Lots of great ideas. Thanks. The sta-tru wheel looks promising, however at 1.75 inches is too thick. I was thinking about something thinner like my bicycle tire at 1.25 inches. The jogging baby carriage wheels look promising, however I've been unable to find any size specs.
Pretty much any bicycle-style tire described as "12 inch" is ETRTO 203 mm. There are also 10 inch and 8 inch sizes. You'll find a lot of 1.75" tires at that size and some 2 inch. But small tires ride harshly, so I don't think you are going to find a lot that's narrower unless it's solid or foam stroller wheels.
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."