It is related at the alpha layer of the textures. If it is black (or close to be black) and the "Alpha blending" option turned ON then GP4 Builder thinks it is a transparent part.
Remember that GP4 builder is more focused at Track modding than cars and that alpha layer is used differently for track textures than for cars ones
Edited 1 time(s). Last edit at 01/12/2018 06:13PM by gezere.