Thanks for all you comments, I should have pointed out the caravan is a Eddlis Crusader Storm 2007 (twin axle so is very stable when towed) with a ULW of 1625KG this is under the ULW of the E220 so would be legal but a little outside the general 85% rule advised by the Caravan Club. Obviously when loading you take account of this and stick the heavy stuff in the car.
The power output of the E220 CDI engine is around 204 BHP and around 455NM with the Power Box fitted.
The car feels like it would do the job with ease but I was hoping some members would have used this model for towing and could have given me some feedback that would help me to decide whether to put a ball on this or carry on using the 4x4.
This is what I "think" is correct...
What is the maximum caravan laden weight on the caravans chassis plate? What is the Mercs max train weight and kerb weight? Deduct one from the other and you derive tha maximum towable weight. The maximum towable mass might also be listed seperately in your handbook. The plated figures though are the ones that count.
If you exceed any of the maximums then you are not legal. The ULW of your caravan is only a guide as to how much payload your caravan might be able to carry. MLW-ULW = payload. It is the MLW that is more important. If unsure then you will need to put your caravan on a weighbridge when everything is packed.
The Mercs maximum plated train weight must be heavier than the caravans plated MLW+the Mercs plated unladen kerb weight. The Mercs maximum train weight must never be exceeded.
In addition I would also pay close attention to the noseweight and aim to run it at the maximum. If you are also close to your limit then you should also consider a hitch stabiliser to reduce snaking, or just fit one anyway.
Lastly, tyre pressures are extremely important. Under-inflated tyres cause premature tyre failure and instability. Check your tyre pressures are inaccordance with the manufacturers recommendations, and also that the correct type of tyres are fitted. Some people fit cheaper un-reinforced tyres to save money, but these tyres can not take the load or required pressures needed.
Tyre pressures are often much higher than you would expect on a car. My horser trailer runs at 93psi, and from memory the last caravan I had was running at around 55psi, but they will all vary.
DISCLAIMER:
I am not a legal expert nor qualified to give any advice on towing and any advice given is not to be relied on under any circumstances. If you want any towing or legal advice then you should ask a competant expert in those fields.