I recently had 2 new tires put on my Buick. (dont ask why I have a Buick! lol) I consider myself to have a very good eye. the problem is that the 2 new tires appear smaller in diameter than the older 2. All are 225/60 16. I remember from my Jeep days that the off road tires were sometimes measured with the tread and sometimes without the tread. Is this the case with cars tires as well?