2015 McLaren P1 GTR - v1.03 2015 Audi R8 LMS - v2.01 2016 Pagani Zonda LM-R Ragno - v1.0I've used mods and they work fine for me. You have to follow the instructions exactly, most times than not people are not copying the files to the correct directory. But it's been a while since I used them, which one are you using exactly? Porche or the Audi?
All I can say is if you are copying the files to the correct folder.
"2. Copy the folder "Audi R8 LMS 2015" into the folder "MODS" in the game's dictionary."
Make sure the directory is the PCars' folder inside Steam's folder structure. NOT the PCars folder that you can find at MyDocuments. You have to copy all the files, which means the 2 text files as well, in case you only copied the folders from the .rar
If you are doing all these correctly I can't help you any further, mine works like this.