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Towing Definitions

For any discussion of trailer sway to have any meaning we need to start with a list of towing terms and definitions. Most discussions assume that everyone participating has the same understanding of trailer hitch information. I have found that isn't usually the case. In fact, it is more often not the case when discussing such a dynamic topic. There are many variables involved in towing and all of them play a part in trailer sway.

Gross Vehicle Weight Rating (GVWR) – The maximum allowable total weight of a vehicle or trailer that is loaded. It includes the weight of the vehicle or trailer itself plus the passengers, fuel and cargo.

Gross Trailer Weight Rating (GTWR) – The maximum allowable load of a trailer that is loaded. It includes the weight of the trailer itself plus the fluids and cargo. Note: this is sometimes designated as the GVWR of the trailer.

Gross Combined Weight Rating (GCWR) – The maximum total load of a towed combination.

Tongue Weight (TW) – The static downward force exerted on the hitch ball by the trailer coupler.

Tow Rating – The allowable weight limit for a tow vehicle. GCWR minus the GVWR of the tow vehicle.

Tow Angle – The angle created between the tow vehicle and trailer when the trailer moves away from the centerline of the tow combination. A trailer in line with a tow vehicle has zero degrees of tow angle. A tow angle of zero to a maximum of ninety degrees allows the trailer to be towed around a corner.

Pivot Point – The point at which the towed trailer pivots to create a tow angle.

Pivot Point Projection™ - Projection of the trailer's effective pivot point.

Weight Distributing – The act of distributing the load exerted on the hitch ball, the tongue weight, onto the tow vehicle and trailer axles.

Wheelbase – The horizontal distance between the center of the front axle and the center of the rear axle on the tow vehicle.

Friction Control – damping of trailer sway by a friction between two surfaces. The friction control works by "stiffening" the connection between TV and TT. This causes the combined mass and rotational inertia of the TV and TT to resist the forces which are attempting to make the TT "sway".

Overhang – The horizontal distance from the center of the rear axle to the rear end of the tow vehicle.

Oscillating or Oscillation – A movement back and forth between two limits over time.

Amplitude – The displacement of the oscillation wave.

Yaw - Yaw is the side to side movement of the trailer on the hitch ball.

Trailer Sway – Oscillating tow angles. This last definition is important in our discussion here. A tow angle created by turning a corner IS NOT trailer sway. Trailer sway is defined as OSCILLATING TOW ANGLES. That is multiple tow angles over a period of time. The trailer continues to oscillate away from the centerline of the tow combination at various amplitudes. Clear? I hope so because this is where most of the discussions I have witnessed break down.