Numbers stamped on the tyre sidewall will tell you what your current tyre size is. Most common tyre sizes are 26 x 1.5, 26 x 2.0, 700 x 25c, and 27 x 1 1/4 inches. The first number is the diameter of the tyre and the next is the width.
Standard adult bikes, such as mountain bikes, require 26, 27.5, or 29-inch tyres. Twenty-four-inch tyres are found on cruisers or BMX bikes. Road bikes need 700c or 29 inches. This "c" is a French tyre naming system that has been used through the years up until the present; no need to panic.
All these measurements may be confusing. But what you have to keep in mind is that whatever your current tyre size is, you should pick the same tyre size if you ever need replacement. If you want to upgrade your bicycle tyres in terms of size, go a bit higher or lower only with the width.
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