Trailer Tongue Weight and Sway
For 17 years I towed my 6,500 lbs. S2 7.9 Meter (25''11",over 8'' beam)
I towed with a car, jeep and mini van. With each vehicle I had to adjust the tongue weight. Too much weight on the tongue takes too much weight off the front end steering.
VERY DANGEROUS. Every time your encounter turbulence, the front end of your tow vehicle sways, and you can''t control it. It is a little like the tail wagging the dog, only a little more violent since you have less weight in the front end thus on the road. I would suspect the smaller tires to also add to the problem.
An equalizer hitch as mentioned will help. The hitch is made to take the weight off the tongue and level the car, thus giving you much more control. The car and the boat sway together and are level. But you still have to have the boat and the car completely level. My hitch had about seven different positions to set the ball to accomplish leveling the two vehicles.
The smaller tires may also add to the sway problem. If the side walls are weaker than your other van (smaller usually means weaker) when you sway, they give and don''t hold you firmly to the road.
I am sure once to balance both rigs you won''t feel the sway and you will feel the control.