Sizing the Weight Distribution Hitch

As mentioned in an earlier post we selected a travel trailer over a 5th wheel purposing to take a no compromise approach to the hitch setup. Because of the Class V hitch we installed on the truck we can safely tow the trailer without a weight distribution (WD) hitch. But, the trailer tongue rides just a little low when hitched up. This means the trailer weight is not evenly shared between the two trailer axles.  It also means the truck weight is not evenly shared between the front and rear truck axles.  These imbalances are modest, but we hope that a WD hitch will allow us to dial these out.

When we are passed by a semi or tour bus we get a slight sway input but everything remains well under control. Perhaps having a WD hitch with anti-sway features will be able improve this even more.

The problem is that we are running out of time to order a WD hitch, get it delivered and install it without causing a delay to our departure. The hold up is that we need a good idea of the tongue weight of the trailer when loaded for travel in order to choose a hitch with the proper weight handling capacity.  Fortunately, there are only two capacity ranges that might apply to our rig.  If we can determine that the lower capacity hitch is inadequate the choice is made and the order can be placed.  This requires measuring the current tongue weight and taking into consideration some expected additional loads.  The trailer tongue weight might be as much as 1,000 pounds.  We don't have a scale that can safely weight that much (but getting one is probably a good idea).  How can we get a reasonably accurate measurement of the tongue weight with an ordinary bathroom scale?  In fact, an $8 scale from Walmart? The method and results follow:

I hope the grand kids are reading this since it provides a good example of weight distribution, leverage and some of the things we have discussed in our Technical Drawing classes.

With an $8 bathroom scale, a wood beam, short lengths of pipe, and some scraps of 2x4, shown in the photo below, the tongue weight, actually the weight carried by the hitch jack, was measured.  The bearing points on the scale and the ground are 4 feet apart.  The trailer jack is 3 feet from the scale bearing point and 1 foot from the bearing point on the right.  Given this setup the weight bearing on the bathroom scale is 1/4 of the total weight being carried by the trailer jack.  The scale read about 235 lbs. so the weight being held up by the trailer jack is 940 lbs. (235 x 4 = 940).  Because the hitch coupler is about 6 inches forward of the jack the actual tongue weight will be a little less (because of the longer moment arm from the rear axles), let's say about 900 lbs.

An Inexpensive Method to Weigh a Heavy Load

So, an astute grandchild might ask why the pipes?  Ahh Grasshoppers, do you remember drawing lines tangent to the arc of a circle in our drafting exercises?  The line and arc touch at a single point. The beam forms a line that rests on the circular pipes.  So the weight is bearing exactly at these tangent points, this helps in placing the bearing points a precise distance from the load point so the weight calculation is accurate.

Transferring the Weight to the Scale

The WD hitch itself weighs more than 100 lbs. and it is reasonable to assume that we will have additional cargo behind the rear axle of the truck which adds to the weight that will need to be handled by the WD hitch.  With this information it was pretty clear that the larger capacity hitch was needed and the order was placed.  More on the WD hitch and its installation in a future post.