After you have worked on a few new truck designs, you start seeing a pattern – a relationship between the pieces. Eventually you grasp why trucks are the way they are, and how hard it is to change their shape.
Let’s start along the centerline of a narrow cab on an older traditional cab-behind-engine diesel truck, starting with the engine — the heart of the truck. A diesel engine has a particular size and shape. In front of the engine are belt-driven accessories. One of those is a very important fan blade. The fan blade has to have room to spin, and enough clearance to help move air around and out of the engine cavity. In front of the fan blade is the all-important cooling module, which needs both thickness and surface area to work effectively.
In front of the fan is the grille – the front end of the truck and arguably one of the brand identifiers. The grille originally was vertical but over the years aerodynamics designs and styling have required it to be tilted back a few degrees to help reduce drag. The grille generally is slightly behind the face of the bumper, so that the bumper is the first thing to hit any obstruction.
Behind the engine block is the firewall. Some clearance needs to be provided between the engine and the firewall because they move differently. The firewall is where nearly everything is located that has to transit into or out of the cab, such as signals to gauges in the instrument panel, air lines, electrical harnesses, air conditioning air, etc. Directly behind the firewall, and directly opposite the left rear corner of the engine block, is the throttle pedal (and the driver’s foot).
Like the old childhood song, "the foot bone is connected to the..." You wind up needing to position the driver’s body in a seat so that the ergonomics — the driver’s comfort — are appropriate for all size and shape of drivers, which includes 5% to 95% of the population.
The seat is slid back to fit the 95% percentile driver. The seat has to have some ability to recline, unlike that airline seat in the exit row of airplanes, so the back of the cab – with its interior trim package – has to be located beyond the seat recline position chosen for the vehicle.
