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27.5 VS 29: Determining Which Wheel Size is Best for You

You’d have to live under a rock to be unaware of the wheel size debate that has gripped mountain biking for the past few years.

Since you’re reading this, you probably don’t live under a rock, unless said rock has Wi-Fi. And while we’ve all heard countless arguments favoring each size, what’s certain is that the classic 26-inch wheel size has lost significant ground, which means that most everyone who’s looking for a new ride is choosing between a 27.5- or 29-inch bike. Your choice will largely depend on your priorities, as each size offers distinct advantages. Let’s dig through them.

Bottom Bracket Drop

Claims of increased contact patch and rollover aside, arguably the largest reason that 29ers have earned such a devoted fan base is due to bottom bracket drop. Many 26-inch bikes locate the bottom bracket above the centerline of the axle in order to provide adequate ground clearance. This gives the sensation of being on top of the bike. A 29er with an identical bottom bracket height, as measured from the ground, will typically locate the bottom bracket far below the centerline of the axle.

This creates a sensation of being “inside” the bike. It has the additional benefit of making the bike more stable by lowering the rider’s center of gravity relative to the wheels. 27.5-inch wheels open up the opportunity to build a bike with bottom bracket drop, except the smaller wheels have a lower centerline, which means that the drop will be less pronounced. Accordingly, at comparable bottom bracket heights, a 27.5-inch frame will be less stable than a 29er but more responsive to rider input.

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Head Angle, Trail, and Pitch Stability

Trail is a function of head angle and fork offset, and it’s the largest determining factor in how a bike corners. 29-inch forks are built with a longer offset than their 27.5-inch counterparts, which means that 29ers require a steeper head angle to achieve the same trail measurement. A more kicked-out head angle yields a bike with greater pitch stability, or fore-aft stability. This means that when things get wild, you’ll be less likely to be ejected over the handlebars. This is mostly a factor for high-speed descending and steep terrain. Accordingly, it’s more of a consideration for the gravity-obsessed than the XC racers among us.

Considering the impact of steering geometry is critical for making comparisons between bikes of different wheel sizes. A 29er with a 68-degree head angle will maintain composure at high speed, but low-speed handling, particularly cornering, will tend to be sluggish. By comparison, a 68-degree head angle on a 27.5-inch bike will yield a noticeably more responsive handling feel, but will be less predictable when initiating turns at high speeds. So, if you’re comparing bikes between wheel sizes, expect a 29-inch bike to be roughly two degrees steeper than a 27.5-inch bike with similar cornering characteristics.

Wheels: Rolling resistance vs. Acceleration

Conventional wisdom holds that 29 inch wheels roll faster than their smaller brethren, and in some cases, it’s true. However, as you’ve no doubt been told, there’s no such thing as a free lunch. First, let’s assume that we’re comparing 27.5 and 29 inch wheels, all built with the same rim, tire, and pressure. Apples to apples, so to speak.

At a given speed, 29’ers do roll slightly more efficiently, and it’s most noticeable on flats or gentle grades, either up or down, with successive small bumps. The difference comes down to angle of attack. In other words, the larger wheel approaches a given obstruction at a shallower angle, enabling it to roll “through” the object, rather than “over” it. However, this example assumes a constant speed, and mountain biking is a dynamic activity.

There’s a price to pay for this improved roll over. Larger wheels weigh more, and that added weight is placed farther from the hub, which further increases the wheel’s inertia. In other words, 29’ers require a stronger effort to get moving. This phenomenon is most noticeable when exiting turns, and during technical climbing, where bursts of acceleration are part of the game. Big-wheel evangelists will of course point to the fact that you’ll run lower gearing to compensate, but gearing doesn’t change the laws of physics. The fact remains that 29’ers maintain speed more effectively, where 27.5 inch wheels accelerate more efficiently.

Advantages of 29ers

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The larger wheel diameter offers a larger contact patch. In other words, all things being equal, a 29-inch wheel will put more rubber on the ground at once. This means that you’ll have more available grip for cornering, braking, and climbing. The added diameter also reduces the angle of attack when rolling over a given obstacle, which enhances the sense that your bike is rolling through trail features, rather than up and over them. And as previously mentioned, the increased bottom bracket drop yields a bike that feels more planted, which is of particular benefit to both beginners and endurance racers.

Advantages of 27.5

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Riding a bike with less bottom bracket drop results in a more responsive handling feel. Along these lines, the smaller diameter wheel frees up more room to shorten chainstays, especially on long-travel bikes. With shorter chainstays, a bike tends to turn on a tighter radius, helping the rider make quicker changes in direction.

Conversely, the use of smaller wheels requires slacker head angles to achieve the same trail measurement. This balance of slacker head angles and shorter chainstays gives the 27.5-inch wheels greater pitch stability compared to a 29-inch wheeled bike with similar handling traits. Ultimately, this is advantageous to aggressive descenders. Additionally, the smaller wheels are both stiffer and lighter, which enhances the lively feel that’s inherent with 27.5-inch bikes.

Common Misconceptions

The most common misconception we hear about 29ers is that they aren’t responsive. Broad generalizations tend to skirt that fine line between exaggeration and flat-out nonsense, and this is a perfect example. Sure, there are plenty of 29ers that are highly stable and handle best when ridden wide open, but there’s no shortage of quick-handling 29er XC whippets. Granted, when comparing similar bikes, a 27.5-inch bike will tend to be more responsive, but there are other factors to consider, mainly suspension design and your position on the bike. And if someone tells you that 29ers don’t jump well, consider the source. Big wheels love to fly. So most likely, it’s not the bike’s fault.

The Verdict

What we’ve found is that, by and large, XC racers, beginners, and fans of all-day trail rides tend to prefer the stable ride provided by a 29er. Meanwhile, aggressive riders with a taste for descending generally favor the more responsive handling offered by 27.5-inch bikes. 27.5 is also an amazing option for those who are hesitant to give up their beloved 26-inch steeds, since it promises both forward compatibility of high-end parts and a ride that’s similar to the old standard. It also provides some distinct advantages in terms of both grip and overall speed. So, if you’re on the fence, do yourself a favor and ride as many bikes of each wheel size as you possibly can. Generalizations aside, there are bikes of both wheel sizes that we absolutely love and that cater to most any taste. Naturally, there are those who will be resistant to the changing tides, but from what we’ve seen, it’s being driven by a genuine desire to make mountain bikes better for all.

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16Comments

Here's what the community has to say.

Brian

Brian

This article helped me make up my mind and get my bike- a 27.5. I love its responsive and aggressive stance. I'm not an expert Mountain Bike rider by any stretch but like Ricky Bobby, I like to go fast! I can understand the benefit of the 29er but just can deny the maneuverability of my bike. Thank you for an excellent and unbiased article.

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John R.

John R.

Oh, one other thing to add to my comment below is that the 27.5+ is a more agile handling setup than your typical 29'er setup due to the ability to run shorter chainstays on the bike. I've had a Ibis Mojo 3 for over six months now and I absolutely love the bike as it is a NON-compromise frameset designed for a 27.5+ wheel. Currently any of the 29/27.5 "switch-up bikes" ARE compromises because with our current bike tech we haven't figured out yet how to design a bike that can be optimum for both wheel sizes.

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John R.

John R.

Ben, great article and good technical description of the effects of different wheel sizes and angles. :-)

After having ridden 26, 27.5/27.5+ and 29 for years I've found that for general trail riding 27.5+ is the best compromise for me. Why ? It rolls over stuff "almost" as good as a 29, has better traction than a non-fat 29 wheel and is lighter. One REALLY nice benefit of the 27.5+ is the ability of the tire to absorb trail vibration. I haven't read much about this benefit but it is HUGE as you get off of the bike and do not feel beaten up like you do on other tire sizes.

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Carlos A S.

Carlos A S.

29 Is the best choice for descending and climbing. You feel always secure!!
Good article, keep going with that.

Regards from Colombia!

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Richard B.

Richard B.

Great info. I have a full-susp 29er and have been very happy with it.

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Garson Fields

Garson Fields

@amason: Contact patch is not a zero-sum game. Length of contact patch is determined by tire diameter. Width of contact patch is determined by tire volume. Both are affected by tire pressure. In other words, with the same tire and pressure, a larger wheel absolutely has a larger contact patch.



@zen2645883: LOL@ Cairns World Cup DH being dominated by 26. All three races (men, women, juniors) were won on 27.5. Seven of the top ten men were on 27.5. Don?t be surprised if those other three are on 27.5 by Ft. William.



26 will always be rad, but with one possible exception, none of the major manufacturers are developing new, high-end 26 inch trail bikes for 2015. The freeride/jump segments will likely be the last holdouts, for several reasons. Sorry to be the bearer of bad (?) news.

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Craig

Craig

I'm casually looking for a new mt. bike, and have been torn between a 27.5 and a 29er. I ride a 26" diamondback mission III right now that i tear trails up in. I have a 29er that i use a commute/gravel trail bike and will say it's an amazing machine. I love both and i ride with groups that all have 29ers and there isn't a thing they can do that i cant with my 26. If all you have is a 26, be all the 26 you can be!!!

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Kristi Y.

Kristi Y.

Really backcountry? The marketing machine is at work and is at its finest. Has everyone drunk the koolaid? The ideal quiver would be to have both a 26er and a 29er. 27.5 feels like a compromise that gives you a bike that isn't as agile or nimble as a 26er but lacks the obvious roll over benefit of a 29er. I've ridden many bikes of many different wheel sizes. My conclusion? 26ers are here to stay. However, I do enjoy the fact that the marketing craze has driven down prices substantially, making my 26er, carbon all mountain steed affordable. As a shorty (5'1 on a good day), 26ers are my ideal and fit both me and my riding style perfectly. In short, ride what you love, and don't buy anything without an objective demo and your own common sense. A 27.5 bike might be amazing for you and your riding style...so too might a (dare I say it!) 26er. And to be honest, the slight roll over benefits of a 27.5 wheel size can be gained easily with a bit more practice and effort.

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Jonathan

Jonathan

Really great write up. A bit jargony, but that probably just means I need to educate myself more

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Shawn C.

Shawn C.

The premise of the 26" wheel being dead is incorrect. In most gravity applications the 26" wheel will out perform its larger cousins. The world cup in Cairns last week was dominated by 26" wheels as are most dual slaloms, 4x, slope style, and downhill events. Every wheel size has advantages and disadvantages and all of them are fun to ride. Don't let "experts" pigeon hole you into a false dichotomy, after all, this isn't an election.

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yourDisplayName

yourDisplayName

Only problem is, 650b isn't really 27.5". You'd be hard pressed to find any wheel/tire combo that comes in much over 27" even, therefore, not quite the "best of both worlds". Also, I take exception to the statement that 26" is " quickly loosing ground". They've been around forever for a reason, and that reason isn't to generate more money by manufacturers. Give people something new and they'll buy it, simple as that. 26" isn't going anywhere people!

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blantonator

blantonator

I tried to love 29er, but I just couldn't. I appreciate it's fast rolling and roll over ability, but I just didn't find it engaging to ride. It felt fast, but not fun. I had a 650b bike back in 2009 and just picked up a new anthem 27.5!

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amason

amason

Great article, except for this bit: "The larger wheel diameter offers a larger contact patch. In other words, all things being equal, a 29-inch wheel will put more rubber on the ground at once," which is incorrect. Contact patch is solely related to your weight and the pressure in the tires. If a 29" wheel has a longer contact patch, it must have a correspondingly narrower one. The benefits of the 29" must come from something else.

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Kirk

Kirk

Love this article because I have been asking the same question myself as my bike, a 2006 Santa Cruz Heckler will be replaced this year.



I will have to ride a couple of the new wheel diameters to really get a on-bike experience but I am not really seeing any big advantages here. I am also kinda hesitate as I already ride a 16" frame. Small frame, big wheels? Does any one have any thoughts on how these bikes ride for shorter people like myself at 5'7"?



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Dave Brown

Dave Brown

Nice write-up. This mirrors exactly what I was told at the local bike shop.

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Vinny Mauro

Vinny Mauro

Great write up! My conclusion is that I need both :) The only point that I think is worth stressing that is not mentioned here is that 27.5/650b wheels do not lie directly in between 26" and 29" as the name would imply.



A 27.5" wheel diameter, measured from bead to bead across the wheel no tire, is 25mm greater than a 26" wheel. And a 29" wheel's diameter is 38mm greater than a 27.5" wheel's. So in other words, a 27.5 wheel is much closer in size to a 26'er, and 29'ers significantly bigger than both. Just some facts to reinforce what Garson has said.

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