Michelin North America Inc. is the first tire manufacturer to publicly address the 2/32-inch vs. 4/32-inch issue. And its position is quite clear.
With the National Highway Traffic Safety Administration (NHTSA) looking into whether or not to create a federal standard setting the minimum legal tread depth at 4/32-inch, Michelin has come out against it.
The federal government only requires that tire manufacturers build "wear bars" in their tires at the 2/32-inch mark. Minimum tread depth standards are regulated at the state level; 37 states plus the District of Columbia have regulated minimum tread depths at 2/32-inch.
Proponents of a 4/32-inch regulation claim the following:
* that wet braking distance gets longer as tread depth goes down.
* that taking tires out of circulation at 4/32-inch rather than 2/32-inch will lead to fewer accidents and fatalities.
At a recent press briefing, Dave Stafford, COO of Michelin Americas Research Co., agreed with the former but disputed the latter.
He claimed that there is no statistically valid data supporting a comparative increase in injuries and fatalities. In addition, "accident databases indicate a small involvement of tires."
(According to NHTSA's National Automotive Sampling System/Crashworthiness Data System, tire blowouts or flats cause 0.5% of fatal and non-fatal crashes. According to the NHTSA Fatal Accident Reporting System, tires are a factor in 1.1% of all light vehicle fatal crashes.)
Conversely, the 2004 German In-Depth Accident Study indicates road safety is not compromised. (Europe follows a 2/32-inch standard.)
Stafford said differing road surfaces, vehicles and tire brands also affect stopping distance. So does usage. That's why braking distance alone is not a good indicator of accident frequency.
Michelin is always concerned with safety, he continued. But with safety not a factor in this debate, other issues must be taken into consideration. For example, the United States alone would require approximately 65 million more tires annually if the minimum standard was set at 4/32-inch. That capacity is not available, said Stafford.
The environmental impact also would be negative. Tires with 2/32-inch tread depths have lower rolling resistance than tires with 4/32-inch tread depths. Removing tires too soon would cost the U.S. hundreds of millions of gallons and billions of dollars in fuel. Scrap tire disposal also would increase.
In 2001, NHTSA reported that 9% of cars have at least one tire below 2/32-inch, according to Stafford. The emphasis, rather than on setting a minimum 4/32-inch standard, should be on enforcement to remove tires below 2/32-inch on the road today, he added.
