*European Tyre and Rim Technical Organisation The actual difference between these two wheel-tire combinations is a whopping 29 mm, though this also depends on the specific rim and tire used. Considering the immense differences in tire volume, a tire with a width of 25 mm (i.e., 700 x 25C) will never have the same outer diameter as a tire with a width of 45 mm (i.e., 700 x 45C). Since the “700” refers to the outer diameter of the tire, as we learned above, it becomes clear why this designation is technically incorrect. Therefore, a tire with a size of 45-622 is 45 mm wide and has an inner diameter of 622 mm, which corresponds to 700 x 45C in the French system. Contrary to popular belief, the nominal rim diameter isn’t the outer rim diameter, but the diameter of the bead seat on which the tire sits. It contains two pieces of information about the tire width and the inner diameter of the tire, the latter being identical to the nominal rim diameter. To put a stop to this and to introduce an up-to-date system, the industry introduced the ETRTO* notation standard. At some point, we started seeing 700 x 25C tires that measured only 24 or even 23 mm wide when inflated on the rim. In the meantime, we will continue using, like the rest of the industry, throughout this article!Ī lack of agreements between tire and rim manufacturers has meant that the outer rim diameter and the width of the rim base have never really been standardised. Strictly speaking, the 700C and 650B size designations are technically wrong, though we’ll explain why in further detail below. In contrast to a mountain bike with thousands of settings and adjustments, everything on a gravel bike comes down to the correct tire choice and the differences between options can be extreme! Ultimately, in this article we’re not discussing the differences between wheel sizes but the differences between wheel-tire combinations, that’s to say a comparison of the common 700 x 40C and 650 x 47B gravel configurations. However, look closely and you will see that the 650B tire (front) has a taller profile than the 700C tire (rear). For example, a 28 x 1.4″ tire has an outer tire diameter of 28″, about 711 mm, and a width of 1.4″, which corresponds to just under 36 mm. Along with the French standard explained above, the other common standard relies on inches. As such, a 700 x 25C tire should have a width of 25 mm when fitted and inflated. To specify the tire width, another two-digit number can be specified in front of the letter, giving you all the important parameters. Besides 700C from the road bike sector, 650B is the most common bicycle wheel size – no doubt very familiar to mountain bikers and gravel fans. In this case, the nominal rim diameter refers to the bead seat, where the tire sits on the rim. The number, in this case 700, indicates the tire’s outer diameter in millimetres and the letter represents the nominal rim diameter. This is where the confusion starts: the most commonly used French system consists of a metric number and a letter, such as 700C. Let’s start with the classic system of measurement which refers to the tire’s outer diameter.
The added agility of smaller 650B wheels encourages playful riding. It’s not surprising that we’re still relying on completely outdated standards that have little to do with current reality, leaving the unsuspecting cyclist struggling to make sense of it all. As is so often the case, today the result is a confusing mess of various size and type designations, some of which have been adopted without question despite the continuous evolution of the sport. In the past, with the growth and the accompanying professionalisation of cycling, many countries defined their own wheel size standards. What exactly are the differences and which size is right for you? Our article addresses wheel size myths, prejudices and the advantages and disadvantages of both.īefore taking a closer look at the advantages and disadvantages of 700C and 650B wheels, we should clarify the various terms and standards. 700C and 650B have established themselves as the two gravel bike wheel sizes to choose from.
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