Well, took me 1 day of my life to find this out, i just rent a dedicated pcars 2 server,
after joining it i can only choose just one car class, all others who join me can choose anything.
I read everthing about disable lua, flags calculator ect. ect.
Then just before i gave up i started a online race from my PC (this is the menue under the browse online game)
there i found out i limited my cars to just one class a week ago

So a reminder for you, some things you choose at "create online event" can affect your dedicated server joining too!