Problem with adding Forza 4 DLC via a USB stick

I was able to download a .rar file of all Forza Motorsport 4 DLC Cars and I now got them all on a USB stick but when I add the DLC Car files into the Forza 4 Game itself it just says connection corrupted. Can anyone please help me with this problem. I haven’t seen a youtube video for a guide on how to fix this problem ether.

I do not believe that is permitted and would be considered game hacking.