elchtest mod :)

[joevenzon]

When accelerating, vdrift calculates the new rotational speed, uses that and the old linear velocity to calculate the slip and then uses this to calculate the new linear forces (and speeds). Thus the resulting forces depend on the timestep, although they shouldn't.
Doesn't raising the wheel inertia change the whole car behavior?
There is no way to calculate that in a closed formula?

Maybe I don't quite understand, but isn't what you're describing basically the shortcoming of numerical integration? I'm not aware of any way to analytically integrate the car's physics response, but that would be cool!

Additionally, I think the susppension does not need so high framerates. Just like the chassis does not need as high framerates as the suspension.

I agree, it's really just the tire/wheel sim that needs the smallest delta-time. There are a few racing sim engines that indeed use their highest framerates for the tire/wheel rotation only, and lower framerates for everything else.

what i can already do is check for collision with the world (this is no problem, even with the high update rates, as vdrift runs on something like 1/480s^-1 and bullet uses 1/60 at the moment).
Which means, at the moment the car moves/"rolls" 8 steps in a static bullet world, then the bullet update checks for chassis crashes and sets the bullet world forward.

That's actually similar to how the current system works, in a way. Even though the car's physics are updated at 1000 Hz, collisions with other vehicles are only checked and added as impulses at 100 Hz. Also, the raycast to the actual ground geometry (bezier and triangle mesh) is only run every 100 Hz -- a plane equation from the collision is stored, and then for the other 9 frames we do cheap ray/plane intersection tests.

Just an off topic question: Are there different kinds of suspensions modeled in vdrift?

The suspension is modeled as a fixed instant center (IC) that the wheel rotates around:
http://en.wikipedia.org/wiki/Suspension_...ant_center

This is a generic simplification of a suspension that can approximate various kinds of real suspensions (different suspension types have ICs at different locations). Real suspension systems however will have their IC change somewhat as the suspension goes through its range of motion.

Unfortunately, the suspension model VDrift uses (like with the tire model) isn't conceptually easy to think about and tune with respect to a real vehicle that you're trying to emulate. I was thinking it'd be nice to have a number of real life suspensions (and tires!) defined somewhere so in the .car file someone could just point to one and say "yes, that" or "yes, 70% that, 30% the other" without having to think about the IC points or pacejka coefficients.