I understand. However, I want to examine the drag coefficients at different distances between the cars. When the distance between the cars is 1m, I obtained the drag coefficients that seem appropriate for both cars' bodies. But when I kept the domain and the front car's position the same and only changed the distance between the cars to 2m for the simulation with the same settings, I found that the drag coefficient of the front car decreased from around 0.4 to 0.06, and the drag coefficient of the rear car became larger than the front car's coefficient. If the domain size and the front car's position are the same, the drag coefficient of the front car should remain the same, so I'm not sure why it changed.