Q&A: Bumpers
February 2013
- 1 What is the purpose of bumpers?
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Bumpers are supposed to keep damage away from safety-related equipment such as headlights and taillights and protect vehicle parts such as hoods, fenders, and exhaust and cooling systems that are expensive to repair. When bumpers are poorly designed, these parts sustain most of the damage in parking-lot collisions and other low-speed impacts. Bills to fix fender-bender damage can add up to thousands of dollars.
Insurance claims related to fender benders add up, too. This is reflected in the premiums consumers pay for auto insurance. More than $6 billion is paid out each year to cover claims of $4,500 or less, the kind of damage claims associated with low-speed collisions. Highway Loss Data Institute. 2008. Unpublished analysis of passenger vehicle insurance loss data. Arlington, VA. Such huge damage costs are why it's important to equip passenger vehicles with bumpers that effectively reduce damage in low-speed collisions. Better bumpers mean less out-of-pocket costs for consumers and lower insurance costs.
- 2 What are bumpers made of?
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Front and rear bumpers on today's cars generally consist of a plastic cover over a reinforcement bar made of steel, aluminum, fiberglass composite or plastic. Some automakers design the bumper bar and its attachment brackets to crush in a low-speed crash to absorb energy. Polypropylene foam or formed thermoplastic sometimes is used in addition to or instead of crushable brackets and a bar. But frequently their main purpose is to serve as a spacer between the bar and the bumper cover and not as an energy absorber. Very few bumper bars are attached to the vehicle structure through mechanisms like shock absorbers.
A bumper reinforcement bar, shown without the plastic bumper cover
- 3 What are the attributes of a good bumper system?
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Geometry, stability and energy absorption. Bumpers on colliding vehicles should line up geometrically so that they engage each other during a low-speed crash to absorb crash energy. The bumpers should overlap each other enough to account for variations in ride height and preimpact braking, which can lower the front end or raise the rear end of a vehicle just before impact. Bumpers should stay engaged with the other bumpers in collisions instead of overriding or underriding them, which often results in damage to vehicle grilles, headlights, hoods, fenders and trunks. Bumpers also should have sufficient energy-absorbing capabilities to confine damage to the bumper system itself. Aylor, D.; Ramirez, D.L.; Brumbelow, M.; and Nolan, J.M. 2005. Limitations of current bumper designs and potential improvements. SAE Technical Paper Series 2005-01-1337. Warrendale, PA: Society of Automotive Engineers.
Beyond these basic attributes, good bumpers extend to the corners of vehicles to protect headlamps and fenders. Aylor, D.; Nolan, J.M.; Avery, M.; and Weekes, A.M. 2007. Corner protection in low-speed crashes. SAE Technical Paper Series 2007-01-1760. Warrendale, PA: Society of Automotive Engineers. They're outset somewhat from the sheet metal parts they're intended to protect, leaving space for energy absorption. Bumpers also should be designed so they'll be relatively inexpensive to repair or replace after low-speed collisions.
- 4 Does the federal government regulate bumpers?
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The U.S. government sets minimum bumper performance requirements for passenger cars, Office of the Federal Register. 2006. National Highway Traffic Safety Administration – Title 49 Transportation, Part 581 Bumper standard (49 CFR 581). Code of Federal Regulations (October 1, 2006 edition), pp. 1199-1202. Washington, DC: National Archives and Records Administration. but these regulations don't apply to vans, SUVs or pickups. The agency issued its first bumper standard for cars in 1971.
Current bumper rules, in place since 1982, specify 10 bumper tests, including pendulum tests and crashes into a fixed flat barrier. The pendulum tests include two front and two rear-corner impacts at 1.5 mph plus two front and two rear tests at 2.5 mph. The pendulum has a bumper-shaped protrusion that may impact the vehicles anywhere between 16 and 20 inches from the ground, and the mass of the pendulum equals that of the tested vehicle. Following these tests, the fronts and rears of the vehicles crash into a flat barrier at 2.5 mph. In these barrier and pendulum tests, unlimited damage is allowed to the bumper, but none is allowed to other parts of the vehicle. The hood, trunk and doors must operate normally. Propulsion, suspension, steering and braking systems also must operate normally. There can be no broken headlights or fuel, cooling or exhaust leaks or constrictions.
- 5 Could the requirements be tougher?
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Yes. Bumpers used to do a better job of resisting damage in minor impacts. Under federal requirements that were in effect until 1982, car bumpers had to keep damage away from vehicle safety equipment and sheet metal parts in collisions at speeds up to 5 mph. Even allowable damage to the bumpers themselves was limited. Since 1982, the test speed under the standard has been cut in half, and unlimited damage is allowed to vehicles' bumper systems. Federal bumper rules also should extend to vans, SUVs and pickups, and address the mismatch between car bumpers and those of these higher-riding vehicles.
Aesthetic concerns often mean that manufacturers aren’t interested in going beyond the government’s minimal requirements for car bumpers. Automakers use a variety of designs to meet federal performance requirements for car bumpers. Some designs result in bumpers that don't protect expensive vehicle parts from damage in real-world low-speed collisions. For example, the bumper covers on most modern cars fit snugly against the vehicle body. This stylish look doesn't help when it comes to resisting damage in low-speed collisions because there's not much room for absorbing crash energy before it reaches the car body and damages it. The emphasis on a sleek look also encourages designers to shorten the width of the bumper bars that extend across the fronts and backs of vehicles, resulting in bumpers that don't do a good job of resisting damage.
- 6 What are the consequences of excluding vans, SUVs, and pickups from federal bumper standards?
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Even though the federal requirements for cars are weak, they do ensure that cars are equipped with bumper systems located at least partially in the test zone of 16-20 inches from the ground. Pickups and SUV bumpers are often higher than that. This means that when cars and SUVs collide, the bumpers can go right past each other. The energy of these collisions will bypass the bumpers and go directly into the vehicle bodies. Even if the bumpers do overlap, they may slide off of each other instead of staying engaged. Either way the result is expensive car body damage.
The Institute has performed low-speed crash tests that demonstrate what happens when SUVs and cars collide and their bumpers don’t line up. The latest series of tests, in 2010, involved seven pairs of vehicles, each composed of a small car and a small SUV from the same manufacturer. Insurance Institute for Highway Safety. 2010. SUV and car bumpers underride and override each other in low-speed crashes, contributing to pricey damage. Status Report 45(12):1-7. First, a car going 10 mph struck the back of its paired SUV, which was stopped. Then the configuration was reversed, with the SUV striking the back of the car. Results of these low-speed impacts varied widely, from a total of about $850 damage to one vehicle to $6,000 damage in another. In real-world collisions like these, many of the motorists would not have been able to drive away.
Later, working in collaboration with Tech-Cor, Allstate’s auto repair research center, the Institute showed how easy it would be to reduce the damage in these collisions. Insurance Institute for Highway Safety. 2012. Bumper demonstration test shows easy way to solve mismatch problem when SUVs and cars collide. Status Report 47(1):6-7. Tech-Cor engineers modified two of the SUVs to lower their bumpers, and the Institute tested them with their partner cars again The result was large reductions in repair costs for both cars. Damage to the SUVs also decreased.
Bumpers on cars and SUVs often don't match up in collision
- 7 How does the Institute assess bumper performance?
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The Institute rates bumpers good, acceptable, marginal or poor based on performance in four tests — front and rear full-width impacts at 6 mph and front and rear corner impacts at 3 mph. Each vehicle is run into a steel barrier that's designed to mimic a car bumper. The deformable barrier's plastic absorber and flexible cover simulate typical cars' energy absorbers and plastic bumper covers. The Institute began using this new rounded barrier in 2007 instead of a flat barrier when it revamped its bumper test program to better assess how well bumpers protect vehicles from expensive damage in everyday fender-benders. These new tests are designed to drive bumper improvements that lead to better damage resistance in a range of real-world crashes. Then in June 2009 the Institute introduced a ratings protocol based on repair costs averaged and weighted to reflect real-world damage patterns and insurance claim frequency.
In the rear full-width crash tests the barrier is set 18 inches off the ground, and in the corner impacts the distance is 16 inches. These measurements are in keeping with federal rules that specify a zone for car bumpers 16 to 20 inches from the ground. The Institute's test barrier is 4 inches tall, or about the same as many real car bumpers. Results indicate not only the strength of car bumpers but also how well they engage and then stay engaged with the bumpers on other vehicles with which they collide. The test configurations produce the kinds and amounts of damage that commonly result from actual low-speed collisions.
When it comes to assigning a rating, the full-front and rear test results carry twice the weight of the corner test results. That’s because in the real world full-width impacts occur roughly twice as often as corner impacts. Weighted average repairs must be less than $500 for a good rating, less than $1,000 for acceptable, and less than $1,500 for marginal. Repairs of $1,500 or more earn bumpers a poor rating. In addition, no vehicle can earn a good or acceptable rating if it's unsafe to drive after testing or can't be driven at all. Inoperable headlights or taillights, severely buckled hoods or a compromised engine cooling system would prevent any vehicle from achieving the top two ratings.
IIHS bumper barrier test configurations
- 8 How have car bumpers performed in these new Institute tests?
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Not great. The bumpers often don't line up geometrically, and if they do engage they don't stay engaged during impact to absorb crash energy. Another problem is that the bumpers on many vehicles aren't wide enough to protect the corners. Cars and minivans that have undergone the new Institute tests show that automakers still are using bad bumpers. Under the ratings protocol introduced in 2009, no car or minivan has earned the top rating of good, and only five cars have earned an acceptable rating. They are the Ford Focus, Subaru Legacy, Mazda 6, Scion xB and Smart Fortwo.
