MOUNTAIN BIKE WHEEL SIZE 101
A Little Bit of History
Wheels didn’t need much explanation until the early 2000s. They were 26-inch and mostly interchangeable between mountain bike frames. The 26-inch wheel dominated off-road tracks for many years but in 1981 the introduction of multi-terrain, knobby 700c road bike tires began to raise a few eyebrows in the mountain bike industry. A road bike wheel is measured as 700c, which means it has an outer rim diameter of roughly 622 millimeters. That is the same outer rim diameter of a 29-inch mountain bike wheel. 29-inch, or commonly referred to as 29er, wheels and tires are now common on mountain bikes but it took a while for them to first catch on. Initially no one made a wide enough 29er tire for mountain bikes. It took 18 years for the first multi terrain 700c road tire to transform into a full width, knobby mountain bike 29er tire. Wilderness Trail Bikes created the first tire in 1998 and the big-wheeled movement quickly began to spread through the XC mountain bike category. 26, 27.5 and 29-inch are the wheels sizes found on most bikes today. These wheel sizes have divided and united the bicycle industry on various occasions. The following sections will explain standard wheel sizes and their benefits so you can choose the one most appropriate for your riding style.
The Mechanics of a Wheel
The mountain bike wheel is made up of a hub, rim and spokes. The hub holds the spokes and the spokes thread into nipples that are placed into rim through gusseted eyelets. The nipples are threaded onto the spokes until a standard tension throughout the wheel is reached. The perfect harmony of spoke tension creates a durable mountain bike wheel capable of taking a lot of abuse. 26, 27.5 and 29-inch wheels have different spoke lengths and rim diameters that give them their defining design and ride qualities.
29er Wheel Advantages / Disadvantages
The most notable advantages of a 29er include the ability to roll over obstacles easily and maintain momentum. The 29er wheel is able to roll over obstacles easier because of the large 29-inch rim diameter. Think of how a rough surface can prevent a skateboard wheel from passing over smoothly without hang up, compared to how a bmx wheel feels riding over the same surface. Those two wheel sizes are drastically different but illustrate the roll over benefits of the larger wheels quite well.
The added weight of the 29er tire and rim gives the wheel a greater rotating mass. This added weight, paired with the larger rim diameter equals the highest rotational momentum of the three sizes. The overall consensus is that 29er wheels roll faster for longer, in off-road terrain. The tire contact patch on a 29er is also larger than 26 and 27.5-inch wheels. The tire contact patch is the amount of tread that touches the ground while rolling. A larger rim and tire diameter means more rubber on the ground resulting in more traction.
The disadvantages of 29ers are weight and size. There is more material used for a 29inch wheel. Longer spokes, more rim material and more rubber used in the tire. The extra weight addition decreases braking power and wheel acceleration. The decreased braking issue has been solved with the use of larger brake rotors that provide more stopping power. The extra weight and size will still be a slight acceleration disadvantage but is a minimal draw back in the grand scheme. In the early days of the 29er, stiffness and retaining true was an issue. True is the overall roundness of a wheel laterally and vertically. In response to a general lack of stiffness in larger wheels, a wider hub shell standard called Boost was introduced. Boost is helping to combat wheel stiffness throughout the sizes. A wider 148mm hub shell in the rear and 110mm hub shell in the front has been implemented to increase spoke angle and give the 29er the same stiffness seen in current 26-inch wheels.
Today, carbon rims and boost spacing are pushing to make the 29er a competitive wheel size for all mountain biking applications from XC to DH.
Where Are 29ers Found?
The XC category was the first to adopt 29er wheels. The roll over and momentum carrying abilities spoke to riders and racers. That rider group noticed the performance benefits immediately a quickly made the switch to the wheel size. As the industry moves forward in time and space the 29er continues to break down mountain bike boundaries. Many riders from XC to Gravity, now desire the 29er’s momentum and roll over properties. Since the demand for strong and stiff 29er wheels has been met, expect to see them continue to populate the All Mountain and DH categories where they have yet to fully take over.
27.5" (650B) Wheel Advantages / Disadvantages
A 27.5 wheel is lighter than a 29er, has a little less roll over and momentum carrying qualities, and is stiffer. This wheel size is the response to the 29ers delayed acceptance in the Trail category. The jump from 26-inch to 29-inch wheels in this category was difficult for many manufactures to get on board with. The performance benefits and durability of the 29er was still questionable at the time of its introduction. The 27.5-inch wheel was presented to help blend the transition into bigger wheels. It is a bigger wheel but not quite as big as the 29er. 27.5-inch is also a great alternative for people below the 5-foot 4-inch height range who ride small and extra small bikes. They get the benefits of better rolling and more momentum than 26-inch but without the extra stand-over height of a 29er. Stand-over height is the measurement from the ground to the middle point of the top tube. This distance on small and extra small bikes can be harder to achieve with 29 inch wheels but the 27.5-inch makes for a good fit and better frame geometry.
Where Are 27.5" Wheels Found?
You will find 27.5-inch wheels primarily on bikes in the trail and gravity categories. Trail features in those areas mesh well with the needed stiffness, roll over and maneuverability offered by 27.5-inch wheels. The XC category uses this wheel size less often and prefers the use of 29ers.
26" Wheel Advantages / Disadvantages
The 26-inch wheel was the gold standard in mountain biking for many years because of its lengthy list of advantages. The first is durability. 26-inch is the smallest of the three wheel sizes, which means it has the shortest spokes. The short spokes equal higher tension throughout the wheel, making it less susceptible to becoming untrue. The next advantage is acceleration. A 26-inch wheel is the smallest and the easiest to accelerate. Think of a giant windmill versus a tiny windmill. It will take less wind to get the tiny one spinning than the giant one. This added acceleration helps to easily maneuver the bike in a wide array of technical trail scenarios. The smaller wheels put you lower to the ground and the lower center of gravity equals more stability throughout trail features. Cornering is another advantage of 26-inch wheels. The chainstays can be shorter to reduce the overall length of the wheelbase, making the bike fit into tight turns easier. Lastly, 26-inch is the smallest diameter wheel, allowing for extremely lightweight wheel build potential.
Where Are 26" Wheels Found?
Though 26-inch wheels have a long list of advantages, most manufactures have ceased production of frames designed to fit the wheel size. The introduction of 29 and 27.5-inch wheels has triggered the discontinuation of the 26-inch wheel. When considering a bike with 26-inch wheels it is important to understand the increasingly difficult market to find compatible replacement parts. Gravity is the category in which the majority of 26-inch bikes still live. There is still a strong following of 26-inch supporters in this category but even here manufactures have shifted gears to make 27.5-inch the new standard. 26-inch is on the endangered species list with no help in sight and it is just a matter of time before the wheel is a fossil in the map of mountain bike evolution.
27.5 and 29-Inch Plus Wheels
27.5-inch and 29ers wheels have an oversized tire category called Plus. Plus is a wheel with an extra wide rim diameter made to hold large tires. Plus rims and tires fill the gap between a Fat bike tire width and a normal mountain bike tire width. A 27.5 Plus wheel has the same outer diameter as a 29er wheel but with the ability to run much less air pressure and maximize roll over. 29 Plus wheel offers the same but with an even larger outer diameter, comparable to a 31-inch wheel.
Fat bike wheels are 26-inch wheels with extra wide hubs and rims designed to hold massively oversized knobby tires. Though the rims are 26-inch in diameter the overall outer diameter of the tire resembles a size closer to a 29er. These wheels are not lightweight nor do they accelerate quickly. The main benefit of a Fat bike wheel is to hold good momentum with endless traction. The wheels have a large tire contact patch because of the very low tire pressure and oversized circumference of the tire. These wheel go everywhere at a leisurely pace. This 26-inch wheel blend is found specifically on Fat bikes frames that are designed to fit the oversized hubs and tires.
When Considering a Wheel Size
If you will be riding primarily in the XC category, the 29er will most likely be your wheel of choice. If you are looking for a Trail bike the most available wheels size will be 27.5 inch. The 27.5-inch wheel will provide respectable roll over, lightness and maneuverability. If you value the more rollover, larger tire patch and momentum holding qualities of a 29er, there are also many options available in the Trail category. For Gravity the current wheel standard is 27.5-inch. There is a push to introduce 29ers into this category and it is just a matter of time before Gravity bikes use the wheel size regularly. It is important to take note of what wheel size is the current standard of your desired riding category. When purchasing a bike it is important to make sure it has up to date wheel and hub standards so that when its time to replace or upgrade parts ample options are available. Now that you have the information you need to make a decsion on the wheel size that is right for you, take a look at our articles about how bicycle suspension platforms and mountain bike tire options contribute to finding the right bike for you.