WASHINGTON (CNN) - Two popular small cars have subpar bumpers that could mean more than $1,000 of damage from a parking-lot fender bender, a highway safety group announced Tuesday.

The BMW Mini Cooper and the Suzuki Aerio, both new for the 2002 model year, rated either "marginal" or "poor" in tests conducted by the Insurance Institute for Highway Safety.

By contrast, the Audi A4 and Toyota Corolla both earned "good" ratings in the crash tests, which measured how well car bumpers resist damage in low-speed impacts, which often happen in commuter traffic or parking lots.

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The Honda Accord, the fifth car tested, got an "acceptable" rating.

The institute conducted four low-speed tests on each car, gauging how well they performed when their front and rear bumpers hit a flat barrier, when their front bumpers hit an angled barrier, and when the rear bumpers hit a pole.

The Suzuki Aerio, a hatchback-style four-door, had the highest average damage per test: $1,131. The Audi A4 had the lowest average: $216.

Suzuki engineers "simply didn't do a good job with the bumper systems when they designed this car," said Adrian Lund, the institute's chief operating officer.

The Aerio's bumper cover came apart in three of the four crash tests, necessitating replacement at a cost of $500 each time.

"Its bumpers fail to do what bumpers are supposed to do, which is to minimize damage in minor impacts," said Lund. "In fact, these bumpers are just expensive decorative trim."

While the Mini Cooper fared slightly better than the Suzuki, it still netted $800 in average damage per test.

"It's attracting a lot of attention for distinctive styling," Lund said, "but the bumpers aren't praiseworthy."

The worst test for the Mini Cooper was the angle-barrier test, which caused about $1,500 in damage. Lund called the results "disappointing" but noted other BMW cars also generally don't perform well in fender-bender crash tests.

The institute credited a solid bumper design for the Audi A4's good rating. The car has reinforcement bars underneath the front and rear bumper covers that are attached to the car with mounts that act like shock absorbers in the event of a low-speed crash.

Other cars from the same manufacturer, including the Audi A6 and the Volkswagen Beetle and Passat, have similar bumper designs and also have performed well as a result.

Most automakers equip their cars with bumpers filled with layers of foam, which often do not absorb energy before metal parts buckle and bend, the institute said.

The foam in the Toyota Corolla's bumpers did a "reasonably good job" of resisting damage in fender benders, Lund said, but that design caused it to perform less well than the Audi. The Audi sustained no damage in the flat-barrier tests, while the Toyota had an average of $261 in damage in those two tests.

The Honda Accord does not include the energy-absorbing mounts in its bumpers, either. Its bumper bars are attached with mounts that buckle on impact, and the foam in the bumper fails to keep the car free of damage, Lund said.

The rear bumpers for both the Honda Accord and the Toyota Corolla were reinforced in the center, but only so the car would perform well in the pole test, Lund said. Because of that, testers moved the pole from the center of the bumper to the side to get a more accurate measure of the car's performance.

"We're seeing auto manufacturers beginning to do this just to get good ratings in our test," Lund said. "But what we want to see manufacturers putting on their cars are bumper systems that will resist damage in a wide range of low-speed crashes."