Ah, that explains it entirely then
I don't know if you mention the wheels are matte in your descriptions (If you do, then I've overlooked and I apologise) But maybe mention in future as my immediate impression was that the wheels weren't rendered correctly. Now I look back, the wheels look good now I know they're matte.
I saw your Z, and I thought the wheels were actually 'shopped which speaks volumes about what I said above. The tyres still have the 3D look about them though which I noticed on the Z, but I think they could use some more shadow both further inside the tyre, and where they're hitting the floor. The texture itself looks great.
Again, nice work!