NR3 allows us to pick our own car file for use online. A bug in the sim allows more than one person to pick the same car, and this can be quite troublesome when you're in a race that has pace lap or yellow flags turned on. One really great aspect of this is that we're not restricted to using a car in the multi car list. If you want to use a cup car that was supplied with the sim, all you have to do is manually enter the car file name in the space provided on the multiplayer screen. Okay, I have a custom paintjob.
Many people think they have to add their car to the multi list.
Your car does not have to be in one of the car lists unless you intend on driving that car offline. This is only a theory of mine though. You have to change TWO settings on TWO different pages. On the first multiplayer screen, you have to set the number of human players that your server can support. The sim uses these cars as place holders in the pits.