Size has nothing to do with it. The Rangers were body on frame.

truck [truhk] / trʌk / noun

> any of various forms of vehicle for carrying goods and materials, usually consisting of a single self-propelled unit but also often composed of a trailer vehicle hauled by a tractor unit.

> any of various wheeled frames used for transporting heavy objects.

> Also called hand truck. a barrowlike frame with low wheels, a ledge at the bottom, and handles at the top, used to move heavy luggage, packages, cartons, etc.

> a low, rectangular frame on which heavy boxes, crates, trunks, etc., are moved; a dolly.

> a tiered framework on casters.

> a group of two or more pairs of wheels in one frame, for supporting one end of a railroad car, locomotive, etc.

> Movies. a dolly on which a camera is mounted.

> British. a freight car having no top.

> a small wooden wheel, cylinder, or roller, as on certain old-style gun carriages.

> Nautical. a circular or square piece of wood fixed on the head of a mast or the top of a flagstaff, usually containing small holes for signal halyards.

I see no mention of "body on frame" as part of what makes a truck a truck.