first off: thanks for you replies. The problem currently is not so much as to get the vehicle to drift (it already does if I want it to), but to get the new velocity vector into the system without touching the velocity vector (instead using forces or impulses). But your approach in "faking", citrys, is a lot cleaner than my current one (I basically let the rotation "lag" behind in some cases). I've read through the paper on car physics and implemented some (not all) of it: the tangential function, for example - which I in my case replaced by a sigmoid function. It gives the car a nice feeling of oversteering at a special point (e.g. when a combination of too high speed and slippery underground combines - there it is).
But as I said - I solved that. Now the real problem is changing the rotation and speed of the vehicle without touching the velocity vector. So I thought of the forces which would need to be applied.
I've made an illustration (yeah, I'm kind of an artist): http://bildrian.de/n/b/3cad8c19c6a250ae.png
Top is accelerating, Bottom is decelerating/reverse. Left to right is steer left, drive forward, steer right. So the arrows I drew in there should be the points where the (impulse?) force should apply to the body (leaving the driting thing completely out here for now). The problem is that I obviosly don't have a clue when to use impulses and when to use forces. I also totally don't get whe the offset vector "r" should be in world coordinates - sure the doc doesn't mean body coordinates here? When I set "r" to zero I get the results I'd expect when setting the *body* coordinates to zero.
Anyways, I just can't get it done. When I use forces the vehicle continues to accelerate infinitely or rotating like crazy. Resetting the forces every time step every time can't be the solution, or can it? When I use impulses the vehicle first turns but then bounces back like a spring.
The forces thing is so frustrating. I can't even get a freaking car simulated. Currently I'd just like to print out all the code I wrote and make some huge bonfire. God, guess that is currently because I'm really suffering from cerebral shortcircuiting after 8 hours of college classes, maybe I should just go to bed and have a look at it sometime else.
I really appreciate all the help you're giving me here. Please be patient with me, I'd be so proud if I got it running and you could see those little vehicles (yeah the sprites are ugly, but, hey) driving around :-) It's all in my head, I can clearly see it ;-)