Originally Posted by Miss Rita
I think that statement has to be qualified. A travel trailer, or any trailer carrying a heavy load with a high center of gravity probably is more susceptible to side loads, crosswinds, etc. The gunwales of my boat are about 4 1/2 feet off the ground, it's low profile and not going to catch a lot of wind. I'm certain that the center of gravity of my boat and trailer is lower than the Tahoe that's pulling it.
So I agree that some trailers are more susceptible to side sway, but some are not. I'm comfortable that the four passenger tires on my trailer, pumped up to the maximum pressure of 44 psi, are providing good lateral stability. As I mentioned, I wouldn't try this if it was single axle trailer with only two tires.
My point was just that due to the inherent geometry between the tow vehicle and the trailer, there is a natural tendency for a trailer to sway to some degree. That is why tow vehicle length, trailer length, tongue weight, and leveling are so critical. It is for this reason that 5th wheel towing is preferable to hitch towing -- the overall geometry of having the tow point ahead of the rear axle makes for better stability.
Although a trailer may not physically be swaying that is not to say there are not side to side forces, which hopefully the tire-to-ground friction are overcoming at any given time. As you point out, these can be caused by side winds or passing trucks, but also in the absence of side wind -- varying road surfaces, driver steering maneuvers, speed changes, hills, etc. This is what heats up the sidewalls of the trailer tires. Granted, a double axle trailer provides greater stability. A four-wheeled steerable vehicle traveling at the same speed does not have the same lateral forces on the tires. Vehicles also have the advantage of dampened suspension which most trailers do not.
The problem is compounded nowadays I think with longer and heavier boats (necessitating longer trailers) and shorter-wheelbased SUV's (but powered and rated to tow heavier loads.)