Cool, I didn't realize everything was in the .rpf file. Was really easy to extract the handling file and edit things

I did some searching and haven't quite found what I'm looking for. I want to mod the handling of some addon cars I have (for my own use, of course), some of them have handling that makes them act "perfect" when driving, like stops on a dime, can take a corner at 100+ MPH, etc. One thread I read says to edit the car's handling file, but none of the cars I have downloaded have any kind of a handling file, it's just one file for the car, dlc.rpf. What am I missing to make this happen?

Just recently have been having an issue where I can't load in car models. I started with a car to test it (Iroc Z Camaro) and it worked fine, I have it sitting in my garage. Then I decided to try another one and followed the same steps, but my loader refuses to locate the car. Now I can't load the Iroc either. Any idea what's going on?