2008 GMC Envoy Owner's Manual - Page 390

Storing a Flat or Spare Tire and Tools {CAUTION: The underbody-mounted spare tire needs to be stored with the valve stem pointing up. If the spare tire is stored with the valve stem pointing downward, its secondary latch will not work properly and the spare tire could loosen and suddenly fall from your vehicle. If this happened when your vehicle was being driven, the tire might contact a person or another vehicle, causing injury and, of course, damage to itself as well. Be sure the underbody-mounted spare tire is stored with its valve stem pointing up. Notice: An aluminum wheel with a flat tire should always be stored under the vehicle with the hoist. However, storing it that way for an extended period could damage the wheel. To avoid this, always stow the wheel properly with the valve stem pointing up and have the wheel repaired as soon as possible. {CAUTION: Storing a jack, a tire, or other equipment in the passenger compartment of the vehicle could cause injury. In a sudden stop or collision, loose equipment could strike someone. Store all these in the proper place. 5-96