Tire And Tube Sizes

Sizes could be more precise. Of all the complications, figuring out the rim size could be better. Initially, it looks easy. Your tire says 26″, so you look for a 26″. And, most riders replace their tires with the same type and size as came with the bike. When you get to the store, it all starts to unravel. I counted six different tire sizes for 26″. All were 22″ to 23″ in inside diameter and 24″ to 27″ in outside diameter. Worse yet, the only skinny tire actually 26″ (outside) is an old Schwinn, rarely seen anymore. Additionally, some older 24″ tire sizes are nearly the same size as the newer 26″. (Note: outside diameter is the inside diameter, plus two times the tire width. Tread height is not counted.)

Where does that leave us? Thankfully, most tires are stamped with the International Standard or “ISO.” This standard was developed by the European Tire and Rim Technical Organization (ETRTO). The ISO size is written with the tire width first, followed by the tire inner diameter (e.g., 50-559 is our most common 26″ tire size, also called 26X1.95). If you are shopping for a 26″ tire, most likely it will be 559 (50-559 happens to be 22″ inside diameter and 26″ outside diameter and about 2.0″ wide).

Tire width is complicated by how you measure it, what size rim it is attached to, and what air pressure. Two factors are essential when looking at width: Will it fit in the bike frame, and is it the right size for your rim? Generally, tires will fit a rim that is 55% to 65% of the tire width. For example, for a 50-559 tire, the rim should be about 1″ to 1 1/2″ wide.

Fortunately, tubes stretch and come in a range of sizes. In our example, for the 26″ (50-559), our tube would cover tire widths from 1.75″ to 2.4″. This tube would be suitable for nearly all 26″ tires, vintage and new, 22″ to 23″ inside wheel diameter, and most widths.

Learn more, and see a sizing chart: Tire Sizing

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