Making sure your tow bar is level is one of the key steps toward successful “” and safe “” towing.
Tow Bar Forces And Alignment “” PDF version of this article includes an Effective Distance Driving Chart
By Bill Hendrix, F761S
April 2011
An overwhelming majority of FMCA members tow a vehicle behind their motorhomes. Some use trailers and others use dollies, but most towed vehicles are pulled with four wheels on the ground.
With the increased popularity of flat towing, the making and marketing of a variety of towing accessories has become a major part of the RV industry.
During the early years of motorhoming, folks bought a ball-type hitch coupler and took it and their towed car to the local welding shop. A rigid A-frame tow bar was fashioned and often bolted to the car’s front bumper. The car’s stick shift was put in “neutral” for towing. I recall people removing the driveshaft in order to tow the automatic-transmission family car to their winter destination. Hooking and unhooking the towed vehicle was sometimes very difficult, often taking two people to hook up and a pry bar to unhook.
From opportunity or necessity comes invention. Today a wide variety of folding tow bars, custom base plates, towed car brake actuators, and transmission devices are available to make flat towing safer and more convenient. Despite all of these improvements, we still hear horror stories of towing equipment failure.
All towing equipment is subject to a testing and rating system established by the Trailer Hitch Manufacturers Association that is commonly referred to as the V-5 Standard. Roughly stated, this rating system requires critical components of hitches to withstand stress tests at 300 percent of the desired rating. For instance, if you want to rate a hitch ball at 5,000 pounds towing capacity, it must be able to withstand a 15,000-pound test. Seeing the rating and/or the standard displayed on the equipment provides the buyer a degree of comfort, because it indicates that a particular piece was tested and has complied. However, we cannot rely solely upon the V-5 Standard; I know of two instances in which the equipment was approved and the vehicles were within the weight allowed, yet the equipment still failed.
Several factors not controlled by the vehicle owner or the supplier of the equipment might cause a failure. We all should be aware of these pitfalls.
First and foremost, the equipment must be installed (and/or adjusted) according to supplier recommendations. After a short shakedown trip, all connecting points should be checked and retightened and any adjustments confirmed. If any of the bolts are moving “” even slightly “” the thrust will become an impact force that could be a potential failure in the making and must be corrected. To illustrate, if you try to push a nail into a board with a hammer, it doesn’t work very well. But with the multiplying dynamics of impact, the nail is easily driven into the board.
Ball couplers will wear, and the more they wear, the more prone they are to disengage. It’s advisable to lubricate the ball, but this will not totally eliminate the wear. Most couplers have an adjusting nut under the retainer. If the coupler fit is sloppy, tighten the nut just enough to make the fit more secure.
The hitch ball nut itself should be checked frequently for tightness. During a right turn, the coupler exerts a counterclockwise torque on the ball. This tends to loosen the nut, especially when the coupler is in an extreme altitude or has reached the limit of its movement. I prefer to drill and key the nut to the hitch ball shaft.
Now for the more serious part of this article “” tow bar alignment. Most tow bars are installed to be relatively level when in the towing position, but we see many tow bars that are severely misaligned “” and therein lies the hidden danger.
Hitch ball couplers have a limited movement up and down. Although this range of movement normally is adequate for reasonable changes in road and driveway elevations, all ball-type couplers will bottom out with a severe up or down angle. In the down position, the ball retainer contacts the shank just below the ball. In the up position, the forward lip of the coupler will either contact the shank just below the ball or the plate of the ball mount.
If you traverse a deep swale, and the up or down limits are exceeded, a tremendous prying force is exerted against the coupler. Taking into consideration the weight of the motorhome and the weight of the car, one can see that if the angle is severe enough, something is apt to bend or break.
The above scenario presumes the tow bar is level. What if the tow bar is sloping up toward the motorhome at a 10-degree angle? One of the points of contact will be arrived at with much less vertical travel.
What about tow bars that utilize a receiver rather than a hitch ball to connect the towed vehicle to the motorhome? They don’t need to be level, do they? Yes and no. Let me explain. The above situation involves only a prying lever action against the ball and coupler. The receiver-type tow bars have eliminated this problem by incorporating virtually unrestricted three-axis movement.
However, another concern is the amount of thrust and pull exerted on the towing equipment when traversing an uneven surface with any type of tow bar. When the motorhome’s rear wheels go over a 6-inch rise in the roadway, the front of the tow bar is likewise elevated, as it is attached to the rear of the motorhome. Because of the overhang behind the rear wheels, the vertical travel of the rear of the motorhome will exceed the 6 inches. We will disregard that, however, since the length of overhang is a huge variable.
When the front of the tow bar rises 6 inches, this actually pulls the car forward approximately 3/8-inch, shortening the effective distance between the vehicles. If the road gently rises or the speed is moderate, the forward motion will be smooth and gentle. If the road rises sharply or the speed is fast, the forward motion will be very quick. If this modest 6-inch rise occurs over a distance of 10 feet, the resulting forces will be applied in 1/9th of a second if traveling at 60 miles per hour.
Let’s look at the same situation, only with the tow bar installed 9 inches high in front. The geometry changes severely, since the effective length of the tow bar has been shortened and the motion amplified. When the motorhome traverses the same 6-inch rise, the towed vehicle is now jerked forward 1 5/8 inches. With the tow bar mounted 12 inches too high, the motion is near 2 inches. This inordinate shock places a tremendous amount of strain on every weld, bolt, and attachment point. Then, action is reversed when the towed vehicle travels over the same rise; the tow bar returns to level and the pull then becomes a rearward thrust. (See accompanying chart.)
There is no practical way to tell how many pounds of force are exerted on the towing attachments, but considering the weights of the two vehicles, the speed of travel, and the abruptness of the rise, the force could be in the thousands of pounds.
We also may say that the more out of level the tow bar is, the greater the force becomes; at 9 inches out of level, the force will be approximately three times as great as with a level tow bar. At 12 inches out of level, the force is more than five times as great. Each time we traverse a quick rise or drop, this pull-push action is applying extra forces on the towing attachments. If a weak link exists in your towing system, something will go wrong sooner or later.
To be on the safe side, check the bolts for tightness in your tow bar, base plate, and receiver after a shakedown run or a first trip, and thereafter at least annually. When the tow bar is 3 inches out of level, the geometry changes only 1/8-inch, but at 9 inches out of level, the geometry changes a full inch. If your tow bar is more than 3 or 4 inches out of level, I recommend changing something to correct it.
Also, try to prevent the tow bar from sloping downhill toward the motorhome. During braking, this will apply a lifting movement to the front of the towed vehicle, which lightens the contact between its front tires and the road. During a panic stop and with enough lift, the car could lose traction on the front wheels and possibly jackknife. In the event of a collision, the car could actually vault into the rear of the motorhome. With the availability of drop-and-rise ball mounts and drop-and-rise receiver adapters, there are few instances when one must accept the tow bar being grossly out of level.
Safety chains are another tender spot with me. Most states have specific regulations requiring safety chains or safety cables. Even if your home state doesn’t require them, or if the language of the law specifies only “trailers,” you may not always be traveling in your home state. We shouldn’t allow a gray area to overcome common sense. The purpose of safety chains and cables is to control the vehicle should some part of the towing apparatus become disengaged. So, from a practical “” and safety “” standpoint, I view properly installed safety chains or cables as a “must.”
Motorhomers also should become educated in the arena of towed vehicle braking equipment and breakaway devices. The more discipline we require from ourselves, the less apt Big Brother is to overregulate us.