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There have been many different sizes of wheels used on bicycles, but only a few of them are common at the co-op. Here (external link) is a full list of sizes on another web site. It is a good list for reference purposes, but you can learn almost all of what you need to know on this page.

What tire size means

Tires have two sizes, diameter and width. Diameter is more important, because for the most part tires of different widths will fit on the same rim size. Tires of different diameters never will. The major size categories on this page are diameters, but there is some discussion of width within the sections. The diameter of a tire that matters is how big it is where it fits the wheel - it doesn't matter how big it is where it rolls on the road. The diameter where it fits the wheel is called the bead seat diameter, or BSD. It is measured in millimeters, and will be a number between 200 and 650.
[need a picture to contrast the two diameters]

Why it's not easy

It sounds easy - if tires are measured by diameter and width, you can find one with the right diameter and put it on the wheel. However, years ago people who made tires didn't write the correct diameter on the tire. They wrote some number that was a little like the tire's diameter where it meets the road. But as you know, that diameter is meaningless. It's a little easier with common sizes, since manufacturers usually used the same made-up numbers for most of them. We'll concentrate on those.

Common tires sizes

These four are the most common tire sizes that you will encounter if you are fixing bikes at the co-op. If you have a bike, it probably has one of these tire sizes as well. Farther down the page, there is some information on less common sizes. If you can learn how to spot these, you will know everything you ever really need to know.


Known as: 26", mountain bike size, cruiser size, "26 decimal"
Common sizes: 26 x 1.5", 26 x 1.75", 26 x 1.95", 26 x 2.15"

This is probably the most common size made today, since it's on almost all mountain bikes and most "cruiser" bikes. It was also the size of wheels on old American beach cruisers (the big heavy bikes with one speed - not the English-style bikes with three speeds). These are very easy to recognize - if you look at the list of common sizes, you can see that they are all known as 26 inches, and the width is given as a decimal number, like 1.5" instead of 1 1/2 inches. Any tire listed as 26 x a decimal is a 559mm. If you need to replace one, there are a lot of choices in width and tread, and you can choose one to fit the riding style - ask a key volunteer or staff member if you need advice.


Known as: 26" x 1 3/8", 3-speed tires
Common size: 26" x 1 3/8"

These are found mostly on 3-speeds, the old style of city bikes with turned back handlebars, fenders, and 3-speed hubs in the rear. They are also found on similar bikes without the 3-speed hubs (sometimes single speeds, and sometimes with derailleurs). They always say 26" x 1 3/8" on the side, so they are easy to recognize. Bikes are no longer made new with this size, but we have a lot of them at the co-op. If you need to replace one, there is only one type, so the choice is easy.


Known as: 27", old road bike tires
Common sizes: 27" x 1 1/8", 27" x 1 1/4", 27" x 1 3/8"

This size was used on road bikes in the United States for many decades, and there are still a lot of these bikes around. Anything with road handlebars at the co-op that is older than about 20 years will have these wheels. They will always have be labelled as one of the three common sizes, and will not be hard to recognize. Bikes are no longer made with this wheel size, but it is almost the same size as the modern road wheel size (see below), so be sure you check the tire rather than assuming any large wheel is one size or the other. If you need to replace a tire on one, you should typically use a 27 x 1 1/4" tire, although if the bike is very cheap you may wish to use a 27" x 1 3/8" for extra comfort, since people who buy the cheapest 27" bikes (e.g. $50 bikes) are not usually buying them to ride fast.


Known as: 700c, modern road wheels, hybrid, 29"
Common sizes: 700 x 25mm, 700 x 38mm

This size is not found too often at the co-op, but it is very common on new bikes. It is the size on all modern road bikes, and many "comfort bikes" and "hybrids", as well as some recent mountain bikes, known as 29ers (the wheels are referred to as 29 inches when they have mountain tires). It should be very easy to recognize these wheels if they have tires on them, as almost all of them will actually say 622 on the side, and most will say 700c as well. There are a wide variety of tires available for this size, and replacements should be chosen to fit the riding requirements. Ask a key volunteer or staff member.

Created by: admin. Last Modification: Wednesday 24 of May, 2006 15:03:15 UTC by admin.