There's no doubt that the emergence of 27.5” and 29” mountain bike wheels has been a real revolution over the last five years. Like it or not, they've rightly pushed aside the 26” wheels we were so used to seeing. Their advantages are quite varied: better grip, improved rollover angle, increased stability over rough terrain, greater speed and control, etc.
But as we know, not all riders are the same, and that's why not every size of wheel works for every type of cyclist. It's a matter of simple bike fit, in which the cyclist's height and the size of the bike play an important role.
Considerable effort has been made to adapt the new wheel diameters to the geometric standards of mountain bike frames, and more specifically, to those used in the XC and Trail disciplines.
The most work needed to be done on small bikes. Technically speaking, it is very difficult to create a size S or smaller frame for a 29” wheel with the same guarantees of manageability, stability and comfort that are found on the larger sizes.
Currently, size S cyclists who opt for the advantages of 29” wheels have seen how their bicycles no longer have the same ergonomic traits they are used to, and they are forced to turn to quick fixes like inverted stems with extreme negative angles, suspension forks with reduced travel or very forward seat positions, among other modifications.
Something as important as the geometry of the bike frame also changes when we fit a 29” wheel on a small bike. As we can see in the illustration below, which compares some XC bikes on the market to the new Orbea Alma 2017, it is not possible to obtain a stack of less than 600 mm when using a fork with 100 mm of travel and still maintain the optimal height of the bottom bracket.
Likewise, it’s difficult to design a reach of less than 390 mm without the problem of hitting the front wheel with your foot (a very common minor difficulty found on many 29” bikes). These measurements are still “a little big” for a size S cyclist, and these limitations also negatively influence the cyclist's posture on the bike, which is not ideal in terms of achieving maximum performance.
The XC World Cup, the best test bench
If we're talking about competitive XC, where every little detail counts, we cannot penalize size S cyclists by modifying the components or the bike geometry in a way that negatively affects them. The rider's position on the MTB is one of the keys to success, since it is closely related to the transmission of energy, pedaling efficiency, manageability and comfort.
Both Catharine Pendrel and Katerina Nash, elite riders on the Clif Pro Team, are size S cyclists who prefer to ride on 27.5” wheels after having tested both options.
Catharine has used 27.5'' wheels since 2014: “During training, I realized that I preferred the versatility and the easy handling provided by the smaller wheels,” claims the current XC World Cup champion. I felt like with a 29'', I was forced to accept certain bike configurations that were a little risky, and that it was harder to manage the front wheel in aggressive turns, due to weight distribution
In XC World Cup competitions, riders do not normally maintain a constant speed for very long, rather they are constantly changing pace. That's why six-time Olympian Katerina Nash prefers 27.5'' wheels, since “they let me adapt as quickly as I want to the features of the terrain and each situation during the race – such as tight curves, roots and obstacles.
In her experience, Katerina says that, “with this wheel size, I can quickly accelerate after the curves and keep up a good pace when pedaling up the steepest ramps. I can take on any situation and control the bike perfectly at all times, taking it where I want to go.”
Nowadays, XC competitions are organized with shorter laps and everything is repeated five or six times in each race. That's why Catharine Pendrel believes that “by adding a bit of weight to my 27.5” wheels, using tires with more volume, I can take advantage of the benefits in terms of performance that larger-diameter wheels offer. This way, I can conserve or improve my capacity for manageability without compromising the rest of the components on my bike.”
The carefully designed World Cup Geometry by Orbea provides the ideal stability over the toughest terrain. Steeper seat angles and a lower stack increase pedaling efficiency and maneuverability. Shorter chainstays, like those on the new Alma, which measure only 420 and 430 mm on the 27.5 and 29” models, respectively, offer maximum agility without sacrificing stability.
Big Wheels Concept
To remedy this problem faced by shorter riders when choosing their bicycle, Orbea has created the Big Wheel Concept (BWC), which offers all riders the advantages of large wheels, which vary according to the cyclist's size and height.
We offer frames in sizes S and M with 27.5” wheels, and frames in sizes M, L and XL with 29” wheels. This way each cyclist, regardless of his or her height and bike size, can enjoy all the benefits of a bicycle with large wheels designed to provide maximum performance under every circumstance.
As we can see, riders of average height, i.e., size M, have the option of choosing whichever wheel diameter they want. This is not a whim; the frame measurements simply allow us to optimize for both wheel sizes while maintaining all the benefits.
In that case, if my bike size is M, what size of wheel should I choose?
Here's where the type of cyclist you are and your goals come into play. If you're a good all-rounder, if you like speed, competition, pedaling and don't pay a lot of attention to the ruts along the trail, 29” wheels are definitely your best choice. A larger diameter wheel means more speed, more grip, better inertia, greater safety over uneven ground, etc.
On the other hand, if you are more explosive, you like to take curves more decisively, move around a lot on the bike, feel more agile on winding trails, 27.5” wheels might be better suited to your riding style.
Large wheels are the present and the future of mountain bikes, and Orbea wants to offer you all the advantages of these wheels, regardless of the type of cyclist you are and, above all, your bike size.