Mr. Kevin Manke
P.O. Box 1188
Mitchell, SD 57301
Dear Mr. Manke:
This responds to your letter asking about the force application test procedures of Federal Motor Vehicle Safety Standard (FMVSS) No. 223, Rear Impact Protection. You ask whether the energy absorption test referenced in S6.6(c) of the standard requires that a manufacturer apply a load until the achieved deflection is 125 millimeters (mm). As explained below, the answer is no.
By way of background, the National Highway Traffic Safety Administration (NHTSA) is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment (see 49 U.S.C. Chapter 301). NHTSA does not provide approvals of motor vehicles or motor vehicle equipment. Instead, manufacturers are required to self-certify that their products conform to all applicable safety standards that are in effect on the date of manufacture. NHTSA selects a sampling of new vehicles and equipment each year to determine their compliance with applicable FMVSSs. If our testing or examination reveals an apparent noncompliance, we may require the manufacturer to remedy the noncompliance, and may initiate an enforcement proceeding if necessary to ensure that the manufacturer takes appropriate action.
Paragraph S5.2 of FMVSS No. 223 states, in pertinent part: When tested under the procedures of S6 of this section, each guard shall comply with the strength requirements of S5.2.1 of this section at each test location and the energy absorption requirements of S5.2.2 of this section at test location P3. S5.2.2 states that a guard shall absorb by plastic deformation within the first 125 mm of deflection at least 5,650 J of energy at each test location P3. S6.6(c) states that if conducting a test to be used for the calculation of energy absorption levels to satisfy the requirement of S5.2.2 of this section, apply the force to the guard until displacement of the force application device has reached 125 mm.
You state in your letter that your guard meets the load and energy absorption requirements of the standard at a deflection of less than 125 mm. You ask whether in the course of performing the test described in S6.6(c), you need to continue applying force beyond the required values until the displacement of the force application device has reached 125 mm.
You state that due to the increasing rigidity of the guard, a force application device capable of providing a force large enough to produce the full 125 mm of deflection may not be readily available.
Under S5.2.2 of FMVSS No. 223, your guard must absorb at least 5,650 J of energy by plastic deformation within the first 125 mm of deflection. You do not need to continue applying force beyond the required levels in order to certify your product to FMVSS No. 223. It is not necessary for you to continue applying load until 125 mm of deflection is achieved if you are reasonable in your conclusion that the guard meets the standards requirement with less than 125 mm of displacement.
Keep in mind that the test procedures in FMVSS No. 223 describe how NHTSA will test guards for compliance with the standards requirements, and are not binding upon guard manufacturers. A manufacturer is not required to use the standards procedures when certifying compliance with the standard.
Based on the language of the standard, even if the guard appears to have absorbed the required amount of energy before the displacement has reached 125 mm, NHTSA will continue the test because S6.6(c) states "[i]f conducting a test to be used for the calculation of energy absorption levels to satisfy the requirement of S5.2.2 of this section, apply the force to the guard until displacement of the force application device has reached 125 mm. NHTSA follows this procedure because it needs to know how much elastic rebound the guard will exhibit once the load is removed, and the energy returned during the rebound will have to be subtracted when calculating the total energy absorbed. Again, however, a manufacturer is not required to test in the manner specified in the standard; instead it must ensure that the guard will meet the requirements when tested by NHTSA as set forth in the standard.
For your information, NHTSA answered a similar question in a 1997 letter to Mr. Frank Smidler. A copy of that letter has been enclosed for your convenience.
If you have any further questions, please contact Ari Scott of my staff at (202) 366-2992.
Anthony M. Cooke
 April 29, 1997 letter to Mr. Frank Smidler, available at http://isearch.nhtsa.gov.