Depends which tires you have. Some of Hoosier's treaded tires were designed for winged outlaw cage karts that use 250 & 500cc engines and have a roll-out of 37-38". If that's the case, then no, you will not be able to shrink them that much.
We offer sizes for flat karts that use 34" right side tires that are a MUCH better fit for low horsepower karts. I'm working on a couple sets like this today in the tire shop.
Give us a call if we can help you.