Doesn’t work for me:
Charger @ Gravity -1500 [^]
Charger @ Gravity -2500 [^]
Camaro @ Gravity -2000 [^]
Except for springarm length all values are default.
Edit: I guess this is a relevant topic for the mass issue: Mass doesn’t seem to affect “spring like” constraints
Unfortunately it doesn’t provide much in terms of answers.