If you are able to use UV mapped textures, you could also try SDF's generated in Substance Designer (if you have that as well). I think you would get best results if you set Distance Node to "Manhatten Distance". It's not 100% perfect but this is extremely fast for iteration since the process is completely automated and…
I'm not really following a reference 100%, but the one i use is egarage.com and from forza horizon game's garage i take screenshots or just look at them, their version is way different from the actual car. Here are the wireframes: Low Poly "Kinda": And here are the high poly screenshots: