(From the May 14, 2012, issue of Rubber & Plastics News)
HILTON HEAD, S.C.—“New-tires-on-rear” is a universal axiom propagated by tire manufacturers, according to John M. Baldwin, principal scientist at Exponent Engineering.
But extensive testing, plus a thorough review of accident and fatality statistics, doesn't necessarily demonstrate that placing new tires on the front of a vehicle is always dangerous, Baldwin said in a speech at the 28th annual Clemson University Tire Industry Conference in Hilton Head April 18-20.
Baldwin, who at the time of the speech was moving to a new position at Discount Tire Co. Inc., also called out the Rubber Manufacturers Association for what he said was a mischaracterization of the tire aging research he performed while working as a tire research specialist at Ford Motor Co.
In his speech, Baldwin evaluated common tire industry policies from the perspective of tire retailers.
“In the tire industry, a lot of decisions are based on tread depth,” he said. “But what is the significance of tread depth? There is uneven wear on damn near every tire.”
The general rule of thumb, Baldwin said, is to replace a tire when it reaches 2/32 inch of tread depth. “But you don't know what part of the tire you're at,” he said. “It could be the best or the worst part of the tire.”
Tire age also can't be left out of the equation, according to Baldwin. Based largely on the results of Baldwin's testing, Ford recommends that vehicle owners replace their tires after six years regardless of the tires' remaining treadwear.
“The average full-sized spare tire is nine years old,” he said. “You can tell your tire store to take that perfectly good spare tire and put it on your car. But if you're in Yuma or Miami, do you really want that nine-year-old spare going on?
“Meanwhile, the average mini-spare is 12 years old. That means you're screwed.”
As for new tires, the RMA position is that they go on the rear of a vehicle unless the tires have a low speed rating, Baldwin said. This common wisdom is backed by videos by Tire Rack, Michelin North America Inc., Continental Tire the Americas L.L.C. and others depicting the dangers of fitting two new tires on the front of a vehicle.
“The industry's position is that if you put two new tires on the front, you are going to die,” he said. “The absolutism of this is astounding to me.”
Old axioms need testing
Along with the inflexible “new-tires-on-rear” policy is a “no-rotation” policy if newer tires are on the rear, according to Baldwin.
“One company put out a memo last month stating that you can't rotate your tires if there is more than 4/32-inch difference in tread depth between the axles,” he said.
No one has taken a hard look at the “new-tires-in-rear” policy since the 1970s, according to Baldwin. “These things get into an emotional debate,” he said. “We ought to back them up with cold, hard facts.”
Currently there are about 240 million vehicles on U.S. roads, according to Baldwin. “The average age of those vehicles is 10.8 years, which means half of them are older than 10.8 years,” he said.
The average age of a tire at replacement is 3.7 years, and about 40 percent of the time a motorist buys either one or two tires, Baldwin said.
“Millions and millions of vehicles carry more tread in front than in back,” he said. “If you look at a parking lot, you will not find a single vehicle with four of the same tires.”
Using figures from the National Highway Traffic Safety Administration and interpolating from the rules of straight probability, the minimum number of vehicles in the U.S. with at least 9/32 inch of tread on the front and 4/32 or less in back is 8.8 million, he said.
“You'd think there would be a heck of a lot of accidents because of this, based on the videos,” Baldwin said. “From NHTSA accident statistics, we should be able to pick out what's going on with new-on-rear vs. new-on-front.”
Yet a statistical analysis of NHTSA data did not indicate an increase in accidents when new tires were on the front of vehicles, Baldwin said. Baldwin also showed videos of his own vehicle testing, using tires of different makes, models and tread depths.
“The results showed that the lowest tread depth, regardless of position, dictated where vehicle control was lost—except for shaved tires,” he said. “In videos, that fact is generally left out. Shaved tires with 5/32 inch tread depth behave like a 2/32-inch worn tire.”
Dispute with RMA
At the end of his speech, Baldwin discussed a tire aging bill before the Maryland House of Delegates and a Feb. 21 hearing on the legislation.
At that hearing, the bill's sponsor cited the recommendations of Ford and other auto makers that tires be removed after six years.
The RMA testified that Ford's testing covered only tires it retrieved in the catastrophic Ford Explorer-Firestone recall of 2000.
“The problem is, that isn't true,” Baldwin said of the RMA's testimony. “You hurt the credibility of your organization when you lie about the research of others.”
After his speech, Baldwin said Ford did test Firestone tires collected from the recall for the effects of aging.
But to ensure the validity of the testing, it also performed the same tests on tires made by other manufacturers that were specified as original equipment on the Explorer.
“The results of the tests were consistent,” he said. “Tires deteriorate as they age.”
An RMA spokesman said the association stands by its testimony at the hearing in Maryland.