The blazer came with either 15 or 16 inch wheels that year and the largest tire that was installed from the factory was a 265/75/16. Which is about 10 inches wide and 31 inches tall. The only true way to determine if they will fit is to mount them and try. But I have had to cut some of the front bumper and plastic lip on a lot of these trucks. Backspacing on the stock wheel might be an issue as well
Those tires should fit.
31x10.5 is STOCK on an '04 Blazer ZR2.
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