You'll need to check one of the following:
* Your vehicle's owner's manual: This is the most reliable source.
* The sticker on your driver's side doorjamb: This often lists tire size and other specifications, sometimes including the bolt pattern.
* The wheel itself: The bolt pattern is often cast into the wheel.
* A reliable online parts database: Enter your vehicle's year, make, model, and trim level to find the correct specifications. Use reputable sites for accurate information.
Without knowing the specific configuration of your 1985 GMC Sierra Classic, I cannot provide the bolt pattern.
