A dirt map contains three textures. Each texture is a seperate greyscale texture saved in one RGB channel:
- Red: Applies dirt effects while roads are dry.
- Green: Decreases specularity. By default it's a high contrast version of the red channel.
- Blue: Applies dirt effects while roads are wet.
The diffuse will be applied as a brown overlay on top of the surface. Lighter areas on each channel will have a stronger effect, darker areas a weaker effect. Black will have no effect at all.
Mapping a dirt map
By default, the game uses one shared dirt map for all cars. Some mod authors also use custom dirt maps made for specific vehicles for better looking results.