The classes are something that Nick Pon does. He eyeballs every car on friday and decides what class they should be in -- on Friday.
So, for instance, cheaty Integra would be in the "Good" class
cheaty-ish Ford Escort (your car) would be in the "Bad" class
and the Lincoln with the hamburger on its roof would be in the "Ugly" class
So, if a "Bad" car managed to finish 2nd overall, it would still be the "Bad" class winner. Same goes for the "Ugly" class.
As it happens, cars in the "Good" class tend to win and finish 2nd overall, though we've had a few times where a "Bad" car has finished 2nd overall, and I even feel that an "Ugly" car once finished 2nd overall.
anyhow, the classes are just something to keep nick amused.
"This is the scene where I get shot," Bronson said. "I have these little squibs that explode to make it look like bullets are hitting." "Fascinating," said Bergman. "I never knew how they did that." "You mean," asked Bronson, "you don't use machine guns in your movies?"