* The sticker on the driver's side doorjamb: This sticker lists the recommended tire size and inflation pressure.
* The owner's manual: If you still have the original owner's manual, it will specify the tire size.
* The tire size molded into the sidewall of your existing tires: This will tell you what size is currently on your truck. However, this might not be the original or recommended size.
Common tire sizes for that era of GMC Sierra Z71 4x4 include LT265/75R16, but other sizes like LT275/70R16 or even LT285/75R16 might have been used depending on the options and the factory's stock. Do not rely on this information; check your door jamb or owner's manual first. Using the wrong tire size can affect your speedometer accuracy, handling, and even damage your drivetrain.