And the wider the whitewall, the more you'd paid for the car, lol!

Another popular feature of muscle cars of the era were the "red line" tires offered as a factory option on many of the high-performance GM and Mopar (Chrysler) models.  BTW, putting wider rear tires on a car wasn't just for aesthetics, it was to reduce a condition known as understeer oversteer.  A lot of my fellow hot rodders and "shade-tree mechanics" would use the technique as a cheap way to improve the car's handling going into the corners.

Regards,
Scott Perry