There are many different sizes of tires and rims, which play an important part of how your bike will ride. You need to take your height, weight and bike size into consideration before purchasing a tire. Before deciding what size tire you want for your mountain bike, you must first understand the basics of tire sizing.
Tire Measurements
Tire sizes are marked on the outside of the tire, typically in brackets. The first number is the diameter measured to the outside of the tire, 26 inches. The second number is the width of the tire, 1.75 inches. Some manufacturers use decimal points, ISO system, or fractions to indicate the width. Keep in mind a 1.75-inch tire size marking is not interchangeable with a tire marked 1 3/4 inches.
Differences
Standard mountain bike tires are 26 inches, a universal tire size for all types of trails. This size tire has low-tire pressure and has excellent shock absorption properties. Tires that are 29 inches are wider than 26 inch tires, give you better traction on steeper softer surfaces and perform better on critical trails.
Tire Information
Tire size must always match the rim size using the diameter number. Most rims can support many different widths, typically between 1.8 and 2.4 inches. As you add width there may be issues with the tires clearing the brakes and frame. Always check clearance prior to purchasing the tires. Width also plays a factor in the comfort of the ride. Wider tires have better contact with the trail and make for a smoother ride. Thinner tires require greater tire pressure, which makes the tires faster but rougher on uneven trails. Purchase a tire that fits your style and the type of trails you commonly ride, smooth fire trails or rutted bumpy single trails.
Rims
Most off-the-rack bikes come with stock size rims relative to the frame size. Most manufacturers do not mark the rim size which can make it difficult to determine the size. To determine the rim size of your mountain bike, measure the rims yourself, find the manual for the bike or take it to your local bike shop. To measure the rim yourself, use a tape measure and measure from the outside of the rim to the inside axle bolt and then double the measurement.
Considerations
A 26-inch tire is the most common tire size and is great for the novice to intermediate rider. A 29-inch tire is for more technical advanced riders or the larger taller rider. If you are currently riding a 26-inch tire and want to move up to a 29-inch tire it will require changing to a larger rim.
Member Comments
smalliver October 7
Generally you cannot just change to a larger rim. Bike frames are made with specific wheels in mind. A 29" tire will not fit in a 26" wheel designed bike. With the advent of disc brakes there is the possibility to go smaller, but bike companies spend a lot of time and money designing optimal geometry for the specified wheel size.
Also, the difference in tire sizing (decimal points or fractions) vary by bike designer and now age. Over 90% of new bikes work on the decimal system and finding tires on a fraction system is sometimes hard.
A trip to your local bike store and a 10 minute conversation with an experienced mechanic would have been helpful in writing this article. There is really no information that is helpful here, just random ramblings about half learned facts.