Hi Erik,

From my experience I think you are right on! Trailer tires are usually
a bias belted tire which have a much stiffer side wall. A previous
thread cited great improvement by using a 17 inch wheel with low
profile (aspect ratio) tires. One way to improve the situation you
describe is to signifigantly increase your rear tire pressure (36-38
psi) and also the pressure of the trailer tires (40 psi). To get a
better feel for the situation, try pushing the rear of your vehicle
sideways with a pulsing effort. When your frequency is close to the
natural frequency in that mode you will be surprised at how little
effort it takes to sustain the motion. If you watch the sidewall while
doing this you will notice that the majority, if not all, of the motion
is in the side wall. The increased pressures will increase the natural
frequency and thereby allow a higher speed before the swaying becomes
objectionable.

Lorry charchian