A logical approach for chassis and body design

Published in the April 2018 issue of Fleet Affiliation

Oftentimes there is a theoretical disconnect about what came first, the chicken or the egg. This metaphor can be applied to the fleet community when it comes to designing vocational vehicles. When spec’ing - what should come first the truck chassis or the body? The answer may appear to be counterintuitive. Following a logical approach for both chassis and body design will ensure an efficient work truck.

Defining the proper chassis
When selecting a replacement chassis, we often buy something comparable to what we are replacing. Although this is an easy strategy, vehicle requirements can change from year to year, and this is compounded by the replacement vehicle’s age. Additionally, the application may have changed over the years. It is beneficial to evaluate operations, applications and requirements to optimize every new truck purchased. There are several logical steps involved to ensure the end result is efficient, regulatory compliant and serves your organization for its entire intended lifecycle.

Before considering writing a spec, it is important to plot out some basic truck design constraints and fundamentals. It is imperative to match the chassis to the application without overloading the chassis while complying with regulatory standards and manufacturer upfitting requirements. Doing this will improve safety and increase productivity while reducing operating and maintenance costs.

Design the body first
After precisely defining the application and intended use for this work truck, the body (or second unit) can be designed. When designing the body (or second unit), begin by identifying the functional requirements and design constraints. With that completed, you are able to put your design to paper.  Working with knowledgeable upfitters can sometimes streamline this process. It is imperative that there is clear communication about all aspects. Your upfitter can only help by using information they have and understand. After the body is designed, the next step is to determine payload and component weights. With this information identified, the primary chassis can be designed.

Design the chassis second
Once a body is designed, a similar process can be followed for proper chassis design. Much like body design, begin by defining constraints. These can include overall weight, dimensional, regulatory and environmental concerns. Once these have been identified, you are in the best position to pick the applicable chassis to fulfil your organization’s needs. Considerations sometimes overlooked include weight distribution and axle overloading. Additionally, ensure the required gross vehicle weight rating and gross vehicle axle rating are available. Axle, tire and suspension ratings must meet or exceed calculated weights. Visibility, turning diameter and ride comfort are all important aspects as well.

We may never know which came first, the chicken or the egg. However, when designing a truck, overall costs can be reduced by following a logical approach and designing the second unit first. When a chassis is purchased, we tend to make them work for our application without first completely defining the application. This can lead to high operating costs, premature component failure and safety and liability concerns.

If you would like to discuss this, or any other fleet issue with NTEA, contact Chris Lyon, NTEA director of fleet relations, at chris@ntea.com.