The IIHS conducted a battery of tests on 20 small cars that found fault with many in the test, with 3- and 6-mph simulated impacts resulting in damages totaling nearly one-third of the vehicle price in some cases.
At the speeds used by the IIHS, only the bumpers should sustain damage, and then it should be cosmetic, they reasoned. The bumpers' job is to protect the expensive, structural portions of the vehicle such as hoods, headlights, and fenders. Automotive designers can take these realities into account while designing bumpers, but in most cases the IIHS found that bumpers in the economy class were substandard when it came to protecting the vehicles' sheetmetal.
Worst offenders in the class were the Hyundai Elantra, Toyota Prius, and Volkswagen Rabbit, all of which sustained damage of $4,000 or more in a single test. The Ford Focus was the best performer, with its worst damage about one-third of the cost the worst performers' in a single test.
It is the physics of these low-speed collisions that often quickly turns a fender-bender into a hefty insurance claim. A properly designed bumper, such as in the Ford Focus, meets the colliding vehicle square at bumper height, and both bumpers are able to absorb impact and protect other parts of the vehicle. But it was aggressive and trendy styling mixed with less than thorough engineering, found the IIHS, that contributes to bumpers that either push the colliding vehicle underneath the bumper (underriding) or push it above the bumper (overriding). In both cases, pricey components and accessories are damaged, and sheetmetal can also be deformed. Also at fault were flimsy bumpers that, even when colliding properly, weren't stout enough to handle the impact. Finally, bumper shape and height are critical design factors that can mean thousands of dollars' difference in an impact.
A series of four crash tests were performed to assess and compare bumper performance: full front and rear into a barrier designed to mimic the front or back bumper on another vehicle, and front and rear corner impact tests as well. Full-width impact testing was done at 6 mph, corner impact testing at 3 mph.
"Small cars are supposed to be economical, but there's nothing economical about three or four thousand dollars in repairs after a low-speed collision," says Insurance Institute for Highway Safety's senior vice president Joe Nolan.