Tires on bikes come in a a vast array of possible sizes, but here is a simple a guide.
First, tires are sized by their diameter and width. A common size is 26" x 2.125". This means that the tire is approximately 26 inches in diameter and the tread is about 2 and an 1/8th inch wide. All sizes on tires are "nominal" designations, meaning they are really just names, not precisely accurate measurements.
Almost all adult bikes will be one of only two sizes.
Most cruisers and many mountain bikes are size 26" (26-inch).
Many hybrids and most road bikes are 700cc (700 millimeters, or roughly 27.5-inches).
There are other diameter sizes, but they are encountered less frequently.
On a 26" bike, the width will normally range from about 1.5-inch to about 2.25-inch. There are tires outside this range, but they are far less common. Almost all cruisers come with a 26" x 2.125" tire.
The 700cc tire has a larger diameter and usually comes with a narrower (skinnier) width. Width on these tires generally ranges from about 23mm to 40mm. A 700 x 23 tire is very narrow and is used for racing. However, a 35mm or 40mm wide tire is standard for many hybrids. This tire is about 1.5-inches wide and offers a safer, more stable ride.
How should you choose a tire?
For most general riders, ignore diameter and pay attention to width.
Tread width is really the main consideration, especially since cruisers, hybrids, and road bikes come equipped with a standard diameter size. Here's all you need to know: wider tires offer more grip, stability, and cushion, but they are slower. Narrower tires are harder, jumpier, and more easily spooked by road debris, but they allow for maximum speed. Look for a width that balances these various attributes for your needs.
As for the tread itself, a smoother tire will be faster, but a knobbier tire will give you more grip if you want to venture onto unpaved terrain. Within these two basic categories, different tread options do not make much difference for general recreational riding. At this level, tread is an aesthetic consideration, not a performance consideration.
Feel free to check this video too to check how to find the right tire for your bike / ebike:
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