Have you ever picked up a bike tire labeled 700x38c and wondered if it truly measures 38mm wide? It’s a common question in the cycling world, and the answer is often more nuanced than a simple yes or no. The sizing of bike tires, particularly widths, can be a bit of a historical artifact, rooted in practices that predate the precision we might expect today.
One compelling theory suggests that these discrepancies stem from the legacy of imperial measurements in the cycling industry. In the days when inches and fractions reigned supreme, tire sizes were frequently quoted in increments of 1/8″. Manufacturers, aiming for simplicity and perhaps dealing with variations in production, would round their actual tire sizes to the nearest 1/8″ equivalent. This rounding could go either way – a slightly narrower tire might be rounded up, while a slightly wider one might be rounded down, all to fit these convenient imperial fractions.
This practice, it’s argued, carried over into the metric system. We see it in the common metric tire sizes: 25mm, 28mm, 32mm, and so on. Notice the gaps? You rarely encounter tire markings like 27mm or 29mm, especially in wider sizes. Even below 25mm, sizes like 19mm or 22mm are less frequently seen in markings, even if tires of those actual widths exist. This suggests a continuation of the rounding habit, now adapted to metric but still influenced by the old imperial mindset.
It’s not just bike tires, either. Think about the lumber industry. A “2×4” piece of wood hasn’t actually measured 2 inches by 4 inches for a long time. Nominal sizes and actual sizes often diverge, and bike tires, including your 700x38c, are another example of this phenomenon. Understanding this historical context can help cyclists make more informed decisions, recognizing that the labeled size is a guide, but actual measurements can vary.
