Speedometer and Bigger Tires

I have a 1999 GMC Z71 sportside. Whats the biggest tire I can fit on the stock rims without any rubbing? Will this affect my speedo and if so how can I recallibrate it?

Thanks in advance.

I was told that I could possibly squeeze a 33 inch tire on my 97 sierra, and as for the speedo, yes it will, it will also make it harder for the truck to stop, the way to fix that is a caliper upgrade, and as for the speedo, they sell tuners for around $250 - $300 online that can recalibrate your truck for more horsepower and bigger tires.

I have a 1997 z71 stepside, I fit 285/75/16 BFG All Terrains (32.9") and have no rub at all. I was told that we might have to crank the torsion bars, but there was no need for that.

Also, I thought with the bigger tires that my speedo would be off. I checked it with a GPS and it was right on.

Same here, checked with GPS and mine is right on with the bigger tires. :-)