An important factor in controlling trailer sway is the amount of tongue weight and how that weight is distributed to the axles on the tow vehicle and the trailer. A general rule is trailer tongue weight should be 10% to 15% of the fully loaded trailer weight, for trailer’s weighing over 2,000 pounds. The Toyota Highlander owner’s manual addresses the need for a sway control device on trailers exceeding 2,000 pounds. Where I get confused is the statement in the Highlander owner’s manual that implies, at least to me, a gross trailer weight under 5,000 pounds does not require a weight distributing hitch. Remember what I said a moment ago about too much tongue weight contributing to poor steering, handling and braking. This would be especially true on a front-wheel-drive vehicle. The bottom line is chances are very good that a vehicle rated to tow 5,000 pounds with a 500 pound tongue weight will indeed need a weight distributing hitch to safely tow a trailer approaching 2 ½ tons. The owner of the vehicle in question stated even with a Blue Ox Sway Pro hitch that incorporates weight distribution and sway control the front wheels (drive wheels in this situation) were nearly off the ground and the engine RPMs revved to 7,000 while towing a 4,053 pound trailer. [links]