Not entirely true. Those are called spring bars and have little to do with anti-sway control and everything to do with transferring tongue weight between the front of the tow vehicle and the trailer axles. Think of it as adding wheel barrow handles to the rear of the tow vehicle. Lifting the handles removes weight from the rear of the vehicle and transfers some of it to the front. In application, the ends of the spring bars attach to the trailer frame so that weight goes to the trailer axles. It is all about geometry. Equalizer setups are available with an additional anti-sway feature built in. These are typically an adjustable friction device that must also pivot as turns are made. One of the hitch manufactures demonstrated this concept in 1965 by removing the rear wheels from a front drive Olds Toronado and towed a travel trailer. Tension is adjusted by varying the length of the chains on the snap up brackets. Lastly, wind off the nose of a semi does not push the trailer off the road. In fact the bow wake off the semi pushes the rear end of the trailer to the right which pivots the tongue of the trailer to the left. At the same time the rear of the tow vehicle tends to push left which pivots the nose of the tow vehicle toward the ditch. When that goes on, the inexperienced driver overreacts and sway sets in and it gets worse with each over-correction. An experienced driver will see the semi coming and be ready for the movement. A simple touch on the manual trailer brake control is all that is required to snap the rig straight should excessive movement occur..
