A few years ago, the Federal Government reduced the crash threshold on automobile bumpers from 5 mph to 2 1/2 mph.

What that means, is that an automobile bumper must be able to withstand a 2 1/2 mile impact without sustaining any damage. Well, if you have ever tried to coast at 2 1/2 mph you would know that this is not saying much.

When the limit was 5 mph, the typical bumper consisted of face bar (steel or aluminum) that was mounted to 2 hydraulic pistons (absorbers). These absorbers were in turn bolted to the body of the vehicle. Upon impact (up to 5 mph), the absorbers would compress and absorb the bulk of the impact. This system worked reasonably well.

The 2 1/2 mph bumper systems are a different animal. You still have the face bar, but instead of absorbers, the face bar is bolted directly to the body of the vehicle. At 2 1/2 mph and under, this is fine. Anything above 2 1/2 mph, you get the following (actual case):

This is a picture of a rear trunk floor in a 1996 Mazda 626. Not to pick on Mazda, this is typical of most unibody vehicles today. Although difficult to measure the speed at impact, the resulting damage was compounded by the bumper design. By bolting the bumper (with no energy absorbers) directly to the body of the vehicle, the force of the impact to travels directly INTO the body of the car.

What would you rather have? A damaged rear bumper or a trunk floor like the example?

The speed threshold was reduced as a result of pressure from the automobile industry. The 2 1/2 mph bumpers weigh less (no energy absorbers) as a result a vehicle that weighs less and guess what? Better gas mileage? Better gas mileage...more damage in an accident. Who's the winner?

Jim Wetzel
Hudson Valley Auto Appraisers of Newburgh, NY

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