That's expected, unfortunately.... If you know how to fix these self-shadowing artifacts at a reasonable framerate, let me know. I do have one idea, but I'm not sure it'd work for all cars because it would require them to all be closed geometry.
Finite shadow map size and finite z-buffer resolution. There are ways to deal with it, but some of them require performance hits...
HOWEVER! I found a bug in the way the diffuse lighting was calculated that caused it to not line up with the shadow lighting, so things should look much better now in source R1941 and shaders R153.
speaking of shadows, they might look better in 24bpp (according to the comment in game.cpp added on release 1940) but on my 16bpp display vdrifit doesn't work any more, instead i get:
changing SDL_GL_DEPTH_SIZE back to 16bpp gets vdrift working again on my laptop. i really think we should query the display capabilities before we set things like this. i like nice shadows but i can live without them on my laptop if it means instead being able to run the program.
Also, Joe has modified the shadows so that it's possible to see soft shadows. He left it commented out in the last SVN upgrade and it makes the shadow jaggies a little better. It doesn't quite fix it, but it masks the problem somewhat.
Joe why did you leave it commented out - performance issues? Still working on it? Should we include that in the next release?