Why Were the Pioneers’ Wagon Wheels So Large?

I have researched how and where the emigrants traveled along the Oregon Trail for ten years, and I’m still learning. Recently, I learned from an article in The Wall Street Journal about why the wheel is round. The article contained the sentence:

“The difficulty of moving a wheeled object increases to the point of impossibility when the bumps that a wheel encounters approach one-quarter its diameter.”

That, the author said, is why wheels on Conestoga wagons were so big and those on steam locomotives so small.

Now, keep in mind that the travelers to Oregon did not use Conestogas, which were too heavy to pull over mountains (Conestogas were used primarily in the flatter eastern United States and Canada). But the principle applies to the prairie schooners that were used in travel to the West.

Also, the front wheels on covered wagons were often smaller than the rear wheels. I’m not an engineer, but I suppose the front wheels were the limiting factor on how rocky a road the wagon could traverse.

I didn’t know this information as I wrote Lead Me Home and Now I’m Found. I wrote about the jostling wagons, but never thought about the physics behind why—other than that the trails were unimproved ruts and bumpy. Now when I write about travel to the West, I’ll think about the necessity of moving large rocks out of the way so the wheels could physically maneuver. (I did have a scene in Lead Me Home about having to cut down trees to get the wagons through the mountains.)

The article made me ponder once again the difficulty faced by the emigrants to Oregon. The more rocks a wagon was likely to encounter, the larger the wheels needed to be. If a wagon wheel had a diameter of four feet, then it conceivably could get over rocks that are one foot in diameter. But I imagine that ride would have been extremely uncomfortable.

Most likely the emigrants would have worked to go around large rocks, or move them, or otherwise avoid the rattling about that the uneven terrain would have caused. The wheels weren’t the only problem with wagon travel. The axles could break and the boards could loosen and crack. The emigrant diaries talk of frequent wagon repairs, often with only rudimentary tools and replacement parts.

Still, finding references like this one to wheel size is one of the things I love about writing historical fiction. I never know what I’ll learn—some of it necessary in the moment, some of it perhaps will be important in the future, and some of it I’ll never use. But I think again about the difficulties our ancestors encountered in their quest for a better life.

What have you read recently that taught you something?