A full size vehicle simulation in ROS Gazebo

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I can't help you with 'real size vehicle simulation' but I wouldn't choose a real size car simulation. It sounds like you don't have alot of ROS experience, so I advise to work with a widle used type of robot (simulation). for example a turtlebot (or if you want to replicate car behaviour more accurate, a 4-wheel robot). Gazebo is to simulate behaviour, it doesn't matter if it's a real size car or not, but please elaborate on your intentions maybe for your usecase it matters.