29 vs 26 inch Wheels - Is Bigger Really Better?

Are 29ers set to take over the world? Let’s peel away the hype and look at what’s real and what’s not in the great wheel size debate.

As I sit here and type, I’m wearing a T-shirt that declares, ‘29er Ministry of Mud – Wheel Worship’. Sounds religious but it’s only referring to a MTB wheel size. Log onto your choice of MTB forum and there’s no end of threads questioning the pros and cons of 26-inch versus 29-inch wheels, and more often than not the views seem very opinionated—heated and fiery discussions are the norm. While I’d like to think of mountain bikers as a relatively peaceful and easygoing bunch, it seems you only need to toss the wheel size debate out there to start a war—it really does seem to assume religious overtones.

On forums you’ll read statements such as, ‘In three years time you won’t be able to buy a 26-inch bike; 29ers will dominate the market.’ Or, ‘Twenty niners do everything better, why would you ever ride a bike with kiddie wheels?’ Top this off with the marketing campaigns from nearly every manufacturer who wants to tell us how good their new 29er line is and you’ll feel a little inadequate if you’ve only got 26-inches down there.

So now there’s more wheel size option; 26er and 29er (as well as 27.5-inch or 650B which sits in between). Why does this choice get people so worked up? Trail ride taunts of clown wheels and kiddie wheels may be tongue in cheek but there’s undeniably a lot of passion surrounding the great wheel size debate. You certainly don’t see the same level of forum flaming when the topic of 2.1 versus 2.35 tyres arises and nobody gets too evangelical on the pros and cons of butted versus straight gauge spokes!

The debate clearly isn’t going anywhere in a hurry—if anything it’s hotting up with the apparently imminent rise of 650B (even though very few manufacturers actually sell them at the moment). With this I’ve decided to don my flame suit and express my thoughts on the wheel size debacle.

In my role at Mountain Biking Australia magazine I’ve have the opportunity to ride countless bikes with 26-inch as well as 29-inch wheels (I’ll admit to only having ridden two bikes with 650B however). With this experience I’m entitled to have my wheel size preference, but the aim here is present a few facts and independent study results, as well as my thoughts to provide a balanced and hype-free overview. Something that I feel is needed, as the wheel size debate is really getting ridiculous at times.

So let’s break it down and have a look at some of the facts and furphies that surround the great wheel size debate…

Rolling Resistance

A long-held belief is that 29-inch wheels roll along with less effort than their smaller cousin. Until recently this has been based on theory and inherently subjective rider feel. The theory relates to energy loss through deformation of the tyre casing.

Assuming a comparatively hard trail surface, the tyre deforms and ‘squashes down’ when you sit on a bike. It squashes until the air pressure within the tyre supports your body weight. In theory 30psi (pounds per square inch) will create a three-square inch contact patch on the ground—that’s assuming a 90lbs or 40kg load on one tyre, divided by 30psi which equals 3sq inches of contact. Given the same casing construction, the same formula will apply to a 26-inch bike and you’ll also have a three-square inch contact patch. To create this contact area with a bigger wheel, the tyre distorts less and the sidewall flex is spread across a longer section of the casing. On a 26er the ‘tyre bulge’ is more pronounced and localised.

On a fast hard pack fire trail, 29-inch wheels may well offer lower rolling resistance, but if they weigh more and result in more aerodynamic drag, then the speed benefits may be close to non-existent.

As you roll along, the tyre deforms and that absorbs some energy. Not all of this energy is released when it rebounds and returns to its normal unweighted state—this stored energy explains why car tyres heat up at high speed. So more tyre deformation leads to greater energy loss and that means more rolling resistance. With the same casing construction, width and air pressure, larger diameter tyres deform less and therefore roll faster.

There’s certainly a sense that 29ers roll along better than 26-inch bikes but there are plenty of things that can blur human perception—are we just feeling the increased rolling inertia in the larger diameter wheels or do they really take less effort to pedal?

Given the dollars pumped into various pro-29er marketing campaigns, it seems there’s a decided lack of independent studies on this topic. Testing this in a lab is the best way, as it totally isolates the result from external factors such as wind, trail surface and line selection, not to mention what you ate for breakfast.

Thankfully there have been a couple of studies and German tyre company Schwalbe has been kind enough to let us in on their findings. Conducted at the German Sports University in Cologne, they did in-the-field assessment on the handling and ride characteristics with 50 individuals, who were not told which wheel size they were riding (although I can’t help but think it would be pretty obvious). This aspect was used to assess traits such as stability and traction but rolling resistance was tested in the lab.

Their testing found that 29ers do have lower rolling resistance than their 26-inch equivalent. The most pronounced difference was found on asphalt and gravel (harder surfaces) at lower tyre pressures. Powering the 26-inch wheel uphill at 20km/h on asphalt required 214.3-watts while the 29er only took 206.4-watts. That’s 7.9-watts less energy loss in the 29er—approximately 4% difference. This ‘best-case’ test result was achieved whilst running 21.7psi in both wheel sizes. Higher air pressures and softer surfaces brought the results closer together, although the 29er always had the rolling edge.

With tubeless set-ups most people will run between 24 and 30psi to avoid excessive tyre squirm, so the roll enhancement on smooth hard pack surfaces is likely to be closer to 3%. The threshold for human detection is generally considered to be 5%, so a 3-4% best case scenario is certainly not a big one. As for oft heard boast, ‘I have to brake-check myself or I’ll just mow down those kiddie wheel bikes when coasting downhill,’ well this data suggests that it’s not entirely due to improved rolling resistance.

On a smooth hard surface, wind is the main form of resistance when riding above 25km/h. Overcoming gravity takes the most effort when climbing. Rolling resistance consumes a comparatively small percentage of your total effort.

My personal observations also back this up. There’s a ride I do regularly with my test bikes, and it finishes with a steep, straight tarmac descent—it’s a simple case of tuck down and roll. With a GPS to log the data, I’ve recorded this stretch around a dozen times. My top speed has varied between 75km/h and 77.6km/h with no trend towards the 29er test bikes being at the faster end of this narrow speed range. Likewise, my 29er equipped riding buddy (who is similar in body-weight) does not roll effortlessly away from me on smooth open trails when I’m on a 26er. It’s not as scientific as Schwalbe’s lab testing, but it seems to back up their stats and suggests that the big-wheel rolling resistance benefits are not as earth shattering as some may believe.

Furthermore, there are things you can do with a 26-inch bike that will narrow that rolling resistance gap. Studies conducted by tyre manufacturers Schwalbe and Continental as well as independent labs such as Wheel Energy in Finland have all shown that wider tyres offer lower rolling resistance than narrow ones at the same air pressure. Why? Once again it comes down to distortion in the tyre casing; a wider tyre has a larger air volume and produces less sidewall flex at a given air pressure. Most of these studies suggest 4-5% improvements with wider tyres, so running some fatter tyres on your 26-inch bike could enhance your rolling resistance whilst also offering better pinch flat protection. Comparing fat 26 to thin 29 mightn’t seem fair, but in some ways it makes sense. A 29x2.1 Schwalbe Racing Ralph weighs 495g which is exactly the same weight as the 26x2.25 version. So given tyres of equal mass, the fat 26er may come even closer to the rolling resistance of a 29er.

With all this talk of rolling resistance, we have to pose the question, ‘does it really matter?’ The answer is a sufficiently vague ‘it depends’. When climbing a 10% grade on hard pack, around 82% of your effort goes into overcoming gravity (RST Sport Solutions - www.rstsport.com). In this case, rolling resistance only takes 12% of your effort, so power to weight ratio is a bigger factor when climbing (assuming the trail is smooth).

On level ground, rolling resistance becomes more important taking around 35% of your effort but wind resistance becomes the predominant force once you get over 25km/h. So once you get up to speed on a fast hard pack fire trail, aerodynamics will become a factor, and the 11.5% smaller frontal area of the 26er could well override the 29ers rolling advantage (see table; ‘Relative importance of aerodynamics, rolling resistance & weight in mountain biking). I’m not suggesting we all don aero helmets and tri-bars, but I do feel that pure rolling resistance isn’t the biggest thing influencing your speed on a smooth hard pack trail.

When the trail surface is soft, rolling resistance can vary greatly. Again courtesy of Schwalbe, one test (conducted by Peter Nilges, German College of Physical Education, Cologne) showed that on a grassy meadow, rolling resistance can consume over 50% of your energy. The same study showed that a rock hard 54mm wide tyre requires 50-watts more energy to pedal on soft grass when compared to a 62mm wide tyre inflated to 21psi. Flotation and the size of your contact patch on the trail becomes the important factor when traversing soft terrain.

Some may dismiss these tests and theories as being irrelevant, as they feel that their 29er is much faster than their old 26-inch bike (and they’d never go back). That’s fine and I’m not questioning what they feel. All I’m suggesting is that the issue isn’t as straight forward as many people think. The marketing constantly tells us that 29ers roll faster but the difference in pure rolling resistance isn’t that great.

Footprint Size & Traction

Another frequently espoused furphy is that 29-inch wheels have a bigger footprint on the trail and therefore provide better traction. Well as explained earlier, it’s the air pressure within the tyre that determines the contact area on the trail. With both running 27psi, a 26x2.2 and a 29x2.2 tyre will put the same area of rubber on the trail. What changes is the shape of the footprint with the 29x2.2 tyre producing a longer but narrower contact patch than the 26x2.2. With the same amount of rubber on the trail, straight out traction on level ground shouldn’t vary radically, although I’m not aware of any studies that back this up. Perhaps the long but skinny 29er tread acts more like an ice-skate blade to prevent sideslip but I’m only speculating.

At the same air pressure a 29-inch tyre (bottom) does not have a bigger contact patch when compared to an equivalent 26er (top). It's simply a different shape with the 29er being longer but narrower.

To put more rubber on the trail you need to run lower air pressures. You can ride a fatbike with 6psi in the tyres and they have a massive footprint on the trail—the traction that they produce is a total game changer. With a circumference that’s 11.5% bigger, a 29er tyre will have an 11.5% larger air volume. So all things being equal, you should be able to run a 29er tyre with 11.5% lower air pressure than an equivalent 26-inch tyre. If you typically run 30psi in 26-inch wheels, you should be able to use 26.5psi with 29-inch wheels. A 3.5psi drop in tyre pressure will undoubtedly help to improve traction but it won’t make you float on water.

Of course you can mount 11.5% fatter tyres on a 26-inch bike and drop the air pressure to match. Swap from 26x2.1 up to 2.35-inch tyres and you’ll also get improved traction, comfort and pinch-flat resistance. Wider mightn’t be practical if you already run 2.4-inch rubber, however swapping to wider rims will provide more sidewall support and air volume in the same tyre. This again permits lower air pressures and creates better traction with less tyre squirm when cornering.

So yes, on a consistent trail surface 29-inch wheels can improve traction, but you can also enhance the traction of a 26-inch wheel by mounting fatter tyres (which will probably be similar in weight to the 29er rubber too). In other words, there are plenty of variables that you need to take into account and it’s not as simple as ‘29ers have a monster-truck footprint and traction to match’. Listen to the hype but just don’t swallow it whole, okay?

Rollover Ability

This is where the big wheels really deliver their killer blow. It is their true and undeniable strong point. The angle of attack is better on a big-wheeled bike—think of what it would be like to run into a kerb on a razor scooter versus a mountain bike and you’ll get the picture. Between a 26-inch wheel and a 29er the angle of attack improves by around 5%. Not a huge figure in itself but it’s a difference that’s clearly felt in certain situations on the trail.

In my experience 29ers are noticeably better at clambering up steps and ledges—especially when going uphill where momentum isn’t on your side. The big wheel will contact a ledge earlier and roll up it in a more gradual manner—you are more likely to roll up an obstacle rather than run into it.

The same applies to smaller bumps and holes in the trail. Every bump that you hit forces the wheel to rise and then fall on the opposing side. The 29er starts to rise earlier and this makes the resulting jolt less violent. A larger diameter wheel is also less likely to fall into smaller holes; again producing a smoother and more settled ride.

I feel that this ‘roll-over ability’ is the main factor behind the rolling resistance and traction improvements that many people feel when they swap to a 29er. When laying down the power on a climb, if the wheel isn’t unsettled by trail irregularities, then you feel that it has better traction. If you roll straight over smaller holes and have a smoother ride up and over the other bumps, then your forward progress isn’t disrupted and you roll faster.

Big Wheels vs Suspension

Thanks to their roll-over ability, 29ers are credited with providing a smoother ride. Many equate it to suspension travel and suggest that you don’t need as much travel on a 29er. There’s no doubt in my mind that a 29er hardtail offers a smoother and more settled ride than a 26-inch hardtail, but can you equate the wheel size to suspension travel? I’ve heard people suggest that a 29-inch hardtail matches a 100mm travel 26-inch dually when it comes to descending the rough stuff. If this is true they’d have to be comparing their hardtail with a very poor performing dually, well either that or they’ve sipped too much 29er Kool-Aid.

I own a 29er hardtail and have tested many, and I know that if I don’t lift my butt for a bump, I’ll get a boot up the rear end. The bump may have a fraction less kick than on a 26-inch hardtail but it really isn’t a massive difference. A 29-inch wheel doesn’t magically create 20mm of travel, let alone 100mm as the Kool-Aid drinkers propose. A hardtail is still a hardtail; it’s just that a 29er is a touch smoother to ride. Think of the difference between a nice titanium frame and an oversized alloy one and you’ll be getting close to the mark.

What about full suspension 29ers? I’ve seen plenty of wheel size shootouts where they pit bikes of equal travel and conclude that the big wheels are smoother and better. But how often do you get the same travel on equivalent 26 and 29-inch bikes? Not that often. Most 26ers have an extra 20-30mm of suspension at their disposal. What’s better in the rough, a 120mm travel 29er or a 140mm 26er—can less travel do the same job with the big wheels in tow?

The answer here depends on the type of bumps that you encounter and how fast you hit them. At lower speeds I’d say that big wheels have the most effect, especially on smaller bumps—say up to 50mm in height. In these situations dual suspension 29ers definitely feel longer legged than they really are. I’m reluctant to put a figure on it but lets say it might feel like an extra 10-20mm of travel.

Travel faster and hit the bumps harder and suspension travel starts to become the dominant factor. Anywhere you land from a jump or drop, more travel will make all the difference and the wheel size does nothing to assist.

Once you are flowing along the trail at speed, small bumps, big bumps, square edged hits and drops all meld together. Some trails may be better on 26-inch wheels and more suspension travel while other situations will be better with bigger wheels and shorter travel. If your penchant is to ride at speed through the rough and chunder, it’s pretty hard to refute the benefits of a true long travel dually.

We are now seeing a growing number of long travel 29ers, but mixing lots of travel and big wheels can come with compromises, as many of these bikes feel long and boat-like with an unavoidably tall handlebar position if they have a matching long travel fork. Whilst the bike fit and handling will always be a matter of personal preference, there’s no denying that shoehorning lots of travel under a 29er is no easy task.

Handling & Geometry

Twenty-niners are more stable; we hear this one a lot and I think it’s a fair call. Why they are more stable comes down to three interrelated factors.

First off, 29ers generally have longer chainstays and wheelbases. Through the early 90s, performance oriented mountain bikes had short 1,040-1,070mm (41-42-inch) wheelbase lengths. When combined with a steep 71 or 72-degree head angle, these bikes were nervous, twitchy and a real handful on the trail. While the head angles and wheelbase lengths of 26-inch bikes have mellowed, they’ve always clung to this ‘faster is better’ mentality.

Enter the 29er and manufacturers have been forced to extend their wheelbase lengths to make room for the additional wheel inches. Now it’s pretty common to have a mid-sized 29er hardtail with a 1,117mm (44-inch) wheelbase. This has done a lot to improve stability and is one reason why 29ers are more stable, predictable and less ‘tippy’ in steep terrain. Build the same limo-like wheelbase into a 26er and it too would be more stable. Longer travel 26-inch duallies have longer wheelbases and they are very stable and confidence inspiring. It’s not all about the wheel size.

Next up is the bottom bracket drop in relation to the wheel axles. Both 29 and 26-inch bikes tend to place the bottom bracket at a similar height off the ground. It’s just that you sit about 38mm lower down and between the wheel axles on a 29er. Once again this adds a sense of stability and makes you feel less likely to be pitched forward and over the bars.

Finally, there is more rolling inertia in 29-inch wheels. The tyres and rims are not only bigger and heavier, but they are also further out from the hub. Get them up to speed and they’ll want to keep going in a straight line, rather than being pinged off in this direction or that.

Of course every positive brings a potential negative and more stability can also be viewed as compromised agility. Smaller, lighter wheels and tighter chainstays will switch direction faster. Whether you can handle this depends on your skill set, reaction time and level of tiredness. Regardless of wheel size, the geometry of any bike needs to suit your skills and confidence level. There are 26-inch bikes that are inherently stable and some 29ers that are less so. Don’t get caught up in pigeonholing all bikes by their wheel size as there are good and bad examples in every batch.

Sizing

Bike fit is an area where you’ll find a lot of conflicting opinions. Some feel that a 150cm tall rider will be fine on a 29er. Others believe there are compromises for anyone shorter than 175cm. I’m not going to argue with either view, as bike fit is a very individual matter. The extra height of the front wheel and fork makes it harder to slam the bars down low. Flexible riders who like a lower handlebar position are more likely to face a compromised fit with a 29er. You’ll see some pretty extreme efforts to drop the 29er handlebar height at World Cup races—especially amongst the female competitors. Flat handlebars are a given but you’ll see negative 17-degree dropped stems sitting directly on the headset bearing with the dust cap removed and the fork travel dropped to 80mm. Everyone’s entitled to their own opinion but surely there comes a point where shorter riders are better off on a 26-inch bike. Where that point is depends on the individual and most trail riders will be pretty content with a slightly taller handlebar position. At 177cm and 64kg, I usually need to run flat bars and a negative 6-degree stem to get the right handlebar height on a 29er hardtail.

Certainly when you get to taller riders, the big wheels really look in proportion. Rider heights vary a lot more than the wheel sizes do. Someone who’s 185cm tall and on a 29er is roughly comparable to a 165cm rider on 26-inch wheels, so big wheels are likely to feel more in proportion.

Goldilocks Wheels

And where does 650B sit? While actual diameters vary with different tyre sizes, they sit a little less than halfway between the other sizes; 26-inch at 673mm, 650B at 698mm and 29-inch at 736mm. As a result it will have a bit less than half the 29er advantage and compromises won’t be as pronounced. For those who want bigger wheels but can’t get the desired fit on a 29er, 650B may be the sweet spot. It also looks promising for longer travel trail and all-mountain applications. Are the not-quite-halfway-there advantages worth the effort of yet another wheel size? Well that’s up to the market to decide.

Rider Perception & Opinion

To sum it all up, we can pretty safely say that 29-inch bikes offer a very slight advantage in rolling resistance that becomes far more obvious on irregular trail surfaces. They roll up and over obstacles more easily and maintain momentum and traction better as a result. Stability is generally improved and they can be a better match for taller riders.

On the negative front they are heavier with slower acceleration due to their added weight. It’s not just that the tyres are heavier, the fact that the extra weight is placed further out from the hub centre makes the additional mass even more noticeable. Some will argue that fancy carbon 29er wheels are now as light as a good set of 26-inch race wheels. Sure, that’s true but apply the same construction to a 26er and they get lighter yet again. Given equal materials and construction techniques, small wheels will always be lighter and accelerate better.

The weight difference is accentuated as 29er forks, frames and other structural parts need to be stronger to maintain equivalent levels of rigidity with the added leverage created by the bigger wheels and longer fork. Either that or 29ers start to get kind of flexy.

The added weight, slower acceleration and greater stability tends to make 29ers feel a little sluggish and less agile when stacked up against a comparable 26er. Whether this works for or against you is really a matter of personal preference.

New riders and those with an average skillset can find that the stability and roll-over ability gives them the confidence edge that they’ve been looking for, and with more confidence you’ll always ride above your perceived ability. Some say that 29ers dull your riding skills, but if you gain confidence you’ll attempt harder obstacles and develop into a better rider as a result. A little extra confidence can go a long way. Of course you could also gain your confidence boost on a lightweight 130-140mm travel 26-inch dually, but some will always be drawn by the simplicity of a hardtail.

Technically adept riders who pump the terrain and can really handle their bikes may prefer the lighter weight, better acceleration and all-round ‘flickability’ of a 26er. Others may want stiffer/stronger 26-inch wheels with big volume (but still comparatively light) tyres and lots of travel to tackle rough and challenging terrain.

As for XC racing, the area where 29ers are really gaining traction, I feel the best wheel size will vary depending on the course. With lots of stop-start corners and steep climbs, a 26-inch wheel may be fastest. On bumpy trails where the speed is more consistent, go the 29er. If the course combines all of these traits, as is often the case, just toss a coin. In any case, no wheel size is going to win the race for you. Even at the elite level, where races are won by fractions, it’s the rider that wins the race. World Cup races now see 29ers predominate, but that doesn’t stop Julien Absalon from winning on a 26er or Nino Schurter winning on 27.5-inch. If you’ve already got a perfectly good 26-inch XC bike, you don’t ‘need’ a 29er to be competitive. Sure, the big wheel benefits can be attractive – especially on a hardtail – but remember that smaller wheels also have their own strengths in weight and acceleration. Smaller wheels can also offset the added weight of suspension, making a lightweight dually a competitive choice on a rough course.

So there you have it, there may be some myth surrounding 29ers but they clearly have a lot of merit. Is the 26-inch wheel format in its death throws? I certainly hope not, as it’s got clear benefits that some riders will value too.

In the end it’s always best to try different bikes, suspension formats and wheel sizes for yourself to decide. Borrow mates’ bikes, go to demo days, research and form your own opinion. In many ways the wheel size is irrelevant, it’s the complete bike package that matters—suspension, handling, acceleration, stability and fit. After all, you don’t want to buy a fashion statement; you want a bike that suits your favourite trails and makes them more fun to ride!

Thanks to RST Sport Solutions (www.rstsport.com) and Schwalbe (www.schwalbe.com) for their assistance and sharing of technical data.

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