We tend to take them for granted, but car bumpers are there for a reason -- to prevent serious damage in a minor crash.

The problem is, bumpers don't always work when the fender bender involves an SUV. There's a reason for that.

Here's what can happen when an SUV rear-ends a sedan. The SUV's higher bumper rides over the car bumper, causing extensive damage to the body of the car.

"What should be a no-damage bump turns into a thousand-dollars repair job," said John Karp, claims analyst with Pemco Insurance. "There's no question this is millions of dollars, maybe billions across the country."

Here's an example. When a 2006 Subaru sedan rear-ended an SUV, the crash crumpled the hood, busted the headlight assembly, damaged the fender and broke a number of components under the hood.

But the damage didn't have to take place at all. All of it occurred because the two bumpers didn't match up in the crash.

Lonnie Caraveo at Phil's Auto Body sees this sort of thing all the time.

"You take something like this (a crash involving an SUV and a sedan), that if this was to meet bumper to bumper, you're probably looking at a $1,500 repair. But because it went under, now you're looking at $6,000 in repairs," he said.

In the worst cases, Karp said, the drivers involved might not realize the extent of the damage done until much later.

"Somebody's in a pickup truck. They're backing up, they hit your headlight assembly on your car. There's $1.500 damage to replace it. They go forward and leave; they don't even know it happened. You can't even feel the impact because the bumpers aren't lining up," he said.

The Insurance Institute for Highway Safety has petitioned the federal government, demanding that SUVs, pickups and minivans be covered by federal bumper standards.

To prove its case, the institute crashed four mid-size SUVs into a mid-size sedan, a Hyundai Sonata, at 10 miles per hour.

While the 2008 Grand Cherokee caused $4,600 worth of damage to the Sonata, the Ford Explorer did significantly less -- just $1,500 worth of damage.

Why such a difference? The Explorer's bumpers are the same height as sedan bumpers.

"Automakers know how to design bumper systems that limit the damage they cause when they collide with other cars," said Adrian Lund with IIHS.

And consider this: when bumpers don't match up, the SUV or pickup also suffers more damage.

The auto industry is not commenting on this petition, and neither is the federal government.

The feds say SUVs and pickups won't be able to do their jobs with lower bumpers. The insurance industry says that's pure nonsense.

More Information:

Insurance Institute for Highway Safety Report on Bumpers