I needed to shrink some treaded tires for a specific track tire rule mandating silly size tires for their karts just yesterday. Needing to shrink them as much as possible (3 inches would be ideal) I did get them to shrink 1" from the smallest size that I could mount them at. Still going to be 2" of rear stagger unless we stretch the left rear and change gearing.
Gotta love these tracks that think they've got the answer to cutting and prepping by spec'ing silly tire sizes made for 500cc winged outlaws.
Heat, cold, pray, repeat.
Heat and pressure are your friends when sizing (just remember that when your tires are sitting in the trailer all week long.)