Originally Posted by Seann45
Since I did not see anyone touch on this... Sway is caused by too little weight on the tongue of the trailer... you should have 10-15% of the trailer weight on the tongue... I am on the plus side of 15% and no problems with sway... but then I also have a Hensley Arrow... but got that for my last trailer and eventually moved it over to the J.
Too little tongue weight is one cause. Not enough weight on the front of the tow vehicle is another, possibly the biggest, reason. The main purpose of weight distribution hitches is to transfer weight from behind the tow vehicle's axle to the front wheels.
When one hitches a trailer to a point behind the tow vehicles rear axle, the entire tow vehicle behaves like a lever with the rear axle becoming the fulcrum of the lever. The trailer tongue presses down on the hitch, causing the front end to be levered up. Without enough weight on the front tires, they do not have enough traction to keep the tow vehicle pointed where it is supposed to go, creating a tail wagging the dog situation).
Fifth wheel trailers and semis avoid this problem by cantilevering the hitchpoint of the trailer over the back of the tow vehicle so the weight is applied a little ways in front of the rear axle (or the virtual centerpoint of dual rear axles). This ensures enough of the weight of the "tongue" is transferred to the front wheels to ensure they can have enough weight to keep the two connected vehicles pointed in the proper direction.
Something different is needed for conventional trailers such as travel trailers. Past solutions have included contraptions such as tow dollys that took most of the tongue weight off the tow vehicle (those were heavy, expensive, and didn't work all that well), hitches that used spring bars to transfer weight to the rear axle (also heavy, expensive, were murder on the axles--most tow vehicle warranties are now voided by them--and usually required relocating the spare tire), and hitches mounted under the tow vehicle (one is still being sold) that moved the pivot point of the tongue to the tow vehicle frame at a point closer to the rear axle (though they do work very well, they limit turning radius, are very expensive and heavy, and require relocating the spare tire).
The most successful and practical solution for conventional trailers is something that will transfer some of the tongue weight forward to the front wheels. This is most commonly done with a weight distribution hitch. It works by making the hitch work as though the connection between the trailer and tow vehicle is a rigid connection so the lever action on the tow vehicle can't occur. A rigid connection would work great as long as the combination was on level ground and no turns were needed. Unfortunately, at some point the combination needs to turn and there will be grade changes that will require the connection to pivot up and down and sideways. The solution, the weight distribution hitch, uses spring bars mounted to the trailer to allow up and down pivoting at the hitch while limiting some of that pivoting to reduce the amount of leverage occurring.
To reduce the amount of side to side pivoting that can allow sway to occurr, some hitches use friction devices. Usually separate devices, they stiffen the connection between the trailer and and tow vehicle to reduce the trailer's ability to behave like the tail end of a happy tuna. Others will incorportate the friction in the spring bars or add a cam action that increases spring tension as the hitch pivots from side to side, creating a resistance to turning. Both seem to work well and also allow backing without having to disconnect anything.
One hitch that combines several principles for reducing sway without the disadvantages of the others is the Hensley-Arrow. The manufacturer claims it moves the virtual hitch pivot point forward but there has been considerable debate on the validity of that claim. What isn't debatable is the darned thing actually does work very well and is less work to hitch up since there are fewer heavy components to lug around. The three main disadvantages are expense, a more difficult initial installation (both of which are only a first time problem), and weight (which may outweight the advantages).