Trailer Instability

Core principles to maintaining control & how to counter the 9 causes of trailer sway:


Safety is a critical consideration of any driver using the roads and especially important when pulling a trailer.  A trailer has its own set of  challenges that have to be considered and keeping it stable is one of the most demanding.


This is a side to side motion that can cause a driver to lose control of the vehicle. The amount of tongue weight (the downward force that the tongue of the­ trailer applies to the hitch of the tow vehicle) can be adjusted to control this problem, and most pros agree that a suitable tongue weight for any trailer is between 9 and 15 percent of the Gross Trailer Weight (GTW). To achieve this, weight has to be distributed properly to the rear of the trailer.

A heavier trailer weight is always going to have a worse effect on stability when traveling downhill or when brakes have to be quickly applied.

Weight distribution bars can be used to reduce sway by transferring the hitch weight backwards and allowing the towing vehicle’s front tires to have better, firmer contact with the road surface for steering.

An increased number of trailer axles (wheels on the road) will also help with stability and reducing sway.


Other forms of destabilization can also occur known as porpoising. This can come in the form of a front to rear bounce caused by the towing vehicle first hitting a bump then the trailer hitting the bump. They both bounce independently of each other and create an oscillating motion. Also, a front to back motion can also happen when the brakes are applied, making it feel like you’re pulling a sloshing tub of water.

Many factors can contribute to the cause of these instabilities so it’s beyond the scope of this guide to cover every possibility. The best advice would be to take the rig to a professional for an evaluation or if that’s not feasible, get on the forums for suggestions. Remember, slow down and don’t panic…

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