The entire underbelly thing is kind of a moot point, in a game where the car only rolls over once in a blue moon. I rather have those polys in the body.
Same goes to the tires, theres a lot of polys in a single rim just for the outside. You have to double the amount if you do the inside too. To even this out, you have the to reduce the details. So you end with a double sided rim that is only half as detailed on the side you see like 90% percent of the time. In my view that would be a bad decision.
There is also another little thing to a 3D model you like to ignore. Mesh quality.
Just compare this picture to the one posted by you.
Look how beautiful and even the mesh is, almost no triangles. This gives a very clean smooth and very few distortion. A mesh like this can also be upscaled easily with the press of a button, futureproofing it. Same method on the other mesh will most probably mess it up.