and moving them to an external swingaway style Spare Wheel Carrier gives either more space internally (where the wheel was inside the vehicle) or improved under body room for greater off road clearance or to allow fitment of an extra (auxiliary) fuel tank.
Swingaway Wheel Carriers have a quick release catch and most are adjustable for width of rim / tyre.
Some 4WDs require the fitment of a replacement rear bar to give sufficient strength to carry the wheel properly. Some other vehicles (Jeep etc) have a unit that is part of the tow hitch.
Enquire at your nearest 4WD WORLD outlet for the product to suit your particular four wheel drive.