Here is what I found in
Piechna's book:
According to Carr ([1], nice last name in this field of research, btw), for modern cars the coefficient of surface drag is around 0.08. For a mid-sized passenger car the coefficient of lift is 0.15, which implies that the edge vortex drag coefficient is 0.01 (assuming that coefficient
k in Carr's formula is equal to 0.5).
Based on these assumptions, a typical drag coefficient of Cx=0.30 could be decomposed in the following ways:
| . | delta Cx (Barnard, [2]) | delta Cx (Katz, [3]) |
| Surface drag | 0.08 | 0.04-0.05 |
| Air pressure drag | 0.10 | 0.00-0.45 |
| Wheels | 0.08 | - |
| Engine cooling | 0.03 | 0.00-0.06 |
| Internal airflow, ventilation | - | 0.00-0.05 |
| Edge vortices | 0.01 | 0.00-0.60 |
| Total | 0.30 | - |
[1] Carr G.W., Potential for aerodynamic drag reduction in car design,
Impact of Aerodynamics on Vehicle Design, Proc, International association for Vehicle Design: Technological Advances in Vehicle Design, SP3, ed. Dorgham M.A., 1983, pp.44-56.
[2] Barnard R.H.,
Road Vehicle Aerodynamic Design, Longman, 1996.
[3] Katz J.,
Race Car aerodynamics, Robert Bentley Automotive Publishers, 1995.