27.5 vs. 29er Mountain Bike Wheel Size Explained

It wasn’t very long ago when mountain bikers only had a single option of wheel size. If you wanted a mountain bike, 26 inches was your only choice. You can pick and choose other components of the bike: suspension travel, handlebar width, stem length, type of saddle, etc., yet the venerable 26in wheel size was just taken for granted as the dominant standard.

Approximately 20 years ago, 29er wheels and tires were introduced to the market, and the in-between size, 27.5inm (also known as 650B) soon followed. The ensuing debate of which wheel size is best? is one that is still aflame to this day. Eventually, the 26in wheels and tires went the way of the dinosaurs, becoming almost completely supplanted by the newfangled 29in and 27.5in sizes. It is important to emphasize that, as is the case with everything in cycling, 27in and 29in wheels come with benefits and drawbacks, but isn’t it great to have options? Alas, options can be confusing, and with the dizzying array of bikes on the market nowadays it can be hard making an informed choice when shopping for a new bike. If you’re in the market for a new mountain bike, or just want to understand more about wheel sizes in the mountain bike world, read on for an explanation of the key differences between 29- and 27.5-inch wheels, the unique characteristics and riding applications of each as well as the main considerations in choosing one over the other.

29in wheels: stability, rolling momentum prowess and confidence over rough terrain:

When first introduced, 29ers wheels were controversial, and had many misconceptions that have been gradually cleared up as mountain bike technology advanced. It was generally thought that 29ers were reserved for taller riders and that those of shorter stature cannot reap the benefits of the large diameter wheels. The main reasoning behind this was that early 29er frames were not really designed around the larger wheel size, but have been adapted from the designs based on existing bikes which had 26in wheels. Once 29er geometry was refined and purpose-built around 29ers, the myth that shorter riders should not be on bigger wheels was largely dispelled.

Another myth surrounding 29-in wheels is that they’re only suited for cross country riding. Early 29-in bikes were mostly cross-country bikes with very short travel and aging geometry, suited for smoother trails. For this reason, riders who prefer more rowdy terrain shunned 29ers, favouring 27.5in or even the now almost extinct 26in bikes. Today, the bike market landscape is very different one from what it was 15 to 20 years ago. 29in wheels are, by far, the dominant wheel size in almost all categories of bikes, especially mountain bikes.

What’s great about 29in wheels?

29in wheels have a low angle of attack. That is to say, they can roll over large obstacles with ease compared to the smaller diameter brethren. On mountain bike trails, this means that it takes less effort to pilot the bike through rocky, rooty or sandy sections. When the trail points downhill, 29er bikes feel a lot more stable at high speeds which makes for a more confidence-inspiring ride. 29er wheels also have a larger contact patch with the ground, which translates to a significant improvement in traction as those large knobs on mountain bike tires are able to have a better bite into the terrain, especially in loose or muddy conditions.

What’s not so great about 29in wheels?

29in wheels are heavier than their smaller counterparts. They take more energy to accelerate. The larger diameter can also feel more difficult to maneuver on tight, switchback-ridden trails. The myth about 29ers not being suitable to shorter riders also does have some truth in it, as riders below 160cm (approx. 5’ 2”) can often struggle to find a 29in bike with a geometry that fits them well (to which some bike manufacturers, like the German company Liteville, have responded by making frames with adjustable wheel size).

27in wheels: maneuverability, playfulness and fast acceleration:

27in wheels came from being an obscure wheel size in the cycling world to a strong contender for wheel size dominance in the mountain bike world. The appeal of the 27in diameter lies in occupying the middle ground between the aging 26in size and the exciting yet myth-ridden 29er size. Riders on the proverbial fence found a good spot with the 27in wheels. Bike manufacturers marketed 27in wheels as being the best of both worlds: playful, flickable and fast-accelerating like 26ers, yet having the improved rolling resistance of larger diameter wheels. While some of that is true, being a tweener doesn’t mean they make for the Goldilocks of mountain bike wheel sizes.

What’s great about 27.5in wheels?

The smaller diameter of 27.5ers makes them more easily maneuverable, especially if your local trails are the tight and twisty kind. Rider input feels easier and more immediate, which is especially important for beginner riders. 27.5in wheels are also generally lighter (comparing like-for-like wheels) and accordingly they take less energy to accelerate, so the bike will fill nimbler and more playful (assuming we’re comparing to a an identically-geared 29in bike). Things like manuals, hops and jumps feel a bit easier on 27.5in bikes.

What’s not so great about 27.5in wheels?

27.5in wheels don’t have the same rolling prowess of 29ers. On rough trails, they can feel hampered by large rocks, roots or other trail obstacles, especially at higher speeds. While they accelerate faster than 29ers, they don’t have the same momentum-holding properties of the larger wheel size, which means that they can also decelerate faster if coasting through a rough section of trail.

Conclusion: Which wheel size should you choose?

Firstly, bike fit and geometry are generally more important considerations than wheel size. While wheel size will have a significant impact on how the bike feels and rides, geometry will have a much more palpable effect on handling. All other factors being equal, if you are a taller rider, and/or ride technical trails where high-speed descents are the norm, or even a cross country racer then you’ll certainly benefit from a 29er. On the other hand, if you are a shorter rider, and/or enjoy more laidback and playful kind of riding, and/or your local trails are the tight and twisty kind, then 27in bikes might be better suited for you. Mountain bikers are spoilt for choice now, and it is hard to go wrong with a bike with either wheel size.