EDIT ... ha! typing slow, and ESampson slid his reply in there before me, .... I'm guessing he means that the tread is fuller and makes the sidewall appear more vertical on some tire brands... I kind of get where he is coming from too ... suspension geometry on old cars was way different than modern stuff. Look at old chase scenes and road tests, and it is hysterical how the cars would lay the front tires over at the limits. The biggest reason why the Shelby Drop works as good as it does. Another factor that will change that appearance of the tires, is putting the same tire on different rim widths. It will vary the cross-section measurement (sidewall to sidewall) a bit. A narrow rim will pull it in (squarer), and a wider rim will give a rounder appearance. You can visualize the effect with the tire dismounted, and having a helper pull the tire open to the rim width, while you measure, and it is a great way to get the real actual width in those situations where you are stuffing a car full of tire and worried about clearances.