Introduction

Wheel position weighing is a specialized service that is beneficial for certain types of vehicles.

Recreation Vehicles are particularly suited to this information because of the unique nature and function of the vehicle. It is important to know the overall weights of these large vehicles, which can be measured on platform scales found at truck stops. However, these vehicles function as houses on wheels which go far beyond just carrying people and their stuff from one location to another. Houses have specialized rooms and equipment in those rooms and some of the rooms even expand to increase the living area of the house. Then each family's personal belongings and toys are loaded into all the available storage space. These unique and diverse characteristics of this house on wheels creates concerns with how all this weight is distributed on the foundation of this house, which is a vehicle chassis. The suspension and the tires are the ultimate load bearing components of this moving house but they function much more than a typical house foundation. These components get people and their precious cargo from one location to another safely. Wheel position weighing takes scale readings at the tires on each end of the axle. This provides important information about how the weight on this vehicle is distributed and helps to make sure the vehicle is loaded within the important safety ratings.

The RVSEF weigh report includes the important vehicle ratings, tire information, scale readings, and calculations needed to evaluate how the vehicle is loaded for travel.

Important Terms

Wheel Position

The location at each end of an axle where the wheels/rims and tires are located. This can also be called an axle end.

Single Tire configuration

One wheel/rim or tire at each end of the axle

Dual Tire configuration

Two wheels/rims or tires at each end of the axle

Combination vehicle

The truck and the trailer connected

Pin Weight or Tongue Weight

The weight of the trailer that is not carried by the trailer axles. This portion of the trailer weight is loaded on the tow vehicle or truck when the trailer is hitched or attached. Therefore, the pin/tongue weight is cargo weight just like any other cargo items loaded on the tow vehicle/truck. Pin weight for fifth wheels is usually between 15-25% of the total weight of the trailer. Tongue weight on bumper pull travel trailers is usually between 10-15% of the total weight of the trailer

Orientation – Truck & Trailer Report

Scale Readings

The top section of the report contains the scale readings, vehicle ratings, and calculations of the truck and the trailer combination. The bottom section of the report contains the load inflation tables for the tires that are used on the truck and the trailer.

The boxes above the solid black line (the first two rows of boxes) are scale readings from each wheel position. The measurements are in pounds. The information below the solid line are ratings and calculations from the measured scale readings. The front of the combination vehicle is to the left of the page and the rear of the vehicle is to the right of the page. The first row is the passenger's side of the combination vehicle and the second row of boxes is the driver’s side of the combination vehicle.

From left to right, there are three groups of scale readings.

As the data is discussed in this general situation, we will use the term Truck to describe the tow vehicle. We do this only for simplification in the discussion. The Tow vehicle could be many different vehicles – Pickup Truck, Sports Utility Vehicle (SUV), Motorhome, Heavy Duty or Medium Duty Truck, etc.

The first group of scale readings (left) represents the measurements of the loaded Truck without the trailer attached. The second group of scale readings (Center) represents the Loaded Truck with the trailer attached. The third group of scale readings (right) represents the trailer.

Each column in each group represents an axle on the vehicle. The box in the first row is the passenger’s wheel position measurement and the box in the second row is the driver’s side wheel position measurement. There are three columns for each group because there is a possibility of three axles on both the Truck and the trailer. A vehicle may only have two axles and in that case the third column will be blank.

Axle Data

The third row of boxes, just below the solid line represents the axle weights for each of the vehicles. The loaded axle weights are determined by adding the wheel position scale readings, which are located directly above the axle weight box. Just below each axle weight box is an italicized number. This number is the axle rating or gross axle weight rating (GAWR) in pounds, which was collected form the worksheet and found on the vehicle’s Federal Certification Label. This rating is the maximum allowable weight that can be loaded on the axle. The measured axle weight in the box should not exceed the axle rating or GAWR for that axle.

Total Vehicle Data

The fourth row of boxes represents the overall vehicle weight calculations.

Truck/Tow Vehicle Weight Unhitched from Trailer

The first box (left) is the weight of the loaded Truck that is not connected or hitched to the trailer. This weight is the sum of the scale readings directly above.

Tow Vehicle Weight Hitched to Trailer

The second box is the total weight of the loaded truck with the trailer hitched to the truck. So, the tongue weight or pin weight of the trailer is now loaded on the truck and is considered cargo on the truck. This vehicle weight is determined by adding the scale readings of the second group directly above the box. This represents the total or gross vehicle weight (GVW) of the truck as it goes down the road as the towing vehicle portion of the combination vehicle. Below this box is an italicized number, which is the weight rating of the loaded truck or the gross vehicle weight rating (GVWR). This was collected from the worksheet and is located on the Federal Certification Label on the truck. This rating represents the maximum allowable weight of the loaded Truck. The measured total or gross vehicle weight (GVW) of the truck should not exceed the gross vehicle weight rating.

Pin/Tongue Weight

The next calculation is found in the fourth box on the fourth row. This is the pin weight (fifth wheel trailers) or tongue weight (travel trailers – bumper pull).  The pin/tongue weight is the weight of the loaded trailer that is not carried by the trailer axles. This portion of the trailer weight is cargo weight that is loaded on the truck or tow vehicle. It is calculated by comparing the two truck weights we have discussed above. The difference between these two weights is the pin/tongue weight of the trailer. The weight of the Hitched Truck (box 2) minus the weight of the unhitch truck (box 1) equals the pin/tongue weight of the trailer which is found in box 4 of the fourth row. There is an italicized number that is below this box that is called the pin/tongue weight rating or vertical load rating. It is a rating of the hitch equipment. This rating was collected from the worksheet and found on the hitch equipment or hitch manufacturers documentation/website.

Vehicle Weight of Trailer

The total or gross vehicle weight (GVW) of the trailer is found in the last or 6^th box (right) on the fourth row. This represents the total weight of the loaded trailer. The total weight of the trailer is calculated by adding the scale readings in the trailer group (third) directly above this box, which represent the weight of the trailer that is carried by the axles. This sum is then added to the pin/tongue weight, which is the weight of the trailer that is not carried by the axles. These two weights together equal the total or gross vehicle weight GVW of the loaded trailer. Directly below this box is an italicized number, which is the gross weight rating of the trailer. This was transferred from the worksheet and found on the Trailer’s Federal Certification label. This rating is the maximum allowable weight of the loaded trailer. The measured weight of the trailer (GVW) should not exceed the gross vehicle weight rating (GVWR) of the trailer.

Combination Weight

The third box on the fourth row represents the weight of the total or gross combination weight (GCW), which is the measured weight of the loaded truck and the weight of the loaded trailer. This number is determined by added these vehicle weights. The weight of the loaded truck is found in first box on the fourth row and the weight of the trailer is found in the sixth or last box on the fourth row. Below the third box is an italicized number that represents the total or gross combination weight rating (GCWR). This rating is the maximum allowable weight of the combination vehicle. The combined weight of the loaded truck and trailer should not exceed the total or gross combined weight rating.

Pin/Tongue Weight Percentage

The last vehicle calculation is the percentage of the weight of the trailer that is carried on the pin or tongue of the trailer. This is calculated and reported in the fifth box on the fourth row. This is calculated by dividing the pin/tongue weight in box 4 by the total weight of the trailer in box 6 and then multiplying by 100. Below this box is an italicized number that provides the gross tow weight rating (GTWR) of the hitching equipment. This was collected on the worksheet and was found on the hitch equipment or from the hitch manufacturers documentation/website. This rating should be compared to the Trailers Gross Vehicle Weight found in box 6. The weight of the trailer should not exceed the gross tow weight rating.

Tire Ratings

The maximum load carrying capacity or maximum load rating of the tire is found on the sidewall of the tire and is also located in the far-right column of the tires load inflation table on the bottom section of the report. When inflated to the corresponding inflation pressure, this is the maximum load capacity of the tire. Take care to look at the proper tire configuration, single or dual (wheel position).

The actual Load capacity of a tire is based on inflation pressure, so each wheel position scale reading should be compared with the load capacity of the tire (or tire pair for dual tire configuration) as it was inflated when the scale measurements were made.

Common Overloading Situations

These possible situations and solutions are among the more common issues observed, but each combination vehicle and owner is unique. Owners often assume that because they have the same brand or even model of vehicle as another person, they can use the same measurements of that person. This reasoning is a recipe for a bad outcome. We all load our vehicles differently and that loading is why the vehicle has safety weight ratings and needs to be weighed once it is loaded with our stuff. Some of the listed solutions may or may not help in a given situation. There are often unique dynamics that need to be considered in each circumstance. Sometimes redistributing weight to the other vehicle or another part of one of the vehicles can resolve an overloading issue. However, in some situations, the solution to one issue might create a different overloading issue or exacerbate an already existing borderline condition. Care must be taken to consider each rating and weight when redistributing weight to different locations. This is especially the case when more than one rating is exceeded or the various weights are near the corresponding weight rating/limit.

Combination Overloading (GCWR)

Description

When the weight of the truck and trailer together (Combination Vehicle) is greater than the total or gross combined weight rating (GCWR), then the trucks towing capability is exceeded. The primary concern is stress to the drive train of the truck or tow vehicle. This includes the components of the vehicle that move the weight or mass of the combination up and down the road like the engine, transmission, differential, etc. This usually results in overheating and early failure of these components.

Some Possible Solutions

The only solution to this situation is to remove cargo from either of the vehicles so that the combined weight of the loaded truck and trailer is less than the GCWR. If the combined weight is near the GCWR it is good to reduce the time or mileage between maintenance items.

Vehicle Overloading (GVWR)

Truck/Tow Vehicle

Description

When the weight of the hitched and loaded truck or tow vehicle is greater than the GVWR the Truck is overloaded.  The GVWR is the maximum allowable weight of the loaded truck and is found on the Federal Certification label. The primary safety concern is compromised stopping distance followed by accelerated component wear due to exceeding design limits.

Some Possible Solutions

• Evaluate the cargo on the truck to see what might be removed. If there is additional capacity on the trailer and GCWR then that cargo could be place on the trailer. However, it would need to be place on the rear of the trailer. Any additional cargo in the front of the trailer would contribute to the pin/tongue weight of the trailer, which is weight that is added to the truck.
• The pin/tongue weight of the trailer adds a significant amount of weight to the truck when it is attached. Reducing the pin/tongue weight of the trailer can help to reduce the weight of the truck. This can be achieved by removing cargo from the front of the trailer or by moving cargo in the front of the trailer to the rear of the trailer. Think of the trailer as a childhood see-saw, with the axles as the fulcrum. If weight is moved behind the axles to the rear of the trailer (or the other side of the see-saw) then front will get lighter.

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Trailer

Description

When the total or gross weight of the loaded trailer exceeds the trailers GVWR then the trailer is overloaded.  The GVWR is the maximum allowable weight of the trailer and is found on the Federal Certification label.  The primary safety concern is compromised stopping distance followed by accelerated component wear due to exceeding design limits. The most often issue that occurs on trailers is frame or body failures. On Fifth wheels usually, the concern is observed in the frame steel or welds in the overhang portion of the trailer. Occasionally slides and slide frame openings also show cracks from this vehicle overloading. Lastly the frame may also show signs of bending in the rear.

Some Possible Solutions

• Weight on the trailer needs to be reduced.
• Evaluate the cargo on the trailer to determine what can be removed. Often, we think we need to supply the trailer just like we do a house. This is not always the case and items need to be evaluated to determine their priority and usefulness for living in a mobile lifestyle.
• Evaluate the items on the trailer and maybe there is a lighter version of the same item. For example, instead of a desktop computer use a laptop.
• Evaluate the number of items that are carried and possibly reduce the number of items. Instead of 24 rolls of toilet paper maybe only carry 4 rolls.
• If there is capacity on the truck then items on the trailer may be moved to the truck.
• Check Fresh water (or waste water) tank levels and reduce the amount of liquid in the tanks. Water weighs 8.3 lbs./gal., so adjusting water levels is an easy way to manage weight on an RV.

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Axle Overloading (GAWR)

Truck/Tow Axles

Description

When the weight on an axle is greater that its gross axle weight rating (GAWR), the axle is overloaded and is loaded with weight beyond the design limitations of the components of that axle. For trucks in the combination, the primary safety concern is the rear axle. Rarely does the front axle have an overloading issue. Frequently single rear wheel trucks and SUVs have rear axle overloading. This occurs when the weight on the rear axle of the truck exceeds the rear gross axle weight rating, which is the maximum allowable weight on the axle assembly.  When the rear axle is overloaded there might be several axle components stressed beyond their design limits. The primary component to verify is the tires. Other components that will not function properly and/or wear out faster are the brakes, hubs, springs, axle tube, etc.

Some Possible Solutions

• If the rear axle of the truck is overloaded then weight needs to be removed from the rear of the truck. Most often this means removing weight from the truck. This can be done in many ways...
• Eliminate items that are not needed from the back of the truck.
• Move items from the truck to the trailer. These items will need to be moved to the back of the trailer. As discussed above in the Vehicle Overloading Solutions section, the pin/tongue weight of the trailer is on the back of the truck. So, moving items to the front of the trailer will only add weight to the pin/tongue weight of the trailer, which is weight that is placed on the rear of the truck. This will not be a solution.
• Reduce the pin/tongue weight of the trailer. This can be done by completely removing items from the front of the trailer. This can also be achieved by moving items from the front of the trailer to the rear of the trailer. Think of the trailer as a childhood see-saw, with the axles as the fulcrum. If weight is moved behind the axles to the rear of the trailer (or the other side of the see-saw), then front will get lighter. Adding weight to the back of the trailer might also help to reduce pin/tongue weight.
• Some trucks have auxiliary fuel tanks on the back of the truck. Liquids have weight, so reducing the level of fuel in these auxiliary tanks can reduce the weight on the back of the truck. If the truck is going to be used to primarily to tow a trailer, great care should be taken when considering additional components in the bed of the truck.

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Trailer Axles

Description

When the weight on an axle is greater that the gross axle weight rating (GAWR), the axle is overloaded and is carrying weight beyond the design limitations of the components of that axle.  Occasionally trailers with two or more axles have one axle that is overloaded. This could simply be from overloading or it could be that the trailer is not level as it goes down the road. Another common situation on RV trailers is overloading one side of the axle. The gross axle weight rating assumes an even distribution across the axle. For example, if the rating (GAWR) of an axle is 4000 lbs., then no more than half of the axle rating (2000 lbs.) should be on either end of the axle. Because these vehicles are houses on wheels there can be significant weight differences from one end of the axle to the other end. Loading is most often the issue combined with the floorplan. On trailers the kitchen appliances often contribute to weight differences across an axle. Differences are not necessarily bad but the axle is considered overloaded when half of the axle rating is exceeded on one side of the axle. Loading items in locations where there is equipment needs to be done with care.  

Some Possible Solutions

• When the weight on an axle assembly is greater than the gross axle weight rating of that axle, weight needs to be removed from that axle. There are many ways this might be achieved...
• Evaluate what is stored in that area of the trailer and redistribute those items to different locations throughout the trailer. Sometimes this is easy and sometime it is more challenging.
• When one axle of a multi-axle system is overloaded, evaluate the levelness of the trailer when attached to the truck. Leveling the trailer can shift some weight from one axle to another axle, which might reduce the weight on the overloaded axle.  Care needs to be taken when adjusting the levelness of the trailer to make sure clearances and other issues do not create additional problems.
• If the weight on one end of the axle is greater than half of the axle assembly then it is best to try and redistribute loaded items in that area to other locations on the trailer. Sometimes this is difficult because of the floorplan or equipment that is affixed to the RV, like appliances. Refrigerators are known culprits for this condition. Care will need to be taken with how the refrigerator is loaded. Evaluate to see what other components are in that area and how loaded items might be redistributed or adjusted.
• Check Fresh water (or waste water) tank levels and reduce the amount of liquid in the tanks. Water weighs 8.3 lbs./gal., so adjusting water levels is an easy way to manage weight on an RV.

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Tire Overloading

Description

Tires are overloaded when the maximum load carrying capacity of the tire is exceeded.   It can also occur when there is insufficient inflation pressure to carry the load on the tire.

Some Possible Solutions

• If the maximum load capacity of the tire is exceeded, then the weight loaded on that tire needs to be reduced. If possible, removing or redistributing cargo is the easiest solution.
• Suspension dynamic issues described above in the axle overloading section may help to provide a solution.
• Check to make sure that the correct tire size, load range, and load capacity is installed on the vehicle. Occasionally, when tires are replaced, the new tire may have the same tire size dimensions but different load capacity than the worn tire. This improper fitment creates a load carrying issue. This may be confirmed by checking the Federal Certification Label to identify the original tire size.
• Check with the tire dealer to see if there is a tire with the same or similar size dimensions but a higher load capacity and/or load range. This higher capacity tire may help to solve the issue with an overloaded tire. This may be helpful when there is a significant weight difference from one side of the axle to the other side of the axle.

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