Tandem Axle Boat Trailer Loading for Proper Tongue Weight and Load Distribution

Published 11/21/2017

Question:

Michael H answered the question in FAQ Troubleshooting Trailer Suspension Sag Causing the Equalizers to Pitch Forward fairly completely, but did not suggest how to tell if the load is heavy toward the front. Is it all about tongue weight? or is there another way to tell if the proper amount is on the front vs back tires. My rig is a 2001 Magic Tilt 6000# tandem boat trailer with dry weight of boat, motor and trailer listed as 4300#. With 300# of fuel and 400#? of other equipment, guessing it is a 5000# rig. Can you tell me how to go about making sure it is balanced front-to-back before i start buying springs and shackles? I have always used 10 of total weight for the tongue. what else can I do to assure that the weight is distributed properly? It is already perfectly level frame on flat surface.

asked by: Bill B

Expert Reply:

Your tandem axle trailer's equalizers handle the task of evening out the load across the two axles.

I noted that in your photo the axles appear to have different tires installed on each. It is best to use identical tires on both axles, meaning same type (bias or radial), same weight load range and naturally, the same size. If the tires are not all the same some will tend to work harder and may develop more heat, which is a tire's worst enemy. The hotter tire, the tire that is carrying more load than the other, will typically be the one that fails.

If your boat and trailer were made for each other - literally - as opposed to having been bought separately as non-matched items, then you should not need to alter the geometry. Some boat trailers have adjustable bunks and winch/bow roller stands that allow you some play in the exact positioning of the boat when trailered and this allow some tweaking of tongue weight (TW).

Boat trailers do typically have a lower TW than RV trailers, for instance, since the boat's motor weight is far to the rear along with the that of the gas tanks. So boat trailer TWs will typically be closer to your 10-percent figure than to the 12-to-14-percent found in RV trailers. Since the trailer is level you should not need to alter anything, just replace the rusted equalizers and shackles with new ones of the same dimensions and replace the leaf springs with new ones of the same eye-to-eye dimensions that are rated for the weight indicated on the axles.

Often boat trailer makers place the axles further forward than they would be on another type of trailer to offset this rear-end-heavy state.

If your photo was taken with the trailer unloaded the angled equalizer will correct itself once the boat weight is on the suspension.

The etrailer tongue weight scale # e99044 takes the guesswork out of determining TW and allows for easy and frequent checks that will enable you to find the best overall loading scheme for the boat and cargo items.

expert reply by: Adam R