@@Eva15690 its just a guess. I wouldn't know where to look. It just explains why it crashed straight away with 0 and struggled and then crashed with 0.00000000000001.
Check for exceptions of variable 'Mass'. Reduce any limitations. (doing this will allow your 200kg car to run properly, while making the 780kg cars feel like 10000kg.
It was glitching out because if you lowered the mass, you should have also lowered the 3 moment of inertia values below, otherwise the game thinks your car is the size of an aircraft carrier.
Mass is a measurement of the amount of matter something contains, while Weight is the measurement of the pull of gravity on an object. You basically had an 800KG car with no mass which means it has no integrity to hold the car together.
With down force I would've actually imagined that, with initially a ton of slipping, you would still stick to the road... it seems like down force is counted stock and the weight the wings apply was flipping the car around? or is it the suspension?