elchtest mod :)

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as it needs a high update rate, although i didn't understand why exactly

Vdrift is using a steady-state tire friction model(Pacejka).

adhesion = tire_friction(slip) / normal_force
slip = 1 - v / r*w for v < r*w and slip = 1 - r*w / v else
dw / dt = inverse_inertia * torque

To accelerate/decellerate a car you have to apply torque to the wheels. The real world wheel inertia is about 1-2kgm2. Your wheel is going to get an angular velocity delta dw ~ inverse_inertia, torque, dt.

So slip is proportional to dt. And with slip values beyond 0.5 each time you accelerate/decellerate you can actually forget about the whole tire friction simulation. A way to fix this is to increase wheel rotational inertia(vdrift is using 10kgm2) and/or to increase your simulation rate(vdrift runs at 1000Hz).

cylindershape wheel contact calculation

Do you plan to simulate the wheels as a rigid body? If you can afford to run bullet at 600-1000Hz in you simulation I would propose to create the whole vehicle/suspension in blender/maya. Export it as .bullet and load it into your bullet world.

I could adapt wheel forces function to return tire force/wheel torque dependent on normal_force, wheel orientation and wheel angular velocity. You would apply them to your bullet car model. The only other problem is steering. But I think you could solve it easily using constraints.

This was my initial idea for vdrift. But I think we would have problems to simulate >10 "bullet" cars at 600Hz in real time on commodity hardware(still I haven't tried it ).