I have a 2000 GMC ext cab Z71. What is the biggest tire I can run with out any lift and no scrubbing. The wheels are motto metal so they are slightly wider than the stock wheel?  

285/75-16 unless you crank the torsion bars up a little. then you can squeeze on a little more.  

this is wrong. if you crank the torsion bars you can fit 285s and you will still have a very slight rub on hard turns, especially in reverse. also you shouldnt crank the torsionbars. this causes unneccasary torque on your front end. plus with those tires you will need steeper gears. with 285s or 33x11.50 you will need somewhere around 4.10 or 4.56 gears. this will exyend your trans and t case life. you need to put these things into consideration. if you want bigger tires go with some sort of lift kit and steeper gears  

96chevypowell:
this is wrong. if you crank the torsion bars you can fit 285s and you will still have a very slight rub on hard turns, especially in reverse. also you shouldnt crank the torsionbars. this causes unneccasary torque on your front end. plus with those tires you will need steeper gears. with 285s or 33x11.50 you will need somewhere around 4.10 or 4.56 gears. this will exyend your trans and t case life. you need to put these things into consideration. if you want bigger tires go with some sort of lift kit and steeper gears

Good advise. Also cranking Tbars or using keys throws off suspension geometry and also places suspension at or near the limit of its extension and can result in a pitchy/choppy ride (people that make and/or sell keys never bother to tell you that though).  There is no free lunches here.  

Yup, you guys are right, on the good and the bad...  

Hey guys i just wanna let yall know that with no lift you can fit 285's on your sierra. I got ford torsion keys put on mine and i cranked the hell out of em and i am running 315x75x16's  

Hows the ride?