By Vernon Felton
originally published in the March 2012 issue of Bike

A year ago I wrote this article for Bike and led the story off the following subhead:

“Twenty-niners are poised to dominate the mountain bike world and they're not alone: middle-child 650B is rolling in right behind. Is this the end of the 26-inch wheel? Not quite, but change is coming faster than you might think.”

At the time it was a bold statement. No one was publicaly talking about 650b and plenty of riders were (and to some degree, still are), holding out hope that the 26-inch wheel would continue to be the dominant wheel size in mountain biking.

A year later, much has changed. The debate on chat forums and at trailheads, however, rages on. Thus, we’re trotting this story back out. What’s more, over the coming weeks you’ll find extended Q&As with insiders and engineers from the likes of Norco, Santa Cruz, Specialized, Trek and Giant who are all grappling with the issue of wheel size.

Okay, enough with the intro. Here’s the story.

There's no love lost between those who adore and those who hate 29ers. And, while it shouldn't be, this is a love-hate affair. One side fervently preaches that the 29-inch wheel descended from heaven in 1999 and instantly outmoded all bikes equipped with "standard" 26-inch wheels. The other side is steadfast in its conviction that 29ers are noodly, sluggish piles of crap, entirely unfit for anything other than a Sunday stroll down the sidewalk.

None of this is news. What is newsworthy, however, is that we are on the brink of a paradigm shift: 29ers once the gangly, bastard child of bicycle design, will likely become the dominant wheel size for almost every bike sporting five inches or less of travel.

And, no, we didn't just pull that prediction out of our ass.

Over the past few months we've talked to a dozen of the cycling industry's leading engineers and insiders—people who've seen the future and are, at this very moment, crafting the bikes you'll see in 2014—and the vast majority agreed: in a few years, 29-inches will be the dominant wheel size for hardtails, cross-country full suspension models and the vast majority of trail bikes.

This does not mean, however, that 26-inch wheels are going extinct. The truth is a bit more complicated, and interesting, than that.

The bike industry truly jumped on the 29er bandwagon en masse a year ago. If you didn't have a 29er in your 2010 product line, you probably weren't selling a lot of bikes. The bigger wheels, however, have been skulking around the scene for decades. In 1999, Wilderness Trail Bikes got the ball rolling in earnest when they produced the first real 29er mountain bike tire. Soon riders began touting the benefits of the bigger wheel size. And those benefits are undeniable.

For starters, the big wheels roll over obstacles with greater ease than standard 26-inch wheels. Why? Let's say you're climbing a trail and happen upon a five-inch tall ledge. On a 29er, that ledge strikes the wheel at a fairly low point, which enables the wheel to float up and over the obstruction without much difficulty. That same ledge, however, would hit a 26-inch wheel at a higher point and steeper angle (relative to its axle), resulting in a lot of force pushing back against the wheel. At this point, you need to either pull up on the bars and rise above the ledge or go over the bars. Bottom line, you can clean the ledge on either bike, but the 29er gets over it more easily, seemingly on its own.

This phenomenon is called "angle of attack" and you've probably seen it in action before. Skateboards have tiny wheels and steep angles of attack, which is why they send you rag-dolling to the pavement the moment they strike a pebble the size of a pea. Monster trucks have huge wheels and very shallow angles of attack, which enables them to effortlessly climb over and crush countless Honda Civics and Toyota Tercels.

The relative ease with which 29ers roll over technical terrain often gives riders the feeling that they have more travel beneath them than the spec sheets suggest. Nice. Furthermore, the 29ers help you maintain you speed over technical terrain, since the larger wheels aren't hanging up as frequently in technical terrain. And speaking of momentum, the bigger wheels' greater rotational inertia works in their favor here as well so that, once up to speed, it takes less effort to maintain your speed on a 29er than on a 26er.

Traction? 29ers have gobs of it, thanks to a longer (albeit, narrower) contact patch. This is why you can ride a 29er shod with ridiculously pinner tires and still scale trails covered with kitty litter and scree.

And then there's the extra stability. Adding big wheels to a frame stretches the wheelbase, which adds stability. In addition, the bottom bracket on a 29er sits lower in relation to the axles than it does on a 26-inch wheeled bike. "Having the cranks below the wheel axle line increases the bike's stability at high speed," explains Rocky Mountain Bicycles' designer D'Arcy O'Connor, "this also makes carving corners smoother since you are 'in the bike' instead of 'on top of it'.

In short, 29ers had a lot going for them.

So, with all these things working in favor of big-wheel bikes, why did it take nearly a decade for the industry to glom onto them?

Because most of them sucked.

"They were flexy, had poor geometry, and were good at going in a straight line," recalls Scott Sharples, longtime professional downhiller and current Intense Cycles spokesman. "My first test ride only lasted 10 minutes, and I will never get those 10 minutes back, they are gone forever, wasted on a bad bike. I became a 29 hater."

What was at the root of this, for lack of a better word, suckiness?

For starters, the longer wheelbase adds stability but has the unfortunate effect of also reducing a bike's maneuverability. Cramming a bigger wheel into the back half of a frame generally requires that you add at least an inch to the chainstays to prevent the rear wheel from eating either the front derailleur or seat tube. That may not sound like much, but in terms of handling, those inches might as well be miles. Switchbacks and tight, twisty trails become a lot less fun.

Compounding the cumbersome, long wheelbase problem was sluggish steering. The increased gyroscopic effect of the bigger front wheel requires that you apply more effort at the handlebar in order to make quick steering changes. Plus there's the issue of trail. Trail is the distance between the front tire's contact patch and the theoretical point where the steering axis would hit the ground…

If the steering axis bit is confusing, imagine a straight line running parallel with the head tube and bisecting the ground…or just trust us on this one. Trail matters. Bikes with too little trail have nervous and twitchy steering. Bike's with too much trail tend to steer sluggishly. The latter plagued many 29ers.

Early designers tried to reduce the problem of excessive trail by steepening their bikes' head angles. The end result wasn't always pretty: bikes with steep geometry that somehow still handled tight singletrack with the precision of a shopping cart. A really stretched-out shopping cart.

And did we mention heavy and flexy? Twenty-niner wheels are, all things being equal, heavier, flexier and weaker than smaller wheels. Longer frame tubes also add a degree of flex and a few grams to the equation. Acceleration suffered, handling suffered and, last but not least, until recently 29er tire, rim and suspension fork choices were practically nil.

In short, 29ers had a lot going against them.

So, just like the kid with the dried-phlegm collection, official Hogwarts-edition cape and Dungeons and Dragons fetish, 29ers were, well, "challenged" from an early age. That's why so many manufacturers decided to pass on 29ers for a good 5 or 7 years. Still, a group of designers and riders knew the bikes could be better.

Dylan Howes, Trek Bicycles' director of suspension frame technology, sums up why Trek's Gary Fisher brand kept plugging away at 29ers.

"You had these bikes that were high and steep with bigger, heavier wheels and they just never felt quite right, but that didn't mean they had to stay that way. People tend to forget how long it took for the industry to design decent 26-inch bikes. It took decades."

Intense's Scott Sharples (who, for the record, is no longer a 29er hater) sees it similarly,
"If 26er steering geometry has been evolving for 20 years, for performance reasons as much as acceptance, how far do we have left to go in the 29er evolution?"

Advancements came in drips and dribbles, and as a result most of today's 29ers handle a whole lot better than the monster-truck models of the past. Trek worked with fork manufacturers to create fork crowns with greater offset, which reduced trail while allowing for more relaxed head angles. It was a huge leap forward in reducing 29ers' awkward steering traits. And then there's been the proliferation of thru-axle forks and rear ends, which have decreased some of the flex introduced by the bigger wheels.

The rear end, however, is still an engineer's nightmare; they need to shorten those chainstays, but one component in particular keeps holding them back…

"The biggest issue is really front derailleur and drivetrain clearance," explains mountain bike engineer Dave Weagle. "About 70 percent of the time that we spend designing a typical frame is spent dealing with front derailleur clearance. That's pretty brutal."

Fortunately, designing a 29er has become less of a hair-pulling exercise for engineers thanks to recent innovations. The advent of 2×10 drivetrains has helped, since it popularized shorter-cage front derailleurs and smaller chainrings. Chainstay mounted front derailleurs have been an even bigger boon. Of course, the new crop of fat 29er tires might just gobble up that extra five millimeters of open space, so something still has to give….

Perhaps if someone, say SRAM, eliminated the need for a front derailleur by creating a 1×11 drivetrain, which featured a sprawling 10×42 cassette? Rumors are floating about the Internet of just such a prototype. Eliminating the front derailleur would free up mountain bike design radically. Only time will tell. There is, however, yet another possible solution: 650B. [Editor’s note: Was this the first mention of SRAM XX1? Way back in March of 2012? Yes, yes it was…In response, I heard the sound of chirping crickets. Jesus, people, that was a gimme…]

Though fairly obscure, 650B is yet another mountain bike tire standard that's been around since the dawn of time. At 27.5 inches, it sits smack dab in the middle of 26 and 29. A few companies (most notably Jamis and Haro) have been trying to gain traction in the market during the past few years with their 650B models, but little has come of it.

The rumor mill, however, is rife with news that a large company with a massive following in Europe will go big with 650B next year and that Fox Racing Shox is partnering with them on the forks. Still more talk abounds of bike, tire and fork manufacturers preparing for 650B production.

"I've never been involved with more rumor and intrigue than with the 650B thing right now," notes Giant Bicycles' global product marketing manager, Andrew Juskaitis. " It's a little bit cloak and dagger right now. Everyone in the industry is trying to figure out what everyone else is doing with 650B and what they should be doing themselves."

There's potential for 650B to be huge. The middling wheel size allows for short chainstays, which means that designers can immediately crank out six-inch travel 650B models that still possess the maneuverability of a true "all mountain" bikes.

Norco designer Owen Pemberton sees the potential here. "650B really excites me," says Pemberton. "Preliminary concepts have shown us that the rear-center lengths on current 26-inch wheel bikes can be achieved with 650B wheels… 650B could be the perfect wheel size for the 140-160mm travel range. Essentially, we could see bikes with improved grip and rolling characteristics over 26-inch wheels, but with very few of the handling/suspension drawbacks of 29ers."

And here's the clincher: from a marketing angle, 650B is the best of both worlds—more momentum and better angle of attack than a 26er, yet lighter and stronger than a 29er.

What's not to like?

"650B sounds better on paper than it is in real life," says Brandon Sloan, Specialized Bicycles' mountain bike product manager. "We've had difficulty picking up much of an advantage over 26, which has years and years of good rims/wheels, forks, frames and tires to pick from. Basically, 650 has similar geometry and fit challenges as 29 from a frame/fork perspective, yet has very little in the way of a nice selection of tires, wheels and forks to pick from. So, you kinda have all the problems that 29 had a few years ago with little of the benefit."

Kona product manager Chris Mandell sees it similarly. "We tested 650B, but when our test riders came back they kind of shrugged their shoulders and said, 'Well, it's not a 29er and it's not a 26er and I'd rather just ride a 29er.'"

Still, Mandell views 650B's rise as an inevitability. "It's going to happen, for sure. I won't say it's frustrating, but we are a little bit disappointed by it. We really feel like we tested it and did not find that the performance benefit was great enough. When we look around and see the people around us that are all fired up about it, it seems like a lot of them were late to jump on the 29er boat and they don't want to miss the 'next big thing' boat this time around."

How is this whole wheel-size phenomenon going to shake out over the next five years? Giant Bicycle's product manager makes a bold prediction echoed by most of the engineers we talked to. "Twenty-six isn't going to die, 29ers are only going to increase and 650B, whether you like it or not, is coming," says Juskaitis. "Here's how we see it, 29ers will own everything up to five inches of travel, we do see 26ers remaining for long travel—seven inches and above. It's that middle travel region, the six-inch travel bike, which is the murky part of the crystal ball. What can you do in that all mountain range? How do you want that bike to feel? Should it 26, 650B or 29?"

"It really boils down to who you are as a rider, where you ride, and what you want out of a bike," says Trek's Dylan Howes. "That's exactly why we still have two full lines going forward—26 and 29. There will always be riders who prefer the feel of one wheel over the other and that is ultimately what will keep both wheel sizes around."

So, will the 26-inch wheel dodder off to an early retirement? Not a chance, but the days when it completely dominated mountain biking appear to be at a close, and with good reason: each wheel size has its merits. Do you race cross-country or trail ride somewhere that's not terribly tight and twisty? The latest big-wheel bikes kill it in that kind of environment. Do you prefer to finesse your long-travel bike in particularly tight and technical terrain? A bike with 26-inch wheels generally makes more sense in that application. Downhiller or freerider? Twenty-six inches still rules the gravity market and probably always will.

Dave Weagle sums up a sentiment shared by every designer we spoke with, "The 26- inch wheel isn't going anywhere," says Weagle. "I'll still be riding them in five years, but at the same time, alternative wheel sizes do have a place in mountain biking. I think that some riders and companies are a bit too fanatical about 29er versus 26er… I don't get too caught up in that mentality. If a mountain bike is well balanced in geometry and suspension, then it's going to be a lot of fun to ride. The true mountain bikers will find the tools that work for them and get on the trail, while the fanatics will still be arguing about wheel size at the coffee shop."