looks cut out of a coloring book. But that doesnt change the score i was going to give you.
I think the shirt is too novelty, like its from a car convention gift shop. Plus i think its funny you made a black shirt one of the options, since it cuts off the whole tire effect.
I had a hotrod shirt I made simular to this in highschool and it was my favorite, only it was on white. White wasn't an option, so I just used black yellow and gray because they are the same colors in the picture.. my car is actually 5 colors if you'll notice, and that's no good, so by using black, banna and heather in the car colors, those colors can be left out in printing (as if it would ever be printed) and still serve the same effect. I didn't like the black at first either, like you said, it washes out the underside of the car, but after looking at it I decided I liked it. It doesn't really take too much from the photo, in my opinon. :]