Riding conditions on a mountain bike can be anything from a well-packed trail to a craggy descent, so your tires are critical to how well your bike responds to the challenges you meet on your ride. Tire sizes on bicycles can be anywhere from 12 to 29 inches in diameter and 3/4 to 3 inches wide. Having the best size for your mountain biking needs will give you the best performance possible.
Tire Diameter
The diameter of your tire has a significant effect on how well the mountain bike wheel rolls over the riding surface. Bicycle mechanic Sheldon Brown notes that some mountain bikers prefer 28- or 29-inch tires because they are ideal for riding over gaps and rocks. The problem with very large tires is that they increase the weight of your bicycle and reduce the shock absorption of your suspension system. For this reason, a 26- or 27-inch tire is recommended for the average mountain biker.
Tire Width
U.K. National Cycling Organization executive member Chris Juden states that most mountain bikers require a tire in the width range of 1 1/2 to 2 1/2 inches. Tires at the low end of this range tend to handle muddy conditions better because they have less rolling resistance, which is the friction the tire creates against the ground with its surface area. The widest tires have much more rolling resistance, which can be a desirable trait if you often ride on sand, gravel or other loose surfaces.
Tread Height
Most mountain bicycle tires have some type of tread knob design to provide traction. The recommended height for your tread knobs is largely dependent upon how wet or loose your riding conditions are. Tall tread knobs can be absolutely necessary in muddy or shifting riding conditions like sand, but if you take them onto a hard trail they may fold over and cause your wheel to become unstable.
Aerodynamics
The slope of your average ride can determine how concerned you should be with the aerodynamic relationship of your tire and rim width. Former bicycle industry engineer Kraig Willett states that riders who typically traverse on gradients less than 4 percent should use tires that are slightly narrow for the rim size to maximize aerodynamic efficiency. Once you begin to ride regularly at steeper than a 4 percent grade, the width of your tire matters less than its overall weight in terms of performance.
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