History of Mechanisms: The Odometer of the Mormon Trail

The wagon odometer (or “roadometer”), designed, built, and implemented on the Mormon Trail, has generated much interest because of the documentation of the odometer’s design, the unusual circumstances under which it was developed, the impact it made on the settlement of the West, and the epic nature of the Mormon Exodus. This paper reviews first-person accounts documenting the odometer’s development, discusses the odometer’s impact, and reviews myths and misconceptions surrounding the odometer. In contrast to previous assumptions, this paper argues that enough information is provided from the accounts, combined with knowledge of gear design, to determine the actual gear sizes. Calculations and arguments are provided to support the idea that the gear diameters were 15 inches (38 cm) for the 60-tooth gear, 10 inches (25 cm) for the 40-tooth gear, and 1 inch (2.54 cm) for the 4-tooth gear.