Tire Width
There are a wide variety of tire widths available for the "standard" tire sizes. Which width is best for you depends on your applications. The most common width for road riding is 23mm. This is a good compromise between aerodynamics, weight, rolling resistance, and comfort.
A narrower tire will have lower aerodynamic drag and lighter weight. At the same inflation pressure, a wider tire will actually have lower rolling resistance on most road surfaces because the majority of the rolling resistance comes from the heat loss of tire deformation. Since a wider tire (at the same inflation pressure) will deform less, it will lose less energy while rolling.
Generally though, wider tires are run at lower inflation pressure. The added volume allows lower inflation pressures to be used without the risk of pinch flats and rim damage. The lower inflation pressure will provide a more comfortable ride.
The tire widths that you can use on your bike is determined by the rim width and the frame clearance. The chart above shows the range of tire widths that can be used for a given rim width. The rim width measurement is the inside width of the rim (i.e., the width of the bead seat in the rim). This is a fairly conservative range; you can probably get away with using a tire that is narrower or wider than the range indicated. If you use a tire that is too narrow for the rim, you're more likely to get pinch flats and risk damaging the rim if you hit pot holes or other road hazards. If you use a tire that is too wide for the rim, you risk damaging the rim and tire, and are also likely to have handling problems.
A bike frame designed for 23mm tires is unlikely to have the clearance between the tire and frame to support a 42mm tire, even if the rim could accommodate such a wide tire. Most road bike frames can accommodate a tire as wide as about 28mm. Cyclocross and touring bikes are generally designed to accommodate wider tires.
We recommend 23mm and 25mm wide tires for recreational road cyclists. The 25mm width is nice for long distance riding since it will provide a more comfortable ride. Narrower widths are worth considering for racers that are looking for every advantage.
For self-supported touring, a wider tire is desirable since the added load can be distributed over a larger contact patch. This will improve handling and reduce flatting. If your bike can accommodate it, use a tire that is at least 28mm.
Many touring and hybrid bikes will be fitted with even wider tires - up to 47mm wide. These wider tires will definitely provide a cushier ride, so if comfort is your main priority, sticking with these wider tire widths is a good idea. The main disadvantage to the wider tires is weight. Switching to a slightly narrower tire will give you a little better acceleration performance and provide a zippier ride.
For mountain biking, a wider tire (2.0 to 2.5") will provide more air volume which is beneficial for riding on loose surfaces. It will also prevent pinch flats on very rough terrain. If your riding is primarily on hard-pack dirt roads, a slightly narrower tire (1.5 to 2.2") will reduce weight and provide better performance.
Most modern mountain bikes have rims that are fairly narrow in the interest of saving weight. The cross-country tires that are usually installed when you buy the bike are actually on the wide end of the range that can be accommodated by the rims. While you probably should measure the rims to be sure, most mountain bike rims can easily accommodate a tire that is as narrow as 1.5" or even 1.3" without difficulty.
