![]() ![]() 27” wheels have an ISO measurement of 630 while the standard road bike wheels of today have ISO size 622, meaning they are around 8mm smaller than the outdated size. The older 27” size of road bike wheels are slightly larger than modern 700C road rims. 29” mountain bike tires are much wider than 700C tires, so they can’t be installed on narrow road bike rims designed for skinny, low-volume tires. While technically the same ISO size and inner diameter, most 29” tires won’t fit a 700C rim. The most serious winter tires are studded, meaning they have a heavy tread pattern with small metal spikes placed in each knob to dig into the ice. Wide mountain bike tires or fat tires are appropriate in winter because of their extra surface area to find grip. Winter bike tires help riders achieve traction in tricky, low-friction conditions on ice or snow. Riders should also get new tires if there are cuts, slashes, or cracks in the rubber which can occur due to normal use over time and make the tire prone to punctures. It’s time to replace a bike tire when the tread pattern is ‘bald’ or worn down enough that you notice a loss in grip. This means that tires around 25-28mm roll faster than the traditional 23mm racing option. More recently, though, studies have shown that wider tires actually offer lower rolling resistance than ultra-slim tires. They thought that wider tires would also create more friction and slow the bike down. ![]() Historically, road cyclists used the skinniest tires available (as narrow as 19mm!) to save weight and be more aerodynamic. Since roads are smoother, harder surfaces than mountain bike trails, wide tires and their added weight aren’t necessary for top performance. Road bikes use narrow tires to reduce friction with the pavement. Wide tires can allow bikes to safely navigate dirt trails, snowy paths, or muddy routes. Tires that are relatively wide, such as mountain bike or fat bike tires, use the additional surface area to get extra grip in tricky conditions. ![]() The wider the tire, the more rubber there is touching the road, trail, or other surface. The tires are the only place where bikes make contact with the ground, so tire width is crucial to traction and speed. On a mountain bike, 27.5 x 2.25 means the tire has a diameter of 27.5 inches and a width of 2.25 inches. These days, when brands list tire dimensions, the ‘c’ is paired with the width measurements, as in 700x40c. And don’t be fooled-the ‘c’ isn’t short for ‘centimeters’. The 700C option became the most popular and halted production of the other sizes. Way back when, French tire manufacturers made road tires in different widths- 700A, 700B, and 700C. We use the ‘c’ to refer to road bike tire sizes. This measurement is important for choosing a tire that will both fit onto the wheel rim and won’t be too large and rub against the frame. The second number is the width, typically given in millimeters on road bikes and inches on mountain bikes. Tread and tire width can affect the overall diameter, so the 700 is always a rough estimate. On a 700x40c tire, the first number indicates that the outside diameter is approximately 700 millimeters. The first number refers to the diameter and the second number is the tire width. Tire dimensions are described using two numbers- for example 700 x 40c. Studded tires can damage dry pavement so are reserved only for icy conditions when grip is at a minimum. Other specialty options are studded tires that integrate small metal spikes into each knob to dig into ice or snow. This is a popular tire option because riders can run lower bike tire pressure for better traction and don’t have to worry about trail debris poking a hole and causing a flat tire. Many mountain bike tires are tubeless, meaning they can hold air without an innertube and are less prone to punctures. A smoother central texture is great for straight-line speed while large knobs at the edge of the tire can dig into corners for increased grip. Tread patterns in the center of the tire are often different from the tread around the edge. Trail, enduro, and downhill tires have larger individual knobs with lots of space between them to better interlock with the ground. XC racing tires need to roll fast, so they have a low-profile tread pattern with knobs placed close together. Tire tread varies widely among mountain bike tires. The trickier conditions and bigger obstacles in trail or downhill riding mean only tires that measure 2.3”+ will provide enough traction and shock absorption. XC racing or recreational mountain bikes that ride on lighter terrain can get away with widths between 1.6” to 2.2”. Generally speaking, the more technical the terrain, the wider the tire. ![]()
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