Why do trucks have so many transmission gears?
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Truck engines are designed to haul heavy loads so they need to create huge amounts of torque so they use diesel engines for their efficiency and large amounts of torque. The problem with diesel engines is they have a very how red line, typically, the larger the diesel engine, the lower the red line as well. The red line is the speed at which an engine stops making more power the faster it turns. As a result of this low red line it has a very narrow power band. A typical car engine will red line at 6000 RPMs, engineers will design the engine to be driveable between a certain rang of RPMs e.g. 1700-4000 RPMs so you can stay in one gear a relatively long amount of time. A typical semi-truck engine will probably have the red line of half that at 2500 RPMs which means but is driveable down to 750 RPMs. This narrow band means each gear has a very narrow range of speeds it can operate at resulting in the need for many more gears.
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