GREENVILLE, S.C. (April 11, 2008) — Michelin North America Inc. has weighed in on the debate over what constitutes a safe minimum tread depth standard, taking a stance that may surprise its competitors.
Michelin claims increasing the minimum legal tread depth to 4/32-inch from 2/32-inch “is not a good idea” because of the negative environmental impact.
The proposed change—supported by Continental A.G. and a number of others in the tire industry—“has very high costs but no measurable benefits,” said David Stafford, chief operating officer of the tire maker's Michelin Americas Research Co. subsidiary.
Stafford cited data to back up Michelin's support of the current standard:
* Increasing the minimum tread depth will raise societal costs, including manufacturing, purchasing and recycling of an estimated 65 million additional tires; increase scrap tire disposal; cause higher fuel consumption by as much as 770 million gallons per year; and increase carbon dioxide emissions on the scale of an additional 7.5 million tons per year;
* Real-world stopping distances vary widely because of types of vehicles and tires, road surfaces, driver behavior and speed. Braking distance alone is not a good indicator of accident frequency;
* Data show no difference between wet and dry road accidents because of lower tread depth tires; and
* Changing minimum standards doesn't address the enforcement issue. Rather, emphasis should be on removing tires below 2/32-inch tread depth that are in use. According to the National Highway Traffic Safety Administration, an estimated 9 percent of cars in the U.S. in 2001 had at least one tire below the legal tread depth.
Michelin acknowledged studies that show wet braking distance lengthens as tread depth decreases but said advocates of a change wrongly assume increasing stopping distance equates to more accidents and changing tires sooner will positively impact road safety.
“Changing the tread depth will not make an impact on road safety,” Staf-ford said. He referred to research showing that there was no difference between wet and dry road accident involvement for lower tread depth tires. He also claimed “accident databases indicate a small involvement of tires,” pointing to an NHTSA analysis that indicated 0.5 percent of all crashes is caused by tire blow-outs or flats.
On the other hand, lower tread depths help save fuel. Stafford said as tread wears, rolling resistance improves.
Removing tires at 4/32-inch increases the overall rolling resistance of tires on the road and would equate to the use of an additional 770 million gallons of fuel per year in the U.S., Michelin said.
The District of Columbia and 37 states have minimum tread depth of 2/32-inch.