Explorer tire test

Last week, Car and Driver magazine added more data to the mountain that has been accumulating about the Firestone tire flap. For those who don't already know, at least 119 people have been killed in accidents that have been linked to tread peeling off Firestone tires. Most of those who died were driving or riding in Ford Explorer SUV's that rolled over after one of their tires blew.

Car and Driver wanted to know what was behind the biggest uproar in auto safety in years. They wanted to know if there's something peculiar to the Explorer that caused these rollovers. So about a month ago, when the Firestone outcry was at its peak, the magazine conducted its own series of tests to see what would happen to an Explorer, when one of its tires suddenly looses air pressure. Would that make the Explorer flip over?

A high-mileage Explorer was purchased for $3,800 specifically for this purpose and in case of a serious accident, was fitted with a roll-cage. Csaba Csere, editor of the magazine who's also a mechanical engineer, designed a system that simulates a blowout by releasing all the air in the tire in one third of a second. Police agencies use a similar system to train their drivers how to handle emergency situations.

The left-rear tire was chosen for these tests as most of these accidents have involved the left rear-and losing air in the back is more likely to make the Explorer (and any vehicle) more unstable. According to the magazine, in their experience, vehicles handle pretty well during a blowout unless a wheel literally falls off during a hard corner.

The tests were performed at a dragstrip in Milan, MI. Another Car and Driver editor drove the Explorer at speeds ranging from 30 to 70 mph-and by using a remote control device, the tire simulated a blowout without any warning to the driver.

Each time the tire blew, the driver reacted by letting off of the gas and letting the Explorer slow down by itself. On some of the higher speed tests, the driver also applied the brakes but he never turned the steering wheel hard to the left or right.

The Explorer never shimmied, wobbled, wavered, swerved and had no propensity to flip over. It just stopped.

How does one explain all the accidents? According to Csaba Csere, the tread separating from the tire is usually a noisy event-and because the drivers may be disoriented, confused or scared, they may hit the brakes hard or jerk on the steering wheel, perhaps causing the vehicle to leave the pavement.

Once the vehicle leaves the pavement, a lot of traction is lost. Dips, ruts, holes and other obstructions, and a blown tire coupled with the Explorer's high center of gravity, can cause the vehicle to roll over.

I've had my share of blowouts-all I've ever done is slow down and pull over to the shoulder. However, with all of the blowouts I've had, I've been going straight. I've never had one cornering but I can surmise that in such a situation, it might be a bit more dangerous.

The magazine's tests show that a blowout by itself is not the reason for Explorers to flip over-still leaving rollovers and peeling Firestone tires a mystery.

[Peter C. Sessler has written over 30 automotive books. Besides books, he also writes for several Internet web sites and car magazines. He has also written (with his wife) a children's six-book series on auto racing. His latest books include "Camaro Photo Archive," "Jeep Prototypes and Concept Cars," "The Ultimate American V-8 Engine Data Guide" and "SVT Mustang Cobra Recognition Guide, 1993-2000."]