The life of a tyre depends on many variables, and although a motorhome tyre may cover far less mileage than a car tyre, being sat for long periods can cause the tyre to go out of shape, particularly in respect of the heavier kerbweight of a typical motorhome. In addition, a motorhome stored outside will still experience the extremes of hot and cold as well as exposure to UV, all of which will cause the tyre to degrade. A visual inspection for any cracking may provide some clues as to the state of the tyre, but ultimately there is no single answer that can account for all the variables. We would suggest replacing the tyres when economically viable, and before they reach ten years old under any circumstances.