Vehicles will display a manufacturer data plate on the driver’s “B” pillar that will give you most the information you need to remain within the vehicle’s safe operating limits. There are a few different types of weights listed and these can become confusing, so we will break them down to explain what these limitations mean to your loading decisions.
GVWR (Gross Vehicle Weight Rating): The manufacturer’s maximum recommended weight rating for the vehicle.
GAWR (Gross Axle Weight Rating): The manufacturer’s maximum weight rating for the individual axle designated by front or rear.
GVW (Gross Vehicle Weight): What you actually weigh when measured on a scale including fuel, loads, and the operator(s).
For towing vehicles the following apply:
GCWR (Gross Combined Weight Rating): The maximum allowable weight of the loaded tow vehicle, trailers, loads, fuel, and operator.
Your tires have weight ratings as well and it is found on the sidewalls of individual tires, check all of them to determine if they have the same ratings and are matched appropriately.
The maximum weights of the vehicle, axle, and tires are not the only weights that have to be considered, you must also comply with Washington State Laws. In general, weight allowances are based on overall tire width and axle configuration. For vehicles with single tires you are limited to 500 pounds per inch of tire width and 600 pounds per inch on vehicles equipped with dual tires. For example a single axle with single tires and a sum of 10 inches of tire width would be limited to a maximum of 5,000lbs on that axle even if the GAWR and tire capability was to display a higher rating. In addition to these limitations the following are the maximum weights allowable if you used the formula above to calculate your ratings:
-20,000 pounds on any single axle, depending on tire size.
-34,000 pounds on tandem axles spaced less than 7 feet apart.
-40,000 pounds for any single-unit vehicle supported by 3 or more axles.
-80,000 pounds for any combination of vehicles.
Anything exceeding this weight must be removed or you will have to obtain an overweight permit. You also may have certain local weight restrictions on roads that you must meet and should check with local authorities. Consider your local access restrictions on private roadways as well.
Taking all of the above into consideration, we must determine the maximum amount of weight we can carry. This weight will be the lightest of all maximum weights. For example, if our chassis GVWR is 15,000lbs and our actual GVW is 15,000lbs as measured on a certified scale, there are 5,000lbs on the front axle rated at 6,500lbs with a tire width of 10 inches, 10,000lbs on the rear axle rated at 15,000lbs, our tires are rated at 8,500lbs per tire, and our overall tire width with dual tires on that axle totals 18 inches, then we will be operating within specifications of the chassis, axles, tires, and Washington State. As stated above when we mentioned lesser weight, say you find that the rear axle is actually rated at 8,000 pounds; 8000 pounds would be the maximum weight you could have on that axle regardless of GVWR, GVW, tire width, or DOT weight limitations. The vehicle weight would have to be reduced on the rear axle. It should also be noted that it is advisable to verify through reliable resources the current laws and restrictions prior to the addition of vehicle weight.
The NFPA recommends that vehicles should be weighed annually and this can be accomplished easily by stopping in and seeing your local truck stop, gravel pit, freight company, etc. Many of these companies can provide you a certified weight ticket at no cost or a minimal cost. It is important to use a certified scale in good working order to avoid invalid weights resulting in time consuming equipment relocation, or worse causing overloading of your apparatus beyond the maximum capacity. As stated previously, the GVW is determined with all “normal” loads. With medical transport units it is advisable to include the weight of an additional firefighter with gear(for a rider), and the maximum carrying capacity of the gurney that is installed. This practice will insure that for most all instances you will be working within the capacity of the vehicle and roadway. Lastly, affixing the vehicle weight and height (in compliance with WAC 296-305-04501) to a sticker in view of the operator will allow weight related incidents the best chance of being avoided and provide for improved firefighter safety.
Justin Claibourn
Washington Fire Mechanics Board Member