Hi david, little do you know you have potentially unleashed a debate about the 85% rule/guideline/advice/myth. See recent threads on this topic. Before anyone else piles in, I, who knows nothing, will say that the car to van weight ratio is only one factor in towing stability. Correct loading, noseweight, tyre pressures and driving style all contribute to whether a unit "behaves" on the road. Pay attention to all these things and you should be OK.
mel