Thanks for the kind comments, again.
DM - You're right. I never noticed it before, but the tires are not all touching even. The back two on the left and the front one on the right are slightly up. The whole model will rock ever so slightly back-left to right-front.
I had to use a flashlight to back light them just now to see. On a slightly irregular surface it is very hard to see, but it's there. I guess the judges didn't notice, or maybe it wasn't enough of a defect to drop it out of the "bronze" category.
Paul