[A/S] Re: Hensley jacknife

["Maurice Riggins <maurice.riggins@xxxxxxxxxxxxxxxx>" <maurice.riggins@xxxxxxxxxxxxxxxx>]

Your speculation that the truck skidded and jacknifed the rig is 
probably correct.

In most cases of jacknife, the trailer tires are skidding, and even 
if the tow vehicle brakes are not, maybe I should say especially if 
the tow vehicle brakes are not, the trailer tries to pass the tow 
vehicle on either side.  Sliding tires go faster than hard braked but 
unsliding tires.  That's why a car has a tendency to spin when the 
rear tires lock and why a motorcycle has a tendency to get sideways 
and put itself and the rider down if the rear tire is skidding.  We 
see that on ice here with 18-wheelers all the time.  A fifth wheel RV 
can do it, as can a trailer towed with a Pullrite hitch.  They're no 
different than an 18-wheeler.  A trailer with skidding tires towed 
with a Hensley will resist doing it, and try to stay in line with the 
tow vehicle, as long as the tow vehicle tires aren't skidding.  But 
if the tow vehicle tires skid getting it sideways, or the driver 
turns the steering wheel and introduces an angle betweeen the tow 
vehicle and trailer, even a Hensley equipped rig can jacknife with 
skidding trailer tires.

In your case, the opposite was true.  Draw-Tite controllers are time-
based controllers.  The LONGER the brake pedal is pressed the harder 
they brake the trailer.  How quickly they ramp up braking is 
adjustable with the Synch setting.  They brake too little in an 
emergency stop because things happen too quickly, and they brake too 
much if you're in stop and go traffic with your foot on the brake.  
If you set them to ramp fast, for emergencies, they overbrake the rig 
in most situations.  So people leave them lose, as you admit doing, 
and in emergencies, there are no trailer brakes until the rig is 
already out of control.

So in an emergency stop, the tow vehicle brakes are trying to stop 
the entire rig, and on slippery surfaces, they don't have the 
traction to do that and the tow vehicle tires skid.  In your 
situation, it should've been the rear tow vehicle tires, and here's 
why.

When the tow vehicle brakes, it wants to nose dive and put all the 
weight on the front tires, leaving the rear with no traction.  Yes, a 
trailer tongue puts a lot of weight on the rear, but the stored 
energy in the spring bars is trying to lift it.  Without trailer 
brakes, when the tow vehicle nose dives, and raises the nose of the 
trailer and dropping its rear, the trailer develops momentum in that 
direction and continues to pull the rear of the truck up, further 
lightening the tow vehicle rear.  WITH trailer brakes, the trailer 
also nose-dives, holding the rear of the tow vehicle down and keeping 
traction of the rear tow vehicle tires higher.  That's one of several 
reasons you always want the trailer to brake slightly ahead of and 
slightly more than the tow vehicle brakes.

The principal advantage to Pullrite and Hensleys, besides sway 
elimination, is that they fight the trailer trying to put an angle in 
the rig, while at the same time provide no opposition to the tow 
vehicle trying to put an angle in the rig.  In other words, they do 
nothing to prevent the tow vehicle with skidding tires from 
initiating an angle in the rig and starting the jacknife, as was 
probably your case.  That's not what they're designed to prevent.

Your little 114" wheelbase SUV was then at the mercy of the 31' 
trailer, when the most it should've been towing is about a 21-24' 
trailer.  Even with the new 130" Yukon XL, a safer trailer length 
would be 25-28'.  A 137" Excursion would be a better tow for a 27-
30'.  I'm only moderately conservative and tow a 34'10" with a 158" 
truck (safe for a 32-35' trailer), and Hunter's even more so, towing 
a 25'9" with a 156" truck... and in both cases, we use a Hensley. 

I hear Hensley's video shows a Dodge Intrepid automobile towing my 
triple axle 34' Airstream.  If so, that's absurd.  I use a Hensley, 
but have never seen the video myself.  But I've seen enough posts on 
the 'net from those who say they've talked to a Hensley rep who've 
tried to sell them a hitch as a cure for the problems of a grossly 
mismathed rig.  Even though Hensley apparently touts them as such, NO 
hitch, including a Hensley, is a panacea for a poorly matched towing 
rig... especially one with no trailer brakes in an emergency.  But I 
do know their video and marketing techniques are constantly labeled 
as irresponsible on a number of RV forums.  I own one and gotta 
agree.  I don't have to like the company, their marketing, or their 
pricing, but I'm convinced they make the best hitch in the world and 
all that won't stop me from owning one.

I'm not blaming you for ruining your wife for towing by putting her 
in charge of a poorly matched rig with a poor brake controller.  You 
were probably yet another victim of marketing... and another victim 
of towing with a short wheelbase SUV.  At least you've gone in the 
right direction now with a longer, if not very conservative, tow 
vehicle and a proportional brake controller.  The best thing you can 
do is convince your wife how mislead you were, how poor a setup you 
really had, and why the same situation is less likely to occur in the 
future.

Hope this helps.
--
Maurice
WBCCI 5446