Mitsubishi strongly disputed the magazine's conclusion.
The vehicle "would likely have rolled over if not for the safety outriggers," side struts installed for the tests that prevented the vehicle from toppling completely over, Consumer Reports said.
The influential magazine's "not acceptable" rating is the first for any vehicle since 1996, when it was applied to the 1995-96 Isuzu Trooper SUV. Isuzu Motors Ltd. said the rating cost it $242 million in lost sales and damaged its reputation.
"If you're shopping for an SUV, we advise you not to buy the 2001 Montero Limited until the safety problem has been corrected," the magazine said.
Montero's slice of the SUV market is small: 21,000 sold a year compared to 445,000 Ford Explorers. But in the end, reports CBS News Correspondent Jim Axelrod, it may be another hit for an entire class of vehicles already under the gun for rollover risk.
"The Ford-Firestone case has really highlighted that in a very, very direct way and now this is one more thing on top of that," said Peter Brown of Automotive News.
The "not acceptable" rating applies only to the 2001 Montero Limited, not to previous Monteros or to the Montero Sport or Montero XLS.
Consumer Reports and Mitsubishi both said they found no reports of rollover crashes involving the 2001 Montero, but the magazine believes its test results point to an unnecessary risk.
Of 118 models Consumer Reports has tested during the past 13 years, only three have tipped so severely during similar maneuvers that they were judged "not acceptable." They were the Suzuki Samurai in 1988 and the Isuzu Trooper and its twin, the Acura SLX, in 1996.
Consumer Reports said it uncovered the problem in a test of emergency lane change maneuvers, where a vehicle is quickly swerved to the left and then back to the right. The magazine said the Montero Limited had performed fine in slow-speed tests, but tipped in eight of nine tests at speeds at or above 37 mph.
Mitsubishi Motor Sales of America Inc. disputed the report.
Consumers Union, publisher of Consumer Reports, "forced an outcome that misrepresents the safety of our vehicle," said Pierre Gagnon, the company's president and chief operating officer.
"In the real world, this vehicle's performance has been outstanding," he said. "We are disappointed that Consumers Union chose to attack our vehicle despite overwhelming evidence that their conclusions are wrong."
The company said it was unable to duplicate any tipping by the Montero.
"We have invested thousands of hours in the design and testing of the 2001 Montero, and we have validated its stability with additional testing over the past two weeks," said Gagnon.
Consumer Reports was sued by both Suzuki and Isuzu as a result of its assertionabout those models, but won both cases.
Asked if Mitsubishi might sue, Gagnon said, "We have not decided that yet."
The testing was done in May at Consumers Union's facility at East Haddam, Conn.
The federal government will conduct routine rollover tests on all cars by 2002.
In 1997, Daimler-Benz recalled and corrected the Mercedes-Benz A-class after it rolled over in similar tests conducted by a Swedish automotive magazine.
The magazine, published by the non-profit Consumers Union, tests and ranks a wide range of products and services for its 4.1 million subscribers. It pledges to stay free of corporate influence by accepting no advertising and asking companies not to advertise the results of its tests.
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