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Common Tire Sizes

Generally, bike tire sizes are indicated with two numbers that correspond roughly to the outside diameter of the tire and the width of the tire. For example, a standard road tire is 700c x 23mm, indicating a tire diameter of approximately 700mm and a width of 23mm. Actually, neither of these numbers is an exact measurement, but this hypothetical tire would be quite similar in size to other tires marked 700c x 23mm.

The first number—the tire's diameter—is most important. Your bike's wheels are designed to work with tires with a very specific bead-seat diameter—that is, the diameter of the tire at the bead, which is the ridge at the edge of the tire that hooks into the wheel rim. This bead-seat diameter is indicated by a very specific ISO (International Organization for Standardization) number that refers to the diameter, in millimeters, of the tire measured bead-to-bead. For example, the ISO number for a 700c tire is 622. Each ISO number corresponds to a more general number (like 700c or 26") that is used to indicate the tire's size on packaging, etc. The ISO number is almost always also indicated on the tire, in parentheses, with the tire's width indicated first, and then the ISO number. For example, our 700c x 23mm tire would also be labeled with "(23-622)."

It sounds more complicated than it really is! Below, we'll go over the most common tire sizes in use these days.

  • 26" (ISO 559) is the most commonly used size for modern mountain bikes and is also used on many hybrid or utility bikes.

  • 700C (ISO 622) is the most commonly-used size for many road bikes.

  • 29" (ISO 622, again) is another popular size for mountain bike wheels and tires. It's actually the same bead-seat diameter as 700c tires, but most 29" tires are simply too wide and tall to fit 700c wheels.

  • 27" (ISO 630) was a size used on many older road bikes. It's not used by modern manufacturers, but because so many bikes were made for wheels and tires this size, these tires are still readily available.

  • 650C (ISO 571) is a size used on some high-performance road and triathlon bikes, especially those designed for smaller riders.

  • 650B (ISO 584) was used for some older mountain bikes as well as French utility and touring bikes, and never fell completely out of use. Recently, it's been making a comeback in a big way in mountain biking. Modern mountain bike tires using this size may be labeled 650B or 27.5".

As mentioned above, the second number in the tire size refers to the width of the tire. This number is often exaggerated, however, so a 700c x 28mm tire may only measure 26mm wide. This is probably the result of competitive pressures, since the narrower tire will be lighter, and light weight is the driving force behind many buying decisions in the cycling industry.

Tire sizing is additionally complicated by the fact that older bicycles often used some of these same size designations (particularly 26" and 27") for tires that are not compatible with these sizes (i.e., different ISO numbers / bead-seat diameters). If you have a bike that is more than fifteen or twenty years old, check out the following resources: Tire Size Chart, Older 26" Tire Sizes, Older Tire Sizes.

Get in touch with us if we can be of any help in figuring out what size tire you need! We carry a great variety of tires in common sizes, and also carry tires in old and hard-to-find sizes. Contact us at 1-800-682-0570 or [email protected].

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