Larger wheels sacrifice some strength and handling to roll over larger obstacles.
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The debate among mountain bikers between 26 inch wheels and 28 inch wheels is one of the most contested and undecided aspects in competitive cycling. There are riders who support one size or the other exclusively in their particular sport, and because each wheel size has its particular benefits and drawbacks, neither has completely taken over the market. Understanding the differences between these sizes and what the implication is for the rider can help you decide which style of bike is best for you.
Wheel size in cycling is standardized, and several wheel sizes are ubiquitous across mass-manufactured bicycles, regardless of their brand. The way a wheel size is measured is by the diameter of the tire from edge to edge, known as the bead set diameter. For modern bicycles, the bead of the tire is about 6-8 mm smaller than the rim's diameter. Tire diameter and width affects the traction, handling and rolling performance of the bike.
Mountain Bike Tire Sizes
The 28 inch wheel is often referred to as a "29er" wheel in mountain biking. 29er bicycles have the largest wheel size available for mountain bikes at 622 mm, which is identical in diameter to the common road bike wheel size, 700c. The smaller 26 inch wheel had long been the standard size in mountain biking, and became a cultural standard in most other areas of the world, such as South America. 26 inch wheels have a smaller rim diameter at 559 mm.
26 Inch Wheels
26 inch wheels were initially popular for mountain biking because their smaller wheel size increased their handling and maneuverability, which was a benefit for off-road riding. In addition, the smaller spoke length and rim diameter increased the wheel's strength, which decreased the amount of maintenance a mountain bike needed. These aspects continue to make the tire popular for mountain biking today, and also account for the tire's widespread use across the rest of the globe, especially in underdeveloped nations.
28 Inch Wheels
The 29er's wheel size has been recently mainstreamed in mountain biking because of an increase in rolling performance, which is a measure of how well the bike can roll over obstacles of different sizes. This increase in traversal ability is also coupled with newer methods of wheel building that give modern wheels more strength than in previous decades, which makes the durability of the rim against distortion less of a deciding factor in wheel choice. These larger wheels sacrifice some maneuverability, but for sports like downhill racing and all-mountain racing, this drawback is acceptable for the greater rolling performance afforded by the larger wheel.