To get a good base for all the cars then go to
http://gplea.racesimcentral.com/ and download the Solitude track, and load the default setup for each car and track.
I think i have mentioned this before, but it is the best for all the cars, as the spring rates have been worked out nearly right, all you do then is lower it slightly, 2.75 at most circuits, play with everything else to what suits you. Also put an 85/45 diff on with 6 clutches.