There are many factors to consider when developing technical specifications for a new apparatus. These include: determining the mission of the vehicle, required fire-pump rating and water-tank capacity; staffing levels that will operate on the unit; and desired principal dimensions, including wheelbase and overall length and height.
Often, one of the more contentious decisions for apparatus specifiers is whether to utilize a custom fire chassis or a heavy Class 8 commercial model chassis, such as those that are built by Freightliner and International.
There are applications where a custom chassis would be advantageous for engine company apparatus that’s associated with a crew size of more than four personnel, equipment that’s cab-mounted, shorter overall length and a fleet-replacement budget that’s funded adequately. Custom fire chassis generally are required for any type of aerial apparatus for which specific frame configurations are determined to be necessary to serve the community. Department pride in ownership is another factor that might need to be taken into consideration, along with the capability for servicing and maintaining the vehicle.
Over the past few years, the fire apparatus market has been dominated by custom chassis vehicles, while commercial chassis units make up approximately 40 percent of annual acquisitions.
All that said, Class 8 commercial chassis have a minimum gross vehicle weight rating (GVWR) of 33,000 lbs., which can have two or more axles. Historically, the fire service has utilized commercial chassis in both two-door and four-door configurations for pumpers, wildland apparatus, tankers and tenders. Furthermore, there are several areas in which commercial chassis excel when compared with custom chassis counterparts. From a financial standpoint, a commercial chassis that has a four-door cab and is equipped with a medium-block diesel engine costs significantly less than a custom chassis and can be serviced at the manufacturer’s local dealership.
Depending on the anticipated vehicle life cycle, parts availability for commercial chassis is more accessible when compared with some custom fire chassis. Commercial truck fleets rely on chassis and cab parts commonality to reduce vehicle downtime and provide off-the-shelf parts availability. Apparatus downtime can affect your response capabilities, particularly when insufficient spare or reserve vehicles are available. For this reason, Class 8 commercial chassis often are selected for these applications.