Check it out TOtally Free.
http://racer.nl/FEATURES
* It's totally free! (for non-commercial use)
* Available for multiple platforms; Windows 2000/XP (95/98/ME may work but have some trouble with fonts), Linux and Mac OS X.
* 6 DOF models used (the car can move around freely)
* Uses motion formulae from actual engineering documents from SAE for example.
* Total flexibility; almost everything is customizable through ASCII files.
* Commercial-quality rendering engine (with smoke, skidmarks, sparks, sun, flares, vertex-color lit tracks).
* Support for Matrox' Surround Gaming. See the corresponding page on Matrox' site.
* Lots of addon cars and tracks available on the web.
* Easy integration of your own cars and tracks that you create in ZModeler, 3D Studio Max(tm), Maya etc.
* At least 15 degrees of freedom for a regular car (6 DOF for the car body, 1 for each wheel's vertical motion and 1 for each wheel spinning, and 1 for the engine, several more for the driveline). Depending actually on how many wheels you put on the car.
* Real-time internal clock; no physical dependency on framerate. Controller updates are also done independently of the framerate.
* Not limited to 4 wheels; anything from 2 to 8 wheel vehicles are currently supported (but mostly untested, and some problems with hardcoded differentials for example may exist (v0.5.0)).
* Not much constraints on the track data; surface info is taken from polygon data (VRML tracks), and splines are used to smooth out the track surface (polygons are too harsh for driving on just like that).
* Tools to modify the cars & tracks are freely available on this site (though external utilities are recommended for best results).
* Some used algorithms are explained on this site. Also, references are available. If you are programming a carsim, you might find something useful here.
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