Man, this is the 1st game I have seen slow down to a crawl on my system,
what is up with it?
P4 3.2ghz
1gig Ram
6800GT Video

Down in the low teen's at the start of a race.
F1C, NR2003, GPL, rFactor(over 50fps)

It's all about the cars. They are very detailed and expensive to
render. During the grid fly-by at the start of the race, GTR ignores
your "maximum visible cars" setting and draws every car on the grid. I
wouldn't worry about framerate during the fly-by.

down either "maximum visible cars" or "car detail" (even going from
"full" down to "high" will have a big impact).

I'm using a 6600GT on a P4 3.0GHz machine, at 1152x864, 4xAA, 8xAF, all
video settings on "full" except for car detail which is set on "high",
"maximum visible cars" set to 12. At the start of the formulation lap I
get about 35 FPS. This is the worst-case-scenario. By the first turn,
the framerate is up to 80 and stays between 80 and 120 for the rest of
the race.