Trailer Sway and Friction
We had our usual avalanche of hitch orders the week after Memorial Day. It happens every year when first time trailer owners find out the hard way that trailer sway isn’t just a figment of our marketing imagination, it’s the law.
What you need to understand when having a discussion on trailer sway and towing in general is that no amount of driving savvy will overcome the laws of physics. If you attach a 28 foot box to an 18 foot truck and attach it to 2 inch ball, you’re asking for trouble. The force hitting the side of your trailer can be anywhere from a 200 lbs. to 1000 lbs., depending on trailer size and wind speed. As bad as that sounds, it gets even worse. That’s because your trailer isn’t a stationary building. It’s mobile and it’s anchored at a fixed point.
If you take that 200 lbs. of force and multiply by the length from your trailer ball to the center of your trailer–let’s say about 15 feet–you have 3000 ft.-lbs. of torque, or leverage.
Coefficient of Friction is your friend (sometimes)
Right about now my engineering colleagues are screaming about the tires and terms like “coefficient of friction.” Yes, yes…the tires to provide some reactionary force opposing the massive force hitting the side of your trailer. Rubber on asphalt has a fairly high coefficient of friction. It’s why you stay on the road. It’s also why you get less fuel efficiency than a train (steel on steel has a very low coefficient of friction).
I’m tempted to bore you now with lots of formulas and calculations, but that may get me arrested for unnecessary abuse to my readers. I had to tolerate it in order to get the sheepskin, but you have no need to suffer my fate.
Trailer Sway Happens when Friction Doesn’t
When Friction is low, the risk of trailer sway is high.
I think you get the point, though. The friction between the tires and the road “grabs” and holds your trailer on the road. That’s the coefficient of friction. However, this coefficient varies between a trailer at rest and a trailer in motion, between dry roads and wet. In fact, it is constantly changing as you drive. Ever been behind a trailer where the wheel almost get airborne on a bumpy highway? Not much friction there. If a semi-truck passes at the moment those wheels are at a low point of friction, disaster happens. You’re in the perfect storm of trailer sway conditions.
That’s where the Hensley Hitch comes in. If the trailer comes into that “perfect storm” of trailer sway conditions, it simply doesn’t matter. Because the Hensley Hitch does not allow the trailer to pivot due to forces applied to the trailer, even if the trailer’s wheels completely leave the road, no amount of wind will make the trailer sway. It is simply impossible.
