Re: What causes some trailers to fishtail?

Newton's law that "every action has an exact and opposite reaction" is 
what is causing the trailers you observe to swerve. Why some swerve and 
others not depends upon a number of factors, first and foremost the 
dirver's training and ability. Secondly the condition of his equipment and 
tires, on both the pulling and pulled. Are the tires alligned? Are they 
balanced properly, How is the axle system on the trailer? Are the free 
axles straight? Any number of things could cause this fash-tailing, but 
first and foremost in my mind would be driver experience or lack thereof.
Hope this helps in some small way.

Donald E Duggan