Here are some of the most common causes of trailer sway. They are in order as they came to mind, not as which is most common or not. Some are pretty much self explanatory, some would require you to do some research.
1. Weight distribution hitch (WDH) issues. (a) You're not using a WDH. (b) WDH is under sized for your tongue weight. (c) WDH is not set up correctly. When you hang your tongue weight on rear of the tow vehicle, the vehicle acts like a see-saw, adding weight to the rear axle, taking weight off the front axle, and it creates a pivot point at the hitch ball. The primary purpose of WDH is to (using leveraging) restore that lost weight from your front axle. If you are towing with too much weight off your front axle, even subconscious hand movement (on steering wheel) can cause trailer sway. The pivot point is magnified. The more lost weight the more issues with handling and control. Secondary purpose of WDH is to aide in leveling of truck / trailer combination, getting headlights back down where they belong, and reducing the effect on the pivot point. Note: Air bags, Timbren SES, and helper springs can also be used in leveling, BUT, none of them have the leveraging that restores lost weight on your front axle.
2. Overloading. There is a tire / loading sticker on your drivers door post. It has a number for "max occupant / cargo weight capacity" (AKA payload). That is your vehicle's capacity to carry everything / everybody that has been added to the vehicle, including trailer tongue weight and WDH. If you add up the weight of any aftermarket accessories, people, pets, cargo (in the truck), WDH, and tongue weight, and they are more than your vehicle's carrying capacity, you are overloaded. It's not uncommon to see an overloading situation, even when the trailer's gross weight is within the truck's tow rating.
3. Tires. (a) Under inflated, uneven pressure, or under rated for the load can cause sidewall flexing. This gets the truck shifting side to side and causes the trailer to sway (remember that pivot point in item one). Passenger (P) rated tires (designed for comfort) are known to have softer sidewalls than light truck (LT) tires, and they are not rated to carry as much weight. (b) trailer tires could also be an issue, if under inflated or under rated.
4. Insufficient trailer tongue weight. Most likely a loading issue. Too much weight behind the axles. Tongue weight should never go below ten percent of loaded trailer weight. Average is 12 - 13 percent and in the case of toy haulers, it is usually higher.
5. Bent rim or axle on the trailer. Rare, but it has happened.
6. Towing trailer nose high. Hitch ball is set too high. Maybe you need to just lower the ball, maybe you need a longer shank.
7. Bad roads and wind.
8. Bow wave from big rigs.
9. In a very rare instance, I think a controller could cause sway symptoms. However, that could only happen with an intermittent short in the controller, which is very unlikely. More rare than a bent axle or rim.
In order to figure out your specific issue, you'll need accurate numbers from truck and trailer, while both are loaded for camping. Scale weights (a) truck and trailer with WDH applied (b) Truck and trailer with weight bars removed (c) Truck with passengers / cargo and without trailer. You'll also need truck payload number and GVWR. The weights add up very fast. First time I went to scales, I was quite surprised to find I was right on the edge of being overloaded, even though the trailer was 2,000 lbs under the truck's max tow rating, and I only had one passenger.
Note: Tongue weight IS NOT A CONSTANT NUMBER. It fluctuates during every trip. Example: My trailer had advertised tongue weight of 880 lbs. During any trip, my actual tongue weight can be anywhere between 975 and 1200 lbs. That means my payload has to be high enough to carry that 1200 lbs, plus WDH (about 100 lbs), plus people, plus pets, plus truck cargo, plus aftermarket accessories (I have at least 200 lbs
18 Nissan Titan XD
12 Flagstaff 831FKBSS
Wife and I
Retired Navy Master Chief (retired since 1995)
