Hi,
Choose the tyres you like, put them in the skin folder you want and rename the tyres files properly.
Imagine you want to add the tyres to a Z4 GT3 skin: you move the tyres files to the skin folder and you rename the files as "tyre_d_2.dds", "tyre_d_2_blur" and "tyre_d_2_N.dds".
Hope it's clear, let me know if you are in trouble
