The history of wheel sizes: From the 26-inch dogma through the ‘mullet mix’ to 32-inch

​The history of mountain bike wheels is far more than just a story of different rim diameters. It tells of technical progress, bold visionaries, skilful marketing and an industry that has spent decades searching for the ideal balance between agility and speed. Wars of ideology were waged, manufacturers staked out their positions, and riders defended their favourite size with almost religious fervour. Today, the debate seems largely settled – but the path to this point was anything but straightforward. 26-inch wheels made the mountain bike great. 27.5-inch wheels paved the way for a new generation. 29-inch wheels eventually established themselves as the standard. And the future? It is likely to be shaped not only by a new wheel size, but also by intelligent overall concepts that combine the best of several worlds, depending on the intended use. A journey from yesterday to tomorrow.

Conclusion

I started out mountain biking on 26-inch bikes, but I actually still own a 24-inch street dirt bike. My first carbon full-suspension bike ran on 650B wheels; most of the test bikes at BIKE these days are 29ers. However, I’ve now also added a 32-inch hardtail to my collection. The evolution of wheel sizes is unstoppable and began back in the 90s, thanks to the visionary Gary Fisher. - Jan Timmermann, BIKE editor

The 26-inch era: The origins of the mountain bike

When the first mountain bikes emerged in Marin County, California, in the late 1970s, nobody gave a second thought to alternative wheel sizes. The pioneers, led by Gary Fisher, Joe Breeze and Charlie Kelly, simply made do with what was available: sturdy 26-inch wheels from American cruiser bikes with a rim diameter of 559 millimetres. This pragmatic solution went on to become an industry standard. For nearly three decades, 26 inches was synonymous with mountain bikes. Frame geometries, suspension forks, tyres, wheels and components were consistently designed to suit this size.

The advantages of 26-inch wheels for mountain biking were obvious: compact dimensions, low weight, high stiffness and exceptionally agile handling. On the trails of the 1980s and 1990s, the small wheel was considered ideal. The fact that larger wheels might have theoretical advantages was of little consequence. The frame geometries and suspension forks of the time simply could not be adapted sensibly to larger diameters.

The visionary Gary Fisher and the birth of the 29er

As early as the late 1990s, one of the inventors of the mountain bike, of all people, began to question the established concept. Gary Fisher, together with frame builder Wes Williams and tyre developer Keith Bontrager, experimented with wheels based on the 622-millimetre rim standard – the same size used on road bikes. Fitted with wide MTB tyres, this resulted in what was later marketed as the 29-inch wheel.

The theory was convincing: improved rollover performance, greater traction and a smoother ride on uneven terrain spoke for themselves. In practice, however, the first 29ers had significant drawbacks. Suspension forks were heavy, tyres were scarce, frames looked bulky and the geometries were more reminiscent of elongated 26-inch bikes. Smaller riders, in particular, struggled to find suitable models. The industry was initially sceptical. Many manufacturers regarded the large wheels as a niche product for cross-country racing. It was only with improved suspension systems, lighter wheels and modern frame design that the concept slowly began to gain acceptance.

650B: The compromise known as 27.5 inches

Whilst the 29-inch size was slow to catch on, the industry was searching for a universal solution. The answer came from France – at least historically speaking. The 650B wheel size had already been in use for decades in the randonneur and touring bike sectors. With a rim diameter of 584 millimetres, it sat exactly between 26 and 29 inches. The real boom in this intermediate size began in 2012. From a marketing perspective, 650B was quickly rebranded as ‘27.5 inches’. The name sounded bigger than 26, but less intimidating than 29. The promise was: almost as agile as 26-inch and almost as smooth-rolling as 29-inch. The perfect middle ground, so to speak. Within a few years, almost all manufacturers were jumping on the bandwagon. For the 2014 season, countless new models were released exclusively in 27.5-inch. Some observers were already declaring the 26-inch dead.

The end of the 26-inch generation

Between 2013 and 2017, the 26-inch wheel size virtually disappeared from the new bike market. What many riders initially perceived as an artificially created trend actually had perfectly valid technical reasons. At the same time, mountain bikes as a whole continued to evolve. Geometries were modernised and bikes were fitted with longer reach values, flatter head angles, steeper seat angles and shorter stems. Simultaneously, suspension forks, shock absorbers and rear suspension designs became increasingly high-performance. It was only these developments that made it possible to fully exploit the advantages of large wheels. What had previously made 29ers seem sluggish suddenly became the benchmark for speed and safety.

Why 29-inch eventually won

From around 2018, a clear trend began to emerge. It wasn’t just cross-country bikes that switched to 29-inch wheels. Trail, enduro and, eventually, even downhill bikes also made the switch to the larger diameter. The reason lies in the physics. Larger wheels have a shallower approach angle to obstacles. Roots and stones are rolled over more easily, the tyres lose less speed and make more contact with the ground. At the same time, the larger tyre contact patch improves traction and braking performance. With modern carbon rims, lightweight tyres and sophisticated suspension systems, the previous drawbacks in terms of weight and agility have been significantly reduced. Today, 29-inch wheels dominate almost all competitive mountain bike categories – from marathon hardtails to World Cup downhillers.

The revival of the hybrid concept

However, the 27.5-inch wheel hasn’t disappeared completely. Rather than being used as a complete solution, the smaller rear wheel is now primarily found on so-called ‘mullet’ or MX bikes. The principle: 29 inches at the front, 27.5 inches at the rear. The large front wheel improves roll-over performance and control. The smaller rear wheel provides greater manoeuvrability on steep terrain, allows for shorter chainstays and makes wheelies and tight turns easier. This concept has become particularly well-established in the Enduro and Downhill World Cups and is now an integral part of many model ranges.

Looking ahead: the next evolution is on its way

Is there such a thing as the perfect wheel size? Not really. Developments show, rather, that wheel sizes are always part of an overall design concept. A modern 29er rides completely differently today than a 29er from 2010. Similarly, a current 26-inch bike with today’s geometry would probably perform significantly better than many people, in their nostalgia, imagine. Frame geometry, suspension, tyre width and chassis now influence handling just as much as the wheel diameter alone. And yet the next new wheel size is already in the starting blocks: 32 inches.

​The reasoning behind this is understandable. Even larger wheels promise even better roll behaviour, a smoother ride and additional traction. However, the idea is not entirely new. As early as the 2010s, smaller manufacturers and frame builders were experimenting with prototypes based on 686-millimetre rims. The concept gained international attention partly through the US manufacturer DirtySixer, whose bikes were originally developed for very tall riders. Individual racers and developers were also testing 32-inch prototypes on cross-country trails years ago.

However, numerous technical hurdles have so far prevented a breakthrough. As the wheel diameter increases, so do the rotating mass and inertia, making acceleration and changes of direction more sluggish. At the same time, the design of wheels and forks becomes more complex: To achieve the necessary stiffness, more complex rim profiles, longer spokes and correspondingly adapted frames are required. Added to this is the limited availability of suitable tyres, suspension forks and wheelsets – a classic chicken-and-egg problem that often slows down the adoption of new standards. Another limiting factor is ergonomics. Whilst 29-inch bikes can now be designed excellently even for riders under 1.70 metres tall, 32-inch wheels might force compromises, particularly with smaller frame sizes. It would be difficult to design the top tube height, chainstay length and front end in a way that makes sense.

It is nevertheless interesting to note that development in elite sport never came to a complete standstill. Time and again over the last few years, prototypes have been spotted, with which manufacturers are exploring whether further advantages are possible on fast World Cup XC courses. The performance capabilities of modern carbon materials and new manufacturing methods make designs conceivable that would have been considered unrealistic just ten years ago. The first 32-inch mountain bikes from small-batch production are already available to buy, and experts predict the launch of many new 32-inch models next year, particularly in the cross-country and gravel sectors. Some insiders are already whispering about an intermediate size of 30.5 inches. The mountain bike simply hasn’t reached the end of its development yet.

What do you think: what’s the ideal wheel size for a mountain bike in your opinion, and what do you make of the 32-inch trend? Let us know in the comments!