8. Ff + Fr = ma + Ra + Rrlf + Rrlr + Rg
F = ma + Ra + Rrl + Rg 8

12. Aerodynamic Resistance Ra
Composed of:
Turbulent air flow around vehicle body (85%)
Friction of air over vehicle body (12%)
Vehicle component resistance, from radiators and air vents (3%)
Power is in ft-lb/sec
from National Research Council Canada

14. Drag
In fluid dynamics, drag (sometimes called air resistance or fluid resistance) refers to forces which act on a solid object in the direction of the reletive fluid flow velocity.
Unlike other resistive forces such as dry friction, which is nearly independent of velocity, drag forces depend on velocity.

19. Filled with air, especially compressed air: a pneumatic tire.

23. Grade Resistance Rg Composed of
Gravitational force acting on the vehicle θg
For small angles, Rg θg W