Wheelbase
The distance between the front and rear axles. Tow charts are organized by it.
Wheelbase is set by cab and bed. A regular cab with a long bed and a crew cab with a short bed can share a wheelbase, or they can differ by more than a foot. Ford's 2026 F-150 chart has separate columns for 122.8, 141.5, 145.4, and 157.2 inches. The F-250 chart runs from 141.6 to 176 inches.
A longer wheelbase usually tracks straighter with a trailer and turns wider. It also changes curb weight, so the same engine and axle can have a different trailer rating in the next column.