The aerodynamic drag coefficients and the frontal area for different vehicle types is given in Table 2.

Table 2: Reference values for drag coefficient (CD) and the frontal area (Af in m2) for some vehicle types

Grading resistance

When a vehicle goes up or down a slope, its weight produces a component of force that is always directed downwards, Figure 5. This force component opposes the forward motion, i.e. the grade climbing. When the vehicle goes down the grade, this force component aids the vehicle motion. The grading resistance can be expressed as

                                                                   (9)

In order to simplify the calculation, the road angle a, is usually replaced by the grade value, when the road angle is small. The grade value is defined as (Figure 5)

                                                                                                 (10)

In some literature, the tire rolling resistance and the grading resistance taken together and are called road resistance. The road resistance is expreesed as

                                                                (11)

Figure 5: Vehicle going up a grade