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The truth behind 29ers
By Steve Worland, Mountain Biking UK
Despite opposition in certain circles, 29ers are slowly but surely gaining in popularity. Every year sees more of them on the market and out on the trail. US and UK dealerships almost completely sold out of mainstream-brand big-wheelers during 2010, and world-class racers are now starting to win on them. Perhaps it’s time to take notice.
Size does matterWay back in 1986, Dr Alex Moulton, famous for his comfy small wheelers, made a 20in-wheel, all-terrain bike. Unfortunately, the Moulton ATB had a fairly fundamental ﬂaw. Its 20in wheels were unduly disturbed by all the little dips and bumps you’d barely notice on a 26er. So despite the comfort and control of Moulton’s suspension – in an era when most mountain bikes were fully rigid – his ATB wasn’t around for long.
If you’ve ever ridden a BMX on a proper mountain bike trail, you’ll know it’s not a great experience. Smaller wheels, not to mention shorter wheelbases, are harder to ride on bumpy ground. Think about it. All other things being equal, a bigger wheel’s shallow angle of curve rolls over uneven terrain more easily. But can we also assume that bigger wheels will roll over rough surfaces faster? Not always – complications arise when you introduce stuff that plays with the ‘all other things being equal’ bit, because they never are.
Is the 29er frenzy worth getting caught up in? Figure out what feel of ride you favour before deciding
Take suspension. In theory, all forms of it, including big tyres, make terrain seem smoother. But ﬁtting suspension around 29in wheels is more complicated than it is for 26in ones. Without redesigning frames, there’s not enough room to ﬁt things in. And bigger wheels will usually require a different frame geometry to make a bike behave at its best.
Bigger wheels and tyres also tend to weigh more, so they don’t accelerate as well. And, while they roll over square-edged bumps more easily, they won’t accelerate down the other sides as quickly. Small wheels are simpler to squirt up to speed but bigger hoops can carry momentum better. So even before we get into the ﬁner points of frame geometry, it’s not as simple as saying that bigger wheels roll smoother so they’re better.
How big can you go?The mountain bike market is currently dominated by 26in wheels, and understandably so. They’re a good compromise for average-sized riders in terms of tackling rough terrain on fat tyres. And they slot into a typical frame structure without mud clearances being a major issue.
For the uninitiated, the stated size of a mountain bike wheel is the approximate diameter from tyre edge to tyre edge. But tyre height varies, so it’s rare that a wheel and tyre are precisely 26in across. Big tyres with deep air chambers can be as big as 27.5in – some won’t ﬁt into regular suspension forks or between typical chainstays.
The fact that 29ers make riders look little is something some people can't hack
Actually, ﬁtting a high-proﬁle tyre to a 26in wheel gives you an idea of how 650B (27.5in) wheels with normal-proﬁle tyres will feel. 650B is halfway between 26in and 29in – some say it’s the perfect solution, offering most of the nimbleness we’re used to but with some of the softer roll.
650B wheels can be built lighter and stronger than 29ers, and frames for them usually look neater than 29ers (with better clearances), which often look gangly. There’s no doubt that 29ers – and 27.5ers if more rims and tyres become available – are good options if you value a smoother feel, especially for those without a suspension fork. There’s also no questioning that they’re now becoming an increasingly relevant option for taller riders.
Smaller, 26in wheels will continue to dominate the market for the foreseeable future for the average mountain bike rider, but 29ers are deﬁnitely experiencing a quiet revolution in popularity. Now we’re going to take a closer look at exactly why bigger wheels are becoming increasingly common.
Early daysWhen the ﬁrst mainstream 29ers rolled out, they showed their potential but were hindered by a limited choice of suspension forks and geometry that essentially tried to mimic that of 26ers.
Gary Fisher’s early Genesis measurements were promising, but it’s only in the last couple of years that designers have truly started to understand the differences between ideal 26er geometry and ideal 29er geometry. It’s not just down to tweaking frame angles. The length of the fork, stem, top tube and bottom bracket all have a bearing on the overall stability and ride feel of the complete bike.
And this is all before you’ve even started to consider the pros and cons of longer chainstays, longer wheelbases and the way tyre contact patches inﬂuence how a bike grips terrain. Ideas on these elements of 29ers are still evolving, just as thoughts on similar areas on 26ers are.
Cross-country racers are converting to 29ers to handle previously unrideable ground
Converts to big-wheelers just seem to love their ability to make riding fast, bumpy trails much easier. The rolling advantages of big-wheel bikes may not offer a convincing overall speed gain on a given cross-country circuit to highly skilled pro racers, but the more we’ve ridden them the more we’ve felt that the best ones can do a lot to boost comfort and conﬁdence during those rough outings.
And remember, a boost in conﬁdence and comfort like that usually equates to more speed simply because of the feel-good factor. This may well be why several of the smallest women on the World Cup cross-country circuit are having great success on 29ers. There are times when they just feel easier to ride. But ﬁrst, let’s take a look at the stuff people talk about in the 26er versus 29er debate.
How are wheels measured?Effectively, 26in and 29in refers to the diameter from tyre edge to tyre edge (roughly, because makes obviously vary). A high-proﬁle tyre ﬁtted to a 26in wheel can be 27in or more across. High-proﬁle tyres will roll smoother than low-proﬁle ones, so will offer some of the comfort and traction advantages of bigger wheels.
The halfway-house, harder-to-ﬁnd 650B tyres result in an edge-to-edge diameter of 27.5in, which ﬁts in some 26in frames/forks. Some suspension fork makers are now changing arch heights on their kit so that you can choose to ﬁt high-proﬁle 26in or 650B wheels in the same forks.
Why is rolling smoother?The main reason that bigger hoops roll more evenly is the angle of curve. Try rolling a Hula Hoop crisp along, then doing the same with a napkin ring. Okay, there are other differences, but you get the idea.
A shallower angle of curve isn’t as affected by bumps and dips because it bridges the gaps that form hard edges. That’s why riding a BMX down a ﬂight of stairs is harder than it is on a mountain bike. Taken to its logical conclusion, a wheel could be made big enough to simply ﬁll the hard-edged gaps that form a series of steps and roll the edges like a slope.
26in vs 29in – small difference, big change to your trail experience
What about traction?Some common misunderstandings about traction on 29ers versus 26ers are ﬂoating around. If a rider sits on a 26er and then a 29er with the same tyre pressures, the length of the tyre area making contact with the ground will theoretically be the same. But even with tyres from the same brand and with the same tread, the differences between volume and shape will often create a wider contact patch on the 29er.
And frame geometry?There are many factors to consider here. A typical 29er will feel more stable than your average 26er. That’s partly because of the longer wheelbase and the longer back end to make room for the bigger wheels. This could be mimicked on a 26er but rarely is.
Another stability factor is the fact that, though the wheel axles are 1.5in higher on 29ers than on 26ers, you’re sat lower between the wheel axles on a 29er compared to a 26er. So while a big-wheeler on its own has a higher gravity centre (think of the sideways tipping point) than a 26er, a 29er with a rider on board is actually more stable because the person’s body weight is on an axis that’s below the wheel’s axis.
In terms of the way handling is affected by geometry, designers seem to be gradually coming to terms with the way they can alter fork rake and trail to spice up the steering feel of 29ers. With an increasing number of decent suspension forks becoming available, this has already gone some way to correcting the misguided assumption that a 29er will be worse than a 26er on technical singletrack.
The keys to 29er popularity are wheel curvature angles – they're smaller, so rocky terrain is less problematic
Why aren’t all racers on them?The US men’s and women’s marathon cross-country races were won on 29ers in 2009 and 2010, and several Trek team racers are riding noticeably better since they switched to 29ers. Todd Wells won two US national titles on his 2011 model Specialized Epic full-sus 29er in July. Riders like Willow Koerber and Heather Irmiger have also shown that big-wheelers can suit smaller riders.
Coincidence? Perhaps, but watch the results. It seems that the notoriously conservative attitudes of cross-country racers to bike designs are changing, even if it might seem tempting to just put that down to sponsors’ wishes.
Who are 29ers best for?With several companies experimenting with bigger wheels on downhill bikes and an increasing number of cross-country racers using them, is it all just marketing pressure or are 29ers genuinely better than 26ers for certain riders? We’ve covered most of the contentious issues in this feature, and keep coming to the conclusion that it’s simply a horses-for-courses situation.
Riders who feel good about the softer roll of 29ers over bumpy terrain may well end up going a little faster as a result. But those who worry about the slight lag in instant acceleration might end up feeling slower as a result. At the end of the day, it’s simply a feel preference thing rather than a more obvious speed beneﬁt thing.
What the experts sayWe asked a selection of our test riders, along with some industry insiders, for their views on the 26er versus 29er debate. Here's what they had to say...
James Huang, BikeRadar's US-based technical editor
"Two-niners bring with them some notable advantages but also some challenges in terms of frame, fork and component design. The bigger diameter naturally carries with it increased mass and inertia, more wheel flex, and longer and more flexible frame tubes. But innovations such as wider hub and spoke flange spacing, wider (and thus stiffer) lightweight rims and through-axle dropouts go a long way towards equalizing the playing field. Some manufacturers such as Specialized have already taken the plunge, integrating all three features on their impressive new Epic Carbon.
"Tires need to be different, too. The Finnish test facility Wheel Energy has empirically confirmed that 29er contact patches are indeed longer and narrower than a comparable 26in wheel. As such, side knobs that might grab on one might not on the other, plus the 29in tire can put more center knobs on the ground at any given moment than the 26in, depending on the design.
"Merely carrying over what we know in 26in bicycle and component design gets the job done but real advancement will require a slight shift in thinking. If we're going to be saddled with the inherent drawbacks of 29ers, we may as well fully exploit their potential advantages, too. Once we do that, we may see them gain even more popularity."
Mike Hall, design engineer
“When I ﬁrst heard of 29ers, I rolled my eyes, shook my head and thought, ‘Those crazy niche seekers – what will they think of next?’. My completely untested opinion that they were a rubbish idea was reinforced when I saw one being raced by a short bloke. ‘If this is the new cool, you can keep it,’ I thought. That was the foundation of my opinion – they looked wrong.
"So imagine my disappointment when they started catching on! I started getting my ass kicked by guys on 29ers. Looking at them again I can see an elegant beauty, whereas before I just saw an ugly frame with a stunted head tube and awkward proportions. On the other hand, maybe the designers have found the right design language for them."
John Stevenson, editor-in-chief of Future Publishing's cycling titles
“The 29er craze is a load of fuss over not much at all. Yes, in theory, a bigger wheel rolls faster. But the difference is lost in the noise of all the other things that effect how a bike runs. The other claimed beneﬁts are either imaginary or could be emulated on 26in bikes. For example, 29ers work for tall riders because the big wheel forces long chainstays and a long wheelbase, so weight distribution is more like that of an average rider on a 26er. Just lengthen the stays on a 26er.
“The claim that 29ers have a bigger contact patch and better grip is based on a misunderstanding of physics. If you and your bike weigh 180lb and you have 30psi in your tyres, then to distribute your weight on the ground you’ll have six square inches of tyre on the ground, regardless of tyre size. Bigger wheels are said to be more stable because of their greater angular momentum. But tests have shown that angular momentum makes little difference to stability. What matters most is trail, a function of head angle and fork offset.
"Diversity of choice is great, so if you love your 29er, ride it and be happy. But don’t try to say that it’s technically superior – race results and physics say otherwise.”
Matt Pacocha, BikeRadar's US editor
"I no longer consider myself a serious cross-country racer. If I did, I’d be riding a 29er all the time – no doubt. Instead, I find myself with a 'quiver' of three bikes, which are all well ridden throughout the season.
"One is a 29er, and it’s a hardtail. It’s aluminum and specced for racing. It’s sub-23lb, which is plenty light enough so that I don’t really have any excuses when it comes to climbing or accelerating. After owning – not just testing – this 29er for more than a year, I can comfortably say there's no longer a reason for me to own a 26in-wheeled hardtail for mountain biking, whether racing or riding.
"My second bike is a 100mm-travel full-suspension racer. It’s what I generally choose to race cross-country on – not necessarily because it’s faster than the 29er, but because I generally have more fun riding it. It weighs more than the 29er hardtail, and subsequently doesn’t go uphill with the same zeal. From what I’ve seen coming down the pike for 2011, however, I think it may be time to trade this bike for one with bigger wheels.
"Finally, my third bike is a 150mm trail ride with a relatively light build that focuses more on fun than going fast. It has 26in wheels with big tires and it's the most fun to ride, but you’ve got to reserve yourself to being slower on the climbs. Here, I don’t yet see an advantage to a bigger wheel. It would add still more weight and with all of the extra travel, I rarely seem to lack traction or squish.
"The moral of my story is that those with a 'quiver' of bikes should be able to find room for at least one big-wheeler. For those whose main goal is to race on cross-country trails, either with their buddies or with a number plate on, I see the big wheel as a truly advantageous option."
Oli Beckingsale, pro cross-country racer
“I can see the rolling beneﬁts of big wheels, but the style is always going to produce heavier wheels. I like my Giant Anthem X a lot. I know there’s going to be an Anthem X 29er, but the weight penalty will be more again compared to my hardtail.
“It comes down to logistics too. I have a lot of 26in wheels and tyres and would need more spare kit, so the only way to do it would be to ditch one system and ride the other 100 percent, which would be a big deal. I’ll leave it up to the sponsors to decide what they want me to ride.”
Guy Kesteven, BikeRadar tester
“Big-wheeled bikes are rubbish. They’re sluggish, flexy, heavy and only for really tall people or tragic attention-seeking old men and beginners who can’t ride. I love it when I hear that because it means my cheating secret is safe for a bit longer.
“To be honest, some of the badly designed bandwagon bikes are crap. Even the good ones don’t do stunts and tricks well and they’re more sluggish to accelerate and weave through really tight sections. All of which means they’ll never suit some people.
“If you asked me what bike is the fastest for long, rough, technical trail rides though I wouldn’t hesitate to say, ‘a 29er’. Even more so after riding the 2011 options. Bigger wheels mean smaller bumps, more momentum and more conﬁdence through rough technical sections.
"They give more speed sustain and traction up climbs or through fast corners. Good 29er hardtails descend like 100mm-travel (3.9in) 26ers. Good 100mm-travel 29ers will match most 152mm-travel (6in) 26ers on fast, rocky trail descents.
"Simply put, riders who lag on 26ers will lead on 29ers. This isn’t just hype and speculation either. I’ve seen it happen on group rides, at endurance races and now even the cross-country World Cup. Like I say, though, I’d rather people didn’t believe me just yet so I can carry on kicking their arses for a bit longer.”