A manufacturer determines a tow rating based on the vehicle when it is empty. It does not include the cargo, passengers, after market accessories or any additional weight placed in the vehicle. Any weight added to the tow vehicle reduces the tow rating by that amount.
For Example:
Tow Rating of Vehicle: 7,900 lbs
Cargo in the Tow Vehicle: 200 lbs
Passengers & Driver: 500 lbs
Additional 50 gal. Fuel Tank: 305 lbs
Actual Tow Rating: 6,895 lbs Tow Vehicle
TRAILER:
UVW in the Brochure: 5,730 lbs
Dealer Ordered Options: 370 lbs
Dealer Installed Options: 100 lbs
Cargo in the Trailer: 300 lbs
Water 8.3 X 32 gallons: 266 lbs
LP gas 4.23 X 14 gallons: 59 lbs
Gross Trailer Weight: 6,825 lbs
Tow Rating: 6,895 lbs
Minus GTW: 6,825 lbs
Equals 70 lbs before tow rating is exceeded.
There is another important weight rating that comes into play that is the Gross Combined Weight Rating (GCWR). This is the maximum allowable combined weight of the tow vehicle and the trailer when both are fully loaded for travel.
You should never tow a trailer that is pushing the limit on the manufacturers tow rating or a combined weight that is pushing the tow vehicle GCWR. Pushing the weights over the limits allowed put the driver and passengers in a dangerous situation for them and surrounding traffic.
Remember to include all factors in your weight calculations:
1. Add the UVW of the trailer, make sure that it includes all options.
2. Add the weight of any aftermarket accessories like a battery or a satellite dish.
3. Add the weight of any cargo you put in the trailer.
4. Add the weight of water and LP gas that will be on the trailer. Water weighs 8.3 pounds per
gallon. LP gas weighs 2.4 pounds per gallon.
5. Add all weight of passengers in the tow vehicle.
6. Add the weight of any cargo in the tow vehicle.
7. Add the weight of any after market equipment added to the vehicle.
There are two methods to ensure you do not put yourself or others in danger when towing. A simple method to use, that will add a built in safety margin, is to take the GCWR of the tow vehicle minus the GVW, the actual weight of the fully loaded tow vehicle, and this equals the maximum GVWR of a trailer that you can consider purchasing or renting for towing.
For Example:
GCWR – GVW = Maximum GVWR of the Trailer
GCWR of our Tow Vehicle: 14,000 lbs
Minus GVW of Tow Vehicle: 7,105 lbs
Max. GVWR of Trailer: 6,895 lbs
GVWR of the Trailer: 6,900 lbs
UVW in the brochure: 4,355 lbs
Dealer Ordered Options: 370 lbs
Dealer Installed Options: 100 lbs
Cargo Loaded in Trailer: 300 lbs
Water 8.3 X 32 gallons: 266 lbs
LP gas 4.23 X 14 gallons: 59 lbs
Gross Trailer Weight: 5,450 lbs
GCWR: 14,000 lbs
GVW + GTW: 12,555 lbs
1,445 lbs to spare
To build a better safety margin you can use the 75% rule. The 75% rule ensures a built in margin of safety and is a good rule to follow if you plan to tow in higher elevations. At 10,000 feet above sea level you would need to reduce vehicle ratings by 20% to maintain performance. Before you can apply the 75% rule you need to reduce your ratings to see how you can safely tow at 10,000 feet above sea level.
For Example:
Tow Vehicle GCWR X 80% to get a 20% reduction: 14,000 lbs
X 80%
11,200 lbs
Tow Vehicle GVWR X 80% to get a 20% reduction: 8,800 lbs
X 80%
7,040 lbs
11,200 lbs minus 7,040 lbs = a maximum tow rating of 4,160 lbs at 10,000 feet above sea level.
The 75% rate will calculate the most weight we should tow to still maintain performance.
Tow Vehicle GCWR 75%: 14,000 lbs
X 75%
10,500 lbs
Tow Vehicle GVWR 75%: 8,800 lbs
X 75%
6,600 lbs
10,500 lbs minus 6,600 lbs = maximum tow rating of 3,900 lbs at 10,000 feet above sea level.
By applying the 75% rule and keeping our trailer weight at below 3,900 lbs, we can keep the tow rating below the maximum 4,160 lbs required to maintain vehicle performance. By applying the methods above combined with the proper match between your tow vehicle and trailer. However, the way to get true and accurate weights is to the weigh both the tow vehicle and the trailer fully loaded for travel.: