I agree on the flash.
Couple of tips. Set your Fstop to apptox 7-9. Expose a little longer.
This will give you enough time for manual flash.
Go to a used store, and pick up an old $20 flash that can do multi-mode. While exposing, walk around the car, and flash the wheels and headlights, exposing the discs and giving you a little more shine.
Try to get some more space around the car. Parking spots are fine. (Natural habitat for a hard parker) But keep atleast a couple of empty spots behind the car to give you depth of field.