The National Highway Traffic Safety Administration (NHTSA) is pushing for new regulations requiring tractor-trailer trucks to be equipped with speed-limiting devices. This regulation, if passed, will impact not only the trucking industry but also the manufacturers of tractor-trailer trucks and tires. The intended purpose of this new regulation is to reduce the risk of tire disablement. NHTSA is reacting to recent Associated Press reports that many states have speed limits that are higher than truck tires’ speed ratings. Some states have speed limits of 75, 80 or 85 mph. Most truck tires are speed rated for 75 mph. There are, however, truck tires available with speed ratings in the low 80s.
What are “speed ratings”?
A speed rating indicates that a tire is capable of operating at a certain speed for a specific duration under normal inflation and load conditions. The speed rating is determined by operating a tire under a specific load and inflation pressure for specified durations that are set forth in federal regulations.
Not all tires have sidewall labels indicating the tire’s speed rating because they are not required by law. However, the federal government requires that all tires comply with high-speed test requirements. In contrast to truck tires, passenger car tires must comply with high-speed test requirements above 85 mph. Accordingly, NHTSA’s concern is limited to truck tires.
States with speeds limits of 75 mph or higher were not aware of truck tire speed ratings and did not consult the tire industry before setting their speed limits. While operating a truck tire at speeds above the tire’s speed rating can cause or contribute to tire disablement, such operation is certainly not the only cause of disablement. There are other factors that could contribute or be wholly responsible for the disablement. Those other factors include overloading the truck tire, operating the tire over- or underinflated, and road hazard impacts. So, while a regulation requiring speed-limiting devices might reduce the number of truck tire disablements due to operation above the speed rating, it will not eliminate these other potential sources.
It is important to note that tire manufactures are not to blame for speed limits in excess of a tire’s high-speed tire requirements. Moreover, the initial reaction to this truck tire speed rating/speed limit inconsistency could be overblown. According to the Rubber Manufacturers Association, 70 percent of tractor-trailer trucks currently operate with speed-limiting devices. The American Trucking Association reports that speed-limiting devices in use limit the speed to 69 mph on average.
We will continue to track NHTSA’s interest in regulating speed-limiting devices on tractor-trailer trucks. Be sure to check this blog for updates. We also invite our readers to post their thoughts and comments on this issue.