§ 1037.305 Audit procedures for tractors—aerodynamic testing.
To perform a selective enforcement audit with respect to drag area for tractors, use the reference method specified in § 1037.525; we may instead require you to use the same method you used for certification. The following provisions apply instead of 40 CFR 1068.415 through 1068.425 for a selective enforcement audit with respect to drag area:
(a) Determine whether a tractor meets standards as follows:
(1) We will select a vehicle configuration for testing. Perform a coastdown measurement according to § 1037.528 with the vehicle in its production configuration. If the production configuration cannot be connected to a standard trailer, you may ask us to approve trailer specifications different than § 1037.501(g)(1) based on good engineering judgment. Instead of the process described in § 1037.528(h)(12), determine your test result as described in this paragraph (a). You must have an equal number of runs in each direction.
(2) Measure a yaw curve for your test vehicle using your alternate method according to § 1037.525(b)(3). You do not need to test at the coastdown effective yaw angle. You may use a previously established yaw curve from your certification testing if it is available.
(3) Using the yaw curve, perform a regression using values of drag area, CdAalt, and yaw angle, ψalt, to determine the air-direction correction coefficients, a0, a1, a2, a3, and a4, for the following equation: