One Tool That Built the West: Orson Pratt’s Odometer

Museum Treasures

When you’re traveling an unfamiliar road in the wilderness, how do you accurately measure the distance between landmarks? How do you record the route to help the people who follow?

William Clayton, assistant clerk of the 1847 vanguard company of Saints headed for the Salt Lake Valley, struggled with these questions. He had been assigned to collect information about the trek to benefit later travelers. He tried to estimate the mileage traveled each day, but his estimates usually differed by as much as four miles from estimates made by other members of the company.

Cog-driven odometers were readily available in England and were used by other travelers along the road west, but on the plains of Nebraska, Clayton had to improvise. Almost a month into the journey, he measured a hind wheel on Heber C. Kimball’s wagon and discovered that 360 revolutions of the wheel equaled exactly one mile. Clayton walked beside the wagon all day, counting the revolutions. Meanwhile, he continued to press Brigham Young to “fix a set of wooden cogwheels” to a wagon wheel.

Orson Pratt designed the odometer (or roadometer) to fit Heber C. Kimball’s wagon, and Appleton M. Harmon, an expert carpenter and mechanic, used a wooden feed box and some iron scraps to build the device.

Each turn of the wagon wheel moved a small wheel one-sixth of a turn. Each complete turn of this wheel, or six turns of the wagon wheel, advanced the 60-tooth gear by one tooth. One full revolution of that gear marked one mile. The 60-tooth gear also drove a 40-tooth gear, which completed a revolution every 10 miles.

Clayton published his detailed and accurate information of the Mormon Trail in The Latter-day Saints’ Emigrants’ Guide, which became invaluable not only for pioneer companies but also for those headed to Oregon and the California gold fields, assisting the settlement of the West.