29er: The new bloodline of mountain bikes. Unlike traditional 26-inch wheels, the 29-inch design brings many exciting new features. Some might think these “big wheels” look like clown bikes, but in reality, most of them haven’t looked deeply enough to form that opinion.
Despite resistance from a small minority, 29ers are gradually becoming the mainstream in the mountain biking world. Every year, more and more 29ers appear in bike shops and on mountain trails. In 2010, mainstream brands' 29ers in shops across the US and UK were almost entirely sold out. Moreover, many world-class riders are winning race after race using these “big wheels.” It’s time we paid attention.
Size Matters: 29er vs. 26er
Let’s go back to 1986, when Dr. Alex Moulton, known for inventing the comfortable small-wheeled bicycle, introduced his creation. His bike featured 20-inch wheels and was an all-terrain bicycle. Unfortunately, the Moulton ATB (All-Terrain Bike) had one fundamental flaw. The small bumps that riders could easily ignore on a modern 26-inch bike were fully transmitted to his bike. Although, during an era when the vast majority of mountain bikes had rigid frames, his suspension ATB offered impressive comfort and handling, the 20-inch wheel size was inevitably phased out by the times.
If you’ve ever ridden a BMX on a regular mountain trail, you’ll never forget the painful experience. The smaller wheel size and shorter wheelbase aren’t conducive to riding on rough terrain. Imagine, with all other factors being equal, larger wheels with a greater contact arc make it easier to roll over uneven surfaces. But can we assume that larger wheels will always get through those terrains faster? Not always, because there are more complex factors to consider.
Take suspension, for example. In theory, all forms of suspension — including those on 29ers — seem to make the terrain feel flatter. However, installing suspension on a 29-inch mountain bike is much more complicated than on a 26-inch bike. The larger wheel size leaves less room for mounting the suspension, so the frame must be redesigned. Furthermore, larger wheels require redesigned frame geometry to optimize performance.
Larger wheels and tires also make the bike heavier, which is not ideal for speed. While 29-inch wheels handle square-edge bumps more easily, their performance isn’t uniformly better on other types of bumps. Smaller wheels have less momentum and accelerate more easily, but larger rims maintain rotational inertia better. Therefore, even before we find the optimal frame geometry, we shouldn’t hastily conclude that bigger wheels are superior just because they roll more smoothly.
What Size Wheels Should You Use?
The mountain bike market is still dominated by 26-inch wheels, which is easy to understand. For average-sized riders, pairing them with a thick tire is enough to meet the demands of mountain riding. Moreover, 26-inch wheels fit easily onto frames with standard dimensions without worrying about clearance issues when caked in mud.
Science time. The stated size of a mountain bike wheel refers to the diameter from the edge of the tire (outer tire). However, due to variations in tire thickness and tread height, 26 inches is only an approximate figure. Very thick tires can sometimes make the wheel diameter reach 27.5 inches, or even too large to fit into standard forks and chainstays.
In fact, 26-inch wheels paired with thick tires can give a similar ride feel to 650B (27.5-inch) wheels with standard tires. The 650B specification sits between 26-inch and 29-inch wheels. Some believe it offers a good compromise, providing the responsiveness we’re used to while improving obstacle clearance.
650B wheels can be made lighter and stronger than 29ers, and their frames look cleaner and slimmer with more clearance between the wheel and the frame. Undoubtedly, 29ers — and 27.5ers — offer great choices for those seeking a smoother ride, especially without front suspension forks, provided there are more rim and tire options available. They are also an excellent new choice for taller riders.
In the foreseeable future, 26-inch wheels will continue to dominate the market for average riders. But there’s no doubt that 29ers are quietly revolutionizing the scene. Now, let’s take a closer look at why 29ers are becoming increasingly popular.
The Early Days of 29ers
When the first mainstream 29ers hit the market, they showed great potential, but were still limited by a scarcity of fork options and by closely mimicking the geometry of 26-inch frames.
Gary Fisher’s early research was very useful, but it’s only in recent years that designers have truly begun to understand the differences in ideal frame geometry between 26-inch and 29-inch bikes. It goes far beyond simply adjusting frame angles. The length and size of the fork, stem, top tube, and bottom bracket all significantly affect overall stability and ride feel.
Then there’s the consideration of the longer rear stays and wheelbase, and how changes in tire contact area impact grip. Just like with 26-inch bikes, research in these areas for 29ers is ongoing.
Riders switch to 29ers because they love the increased speed and better obstacle clearance. For professional riders, on the same course, these advantages of 29ers don’t necessarily improve their overall times much. But as they gain experience, they tend to become more confident on rough terrain.
Keep in mind, improved comfort and confidence often equate to faster speeds. This explains well why some shorter female riders in World Cup XC races have achieved great success with 29ers. When the ride feels easier, time is saved. Next, let’s look at some common debates between 26ers and 29ers.
How Are Wheels Measured?
The terms 26-inch and 29-inch refer to the outer tire diameter (roughly, since tires vary). A thick tire on a 26-inch wheel might actually reach 27 inches or more. Thicker tires (in height) roll more smoothly than thinner ones, so larger wheels offer better comfort and traction.
The compromise option, and also one that’s hard to find on the market, is the 650B wheel with a 27.5-inch outer diameter, which can fit on some 26-inch forks and frames. Some fork manufacturers are now starting to adjust the crown height of their products to accommodate both 26-inch thick tires and 650B wheels.
Why Do They Roll More Smoothly?
The main reason larger wheels roll more smoothly has to do with the angle of the arc. Try rolling a hula hoop and a glass — compare the two. There are other differences too, but you get the general idea.
Larger and smoother arcs create a gradual transition between sharp corners and the ground. That’s also why riding a BMX down stairs is much harder than riding a mountain bike. Logically speaking, if the wheels are large enough, when they roll over a protruding edge, it feels more like rolling up a slope.
What about the grip of 29er wheels?
There's a common misconception about the grip of 29ers versus 26ers: if a rider sits on both a 26er and a 29er at the same tire pressure, theoretically they have the same contact patch. But in reality, even using tires of the same brand and series, the larger volume and shape of the 29er result in a wider contact imprint.
What about 29er frame geometry?
There are many factors to consider. A typical 29er feels more stable than a 26er. Part of this is due to the longer wheelbase and the extended rear end designed to accommodate the bigger wheels. While these features can be mimicked on a 26er, they are rarely achieved in practice.
Another reason for increased stability is that although the axle height of a 29er is 1.5 inches higher than that of a 26er, your actual center of gravity while seated is lower. Even though the wheels of a 29er sit higher on their own, when you factor in the rider, the overall center of gravity is lower.
To achieve better geometry, designers have also started rethinking fork dimensions to improve the handling of 29ers. As more brands release 29er-specific forks, the technical trail disadvantages of 29ers will become a thing of the past.
Why don’t all riders use 29ers?
In 2009 and 2010, the men’s and women’s marathon XC champions in the U.S. were both 29er riders. Some Trek team riders also showed significant improvement after switching to 29ers. Todd Wells won two U.S. national titles after riding his new 2011 Specialized Epic full-suspension 29er. Riders like Willow Koerber and Heather Irmiger also proved that smaller riders can adapt well to bikes with larger wheels.
Coincidence? Maybe, but look at the actual results. It seems the XC community’s long-standing reluctance toward mountain bike designs perceived as less user-friendly is changing—even if only to meet sponsor demands.
Who are 29ers best suited for?
Many companies are testing 29er DH models, and more and more XC riders are using 29ers. Is this just due to market pressure or because 29ers are inherently better suited to certain riders than 26ers? In this article, we’ve discussed many controversial technical issues, and concluded that different riders are suited to different choices.
Riders who enjoy the smooth rolling feel of 29ers may ride faster. But for those who can’t tolerate the delay in immediate acceleration caused by 29ers, the experience is worse. Simply put, 29ers mainly affect your subjective riding feel rather than offering a clear objective speed advantage. (BikeNet)