does not approve mounting a 275/70 on a 9-inch rim. In the event that the rim was appropriately changed to a 7.5- or 8.25-inch, the load capacity would be reduced.”

During the Michelin investigation, Volvo Trucks in North America recalled some auto haulers originally equipped with tires speed-rated at 65 mph, according to the report.

“As originally built, the recalled vehicles were capable of exceeding the tire speed rating,” the report said. “Volvo's recall sets the speed limiters on the vehicles to prevent exceeding the tire speed rating.”

To reach this reporter: [email protected]