If you want a good simulation, you should handle the different parts of a car as a rigid body, with their own motion, rotation equations (2nd Newtom law).
You have to apply the forces and torques to them. Perfect physics is too hard and time-expensive, so have to cheat somewhere, which simplifies the model, but doesn't influence much the result.
So the air resistance mainly effects the body opposite the velocity vector of the car, provided their is no wind
I don't know very much about aerodynamics. If it is so important, then look for some formulas with google. With a F1 game is really important. But with lower speed it become less important.
You also will have 4 wheel rigid bodies, which are attached to the body through a spring-damper with some constraints. Constraints are difficult to implement perfectly, so you can probably make some simplification in this area, using a simple suspension model, not double wishbone
The wheels get torque from the engine through the drivetrain. They also get torque form the road as a reaction torque when braking or accelerating, provided there is a contact.
The tyre model is very important, especially you turn or skid with your car. This is much more important than the engine. This can make the simulation realistic the most.
A tyre model usually has constants calculated from the tyre shape, radius etc. Beside that it uses variables as input data, like rotation rate, global velocity of the wheel, wheel's move direction in the wheels local coordinate system, camber angle, holding force. From these the well-known slip ratio and slip angle can be calculated.
The output of the tyre model is the longitudinal force, the lateral force and a moment for force feedback for example.
The widely used Pacejka tyre model has magic constants, which are calculated by measurments, so it's quite difficult to create a good constant set, because they are far from physics. A tyre model based on physics with physical constants is better (I mean easier to use) in my opinion.
So you should describe exactly what you want to do with your car. Is the car in the focus and is controlled by the user? Or is it just a background object. Will it be a car simulator? Etc.
After that I can help more: resources, equations.
[edited by - szinkopa on March 26, 2004 4:11:47 PM]