A new set of crash tests involving minicars has a safety group telling consumers to be wary of very small vehicles.
A round of front overlap crash tests—which replicate how vehicles perform when the front corner on the driver's side strikes another car or object at 40 mph—showed that of 11 minicars tested by the Insurance Institute for Highway Safety, only one, the Chevrolet Spark, received an "acceptable" rating.
Four received "marginal" ratings, while six were rated "poor." None of the vehicles received the highest rating of "good."
"These cars afford drivers and passengers a very low level of protection," said Joe Nolan, senior vice president for vehicle research at the IIHS. "Minicars, as a group, are the worst cars we've ever seen with front overlap crash tests."
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Ranging from the Nissan Versa to the Toyota Yaris to the 2014 Ford Fiesta, minicars have become more popular in recent years. Automakers have introduced them to meet federal regulations requiring more fuel-efficient vehicles.
Last year, more than 425,000 minicar models were sold in the U.S., according to the research firm Autodata.
The IIHS said the front overlap crash tests highlighted a dangerous combination that puts drivers and occupants at risk: minicars' small size and relative light weight.
They weigh an average of 2,000 to 2,500 pounds.
"The results are troubling because automakers could make changes in these cars that would improve how minicars do in front overlap crashes," Nolan said.
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"These cars often fail to manage the crash energy in the front crush zone," he added. "As a result, the occupant cabin gets compromised. You see the steering column pushed into the driver and a cascade of failures in the passenger cabin."
Nolan stopped short of urging people to stop driving minicars, but he did say consumers should realize that some slightly larger cars performed very well in front overlap crash tests.
"The Honda Civic is a blueprint for what automakers can do," he said. "It's only slightly larger than the Fit, but it gets the highest score possible in front overlap crash tests."
Honda Fit, Fiat 500 get poor ratings
The safety group said it is most concerned about the performance of two models with "poor" scores: The Honda Fit and Fiat 500.
"In the Fit crash test, there was a lot of intrusion into the passenger cabin. ... And during the Fiat 500 crash test the drivers door was torn open," Nolan said.
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In response to the Fit review, Honda issued a statement saying, "Honda has an all-new, completely redesigned 2015 Honda Fit that will come to market in just a few months, and we anticipate it will earn top safety scores from the Insurance Institute for Highway Safety, with a "good" rating in all test modes including the rigorous small overlap front crash test."
Fiat parent Chrysler told CNBC, "The Fiat 500 meets or exceeds all government-mandated safety requirements and continues to offer a high level of protection in four main crash types identified by the IIHS—side, rollover, rear and moderate-overlap front."
—By CNBC's Phil LeBeau. Follow him on Twitter @LeBeauCarNews.
Questions? Comments? BehindTheWheel@cnbc.com.