Tow vehicle wheelbase vs TT length

[Apprentice]

I have been shopping for a larger TT since the January RV shows hit town. I have an SUV, and I have been concentrating on the weight of the TT so I can have a good towing experience.
But over the months, I have heard from some salespeople that my biggest concern should be the length of the trailer vs the wheelbase of my TV. Others say not to worry, especially with the right sway control WD hitch (which is always the brand they sell). Or that I don't need a sway control hitch.
My TV has onboard sway control, is AWD, weighs 5000 lbs, has a 114" wheelbase, rated at 7200 lbs tow capacity. It's a turbodiesel, so I don't think power will be a problem with the TT's I am looking at (< 6000 lbs GTW).
I guess I don't understand the sway problem, and why it would be worse with a shorter TV. My experience with sway has been from improperly loaded trailers and a long wheelbase TV.
What is the potential problem for me pulling a 27' TT?

[awarnes]

Make, Model, engine size of TV would also help. But if your manual says you have a rating of 7200 minus cargo, passengers, fuel etc. and you are looking at a TT of max 6000 you should be OK. Check the tongue weight of the TT. Remember that you don't want use the dry weight figures. IF you have the WDH set up properly and the sway is working correct I see no problems.

[wingnut60]

If you really want to tow a TT sway-free, take a look at this hitch:

Trailer Sway Elimination | Sway Control | Truck RV Trailer Hitch Accessories | ProPride, Inc.

Joe

[Apprentice]

My question is more about the relationship of the tow vehicle wheelbase to the length of the travel trailer.
Joe's link to the hitch website confirmed my thought that "sway" is a continuing "oscillation," not a quick response to a blast from an oncoming trunk or wind gust.
But why would the wheelbase of the tow vehicle be a factor?
Or is it?

[wingnut60]

Long length towed units vs short wheelbase tow vehicles are always subject to more 'sway' than if you change to a longer wheelbase/shorter towed unit. Commonly, the sway is started by the air displacement of a large vehicle passing the towed combo--the larger the towed unit, the more side area to be pushed by the air from the passing vehicle. I can't explain it in physics terms, but it is a real phenomenom and can create a dangerous situation. The larger the tow vehicle in relation to the towed unit, the less the effect should be. And the 3P hitch (as does the original Hensley Arrow) counters this effect very well.
Sway can also be caused by tail-heavy towed vehicles (improper tongue weight).
Joe

[Apprentice]

Quote:

Originally Posted by wingnut60 I can't explain it in physics terms, but it is a real phenomenom and can create a dangerous situation. The larger the tow vehicle in relation to the towed unit, the less the effect should be. Joe

I can see the "larger tow vehicle" from a weight standpoint, but is it more weight of the TV than wheelbase?

I would like to give the hitch as little to deal with as possible (the 3P is interesting), so I am wondering if I should go shorter than 27'. Or make aerodynamics a prime consideration.

Quote:

Originally Posted by wingnut60 Sway can also be caused by tail-heavy towed vehicles (improper tongue weight).Joe

I am familiar with this condition and it's scary!

[wingnut60]

weight vs wheelbase--both have an effect, but I feel the shorter WB has much more influence than the weight of the TV. Of course, the longer the WB, the weight of the TV will go up accordingly--very hard (impossible?) to find a longer WB weighing less than a comparable type truck in a short WB. I used to tow a Sunnybrook 30FKS weighing in at 9100 with an F150, and it was tough to handle. Got a Hensley Arrow and all towing stability problems went away--I feel the 3P is an improvement to the Hensley at a lower cost. Should I ever go back to a TT, it will be pulled with a 3P hitch.

Aerodynamics should be a consideration--the frontal area above the TV profile causes a lot of drag, but not sure how much effect on sway tendencies--still mostly dependent on the hitch setup and front-rear balance of trailer. There are several brands with the 'ship bow' shape to help with drag, but they will still sway when set up incorrectly. Minor details such as where the water tank is if you tow with water in it will have a lot to do with towing characteristics. As far as I know, EVERY towed unit should have weight bias toward the front--how much? TTs are said to need 10-12% of total weight on the tongue?
Joe

[jspande]

I don't have either direct experience or direct knowledge to back this up, but I would think that the issue would be the ratio of rear overhang (tow vehicle) to wheelbase. If the ball is a greater distance behind the rear wheels, then you need a greater distance from rear wheels to front wheels to give the same stability, or, in other words, to let the dog wag the tail instead of the other way around.

[Apprentice]

Quote:

Originally Posted by jspande I don't have either direct experience or direct knowledge to back this up, but I would think that the issue would be the ratio of rear overhang (tow vehicle) to wheelbase. If the ball is a greater distance behind the rear wheels, then you need a greater distance from rear wheels to front wheels to give the same stability, or, in other words, to let the dog wag the tail instead of the other way around.

Interesting thought, and I'll bet there is more than a little truth to your theory!

[wingnut60]

You are probably correct on rear overhang.

[Apprentice]

Thanks everybody for your responses. This has been an informative discussion and I have learned a lot.

Especially instructive was the link that wingnut provided in post #3 - the Product Reviews for the 3P hitch had several stories about towing experiences with TVs similar to mine.
I think that I can tow one of the lightweight TTs in the 25' to 28' range and that there is sway control out there that can control my rig.

Now I need to figure out how to improve my uphill, twisting driveway so I can back in while preserving the corners of my TT!

[CD]

The WB length and the amount overhang have similar chariteristics. That is leverage. The more overhang the more leverage the trailer will have. The more WB on the TV, the less leverage the trailer will have.

[locoliner]

Quote:

Originally Posted by wingnut60 weight vs wheelbase--both have an effect, but I feel the shorter WB has much more influence than the weight of the TV. Of course, the longer the WB, the weight of the TV will go up accordingly--very hard (impossible?) to find a longer WB weighing less than a comparable type truck in a short WB. I used to tow a Sunnybrook 30FKS weighing in at 9100 with an F150, and it was tough to handle. Got a Hensley Arrow and all towing stability problems went away--I feel the 3P is an improvement to the Hensley at a lower cost. Should I ever go back to a TT, it will be pulled with a 3P hitch. Aerodynamics should be a consideration--the frontal area above the TV profile causes a lot of drag, but not sure how much effect on sway tendencies--still mostly dependent on the hitch setup and front-rear balance of trailer. There are several brands with the 'ship bow' shape to help with drag, but they will still sway when set up incorrectly. Minor details such as where the water tank is if you tow with water in it will have a lot to do with towing characteristics. As far as I know, EVERY towed unit should have weight bias toward the front--how much? TTs are said to need 10-12% of total weight on the tongue? Joe

Hello Everyone, I'm new to this forum and just purchase a 33ft Rockwood Ultra Lite. Came up thru the ranks tenting, then pop-up, next was a 23ft hybrid. My question is, how do you know how much weight is on the tongue. I'm towing with a F150 4.6l with a wheelbase of 139" and have some concerns about what I'm using to tow.

[Glenn and Kathy]

It all comes down to the lever. You have 3 levers at work, trailer axle to hitch, hitch ball to rear axle of TV (rear overhang) and wheelbase of TV. In a sway condition the trailer lever puts the load on the rear overhang lever which passes it on to the wheelbase lever. A levers effect is determined by it's length, ergo longer wheelbase better control of sway. It's the same thing as they're talking about when they discuss the wheelbase to rear overhang ratio on a motorhome except 1 less lever.

Glenn