If the rig is moving as a unit, with no sway, then a Hensley is a waste of money.
You've got an issue with the lateral "traction." Most likely it is due to the mushy passenger tires on the Grand Cherokee. Towing that heavy is putting a lot of extra strain on the tires causing them to flex excessively even though they may be pumped up to their maximum.
What you need is a set of stiffer LT, light truck, tires. Even though you can only pump them up to about 45-50PSI before reaching the rim limit vs. their 80PSI rating, they're made of much stiffer/thicker rubber and don't flex as much.
campercajun wrote: With all my Dual-Cams, when the "bow wave" of air of a passing vehicle hits the rear of my trailer, there is always an initial "wiggle". From what I've read on the forum, even the Hensley Hitch is prone to this initial "wiggle". But the Dual-Cam does it's job, and the increased tension on the WD bars, caused by the movement of the trailer, automatically push the "cams" back into the bottoms of the "saddles" on the WD bars, and the trailer resumes its position directly behind the tow vehicle, with very rarely any steering correction required by me.
In fact, steering correction upon this initial "wiggle" can cause a tow vehicle-induced oscillation, completely controllable (by ceasing the steering corrections), but uncomfortable. This positive, forceful self-centering action is the reason I chose the Dual-Cam instead of the Equal-I-Zer brand hitch/sway control. The Equal-I-Zer does an excellent job of controlling sway, but works by friction only, and has no positive self-centering action to force the trailer to return to the directly-behind position, depending on the drag caused by air and tire friction to re-center the trailer directly behind the TV if it does move sideways, and the friction of the WD bars on the L-brackets to keep it there. I just preferred the concept of the Dual-Cam's positive self-centering action and positive, center-detent position. Both the Reese and Equal-I-Zer work well.
However, the "sucking" you are talking about is due to the laws of physics, and even the Hensley Hitch, which is 3 times the cost of the Dual-Cam or Equal-I-Zer, and theoretically "locks" the hitch connection so that the trailer cannot put any sideways force on the tow vehicle's hitch, is not likely to correct this "sucking".
The "pushing" or "pulling" of the entire TV/trailer combination sideways by the positive air pressure of a passing vehicle's front "bow wave" or the negative air pressure of the passing vehicle's rear "vacuum" is not sway, and that is what is causing the effect you are experiencing.
This movement of your entire rig is dependent on the aize, weight, and relative closing speed of the passing vehicle in relationship to the size, weight, and surface area of your vehicle combination, and generally, the bigger, heavier, and faster the passing vehicle is going in comparison to your weight, side surface area, and relative speed, the more force it will exert on your combination (Try having an 18-wheeler to blast by you while you are riding a motorcycle, and you will gain a unique and special insight into how these physical forces work!). Since you can't control the size, weight, or speed of the passing vehicle, about the only way to lessen the effects of this airflow on your vehicle is to reduce the side profile area of your tow vehicle and trailer that the air has to push or pull against, increase the weight of your rig to more effectively resist these forces, or speed up to more closely match the speed of the passing vehicle.
My 3/4-ton crew cab truck is heavier than your Jeep Grand (Cherokee?), but I pull a 33' TT, and I still occasionally have to make a steering correction in order to maintain my lane position, depending on the size, weight, and relative closing speed of the vehicle which is passing me. Even the excellent but expensive Hensley hitch can't prevent the laws of physics from moving your entire vehicle combination sideways, either away from or toward the passing vehicle, depending, once again, on the size, weight, and relative speed of the passing vehicle.
"Airtabs" are supposedly for changing the airflow to reduce drag in order to improve the fuel mileage of a vehicle. Changing the airflow on your vehicle combination, by using "Airtabs", is very unlikely to change any of the physical forces which are causing the "sucking" you speak about. You could spend $2500 to try a Hensley hitch, but I doubt it would improve upon the problem. And I doubt you would want to buy a heavier tow vehicle. So you will probably just have to learn to live with this phenomenon, like I always have. Just keep an eye on your mirrors, and be alert to and forewarned of an overtaking vehicle before it gets to you, so that you can be prepared to react if needed.
Actually, the Hensley will eliminate feeling this bow effect, because the trailer cannot move on the hitch ball, which is what causes you to feel the bow effect. Yes, the forces still exist, but with the tow vehicle and trailer, from the trailer perspective, being one connected unit incapable of any movement between them, the forces have to overcome the traction of the trailer wheels, which is minimal at best, and the traction of the tow vehicle wheels, drive wheels and steer wheels, which are substantial. The forces have to overcome all of this traction at the same time, not the trailer and tow vehicle separately.
Think about this, how often do you feel the bow effect just while driving the tow vehicle without the trailer attached? Yes it is still there. The tow vehicle is not affected because of its traction and aerodynamic design. Attach a trailer, and the trailer is dramatically affected by the bow effect, and exerts those forces upon the tow vehicle. Eliminate the trailer's ability to exert those forces upon the tow vehicle, and you then eliminate feeling the bow effect while towing. That is the beauty of the Hensley.
mkirsch wrote: If the rig is moving as a unit, with no sway, then a Hensley is a waste of money.
You've got an issue with the lateral "traction." Most likely it is due to the mushy passenger tires on the Grand Cherokee. Towing that heavy is putting a lot of extra strain on the tires causing them to flex excessively even though they may be pumped up to their maximum.
What you need is a set of stiffer LT, light truck, tires. Even though you can only pump them up to about 45-50PSI before reaching the rim limit vs. their 80PSI rating, they're made of much stiffer/thicker rubber and don't flex as much.
I do not agree that the Hensley is a waste of money. Now I agree that there are many set ups where a Hensley is not necessary- a 16 foot trailer attached to dually pick up as an example. However, the advice about the tires is very good and should be heeded.
I'd also have the entire combo weighed ready to go....and make sure you're TW is adequate....somewhere in the 10% to 15% range....would suggest with your TV that you shoot for close to the 15% if it doesn't overload your TV.
J
I don't have a dual cam but I added a 2nd friction bar to my 35 foot trailer and towed it over 700 miles. It did have the "suck" before I added the second and now it does not.
________
2008 F 250 FX4 4WD, V10, 4.10 Tow Command
35' 2007 Crossroads Cruiser CT32SB
Wonderful Wife and 3 small kids
Yes, the Hensley will not solve the push/pull (suck effect), although owners of them swear they do. if you are not experiencing sway then I would suggest a switch to a "C" rated LT tire would probably help some.
I had the push/pull up untill last month when I added an extra washer to my hitch to get more weight on the front axle. now I don`t even notice a semi untill he is even with my door. sometimes you just need to play around with the setup/adjustments till it tows perfect.
Wife kim
Son brandon 7yrs
Daughter marissa 6yrs
Dog shadow
07 Cherokee 32B
02 Excursion 4X4 V-10 4.30 gear
Reese HP dualcam,Prodigy brake controller,
Air lift air bags.
Better to have a bad day of
camping than a good day at work!
another in agreement that it's not any 'one' thing, but the whole
system (which includes stuff like tires and even the truck).
Also, as stated, if the whole is moving, the greatest WD system won't
do enough to solve this.
Cheapest and easiest first. I'm also assuming your trailer and cargo
in the TV has you within your ratings (real ratings, not the published
ratings).
Air up the tires to their max sidewall rating and make sure they are
the min size for your conditions. This includes the trailer tires.
Re-adjust the WD hitch system. Mainly that the TV should have enough
weight transfered (distributed) from the rear axle to the front axle.
That the Trailer is slightly pointing down, or at it's highest
pointing, level. Your WD bars may not be large enough for the load.
You may have to tilt the hitch head back a bit more to give the bars
more tension (travel).
Best to actually weigh your setup axle by axle, both empty and fully
loaded. That is the only way to know where you are in reference to
your ratings.
Most likely "P" rated tires and also suggest you go to the next higher
class tire, "LT" rated. Also make sure your wheels are rated for the
higher pressures required by LT tires. If you need to go to new wheels
go as wide as possible and still fit in the wheel wells. This will
increase the effectiveness of the higher/stiffer sidewalls of LT tires
by reducing the sidewall bendback (less fold over). This will also
tighten up the slip angle, which will give you more precise steering
therefore less the tire will willy-nilly point from outside forces.
Try these as a 'start', there are many, many more things you can
do...up to getting a bigger truck...
Edit...Oh, if your TV is lifted, this is one aspect of
doing that, there 'usually' more slop in the suspension and that
allows outside forces to tweak it before your steering controls can
do anything about it. This is very dependent on the brand and the
installer's fastidiousness...
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...
I am one who agrees with the length of TV to trailer length being a factor.
I use to tow my current 25 ft TT with a short wheel base, standard cab Chevy Silverado and I had the feeling of being pulled toward the vehicle when it passed and a semi was really good.
Now, with my Sierra extended cab, which is almost as long as my TT, the effect is not there anymore, or at least not enough to feel it like I use to.
I saw one setup that passed through my area a couple or so years ago that an rver must have done to prevent this effect, and I thought it was a pretty cool mod and idea.
The rver had a half ton truck, long wheel base extended cab, a camper cap, and somewhere around a 34 or so fter TT. BUT, on the rear of the truck, they had designed and made something that looked like two pieces of fiberglass or something like that that was attached to the rear of the truck with just enough leeway to allow the truck and trailer to turn, and just high enough above the tongue to go over it, and as high above the truck as the top of their TT. They also had a wind deflector on the top of the camper cap to let the air flow over the truck and over the TT.
This looked like two flat pieces as if they were making the truck part of their TT siding, only it did move over and between the two with just a little room of an inch or two. It kinds looked like two wings sideways on their truck.
The only thing I can guess is that they were making the airflow that passes between the truck and the TT flow around the side of the truck and over these pieces and then continue over the side of the TT without going between them against the front of the TT to cause drag.
I wish I could have a picture of this setup because it's hard to explain, and I thought it was very ingenious and a fairly good idea. It looked like the air would flow over and around and not hit the front of their TT or come in from the sides so it was directly flowing over and around. I've seen a few semi trucks with this basic setup, so I guess they got the idea from them.
The only drawback I saw was you had to duck down pretty low or get on your knees to get between the truck and the TT to unhitch or get into the rear of the truck. But, they had everything custom painted to match, and the truck and camper top were painted the same, the air deflector on top was painted to match and had their names and location on it, and the side pieces matched the truck, as did the TT itself. It was like looking at one solid piece made together...truck and TT...if you saw it sitting sideways from a distance.
Anyway, cool idea and i've thought of the idea myself, but i'm no way close to being able to make something like that. But, it might be an idea for others who want that custom look and for making the airflow effect over and around their rigs flow seamlessly and still look cool.
Tim
If I don't meet your expectations
Maybe you should lower your standards.
More commonly, you first get a "push" away from the passing vehicle; you compensate for that. As it moves along side, the "push" lessens, turns into a slight vacuum (venturi effect), and since you are steering into the passing vehicle, you have to adjust again. As the pass is completed, you get a second push from the wake, another steering compensation. Then you ride out the buffeting as the passing vehicle pulls away.
The bigger the passing vehicle, the more push. The greater the speed difference, the more push. At 65 in the right lane, I get more push from the passing 90 mph Suburban than from the 75 mph semi.
We all feel this. I feel it even in DW's low-profile mid-size sedan (although it seldom gets passed by a truck moving much faster). The trick is to learn to not overcompensate each phase, because the next phase is opposite direction and coming up fast.
It helps to watch your mirrors so the passing vehicle doesn't catch you by surprise. It helps to move more to the right of your lane, to increase the spacing with the passing vehicle. It helps to slow down, so you have more control (even though this increases the amount of push).
Air Tabs would help, if you put them on every passing vehicle. But they would only help with the final phase, that last push and the buffeting, not with the first push and the suck.
There is a high pressure wave front and the negative wake just behind it
All things moving through the air has this. The bigger and the faster
it is, the greater the pressure and vacuum. Laws of physics at play
and nothing can be done about 'that'.
Since it is the air pressure at play, the surface area of both the
TV and trailer factor (PSI...Pounds 'per square inch'). Both from
the pure size (that PSI again) and the shape of that surface (think of
a kite or sail boats sail).
To manage this, the various components need to be of the right size,
in the right adjustment and in the right place, etc.
EVERYTHING is effected by this bow/wake. I've been eating lunch
at a road side cafe, about 20 feet from the road and saw the plate
glass window bend in and out after a semi passed. Ditto standing out
on that parking lot and felt the semi push/pull me almost off my feet.
Your setup 'may feel' like the whole is moving over at once, but it is
not and is 're-aimed' by that bow/wake affect.
There are several pivot points to most any towing setup. The main one
is the hitch/ball and the TV/Trailer on either end of that pivot point
The longer the trailer is, the greater it's lever arm on that fulcrum,
the hitch/ball. So the smaller the TV is in reference to the trailer,
the greater or more affect that lever arm is.
The 'push/pull' of that bow/wake will cause the setup to pivot on the
ball. If on coming, then the bow wake will hit your TV's front end
first to cause it to want to go 'right'.
Then as that bow wake travels along the side of your setup, it will
get to the pivot point, the hitch ball, and push the TV's tail 'right'.
By this time the vacuum 'might' be getting to the front of your TV to
'pull it left', exacerbating the push to the right on the TV's tail.
Ditto this as that bow wake travels to the trailer.
This happens all along your setup.
While all this is going on, your tires sidewalls are trying to keep
you 'steered' where you are aiming it. Even if you held the steering
wheel rock solid and not moved in any direction...if the tire sidewall
isn't stiff or strong enough, it will allow the tread to 'turn' or
're-aim' (this is part of the slip angle of any tire). That is why
a higher class (LT) tire will have stiffer and stronger sidewalls. BUT
if the air pressure in the tires isn't high enough, even LT rated, it
will have the side walls too soft to manage this well.
Why distributing more weight from the TV rear to the TV front helps,
as it will have the front tires 'more' weighted to help it steer. Too
often the fronts are 'unweighted' and they won't/can't steer as well.
Why the trailer should be slightly pointed down and at it's highest
pointing, level. This affects the trailer axles 'caster' and if wrong,
it won't steer well and be too light or too easily redirected.
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