Determining the effect of a grade or slope on a loaded trailer

By Dimo: May 22, 2007
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Without going into all of the detail of the physics involved, we all know that moving a trailer up or down a hill is quite a bit different than moving a trailer over a level surface. Here is an example of what we are talking about.

Assume you have a slope beginning at your garage going down your driveway. In deciding if a powered trailer mover is right for you, it is necessary to determine the slope and compare this to the weight of your trailer.

Let’s assume you have the following:

Your trailer weighs a total of exactly 2,000 pounds. This is not the empty weight. This is the total weight of what you pull behind your towing vehicle whether it is a RV, boat, or whatever.

1. The distance from the driveway edge of your garage floor (where you park your trailer) to the low point of your driveway (where you would begin to move your trailer) is 35 feet or 420 inches.

2. The low point of your driveway is 21 inches below the level of your garage floor. This means that in a run of 420 inches, there is a drop of 21 inches. How do we accurately determine this?

It used to be complex to accurately determine this as you would need a surveyor’s transit but technology has given us a very inexpensive device to get this done. It’s called a laser level and a stick and we’ll tell you how to get one cheap.

Let’s look a crude drawing to see the setup. Excuse the lack of artistic skill.

Click Image to Enlarge

Make sure the bubble in your laser level is centered in order to project a level beam. If necessary, place something under the front or rear to raise it to a level position.

Step 1. Measure and record how many inches up the beam (red dot) is from the bottom of the stick .

Step 2. Measure the distance from the edge of your garage floor to the low point (where the stick was) and convert this to inches.

In the foregoing example, you have determined that the falloff is 21 inches over 420 inches (or 1.75 feet over 35 feet).

Now the computation of what effect this has on the effective weight of your trailer going up this grade gets a little complex in that you must first determine the degree slope and then apply that to the weight of your trailer. For purposes of this computation, we assume a constant movement speed and we do not factor in the coefficient of friction and all of those other scientific things. A NASA engineer might take exception to this method.

However for this purpose, the degree slope is approximately 2.86 degrees and the “effective” or perceived weight of your trailer is approximately 2,979 pounds as far as the trailer moving machine is concerned. That’s a 50% increase in weight.

The whole point of this is just to just show the effect of grade on the ability of a trailer mover to move a load up a slope. If you were to purchase a trailer mover rated at 2,500 pounds thinking it will be sufficient for your particular circumstance, you would very quickly find that you have a problem when you begin up this grade. This is why we always recommend in your selection process that you purchase a machine with excess capacity so that you can handle the variables you will encounter from place to place.

 

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