I have just been trying to find the origin of this 5 year rule and it appears that it may have come from the Caravan Club before it rebranded itself to the Caravan and Motorhome Club. They made a recommendation that tyres should be changed ideally at five years and certainly no longer than seven years. They also said that consideration should be given to replacing tyres with inflation pressures above 50psi after three years and no later than five years. But, it is just that, a recommendation, yet some insurance companies have set it in stone as a hard and fast rule.
The point is, this isn't law. Providing the tyres on a caravan or trailer are in overall good condition they could remain in service for up to ten years. However, should a blowout occur causing damage to the caravan or the caravan is involved in a collision and it is fitted with tyres over five years old, the insurance company may not pay out.
Caravan wheels may look similar to car ones, but they are usually specially made for caravan use.
www.caravanclub.co.uk