The overlap front crash test was devised to simulate an accident in which the front 25 percent of a car strikes a barrier, simulating a tree or utility pole, as opposed to the straight-on front crash tests in which the entire front end suffers impact.
The IIHS said the Chevrolet Spark passed the overlap front crash test and made it through the organization's four other crash evaluations to earn a 2014 Top Safety Pick award.
But six other minicars were rated poor in the small-overlap front crash test. The Mazda2, Kia Rio, Toyota Yaris and Ford Fiesta earned marginal ratings.
"The test is more difficult than the head-on crashes conducted by the government or the long standing IIHS moderate overlap test because most of the vehicle's front-end crush zone is by-passed," IIHS said. "Nevertheless, in many size categories, manufacturers have found ways to improve vehicle structures to meet this challenge."
"Small, lightweight vehicles have an inherent safety disadvantage," said Joe Nolan, IIHS senior vice president for vehicle research. "Unfortunately, as a group, mini cars aren't performing as well as other vehicle categories in the small overlap crash," he said.
IIHS said minicars were routinely flunking the overlap front crash, but the small car category was faring much better. Five small cars were given good ratings and five acceptable ratings out of 17 small cars evaluated, the institute said.
Among minicars, IIHS said, the 10 that flunked the overlap front crash test did not fare much better in other tests.
The other 10 minicars were given marginal or poor ratings for structure, which IIHS said was "the most fundamental element of occupant protection."
Seven of the minicars were given poor marks for allowing occupants too much forward motion in the event of a crash. In some, the safety belts functioned poorly. In others, the crash dummy's head missed or slid off of the airbag.
IIHS said regardless of its rating, consumers might think twice about buying a Spark. The car tested well against a barrier, but it weighs only 2,500 pounds and on the road it could be the equivalent of a wrestler in a lightweight division taking on a heavyweight.
The Spark "doesn't protect as well as a larger and heavier vehicle with a comparable rating," IIHS said, noting that "frontal crash test results can't be compared across weight classes."