I wonder if a higher overall mass or more aggressive gravity would improve time on track, easy to launch right now :). Maybe add a collider plane a ways below the car that when contacted will reset vehicle to last valid location for you.
Hey! Yeah, the vehicle physics need a lot of improvement, wheel collisions are very jank. Also didn't have the time to tweak the collisions for the vehicle, so it's a small box that doesn't entirely cover the car.
