usually what I do... is use the magnetic laso tool.... and come in from the absolute far right of of image... follow the bottom of the car up around the fenders down under the car again and then out over to the absolute left side... then up ALL the way to the top... then ALL the way over to the side... then down to where you started...

then drag the whole thing down till you have it where you want it... then just crop as needed. tada