Found this website awhile back Oppo - thought I’d share as some of my fellow Opponauts may get some use out of it! Very handy! :)
Enter your current (or factory, or whathaveyou) tire info plus the info for your new or considered set of tires/rims and you get visual output showing the size/shape difference and data showing stat differences between the two, including the displayed speed difference!
A period Citroën Traction Avant taxi for your time! :)