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|11-12-2000, 12:39 AM||#1|
Moderator In Memoriam
Join Date: Jul 1999
THE STEERING COLUMN
Why are Ford Explorers crashing?
BY CSABA CSERE
We know that certain Firestone Wilderness tires, which were fitted primarily to Ford Explorers over the past 10 years, have been experiencing tread separations at a higher than normal rate. As this is written in late October, no one yet knows why these Firestones have been failing.
For those of us who have experienced tire failures, however, there is an even more interesting question. Why are so many of these Explorers crashing after they sustain one of these tread separations?
It's interesting because during our countless miles on public roads, test tracks, and racetracks, many of us on the staff have also experienced tire failures. We've also suffered broken wheels and had complete tire-and-wheel assemblies fall off. These incidents have occurred in a wide variety of vehicles, and occasionally at very high speeds, but we've never had any trouble maintaining control.
Control is the key here because the fatal accidents related to Firestone tires mounted on Explores have, in the vast majority, involved rollovers. And the overwhelming majority of these rollovers occurred after the vehicle left the pavement. If you maintain control of your vehicle, however, why would you leave the pavement? In our numerous tire and wheel failures, our vehicles have never left the pavement.
Is there something about a Ford Explorer that somehow renders it unstable during a tread separation? We resolved to conduct a test to find out.
Our first step was to procure a suitable test mule. We found a '94 five-door, four-wheel-drive Explorer XLT at C&S Auto Sales, a tiny used-car lot in Redford, Michigan, about 30 miles from our office. The ad said the XLT had 125,000 miles on it. The odometer read 37,273. Whatever the true mileage, it was clearly a well-used Explorer. But it had shiny blue paint, drove down the road reasonably well, had four brand-new Goodyear XL/T tires, and was listed for just $3800. We didn't even haggle.
We then had a roll cage and competition seatbelts installed at Big Sky Motorsports near Detroit Metro airport. Then we obtained a test rig that would allow us to dump, virtually instantaneously, the air from one of the Explorer's tires at our command.
Causing a tread separation would have been a more realistic simulation, but we couldn't figure out how to make the tread peel off a tire at the instant of our choosing. Besides, the accident reports have confirmed that in many of these tread-separation incidents, the tires have remained inflated even after the treads departed.
Clearly, the remaining rubber donut is less durable than an intact tire, but such an inflated carcass means that the vehicle remains almost perfectly balanced and level. We felt that by fully deflating a tire, which would allow the corner on which it was mounted to sag by about six inches, we would produce a condition that was far more destabilizing than just a tread separation.
So we fitted the rig to our test Explorer at the left-rear wheel position (statistically, the most likely position for the reported separations). It starts with a modified Explorer wheel with three one-inch holes in the middle of the rim leading to three short lengths of welded-on pipe. Using short lengths of rubber hose, we connected these pipes to a diaphragm valve that protruded from the wheel. On the outside of this valve was a swivel fitting that connected to an air hose from the Explorer's interior.
As long as we maintained air pressure (provided by a regulated air can in the Explorer's cargo area) to this hose, the diaphragm valve remained closed and the tire remained inflated to 26 psi (the manufacturer's recommended pressure for an Explorer). When we released the pressure in the hose to the valve, the diaphragm would open and release all the air from the modified wheel in a third of a second.
By coupling an industrial solenoid valve to a radio-controlled model-airplane servo, we could regulate this air pressure and control the dump valve at will. Furthermore, when we reapplied the air to the control valve, the dump vents would seal and the tire would reinflate, only slightly the worse for wear -- or so we hoped.
With our equipment set up, we took our rig to Milan International Dragway south of our offices in Ann Arbor. We expected that the strip, at five-eighths of a mile, would be long enough for even our tired Explorer to accelerate to 70 mph, leaving plenty of track for slowing down after we performed our blowout test.
Since we had the means to deflate the tire repeatedly, we decided there was no reason to jump into the deep end of the pool and start with a 70-mph blowout. Therefore, our first run was at 30 mph.
With technical editor Larry Webster at the wheel, and an ambulance and fire crew on hand, the Explorer left our impromptu air-compressor service station at the start of the drag strip and proceeded toward us. As Webster passed the timing lights at the end of the quarter-mile, he moved over to the center of the 60-foot-wide pavement and approached our position behind the guardrail and a few hundred yards beyond the lights.
Just before he reached us, I pushed the toggle on my model-airplane controller to the right. With a loud whoosh that could be heard back at the start of the track, the air exploded from the left-rear tire, and that corner of the Explorer immediately sagged about six inches. But the old Ford continued straight ahead and came to a stop in a few hundred feet.
We rushed over to hear Webster's impressions of what had happened. "No big deal. It didn't really pull much at all. I just kept it going straight, eased my foot off the gas and onto the brake. A piece of cake."
For the next run, we upped the speed to 40 mph. Again the big whoosh, followed by the tire's going instantly flat as a pancake. With a bit more speed, Webster ended up farther down the track, but from a control standpoint, the 40-mph run was another nonevent.
The 50-mph and 60-mph runs were similarly uneventful. Finally, we were ready to step up to our maximum speed of 70 mph. We could hear the old V-6 engine laboring as Webster flogged it during his run up to speed. From our vantage point behind the guardrail about 30 feet removed from the centerline of the track, the Explorer's approach seemed impressively rapid.
Yet when I toggled the switch and the rear tire dropped, the Explorer plowed on straight ahead. In fact, we saw barely any deviation from a straight path.
Webster's report was much the same as it had been on the 30-mph run. "I had a little trouble getting up to 70 mph in the quarter-mile, but once I was there and the tire blew, the Explorer didn't do anything tricky or unstable. It just went straight ahead. I didn't even have to brake much because the deflated tire produces a lot of drag and slows the car quite a bit."
So far, Webster had not applied the brakes very hard during any of the runs. That's because we believe that in the case of a blowout, the first priority is to maintain stability, and one of the ways to do that is to avoid any sudden control inputs, such as hard braking. Since the Explorer was so stable, however, Webster and I decided to see what would happen if we applied the brakes progressively harder. The answer was essentially nothing. Other than applying a little steering correction to the right, because the old Explorer's brakes pulled to the left, Webster reported no control problems during moderate braking.
During the next run, Webster braked quite a bit harder. Same result. Finally, Webster applied the brakes as hard as he could -- hard enough to make the ABS pulse. Other than some minor wiggling, which would have been easily contained within an average highway lane, Webster reported no drama.
One might reasonably ask how much of the Explorer's stable performance could be attributed to Webster's driving skill and extensive racing and testing experience. It's a good question, and to address it, we mounted a video camera inside the Explorer to record Webster's control inputs. We could see that they were every bit as minimal as he reported to us.
But Webster was willing to demonstrate the Explorer's inherent stability even more conclusively. For our last 70-mph blowout run, Webster removed both his hands from the steering wheel and was holding them up with his palms clearly visible in the windshield when I triggered the toggle to blow the tire. Again, the Explorer continued straight ahead.
As Webster put it, "The Explorer didn't veer or pull. Only when I applied the brakes toward the end of the run did the Explorer pull enough to require me to put my hands back on the steering wheel."
After performing our initial round of tests, we mounted a fresh Goodyear on our modified wheel (even though the original, after six 70-mph blowouts and four lower-speed runs, looked perfectly intact) and invited journalists from NBC News, the Wall Street Journal, and the Detroit Free Press to witness an encore performance of these tests.
Our results were exactly the same. Based on our tests, the Explorer, like all modern vehicles in our experience, is stable and easy to control in the event of a tire failure.
So why have 119 persons perished in Explorer crashes linked to Firestone tire failures? We're baffled. We know that the Explorer doesn't veer off the road when one of its tires loses pressure. We know that even under heavy braking it doesn't do anything unstable or tricky. And we can't imagine why any driver, on hearing the racket caused by a separating tread beating against the bodywork, would react by jerking the steering wheel so violently that it would cause the Explorer to leave the pavement and possibly roll over.
But we're convinced that if you experience a tire failure -- on an Explorer or any other vehicle -- and concentrate on keeping the vehicle rolling straight and on the pavement, you have an excellent chance of bringing it to a safe halt and ensuring that your tire failure remains an inconvenience rather than turning into a tragedy.
Everyone make sure to watch Car and Driver TV on Nov. 25th to see this test in action. Looks like they agree with what I and others have said all along, the Explorer is a very stable truck.
|01-28-2001, 12:05 AM||#2|
Wannabe Elite Explorer
Bedford, NH AIM: Chief Miscreant
'01 Acura 3.2TL
Join Date: Jan 2001
I read it with great interest and detail, but never saw it on television. I must say I was very impressed by both the thorough reporting done by Car & Driver and the Explorer's stability.
<---doesn't own one
'01 Acura 3.2TL
'99 Honda Accord LX Sedan 5-Speed
"It's not what the car does for others, it's what the car does for me."
|04-11-2013, 01:36 AM||#3|
Wannabe Elite Explorer
97 explorer xlt
Join Date: Apr 2013
Yeah this is true. I had a big stud in my tire and forgot the key for removing the rim at my hone which was 100 miles. Half way home the stud came out and deflated the tire. If it wasn't for the rubber lines I saw through the rear view mirror and trouble to accelerate I wouldn't even notice I had a blow out.
Something that really called my attention is that the thread said that most problems with tires happened in the rear left tire......I just bought some pirelly snowsport tires.....balanced aligned ...everything in the right place.....but I still got an unusual thread wear in that left rear tire.....hmmm interesting
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