There are few things more frightening while towing your recreational vehicle than trailer sway. A sudden gust, a passing semi-truck or a quick steering correction can start your trailer swaying or fishtailing. The loss of control can mean tipping your valuable recreational vehicle or causing a serious accident.
Even the most experienced drivers have lost control of their towed trailers with disastrous results. A brief encounter with sway on the highway can quickly put a damper on your vacation and make you think about putting the camper back in the garage or up for sale. These tips can help you understand what causes trailer sway, as well as help keep your RV upright.
What causes trailer sway?
Below are common causes of trailer sway when towing a trailer.
Hitch adjustments
Any trailer towed with a hitch set behind the rear axle of the tow vehicle can sway or fishtail while driving. The hitch acts as a pivot point in-between the centers of gravity of the two vehicles. Any trailer sway or side-to-side force will turn the vehicle and create an unexpected steering force.
If that sideways force is strong enough it can be more powerful than the road-tire friction for the drive wheels on the vehicle. This can cause the tipping over or separation of the trailer and maybe even the truck or car too.
Wind and drafts
Trailer sway can be a result of crosswinds, drafts from passing semi-trucks or descending hills using incorrect braking technique, according to Mark Polk in his RV Tech Tips series on RVTravel.com.
The front of trailers are aerodynamic to improve towing gas mileage, but the sides aren’t. A 35-mph crosswind could put as much as 3,440 pounds of force pushing on the side of a large trailer, according to a study on commercial vehicle towing accidents by Knott Laboratory in 2009.
Weight distribution and balance
Loading too much gear on one side of your camper can also cause an unbalance, making them swing more dramatically once a sway starts, like a pendulum around its center of gravity. This can also make your RV more likely to suffer a blowout, or additional braking and steering problems.
Balancing weight to the forward and rear is also vital for controlled driving. Between 12-15% of the trailer’s weight should be resting on the tow vehicle’s hitch, according to Bill Estes, writing in Trailer Life Magazine. Any less weight forward may pull up on the tow vehicle’s rear wheels just when you need more traction and control. However, drivers have to be careful not to exceed the tow rating of the hitch or vehicle itself.
How to prevent trailer sway
The best way to correct trailer sway is to avoid it in the first place. Follow these general tips when towing from the National Highway Traffic Safety Administration (NHTSA)[1]:
- Use the manufacturer recommended gear when towing.
- Slow down. Moderate driving speeds produce less strain on your vehicle and trailer reducing the chance for trailer sway.
- Don’t make any sudden steering maneuvers.
- Check the tire pressure. Under-inflated tires reduce the load-carrying capacity of your vehicle or trailer which can cause sway.
Several hitch designs claim to reduce sway through friction control or weight distribution. Friction based hitches create a rigid connection, limiting sway but still allowing the trailer to turn. Weight distribution hitches use special parts to distribute the tongue weight of the trailer among all of the axles, both tow vehicle and trailer[2].
How to control trailer sway
If your trailer starts to sway on the road, the NHTSA recommends activating the manual brake control override by hand. Applying the tow vehicle brakes will generally make the sway worse.
- Lift your foot from the accelerator but don’t step on the brake pedal unless you’re in danger of hitting something.
- Keep a firm grip on the steering wheel to control sway caused by large passing vehicles.
- Find a safe place to park and check for proper weight balance and hitch adjustment.
Hooking up and towing a trailer or camper might not seem difficult, but the hitching process can be tough. Learn how to tow a trailer or a camper.
[1] https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/CG-5PC/CG-CVC/CVC3/training/dmgcontrol/G-PCV-3_CFVS_DC_Trainer_NHTSA_TowingSafety.pdf
