Determining Gross Vehicle Weight Rating (GVWR) for Trailers: Not as easy as it looks

This article authored jointly by Don Moore and Eddy Tschirhart, Canadian Transportation Equipment Association 

In this past while, there have been a number of queries that have come to the Canadian Transportation Equipment Association regarding trailer GVWR

The question usually goes like this, “How do we determine the GVWR for trailers?”  This question has been asked regarding with respect to many configurations ranging from Utility type trailers to Heavy Haul type trailers.

An identified misconception floating around out there is that the GVWR is determined only by the sum of the Gross Axle Weight Ratings (GAWR).  Though each GAWR is part of the equation, there are many factors that need to be considered in establishing a trailer GVWR.

Factors that must be considered in the determining the GVWR include coupler or tow bar rating, upper king pin and bolster plate structure rating, foundation brake capacity, and the structural ability of the vehicle between the suspension and the hitch, whether it is a king pin or a pintle type hitch.

Each trailer manufacturer is responsible for determining the GVWR of the trailers  that they build.  The GVWR rating of the total unit could be considered parallel to that of the GAWR of each axle, the weakest component carries the maximum rating.  For axles the rating could be governed by the beam, foundation brakes, friction material, tires, wheels, rims, etc.  With running gear in particular, the suspension has a rating which could be the determining factor. 

Similarly, the structure between the suspension and the hitch must be capable of carrying the required hitch weight transferred to the towing vehicle.  With a full semi-trailer this is called “king pin weight” and with a pintle or ball hitch vehicle this is called “hitch weight”.

For the king pin or hitch portion of the GVWR, other factors, such as intended use, uniform or concentrated loading and useful life expectancy, must be considered.

It’s no wonder that we at CTEA frequently receive questions about calculating trailer GVWR.  So many factors go into it.  In our next IdeaXchange article, we will show you a couple of formulas you can use that will help determine trailer GVWR with confidence. 

Until then, please feel free to contact us.  CTEA is here to help.

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