Understanding Vehicle Weight Ratings:

We suggest you also read and digest Trailering Tips Getting Hitched? and More Hitching Help along with this one.  For simplicity sake, we will repeat the list of abbreviations and definitions again here.

Abbreviations & Terms:

Tow Vehicle Considerations:

Your vehicle must be able to safely tow your fully loaded trailer.  And, it must be able to do so not only on a flat level driveway, but up inclines, over soft ground, and at highway speeds.  For the past decade or more, auto / truck makers have rated their vehicles for 3 key specifications: Maximum Towing Weight, GVWR, and GCWR.  You must always stay within the limits of these values, all of them!

Note: In many cases, the rated Maximum Towing Capacity is more a marketing term than an achievable reality.  The true towing weight limit is set by the formula (GCWR - GVW), where the GVW cannot exceed the GVWR and the tow weight cannot exceed the Max Towing Weight specification (it hardly ever gets close).

For example, a 2001 Ford F-150 Regular Cab 2WD with automatic transmission, standard V8 engine (4.6L) and rear axle  (3.31:1) is rated at 6,200 lbs maximum towing capacity and 10,500 lbs GCWR.  That sounds like you could tow nearly anything with it! 

But look closer, the curb weight (empty) of the truck is 3,981 lbs, and its GVWR is 5,600 lbs.  (5,600 - 3,981 = 1,619 = maximum "cargo" load).  Adding 2 adults, 1 child, a cooler, camping gear, and typical "stuff" into the truck could easily raise it to GVW (without trailer) 4,600 lbs. 

Now consider your new EquiSpirit 2 Horse Dressing Room Tag-Along trailer; it weighs about 2,850 lbs empty.  Load two 16-hand horses (1,200 lbs each), feed, hay, water, tools, and tack.  It can easily weigh 5,450 lbs (GTW).  You must figure about 13% of the curb trailer weight plus approximately 67% of the cargo weight applies to the TW.  The TW must be added to the tow vehicle's load, so we must add 503 lbs to the truck, bringing its GVW to 5,103 lbs (getting close to its GVWR without much in the way of cargo). 

Since we "loaded" 503 lbs of the trailer's weight (its TW) onto the truck, we can subtract that from the trailer's GTW to get its "pulled weight".  In this case, 5,450 - 503 = 4,947 lbs

The true safe "pulled weight" towing capacity of the truck is its GCWR less its GVW, or in this case 10,500 - 5,103 = 5,397; 450 lbs over (safety margin) the GTW you hope to pull.  450 lbs is not a lot of margin - but it is technically "safe".

Using the same example, at full GVWR load the max towing capacity of this truck is 10,500 - 5,600 = 4,900 lbs... far below the advertised "Max Towing Weight" of 6,200 lbs.

Are the manufacturer's ratings conservative?  Yes, they have to be for liability reasons.  Should you grossly exceed and/or ignore the manufacturer's ratings?  We certainly don't think so!

Also note that your warranty on engine, transmission, and drive train will be voided if you "over tow" with your vehicle.

Note: Air-shocks, Helper-springs, etc.  These devices help the tow vehicle's rear suspension support trailer tongue weight (TW) as well as the weight of passengers, luggage, fuel, etc.. They are particularly useful on "soft-sprung" passenger vehicles (designed more for riding comfort than towing). They are not substitutes for weight-distributing hitches.  They do not re-distribute the trailer weight load to the other axles of the vehicle.  Nor do they alone increase the towing capacity of your vehicle!

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