zt奇門遁甲：Ford has different idea of tire inflation

煙酒輪胎充氣壓力的時候，檢查自己的老福特，門框上居然清清楚楚寫著胎壓26psi!!!

驚詫之餘，再去廣泛搜索煙酒，發現了一篇老文章，專門介紹Firestone與福特的特殊胎壓理念矛盾，以及與其他品牌車和輪胎公司格格不入。哈，見鬼了，反正我不管那套，我自己的福特胎壓，前35psi/後36psi。如果你喜歡開快車，那30-32應該也絕對沒問題。

以下抄來人家的文章，與各位分享。歡迎各位廣泛發表見解。

原文鏈接 http://www.usatoday.com/money/consumer/autos/mauto771.htm

Ford has different idea of tire inflation

Explorer can tend to tip, so automaker calls for lower pressure

By James R. Healey, USA TODAY

Ford Motor disagrees with other manufacturers on the correct pressure for tires like those being recalled by Firestone, and it says its Explorer sport-utility vehicle could become unstable in emergencies if its tires have too much air pressure.

Most of the estimated 6.5 million P235/75R-15 tires that Firestone recalled Aug. 9 are on Ford Explorer sport-utility vehicles. Ford specifies 26 pounds per square inch (psi) of air pressure for those tires on Explorer. The SUVs most similar to Explorer's size, construction and weight use much higher pressures.

General Motors recommends 32 or 35 psi when the same size tire is installed on Chevrolet Blazer or GMC Jimmy SUVs. Amounts vary by specific model.

Chrysler recommends 35 psi in the front tires, 41 psi in the rear, when P235/75R-15 tires are used on its Dodge Durango SUV.

Explorer, Blazer, Jimmy and Durango all are midsize SUVs that use leaf springs and solid axles in the rear, where most of the Explorer-mounted Firestones have failed. All those SUVs are derived from compact pickup trucks, and all use pickup-style frames. Durango's a bit bigger and heavier than Explorer; Blazer and Jimmy are a bit smaller.

Effects of lower air pressure

Watchdog groups and lawsuit-minded lawyers argue that Ford's lower air pressure contributes to the tread-separation problems that forced the Firestone recall. Lower pressure allows the sidewalls to flex more, which softens the ride. Critics say unusual wear also could contribute to the tread separation.

Even Firestone is suspicious of Ford's recommendation. During its recall announcement, the tiremaker recommended 30 psi. It prefers 35, but hasn't said so publicly because of pressure from Ford.

"We ran the tests, and in really severe maneuvers, emergency lane-change maneuvers, 35 is not where you want to go," says Ford's chief truck engineer, Tom Baughman.

Attorneys suing Ford and Firestone say internal Ford documents show that at 35 psi the Explorer is more likely to roll over. "At 35 pounds of pressure, the vehicle is rolling, but at 26 it doesn't," says Little Rock lawyer Tab Turner.

He says the documents show that Ford wanted to use the larger tires to fill up the wheel well but then had to recommend the lower pressure to prevent the SUV from rolling over.

Generally, lower air pressure makes a tire ride softer and steer sloppier. Higher pressure makes the ride firmer and the steering more responsive. Baughman notes: "You may not want crisp steering in a vehicle with a relatively high center of gravity and relatively short wheelbase. Putting more air pressure in your vehicle is not in the direction of goodness in a vehicle with a relatively high center of gravity."

Ford's lower pressure recommendation makes the truck more stable and "absolutely is not the problem," says Baughman, who oversaw a Ford data team that used Firestone information to pinpoint the P235/75R-15 tires as the problem. He notes that Explorers are involved in fewer fatal rollovers than other SUVs.

GM and Chrysler say they are comfortable recommending the higher pressures for P235/75R-15 tires, and that their tests show no stability problems.

Baughman says Mitsubishi Montero and Nissan Pathfinder, both roughly Explorer size, use 26 psi. Those have different types of underbodies, or platforms, however. He says that could make a difference in handling but wouldn't affect what tire pressure an automaker recommends.

Ford picks a range

At Firestone's request, Ford recently changed its recommendation from a strict 26 to a range: 26 to 30 psi. Baughman says the truck handles the same within that range. Above 30 psi, Explorers can go out of control easier during extreme maneuvers, he says.

That's because the more-responsive steering that generally comes with higher pressures can cause the vehicle to swerve wildly when a panicked driver yanks on the steering wheel during an emergency. He says Ford's policy, therefore, is to specify tire pressures as low as possible that don't compromise hauling ability. "Sometimes you want the steering to be a little bit on the lazy side, for safety," Baughman says.

He notes that 500,000 1995-97 Explorers had P235/75R-15 Goodyear tires standard, instead of Firestones, and those have run 26 psi without any tread-separation complaints. In Ford's view, that shows the problem is the Firestone tires, not the Ford truck. Firestone's recall includes all ATX and ATX II tires in size P235/75R-15, and Wilderness tires that size if they carry the code VDHL on the sidewalls, meaning they were made in the company's Decatur, Ill., factory. Those three types of Firestone tires have been standard on most Explorers since its introduction in 1991.

The National Highway Traffic Safety Administration has reports of 62 deaths linked to Firestone tread separation. It opened an investigation May 2.

Contributing: Sara Nathan