U.S. Code of Federal Regulations
Regulations most recently checked for updates: May 30, 2023
(a) Dynamometer testing may consist of multiple drive cycles with both cold-start and hot-start portions, including prescribed soak times before each test interval. The standard-setting part identifies the driving schedules and the associated sample intervals, soak periods, engine startup and shutdown procedures, and operation of accessories, as applicable. Not every test interval includes all these elements.
(b) Place the vehicle onto the dynamometer without starting the engine (for any test cycles) or drive the vehicle onto the dynamometer (for hot-start and hot-running cycles only) and position a fan that directs cooling air to the vehicle during dynamometer operation as described in this paragraph (b). This generally requires squarely positioning the fan in front of the vehicle and directing the airflow to the vehicle's radiator. Use good engineering judgment to design and configure fans to cool the test vehicle in a way that properly simulates in-use operation, consistent with the specifications of § 1066.105. Except for the following special cases, use a road-speed modulated fan meeting the requirements of § 1066.105(c)(2) that is placed within 90 cm of the front of the vehicle and ensure that the engine compartment cover (i.e., hood) is closed:
(1) For vehicles above 14,000 pounds GVWR, use a fan meeting the requirements of § 1066.105(d) that is placed within 90 cm of the front of the vehicle and ensure that the engine compartment cover is closed.
(2) For FTP, LA–92, US06, or HFET testing of vehicles at or below 14,000 pounds GVWR, you may use a fixed-speed fan as specified in the following table, with the engine compartment cover open:
Table 1 of § 1066.410—Fixed-Speed Fan Capacity and Position Specifications for Vehicles at or Below 14,000 pounds GVWR
|Test cycle||Maximum fan
|Approximate distance from the front of the vehicle|
|FTP||Up to 2.50 m 3/s||0 to 30 cm.|
|US06||Up to 7.10 m 3/s||0 to 60 cm.|
|LA–92||Up to 7.10 m 3/s||0 to 60 cm.|
|HFET||Up to 2.50 m 3/s||0 to 30 cm.|
(3) For SC03 and AC17 testing, use a road-speed modulated fan meeting the requirements of § 1066.105(c)(5) that is placed within 60 to 90 cm of the front of the vehicle and ensure that the engine compartment cover is closed. Position the discharge nozzle such that its lowest point is not more than 16 cm above the floor of the test cell.
(c) Record the vehicle's speed trace based on the time and speed data from the dynamometer at the recording frequencies given in Table 1 of § 1066.125. Record speed to at least the nearest 0.01 mi/hr and time to at least the nearest 0.1 s.
(d) You may perform practice runs for operating the vehicle and the dynamometer controls to meet the driving tolerances specified in § 1066.425 or adjust the emission sampling equipment. Verify that the accelerator pedal allows for enough control to closely follow the prescribed driving schedule. We recommend that you verify your ability to meet the minimum dilution factor requirements of § 1066.110(b)(2)(iii)(B) during these practice runs.
(e) Inflate tires on drive wheels according to the vehicle manufacturer's specifications. The tire pressure for drive wheels must be the same for dynamometer operation and for dynamometer coastdown procedures used for determining road-load coefficients. Report these measured tire pressure values with the test results.
(f) Tie down or load the test vehicle as needed to provide a normal force at the tire and dynamometer roll interface to prevent wheel slip. For vehicles above 14,000 pounds GVWR, report this measured force with the test results.
(g) Use good engineering judgment when testing vehicles in four-wheel drive or all-wheel drive mode. (For purposes of this paragraph (g), the term four-wheel drive includes other multiple drive-axle configurations.) This may involve testing on a dynamometer with a separate dynamometer roll for each drive axle; or two drive axles may use a single roll, as described in § 1066.210(d)(1); or you may deactivate the second set of drive wheels and operate the vehicle on a single roll. For all vehicles at or below 14,000 GVWR, we will test your vehicle using the same dynamometer roll arrangement that you used. We may also test your vehicle using another dynamometer roll arrangement for information-gathering purposes. If we choose to perform additional testing that requires vehicle modifications, we will ask you to configure the vehicle appropriately.
(h) Determine equivalent test weight as follows:
(1) For vehicles at or below 14,000 pounds GVWR, determine ETW as described in § 1066.805. Set dynamometer vehicle inertia, I, based on dynamometer type, as follows:
(i) For two-wheel drive dynamometers, set I = ETW.
(ii) For four-wheel drive dynamometers, set I = 0.985 · ETW.
(2) For vehicles above 14,000 pounds GVWR, determine the vehicle's effective mass as described in § 1066.310 and use this as the test weight.
(i) Warm up the dynamometer as recommended by the dynamometer manufacturer.
(j) Following the test, determine the actual driving distance by counting the number of dynamometer roll or shaft revolutions, or by integrating speed over the course of testing from a high-resolution encoder system.