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Why is length such an important factor? Well, it�s not really the length of the trailer that is as important as is the size (or wheelbase) of the tow vehicle trying to pull it. The main focus of this is to minimize trailer sway, which in many cases is caused by the wind from either Mother Nature or large vehicles passing.
Basically, the longer the wheelbase the better! Think of it as leverage. The longer the trailer, the more leverage it can have on the tow vehicle. The longer the wheelbase of the tow vehicle, the more it can resist the leverage being applied from the trailer. You don't need a crew cab long bed truck to pull a pop-up that could easily be towed by a small SUV. But you don't want to pull a 30' trailer behind that small SUV. You want something bigger. Bigger, or longer, is better. But don't get carried away, either. Let's see how it works.
I have found 2 �rules of thumb� on this topic. But wait a minute! Is a �rule of thumb� really a rule? Of course not! I prefer to call them guidelines. It is merely a recommendation to follow. But there could be some basis for these guidelines.
For these guidelines, you need 2 measurements, the wheelbase of your tow vehicle, and the total length of the trailer you are pulling. That length is from the coupler to the back bumper.
Okay, the first guideline:
For the first 110� of wheelbase, this allows you 20� of trailer.
For each additional 4� of wheelbase, this gets you 1� more of trailer.
Here is a chart:
Wheelbase Length Wheelbase Length
110� 20� 154� 31�
114� 21� 158� 32�
118� 22� 162� 33�
122� 23� 166� 34�
126� 24� 170� 35�
130� 25� 174� 36�
134� 26� 178� 37�
138� 27� 182� 38�
142� 28� 186� 39�
146� 29� 190� 40�
150" 30'
That looks pretty simple, doesn�t it? Find out what the wheelbase of your tow vehicle is and find it in the chart above. Is the trailer you are considering at or under the specified length? If not, let�s see if the second guideline helps any.
The second guideline:
The distance from the coupler to the rear trailer axle should be no more than twice the wheelbase.
Wheelbase Length Wheelbase Length
110� 18�4� 150� 25�
114� 19� 154� 25�8�
118� 19�8� 158� 26�4�
122� 20�4� 162� 27�
126� 21� 166� 27�8�
130� 21�8� 170� 28�4�
134� 22�4� 174� 29�
138� 23� 178� 29�8�
142� 23�8� 182� 30�4�
146� 24�4� 186� 31�
Remember, the above length is from the coupler to the rear axle. It is NOT the total length of the trailer as in the first guideline.
Why this second guideline? I think this second guideline applies more to non-RV trailers, like boat or flatbed trailers with short loads on them. Those types of trailers usually do not have the large vertical surfaces (exterior walls) that would be susceptible to wind. You�ve probably seen a small SUV or pickup pulling a very large boat, right?
So let�s go back to the first guideline. If you look at some of the physics and geometry inherent to travel trailers, you might see why. Ever try to carry a full sheet of plywood by yourself, on a windy day? It can be pretty difficult to maintain control. But how about carrying a couple of 2 by 4�s on that same windy day? Not so hard, is it? That�s because the 2 by 4�s do not have the same surface area to catch the wind as the sheet of plywood does. So, in a way, that travel trailer is just like a sheet of plywood for catching the wind.
The next thing to look at is how far is the coupler from the trailer tires? The greater the distance, the lesser the impact it will have on the tow vehicle and the less sway it could create. You will see travel trailers of the same overall length with the axles in different locations. This is probably due to the floor plan or layout of the trailer in order to balance the overall trailer, as well as to provide enough, but not too much, tongue weight.
Finally, the ball, or hitch location. How far is it from the tow vehicle�s rear axle? The farther away it is there is the possibility for more sway.
If you are breaking the length guideline, but are under your weight limits, consider looking at a couple of products that may help this situation. They are the Hensley Arrow coupler and the Pull-rite hitch. Both of these products, as well as their owners, say they do a great job at what they are designed to do, reducing or eliminating sway. So check them out and see what you think. Regardless of the product, I would not go too far over the length guideline by more than about 5'. My opinion is any more than that and you may be pushing it, no matter how good the design! (The references to the Hensley Arrow and Pull-rite products are not intended as an endorsement or advertisement of either product.)
In my particular case, I am towing a Prowler 27H (actually 28� long) with a 2003 Suburban � ton, and I have an Eaz-lift weight distributing hitch and friction sway control bar. I�ve towed on a few windy days and really don�t notice the trailer moving around much, except when the big trucks pass me by. Then I get a little wiggle out of the trailer, but nothing serious or scary. I�m over the first guideline by 3�, which I think isn�t that bad and I would not want to be any further over it. I didn�t know about these guidelines when I first bought the combination, but I knew I didn�t want to go real long with the trailer towing with the Suburban.
How much weight?
How to weigh?
How long?
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