Towbar grounding

Millersmilers

I have a problem in that my detachable towbar hits the ground when going over speed bumps and up or down ramps such as on ferries. Every time I attach the caravan I have to remove the jockey wheel. I am aware of the regulations with the actual height of
the tow-ball but can't find anything in respect of ground clearance. Does anybody know if the relevant standards cover this and if so what the figure is?