yes, you ARE able to make gta cars... thing is, i did it EXACTLY the way fastlane told you to, take the time, and tweak...
you think GTA was made in a week?? you really gotta sit down in front of it and take the time, this is how i got around doing good cars in A6PE.
Now also, you should see where you hinge the wheels, this can cause problems as well, if you make your wheels too low on your car, it feels like it bounces everywhere, make your wheels too low poly and it hops up and down when moving.
all sort of small tricks that you gotta look out for, now... what i did, take a look in the manual, and looked up every physics keyword. then read what they do, and think how any other car game would have that
like for instance, wheel bounciness, it is 100% rubber, but if you fill that in, it wont bounce at all, now you think further, a wheel has air, hey, cool that's about 40% of air, that leaves us 60% of rubber... hhmm... air bounces, rubber doesnt *filled in a car wheel
*, because the rubber overrules in quantity here, make a small value for bounciness.. here comes the tweaking... you allready know you dont need a high value, so you start at maybe 15, then look if it bounces realistic enough for your feeling, keep adding/substracting numbers untill it feels good.
this was a small example on how you should think about these kinda things.
i know it takes up a lot of time, but in the end.. it's worth it
hope it was of some kinda use.
regards and good luck,