First of all you need templates to the materials you might want and you can find them here:
https://github.com/ac-custom-shader...ter/config/cars/common/materials_interior.ini
You don't need to write all of the values but only those you want to edit, the ones not written will keep that material's standard values.
Here is an example to better understand how to write it in an ext_config.ini file that you must create into a folder called "extension" inside the car folder. So Assetto Corsa/content/cars/extension/ext_config.ini and with a text editor you write the config inside the file.
Code:
[INCLUDE: common/materials_interior.ini]
[Material_Aluminium_v2]
Materials = INT_Alu
Metalness = 0.35
BrightnessAdjustment = 0.5
DetailTexture = 1
DetailNormalTexture = common/pbr_metal.dds
DetailNormalPBRSecondaryColor = 0, 0, 0, 0
DetailScale = 30
DetailNormalBlend = 1
DetailNormalPBRSmoothnessGamma = 2
OcclusionMap = 0.8
Detailtexture=1 when added means that the material will keep the texture it already had just with a different shading. If that is removed it will use that "pbr_metal.dds texture instead.
You always need at the beginning of the config the INCLUDE line
After "Materials0 " you need to write that material's name from the model