In case of road bike, 700c refers to the wheel size. The notation is a relic from the past, and no longer an accurate measure of the wheel size. While some manufacturers do continue to use the term for marketing purposes, the term itself has little, if any, value. However, anyone buying a road bike should be aware of what a term such as 700c means. So, here is everything you need to know about it.
The origin of this measuring system can be dated back to the early days of the bicycle evolution. This was a time when there were no global standards in the bicycle industry. Each country had its own system of measurements when it came to bicycle parts. Consequently, two companies operating in two different countries would use the same number of tire size, and in reality refer to two completely different sizes of tires and rims.
The 700c in particular is the gift of confusion by the French. You see, in those days the size of the bike tire was measured in terms of the outside diameter of the tire. So, a 700 then, referred to a wheel whose tire had an outside diameter of 700mm. So far so good. But, as you can understand, different kind of bikes require different types of tires. Mountain bikes require thick ones, while road bikes go with thin ones, and so on. However, the sizes such as 700mm had become quite popular, and the manufacturers wanted to retain them for marketing purposes. Consequently, they began to manufacture wheels with different rim sizes and rim widths. In this system, the rims were marked according to their width from the narrowest to the widest in the order A, B, C, and D. As you can see A referred to narrowest rims, while D referred to the widest rims. Owing to this, a 700C wheel size, and 700A wheel size, although referred to the same outside diameter of wheels, had completely different rim structure and size.
Things only went downhill from there. The alphabets A, B, C, and D soon began to lose their relevance. The rims that were designed for narrow tires soon began to be fitted with thick tires, and vice versa. You must have seen this already. The 700C, which is one of the most recurring terms among road bike wheel sizes, today refers to the narrow tires. Sometimes, the outside diameters of these tires are as low as 660mm. That is why, it is highly recommended, for road bike buyers, to completely ignore the term 700C.
Well then, if the 700C is ignored, then how to check the wheel size? There is a better way. The confusion resulting from these non-standard measurement scales was not limited to France. Each country had its own share of confusion. Finally, the International Organization for Standardization (ISO) and the European Tyre and Rim Technical Organisation (ETRTO) came together and formed an international standard for referring to various measurements of the bikes, including bike wheel sizes.
The new international standard now indicates both the rim size and tire size quite differently. The tire sizes are now represented by two numbers separated by a hyphen, such as 37-622. The first number indicates the width of the inflated tire, while the second indicates the diameter of the tire with which it sits on the rim. The rim size, on the other hand, is indicated by three elements in the form 622x19C. The first part, 622 in the aforementioned example, refers to the diameter of the rim, as measured between the points where the tire sits. The second number, 19 in this case, which is preceded by a cross, refers to the inner width of the rim. Then the last element, the letter C here, refers to the rim type. The international standard recognizes three types of rims – straight-side (SS), crochet-type (C), and hooked-bead (HB). In the ISO standards, all tire size measurements are in millimeters.
Despite the international bodies’ best efforts to standardize the measurement system and eliminate confusion, some manufacturers, especially the German and Italian ones, continue to use the older term 700C to refer to the tire size. Do not purchase tires or road bikes based on this measurement. You may end up with a completely different configuration than you intended. Instead, check out the respective ISO measurements before you make the purchase.