when ive done such i used a lab oven for growing heated to 300-350 with a few pounds of air in them for 15 minutes then took out and inflated a 1/4 inch bigger then what i wanted and then placed in can of ice and water for a few minutes and then took out and set for a few minutes and deflated to air i wanted in tires and most of time sized up well,if not repeated process..............
for shrinking i took valve stem out and placed in 300--350 for 15 minutes,took out put stem back in and placed in ice water and then let set for a few minutes...and repeated process till sized to what i wanted..............