@miser master: you press on upload and choose the file with your phunlet. the you select "group" and choose phunlet.
it looks like the back of the car is too small relative to the rest of the car....
but realy good work, i thought even it was texture when i saw the picture!
Because you need a realistic size if you want the physics work as normal. e.g. if you have something that is ten times as big as the original objekt the gravity will seem to be ten times weaker on this objekt.