Lowering a car tutorial...
Step 1 - pick a car
step 2 open in photoshop & copy 2 layers above the locked background
Step 3 use the Quick Select tool

to select and delete unwanted bottom part of image to delete wheels & tires & etc. out of the selection
Step 4 turn on the eyeball of the full layer also

Step 5 select move tool to lower image down

Step 6 Recrop the image using the Crop tool

Step 7 Save as a PSD & JPG
Here's another example: ......but in reality these tires really wouldn't fit under the fenders!
recrop after you lower it
more examples:
*notice the front & rear tires are widened also...