Low Heat Rating Found in Tires on Ford SUVs
Although the Ford Motor Co. blames Firestone tires for hundreds of fatal and crippling accidents involving its sport utility vehicles, the tires that Ford selected for its Explorer and Mercury Mountaineer have a lower rating for heat resistance--a possible factor in the accidents--than the tires on virtually all similar SUVs made by rival auto makers.
A Times survey of mid-size SUVs sold in the U.S. shows that only the Ford vehicles--and one optional tire on the Toyota 4Runner--use tires with a “C” temperature resistance rating, or the minimum acceptable under federal regulations, while Ford’s competitors use tires that have “B” temperature ratings.
The temperature ratings, which must be molded onto the sidewalls of all passenger vehicle tires sold in the U.S., are important because heat buildup has been cited as possibly weakening the Firestone tires whose treads have peeled off at high speed, often causing drivers to lose control. All of the tires recalled by Firestone--the ATX, ATX II and Wilderness AT models--which were sold primarily on Explorers but also on Mountaineers and some Ford Ranger pickups, had the C rating.
An official with the National Highway Traffic Safety Administration said the temperature rating is one of the factors being looked at as part of the government’s investigation of the 101 deaths linked to the recalled tires, hundreds of which have lost their treads at high speeds. NHTSA has opened a preliminary evaluation, a step toward a full investigation, of the tires’ temperature ratings, said the official, who spoke on condition of anonymity.
A rating of C means a normally inflated tire that is not overloaded can be run in a laboratory at 50 mph for two hours, then half an hour each at 75, 80 and 85 mph without falling apart. Tires rated B and A can withstand higher speeds for longer periods of time, meaning they resist heat buildup better.
Explorer competitors from the Chevrolet Blazer and Jeep Grand Cherokee to the Nissan Pathfinder, Isuzu Rodeo and Mitsubishi Montero Sport all use tires rated B for temperature. Toyota’s 4Runner offers Firestone Wilderness AT II tires, which is not part of the recall, as the base tire among four tire possibilities. The 4Runner’s other tires are not Firestone brands and are rated B for temperature.
Ford’s decision to outfit Explorers with tires with the lowest temperature threshold baffles tire and safety experts.
“I can’t believe they put a temperature-rated C on the Ford Explorer,” said Keith Baumgardner, general manager of Tire Consultants in Alpharetta, Ga.
“If they pass the C, they’ve just passed the bare minimum government standards,” Baumgardner said. “B’s OK, but even on my car, the first thing I look for is an A rating before I buy a tire. I wouldn’t put any of that cheap stuff on mine.”
Bridgestone/Firestone officials did not respond to repeated requests this week for comment on the tires’ temperature rating. But Ford said in a brief written statement to The Times that it does not specify temperature ratings for tires for its vehicles.
“It is the tire maker’s responsibility to design, develop and produce tires to meet the auto maker’s performance criteria,” Ford’s statement said. “Likewise it is the tire maker’s responsibility to evaluate and rate a tire’s temperature grades.”
Clarence Ditlow, head of the National Center for Auto Safety in Washington, said he does not buy that explanation. “When [Firestone] said, ‘Here’s what the grades are going to be,’ Ford could have said, ‘We’re not taking those because they only have a C rating; go back and redo it,’ ” Ditlow said.
Why would Ford accept tires with low temperature tolerance for the Explorer? Some analysts suggest that the vehicle’s sheer profitability is a factor. The Explorer is the country’s best-selling SUV and a huge profit center for Ford, generating profits of $5,000 and more per vehicle. The nearly 429,000 Explorers sold last year cleared at least $2.1 billion in profit for the world’s No. 2 auto maker.
“The presumption is they’re getting it at a lower price, and they’re doing that to keep their profit up per vehicle,” Ditlow said.
The selection of C-rated tires may have been exacerbated by Ford’s recommendation that owners inflate the tires to 26 pounds per square inch, lower than Firestone’s recommendation of 30 psi. Ford’s promoting of a lower tire pressure than recommended by the tire maker has become a central issue in the failures, as lower inflation causes greater friction and thus heat buildup.
“With this type of vehicle, particularly recommending a 26-pound pressure, Ford could and should have specified an A [tire],” said Ditlow. “I was surprised to find that Ford itself was willing to buy a tire with a C rating. It’s going to increase the percentage of failures of that tire over time.”
Since the recall of the 6.5 million Firestone tires on Aug. 9, Ford had maintained that a range of 26 to 30 psi is acceptable. In a letter sent Wednesday to Ford, Bridgestone/Firestone Chief Executive Masatoshi Ono requested for the first time that Ford “inform all Explorer owners that the proper inflation pressure is 30 psi.”
On Friday, Ford said it would agree to raise its recommended inflation of Explorer tires to 30 psi, but only because Bridgestone/Firestone’s congressional testimony “has caused confusion among our customers.”
The tire maker actually dropped the C rating from the sidewalls of Wilderness AT tires for a number of years, said the NHTSA official. Asked by the agency to restore it, Bridgestone/Firestone told the agency it didn’t think the regulation applied to SUV tires.
“We pointed out that was not a correct interpretation of the law,” the NHTSA official said, and Bridgestone/Firestone restored the designation in late January.
The temperature ratings come under NHTSA’s Uniform Tire Quality Grading System, which assigns tire ratings for temperature, traction and tread wear. “Sustained high temperature can cause the material of the tire to degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure,” says a NHTSA regulation known as Federal Motor Vehicle Safety Standard 575.109.
Temperature ratings, however, “are done in controlled labs--on tires that have not undergone misuse,” says Harold Herzlich, an independent tire consultant in Las Vegas. “If a driver chooses to run at low inflation, all bets are off.”
Tires’ resistance to heat can be controlled by altering the compounds used in manufacturing them, changing their design or varying their tread thickness--a thinner tread can dissipate heat better, the reason that racing tires have little or no tread.
“So, in the Southwest, you may be more interested in an A temperature rating, but less interested in an A traction rating. It allows the consumer to make an informed choice,” Herzlich says.
David Champion, director of auto testing for Consumers Union, publishers of Consumer Reports, says a C-rated tire “should be perfectly satisfactory” for the Ford Explorer, provided it is properly maintained and not overloaded. But he said Consumers Union recommends a B-rated tire for passenger vehicles.
He also noted that the large interior of the Explorer raises concerns about overloading. “It’s very commodious--it begs to be overloaded,” Champion said. “And if you set the pressure to 26 psi . . . the safety margin is slightly reduced.”
General Motors Corp. says it also doesn’t specify temperature requirements for its vehicles’ tires, but it uses speed criteria developed by the Society of Automotive Engineers. “What we’ve specified is that tires have a specific speed rating,” says David Wood, engineering group manager at GM’s tire engineering. GM’s mid-size SUV tires “ended up qualifying as a B, and that system has worked very well for us.”
GM’s Chevrolet Blazer and GMC Jimmy use Uniroyal Laredo, Goodyear Wrangler and Goodrich Longtrail tires, all of which have a B temperature rating. The Jeep Cherokee, Grand Cherokee and Dodge Durango, made by DaimlerChrysler AG, all use various Goodyear Wrangler and Eagle tires and Michelin LTXs that are also rated B.
Cliff Stearns, a Florida Republican on the House Commerce Committee that questioned Ford and Firestone officials Thursday, assailed Ford.
“So, you have a typical family packed up for vacation riding in a vehicle with minimum heat resistance tires, which are underinflated, carrying extra weight and speeding down a highway that is being baked by the sun,” Stearns said. “That to me is a recipe for disaster.”
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Jones reported from Detroit and Alonso-Zaldivar from Washington.
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Rating SUV Tires
Top 10 mid-size SUVs sold in the U.S., and the ratings for the original equipment tires sold with them.
