WHAT IS WEIGHT DISTRIBUTION AND WHY IS IT IMPORTANT?

Shermac has been providing engineered-for-purpose service vehicles to the resource sector for two decades. Vehicle configuration must reflect the specific operational needs for the unique environment of the customer and with continually changing fluid levels, weight distribution is critical to safety and productivity. 

Weight distribution is the amount of the total vehicle weight imposed on the ground at an axle, group of axles, or an individual wheel. The weight on a truck must be distributed on the axles to comply with the chassis manufacturer's axle ratings and weight laws. 

CALCULATING AXLE WEIGHT

The centre of gravity of an object is a hypothetical point at which weight is evenly dispersed and all sides are in balance. Each truck component, including passengers and cargo, have a centre of gravity.  

In physics, "moments" are a force or weight times a distance. Moments provide a way to combine several components or items to calculate a centre of gravity for them as a group. When the centre of gravity is known for all items combined, it is possible to calculate the weight on each axle.

LIMITS ON AXLE CAPACITIES

Axle capacities are limited either by the manufacturers weight limits or legal weight limits, whichever is lower. If the vehicle will be used on public highways, weights are limited by both the technical weight the vehicle can carry as specified by the manufacturer, and the legal restrictions as defined in the relevant road transport legislation. For instance, on the highway the allowable weight on a single front axle is seven tonnes but the vehicle’s technical weight limit might be twelve tonnes. Even though the truck is designed to carry the higher weight, it is illegal to do so on a public road.  

For exclusively off-road use, weights are limited solely by the manufacturers technical weight limit, and these will typically be higher than the on-road limits. For off-road applications, an understanding of site conditions is critical to determining chassis and configuration 

DESIGN CONSIDERATIONS

The intended use of a service vehicle will determine the number and type of tanks, the fluid volumes to be carried and the configuration of delivery systems. In addition, items such as roll-over protection, bull bars and tools all add weight that must be considered in load and distribution calculations.   

Once all the critical operating parameters are understood, the appropriate chassis can be determined. Off-road specifications vary greatly, and one 8 x 4 chassis may have double the carrying capacity of another, and this might be the difference between carrying 10,000L or 15,000L of fuel and result in significant changes in vehicle uptime and productivity.

WHY WEIGHT DISTRIBUTION MATTERS

From a vehicle owners’ perspective, it is important to match the capacity of the truck to the weight it is expected to carry. An overloaded truck is unsafe and illegal but if a truck consistently hauls less than its capacity, the owner is not realizing a full return on investment and operating costs will be higher than they should be. 

In addition to being illegal and the risk of penalties, improper weight distribution and overloading cause excessive wear and premature failure of parts, unsafe operation such as compromised directional control and insufficient braking capacity and additional stresses that may be instrumental in causing the frame to crack or break.  

SHERMAC ENGINEERING

Careful consideration must be given to distribution of the load weight to determine how much of the total, including chassis, cab, body, and payload, will be carried on the front axle and how much will be carried on the rear axle, and the total. Moving components a few inches forward or backward on the chassis can mean the difference between acceptable weight distribution for the truck or an application that will not do the job satisfactorily. 

Shermac engineers utilise world-class technology that allows them to exactly measure vehicle load and to ensure that the load is properly distributed between the axles. Weight distribution and compliance is verified at several stages in the Shermac design process. An initial weight report is submitted at quotation, another is submitted at completion of detailed design and engineering, and a final weight report is submitted pre-delivery.    

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