Dear list,
The recent tale of woe regarding a sick Daimler mentioned a fishtailing
motion as the Daimler was trailered to the shop. I've become fond of this
list, and I am not anxious to see any of you shuffle off this mortal coil.
I've found few books that provide useful information on trailering, so I
am passing on some tips learned through some eventful miles pulling a
horse trailer. If others add their hard-won experience, we can have a
pretty fair collection of trailering information. My suggestions
relate to tagalong trailers, i.e. those that hitch to a ball on the rear
of the tow vehicle. So called 5th wheel trailers are a different (and
more stable) kettle of fish.
The fishtailing the correspondant described is a serpentine weaving motion
in which the tongue of the trailer moves from side to side, dragging the
rear of the tow vehicle with it. The trailer ball acts as a sort of
hinge. As the rear of the tow vehicle moves to one side, the front wheels
are pulled in the opposite direction. The amplitude of the movement can
increase in spite of, or perhaps because of, one's efforts to counteract
the movement with the steering wheel. I've watched in horror as a car and
camper trailer began to oscillate gently on a downhill stretch in the New
Hampshire mountains. The driver tried to correct the motion, but the
oscillation increased to the point that the front corner of the camper
crunched the rear door of the car, just before the whole rig crashed down
an embankment.
I have heard this motion called "swaying," although "fishtailing" is a
more apt description. Whatever you call it, it is truly frightening and
dangerous. It is best to avoid this by proper equipment and planning.
Prevention begins with one's choice of tow vehicle. The recent thread on
tow vehicles stressed horsepower and torque. I think it is at least as
important that a tow vehicle have an adequate wheelbase, if it is to be
used to tow a tagalong trailer. The distance from the rear wheels to the
trailer ball is a lever that the trailer can use to make the car change
direction, or fishtail. The shorter the wheelbase, the less the tow
vehicle can resist such motions. (Before anyone asks about the short
tractors that tow 18 wheelers, I should say that these are 5th wheel rigs,
in which there is no lever arm--the hitch plate is directly over the rear
axles.)
A prime cause of fishtailing is inadequate weight on the hitch ball. The
rule of thumb I've most often seen is that 10% of the trailer weight
should be on the hitch. The design of the trailer, the loading of the
trailer, and the levelness of the trailer all can affect the tongue
loading and stability.
In towing a car, even a small one, the combined weight of the trailer and
car are likely to be at least 2000 pounds. This implies a downforce of
about 200 pounds on the hitch, plus the stesses of towing. Obviously, the
hitch and its fastenings have to be up to this. Don't tow a heavy trailer
with a bumper hitch, period. Be very cautious towing even with one of
those massive-looking rear truck bumpers; most of them look stronger than
they are, and rust can seriously weaken them. A properly sized "receiver"
hitch, securely mounted to a strong, unrusted frame, is the only way to
go.
A "receiver" hitch receives a separate ball mount. These are available
with a variety of "drops" or "rises" that raise or lower the ball relative
to the hitch. Choose a ball mount that makes the unloaded trailer bed
level, and which puts at least 10% of the unloaded trailer weight on the
tongue. If you don't have at least 10% of the trailer weight on the ball
when the bed of the empty trailer is level, then your trailer may not be
properly designed. Many trailers are made by small shops, and not all of
them are good.
We have all seen people pulling horse trailers at absurd angles. God
must look after these drivers; they sure are not looking after themselves.
If your hitch is too high, you may have plenty of weight on the tongue
when the trailer is unloaded, but loading the trailer may actually rock
the tilted trailer further back so the tongue load is negative, in other
words, so the trailer actually unloads the rear axle of the tow vehicle.
This is almost guaranteed to cause fishtailing. When you load the
trailer, load it so that you maintain at least 10% of the total weight on
the tongue. When towing a car, this generally would mean having the
middle of the car somewhat forward of the trailer axle(s) and the engine
of the car in the front of the trailer.
You can expect depression of the hitch as you load the trailer properly.
You have to live with that; don't try to balance the trailer so as to
completely unload the hitch, in the hope of saving the tow vehicle, unless
you like seeing the world upside down. If the load threatens the springs,
consider a different tow vehicle, or invest in a "load-equalizing" hitch
(also sometimes called a "Reese" hitch after a prominent manufacturer)
which in effect puts a spring across the ball, resisting depression of the
hitch, so the front and rear wheels of the tow vehicle share the tongue
load of the trailer. I would not do a lot of heavy towing without these.
Some trailer people call the spring bars of load equalizing hitches "sway
bars." This is sloppy terminology. They do nothing to counteract
fishtailing except that they make it easier for a tow vehicle to cope with
the tongue load needed to provide stability.
Once you have experienced fishtailing, you won't be anxious to feel it
again. Reese and other manufacturers offer an accessory that resists
hinge action of the ball hitch, dampening fishtail motions. I put one of
these on my horse trailer, and the peace of mind was easily worth the $125
or so it cost. A brake on a sliding bar allowed the trailer to turn, but
resisted rapid fishtailing; I heartily recommend these.
You are asking for trouble if you tow a heavy load on a trailer that has
no brakes. When you apply the tow vehicle brakes in a curve, the trailer
will try to push the rear of the two vehicle out, which can initiate
fishtailing. Aside from this, you are trying to stop two vehicles and a
trailer with the brakes of the tow vehicle, which may not be up to the
task. Many, maybe all, states require trailer brakes when loads exceed
some minimum, as indeed they should. However, my impression is that
inforcement is ragged, so you have to look out for yourself.
If fishtailing starts, you may find that steering corrections do not do
much, except maybe make it worse. I have been told that the best way to
stop fishtailing is to apply the trailer brakes, and not the tow vehicle
brakes, while accelerating the tow vehicle gently. That is supposed to
pull the tow car/trailer combination straight. It sounds sensible, but I
have not tried it. The one time I experienced fishtailing, it happened
because the trailer brakes failed and pushing the lever on the controller
did nothing. By force of will, I kept my foot off the truck brake, held
the steering wheel steady in a death grip, and rode it out. Fortunately,
the hill was a short one. I almost soiled my armor. The horse did soil
his.
The above prescription implies that one *can* apply the trailer brakes
independently of those on the tow vehicle. This is possible with electric
trailer brake actuators or those activated by a hydraulic connection to
the tow vehicle brakes. It is not possible with "surge" type trailer
brakes. The latter are turned on when the trailer pushes against the
hitch, and there is no actuator available to the driver. For this reason
(and others), I consider surge brakes inferior to the others, but better
than no brakes at all. Some brake actuators turn on trailer brakes in
response to movement of a small pendulum in the actuator. In my
experience, these only work well on level ground. If not adjusted
perfectly, and sometimes even then, these are unpredictable. I prefer
actuators that tap into the tow car's hydraulic system and actuate the
trailer brakes in proportion to pressure in the tow vehicle's brake lines.
As always, I offer this advice believing it to be correct. But it is
free, and worth about what you paid for it. Use these suggestions at your
own risk. If anything happens to you as a result, don't sue me. It won't
do you any good to do it, anyway, since I don't have much.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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