By
Mark Penlerick
Engineering Team Leader
Blue Ox Towing Products
Recently
I read a letter to the editor in a magazine pertaining to how an
RV couple back up their towed vehicle by having one person steer
the towed vehicle while the other backs up the motorhome. I feel
a word of caution is in order here. Last summer we tried backing
up several towed vehicles with a motorhome. While the motorhome
backed up, I was in the towed vehicle steering it. The front tires
suddenly whipped off to one side and the steering wheel violently
spun out of control. It happened so fast my arms crossed up and
hit each other and I was lucky I didn't break my thumb or arm. I
would not recommend anyone try to "steer" the towed vehicle
while backing. We did however have limited success backing in a
straight line using our tow bar. The problem is that inevitably
all vehicles we tried had the same thing happen to the front tires
all at different intervals. We also tried other manufacturers tow
bars with the exact same result.
The
reason this happens is not the tow bar but rather the caster angle
in the front end of the towed vehicle. Caster is the forward tilt
of the steering axis versus vertical. It provides steering stability,
steering returnability and cornering ease. In reverse, the caster
angle makes the wheels want to turn around the other direction like
"casters" on your office chair or shopping cart. We all
know they can't turn all the way around on a car, but they will
turn off to the side as far as the steering mechanism will let them.
This is virtually undetectable from the driver's seat in the motorhome
making this a very scary situation. If you continue to back up,
after the wheels have turned, the tires "scrub" or slide
sideways causing damage to the tires. Other things caused by this
are; severe stress to the steering components, suspension and towing
system components.
Another
good example of caster at work is a bicycle. Nearly everyone in
their younger days has ridden a bike down the street without holding
onto the handlebars, but how many have done it going backwards?
None with any success I would expect as the front tire tries to
turn around the other direction causing
well...a crash. To
be on the safe side, heed the warnings; don't back up with any tow
bar.
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