Needed a replacement 700C front wheel for my commuter bike after the old aluminum rim exploded like a looney tunes cannon. It’s hard enough to find the right size when there are 3 competing tire/rim sizing systems currently in use, it doesn’t help when the people selling the wheels have no idea what the numbers mean either! All of these examples are from separate storefronts at the big online store. Ended up buying the wheel identical to mine from my local bicycle shop at the same price as online and with no shipping fee or delivery time.
The 3 systems in use are the American customary inch fraction notation like 26x1+3⁄4 (which is NOT interchangeable with American customary inch decimal notation like 26x1.75), the French metric notation like 650x45C, and the ISO 5775 metric notation like 47-571. I found the wikipedia conversion tables and Sheldon Brown’s tire size chart invaluable.
To be fair, when I was little I too was guessing that “C” stands for centimeters or something metric. Now I know that “C” in “700C”, the most popular road/hybrid wheel size, stands for the third size in the French “ABCD” notation, where sizes “700A”, “700B”, and “700D” are obsolete and are no longer manufactured.