What is the biggest tire size that will fit a stock 1997 S10 ZR2 truck with factory wheels?

Honey, the biggest tire size that will fit a stock 1997 S10 ZR2 truck with factory wheels is 31 inches. Anything larger than that, and you'll be risking some serious rubbing issues. So, unless you want your truck to sound like a bad date, stick with 31 inches and call it a day.