Tires are one of the most important parts of your bike, as they provide your contact for steering, stopping and accelerating. Good tires make life smooth and easy. Bad tires make for a bad day. Even the best tires wear out over time and need replacing, so whether your old set is falling apart or you are building a new bike, this guide will go over the different types of tires and tubes for different riding styles.
The main rule of tire and tube sizing is this: the tire must match the wheel, and the tube must match the tire. If you don’t know the size of your wheels, check your current tire. There should be a series of numbers on the sidewall, for example "700 x 20c" or "26 x 4.8." These designate the size of the tires.
There are two parts of tire size: width and diameter. Unfortunately, there are a bunch of tire standards. Some are measured in inches, some in millimeters. This can all be a bit confusing, but luckily more and more tires are marked with a standard: the ETRTO (European Tire and Rim Technical Organization) system, which consists of two numbers (for example, 20-622). The first number is the tire width, and the second number is the diameter of the bead (the part of the tire that seats into the rim to lock in place). If the second number matches on the tire and the wheel, it will almost always fit. In the ETRTO system, a 20-622 tire is equivalent to a standard 700 x 20c road tire.
The outer diameter of your tires is not so important for fit, but it does influence traction and speed. Skinny tires are faster and bumpier, while wide tires give softer rides.