Hp = aA + P + tW
where:
Hp = the dynamometer power absorber setting at 50 mph (horsepower).
A = the vehicle reference frontal area (ft2). The vehicle reference frontal area is defined as the area of the orthogonal projection of the vehicle; including tires and suspension components, but excluding vehicle protuberances, onto a plane perpendicular to both the longitudinal plane of the vehicle and the surface upon which the vehicle is positioned. Measurements of this area shall be computed to the nearest tenth of a square foot using a method approved in advance by the Administrator.
P = the protuberance power correction factor from table 1 of this paragraph (horsepower).
W = vehicle equivalent test weight (lbs) from the table in paragraph (a).
a = 0.43 for fastback-shaped vehicles; = 0.50 for all other light duty vehicles.
t = 0.0 for vehicles equipped with radial ply tires; = 3 * 10- 4 for all other vehicles.
A vehicle is considered to have a fastback shape if the rearward projection of that portion of the rear surface (Ab) which slopes at an angle of less than 20 degrees from the horizontal is at least 25 percent as large as the vehicle reference frontal area. In addition, this surface must be smooth, continuous, and free from any local transitions greater than four degrees. An example of a fastback shape is presented in Figure 1.
Table I-Protuberance Power, P. Versus Total Protuberance Frontal Area, Ap
Ap (square foot) | P (horsepower) |
Ap[LESS THAN]0.30 | 0.0 |
0.30 Ap[LESS THAN]0.60 | .40 |
0.60 Ap[LESS THAN]0.90 | .70 |
0.90 Ap[LESS THAN]1.20 | 1.00 |
1.20 Ap[LESS THAN]1.50 | 1.30 |
1.50 Ap[LESS THAN]1.80 | 1.60 |
1.80 Ap[LESS THAN]2.10 | 1.90 |
2.10 Ap[LESS THAN]2.40 | 2.20 |
2.40 Ap[LESS THAN]2.70 | 2.50 |
2.70 Ap[LESS THAN]3.00 | 2.80 |
3.00 Ap | 3.10 |
The protuberance frontal area, Ap, is defined in a manner analogous to the definition of the vehicle reference frontal area, i.e., the total area of the orthogonal projections of the vehicle mirrors, hood ornaments, roof racks, and other protuberance onto a plane(s) perpendicular to both the longitudinal plane of the vehicle and the surface upon which the vehicle is positioned. A protuberance is defined as any fixture attached to the vehicle protruding more than 1 inch from the vehicle surface and having a projected area greater than 0.01 ft2 with the area calculated by a method approved in advance by the Administrator. Included in the total protuberance frontal area shall be all fixtures which occur as standard equipment. The area of any optional equipment shall also be included if it is expected that more than 33 percent of the car line sold will be equipped with this option.
Hp = aA + P + (5.0 * 10-4 + 0.33t)W
All symbols in the above equation are defined in paragraph (c)(2)(i) of this section. The rounding criteria of paragraph (c)(2)(i) also apply to this paragraph.
40 C.F.R. §86.129-80