The main problem with the car skin is that the alpha channel (reflectivity) don't work with the specular shader (direct sunlight). I have seen car skins with a complete white alpha channel and the result on reflectivity is zero (fresnel reflection only). Here is an example of a working specular shader. I made this shot with an older build. Check the "Hankook" letters on the car side. These have an almost white alpha channel (high reflectivity) and as a result they should react like chrome and they do. The blue colour is the reflection of the sky.