I don't work with cars so can't offer specific advice. What I can see is a WorldERP of 1.0. That's how much bounce is aplied when an ODE object passes through a surface, to restore it t the right place. This typically ranged from 0.1 to 0.8 (according to the manual). Hige values mean more bounce.
If your applying a world ERP of 1.0, that'll cause a bit of bouncing in my experience (especially without a low CFM). I've has a sphere roll down a plank onto the floor and bounce of it unrealistically as a result of setting these values wrong. I suggest you try a word ERP of 0.2 or 0.1 and reduce the gravity back to where it was, to see what effect that has.
Even if nothing, changing the gravity to get your objects to work properly is asking for trouble. It means more downward force, faster falling objects, more penetrations and more errors.
If your applying a world ERP of 1.0, that'll cause a bit of bouncing in my experience (especially without a low CFM). I've has a sphere roll down a plank onto the floor and bounce of it unrealistically as a result of setting these values wrong. I suggest you try a word ERP of 0.2 or 0.1 and reduce the gravity back to where it was, to see what effect that has.
Even if nothing, changing the gravity to get your objects to work properly is asking for trouble. It means more downward force, faster falling objects, more penetrations and more errors.