Royal Enfield motorcycles typically do not have rear bumpers, as they are designed in a more traditional style without extensive bodywork. However, if you are referring to the rear mudguard or fender, it is unlikely that the weight of a pillion rider alone would cause it to touch the wheels.
Royal Enfield bikes are built to accommodate a pillion rider, and their rear suspension systems are designed to handle the weight of both the rider and the passenger. As long as the motorcycle is properly maintained and not overloaded beyond its specified weight capacity, there should be no issues with the rear mudguard touching the wheels due to the weight of the pillion rider alone.
It's worth noting that if the motorcycle is carrying an excessive load or if the suspension is not properly adjusted or maintained, it could potentially affect the bike's handling and stability. It's always important to follow the manufacturer's guidelines and recommendations regarding weight limits and maintenance to ensure safe and optimal performance.