To go back to the original question and the salesman’s response, whilst I’m not saying what is right and wrong with regards to towing ratios, (that’s for individuals to decide), I would take issue with his comment about the Practical Caravan tow car reviews.
For the purposes of the testing, David Motton tries to limit the ratio to 85% as per both major Clubs’ recommendations. There’s nothing more to say on that.
As the caravans are borrowed for the testing, it would be totally impractical to either load or ballast them (as we do for the Tow Car Awards, which requires securing framework and boxes fitting to the caravans, and then careful ballasting with water containers to get as exact figures as possible), so David selects a caravan with a MIRO around that 85% mark, so that he is testing at around 85%. It has nothing to do with potential payloads as the salesman suggests, it’s purely as stated above. We know that caravans usually ride and tow better with some weight in them, but as stated, practicalities prevent this.
Each and every car is different. I can say that from experience gained at the Tow Car Awards (where we have experimented with different ratios - between 85% and 100%), there are some popular cars that I wouldn’t personally chose to tow a wheelie bin with, let alone a caravan, whereas others are incredibly secure whatever weight their towing or what the weather’s throwing at us.