I really noticed the difference when I was looking at my vast collection of those fat, dirt track treaded, Goodyear modified tires. You know, the MPC Pinto, Vega, '34, etc... I found about 1/16" difference (width and diameter) from biggest to smallest, and I really don't recall two or three different sizes of those in kits when they first came out decades ago. Although the smallest makes a good left front "pony tire" for these cars. And if you really want to get carried away, ou can put the biggest on the right rear for a little stagger.