Bicycle tyre size impacts ride performance. After you choose the right type of bike for you--road, hybrid, mountain, cruiser--the type of tyres on the bike are the next biggest factor that dictate how fast or slow as well as comfortable your journeys will be. You are not alone, though, if the numbers on your tyre's sidewall leave you dazed and confused.
Tyre sizing explained
Manufacturers print a series of numbers on most bicycle tyres. At a minimum you will see two numbers situated as follows: "700 X 23" or "26 X 2.0." The first number tells you the tyre's diameter. The second number reveals tyre width. In the first example, your tyre is 700mm in diameter and 23mm wide. In the second case, your tyre's diameter is 26 inches, while the width is 2 inches. As VeloNews bike tech expert Lennard Zinn points out, some tyres contain a second series of numbers reflecting the "ISO" or International Organization for Standardization system. On a 700 X 23, tyre, the numbers 23-622 follow. The "23" refers to the width. The "622" reflects the diameter, in millimetres, of the part of the rim the tyre fits into.
Road Bicycle Tire Sizes
From a practical standpoint, the technical side of tyre sizing might mean little to you, particularly if you ride for fun. For most intents and purposes, road bikes come with narrow tyres. A common race bike tyre size ranges from 700 X 23 to 700 X 25, though some go narrower, all the way to 700 X 18, according to Zinn. On hybrid or commuter bikes, you often see a range of 700 X 28 to 700 X 38 tyres. Bike companies often equip hybrids with 26 inch tyres, ranging in width from 1 to 1 1/2 inches. Cruisers are an exception. Though meant to be ridden on pavement, such as beach paths, they use mountain bike size tyres for the purpose of comfort.
Mountain Bicycle Tyre sizes
Mountain bike tyres are straightforward when it comes to sizing. Generally, they come in a 26 inch diameter, ranging from 1 3/4 to 2.35 inches in width. Mountain bikes meant to be ridden downhill tend to have wider tyres, often approaching 2 1/2 inches. You usually have the option, though, of putting 26 X 1.25 or 1.5 tyres on your mountain bike for use on the road.
Brown's website stresses the relationship between tyre width and pressure. Wider tyres tend to require lower air pressure. Narrower tyres need higher air pressure. In either case, underinflated tyres produce more rolling resistance. In practice, it "bulges" as it contacts the ground and slows you down. Overinflated tyres produce a rough ride since they do not absorb bumps and debris as well as a tyre with some give.
Using Two Different Sizes
Consider using two different tyre sizes under certain circumstances. Brown suggests a wider front and narrower rear tyre for comfort. Since the front encounters your terrain first, going wider produces better traction and shock absorption. The narrower tyre will generally produce optimal rolling resistance, which translates into speed. Commuters in search of a more forgiving ride often overlook this relatively easy and inexpensive solution.