if you want to have as much of the car in the smaller image as you can, crop the image first. its easy, use the crop tool on the toolbar, or press "c" - you'll see which tool it is. then just drag a box around the car, cutout the excess crap. you can adjust the box size after you've drawn the box.. when you're satisfied, press enter, and the picture is cropped.

then do the image resizing. if you want the image to maintain its proportions, make sure the "Constrain Proportions" box is checked in the image resize dialog box