I started out with a 16 footer. I moved into a used 18 footer mid career. That's before the cab and chassis craze. These were all step vans. Back then. very few dealers ran anything bigger than a 18 footer. The medium duty trucks usually had 366's or 427's and had 22.5 tires and the like. The lighter trucks like I ran had 19.5 tires. Basically a Motor home chassis.