With the advent of cycling in the modern age, the bicycle companies that produced the most bicycles standardized a few different sizes for bicycle wheels. This was a logistic necessity and an economic advantage, and out of these, the most common sizes are the 700C wheels found on road and racing bikes and the 26-inch and 29-inch wheels common in mountain biking. There are other sizes, especially in older bikes that predate the economic boom of cycling, and an entirely separate discipline of wheel sizes in the folding-bike market. However, each wheel size has its own distinct advantages and disadvantages, and no wheel can be said to be universally superior.
Determining Wheel Size
Modern bicycle wheels were standardized by the ISO, or International Standardization Organization. Two measurements are utilized to determine the tire size and, therefore, the wheel size on a bicycle. The first number is the tire's width, measured in millimeters. The second number, known as the bead set diameter, is the diameter of the tire where the bead meets the rim. Using these two measurements, tire size can be determined. The diameter of the rim is usually 6 to 8 mm larger than the diameter of the bead of the tire.
Common Wheel Sizes
The most common wheel size on American and European bicycles is the 700C wheel, which measures 622 millimeters across. This wheel size is the most dominant and provides a good balance between the control and maneuverability of a smaller wheel and the ability to roll over obstacles of a larger wheel. The 700C wheel is widely available and is the largest commonly produced size, although most bicycles that use the 700C measurement have thinner tires for road use. These tires offer superior roll-over performance at the cost of some maneuverability when compared to a smaller wheel.
Mountain Bike Sizes
Mountain bikes are more or less split between two competing wheel sizes. The traditional size, 26 inches, is just slightly smaller than a 700C wheel at 559 millimeters. This wheel size was once universal in mountain biking until the advent of the 29'er wheel, which is exactly the same size as the 700C wheel, but with much larger tires than a road bike. The debate between the 26 inch and 29'er is near hostile in mountain biking, with 26-inch advocates touting the increased maneuverability and wheel strength and 29'er advocates countering with greater rolling performance and, thus, comfort and traversing ability.
Another wheel size exists far smaller than the common sizes; small-wheeled bicycles have a variety of applications, the most common being folding bicycles for adults, BMX bikes and children's bicycles. Most folding bicycles use a wheel size similar to BMX bikes, the 406-millimeter wheel, while others use a slightly larger 451-millimeter wheel that is much more limited in manufacturing and availability. These bicycles do not need to be pedaled more, but the smaller wheels turn much faster than full-sized 700C wheels. In addition, maneuverability and steering responsiveness increase while hill-climbing difficulty decreases due to a smaller diameter.
Fatbikes are the largest-wheeled bikes available in the commercial loop. These bikes have specially made rims that are either 80 or 100 millimeters wide, far wider than the normal cycling tire. The tires on a fatbike require much more clearance from both the dropouts and the chain. These bikes are specially designed for traversing mud, sand and snow and provide much more flotation than average mountain bike tires at the expense of speed and maneuverability. Most fatbikes are built on the 29'er wheel size and are most popular for winter riding, where conditions often prevent all other types of cycling.
Max Roman Dilthey is a science, health and culture writer currently pursuing a master's of sustainability science. Based in Massachusetts, he blogs about cycling at MaxTheCyclist.com.