Here is some info on how to add cars ... and where to find them.
Together with some friends I have compiled what we call a basic multiplayer set ... let's say some cars which are used a lot (and loved) and where to find them.
To add a car:
add to the racer folder in data/cars/
Tip: racer seems to dislike spaces in the folder name of the cars. But the folder names have to be the same as the people you're are going to play with. So we have agreed on some folder names. Where necessary to change the folder name it will be noted.