Editor's Note: This sponsored post was created in collaboration with Santa Cruz Bicycles.

29 or 27.5 - Which mountain bike wheel size is best?

When you first walk into a bike shop or go online to do some research before buying a new mountain bike, you're quickly faced with a few key decisions. First, what type of category or bike should you get? Hardtail, cross-country, trail, all-mountain/enduro, downhill, e-bike? After choosing the category that's right for you, your second choice should be wheel size.

Which wheel size is right for you? There are a number of factors that go into selecting the right mountain bike wheel size. We'll help you navigate the underlying qualities of diameter, evaluate the pros and cons of each, and arm you with the tools to help decide which is right for you.

Here are some of the main factors to consider when determining the proper mountain bike wheel size for you:
  • Riding style
  • X-factors, like rider height
  • "Mullet setups"
  • What to do if you're upgrading from a 26er
Related: How to Pick the Right Mountain Bike Tire

When it comes to mountain bike wheel size, 27.5 wheels are a good tool for riders who are motivated to go sideways on the ground or in the air.

27.5 wheels are a good tool for riders who are motivated to go sideways on the ground or in the air.​

27.5 - The agile and playful one

This is used to be the middle mountain bike wheel size, but with the decline of the 26-inch option, 27.5 is now the smaller wheel. In a nutshell, it's best characterized as the fun-sized wheel size and its resume will include adjectives like "agile," "playful," and "nimble." It's a versatile wheel size as well, fitting more riders, especially those shorter in stature. And it can handle a wider array of tires and suspension travel. With lighter wheels and tires, it's easier to change speeds and accelerate with less effort.

The downside is that 27.5-inch wheels don't maintain as much momentum as 29-inch wheels. The smaller diameter means they don't roll over trail obstacles as easily. For these reasons, they can be slower on many courses, and with a smaller tire contact patch, there's less traction compared to their big-wheeled brethren.

When it comes to mountain bike wheel size, covering lots of ground efficiently is the 29er's domain.

Covering lots of ground efficiently is the 29er's domain​

29 - The fast one that plows over things

The larger mountain bike wheel size, 29-inch wheels, provides the best confidence, especially at speed. Bikes with larger diameter wheels generally feel more stable and cover ground faster, as they hold their line over rough terrain and roll over obstacles with less effort. Once up to speed, 29-inch wheels maintain their momentum better. Making them faster in many, but not all, situations. With a bigger tire contact patch, 29-inch wheels have better climbing, braking, and cornering traction as well.

On the downside, 29-inch wheels take more effort to accelerate, so changes in speed are less efficient than 27.5 counterparts. Since 29ers carry more momentum and generally have longer wheelbases to accommodate the larger wheels, they are not as nimble as mountain bikes with 27.5-inch wheels.

There is one genetic human attribute that affects the mountain bike wheel size choice and that is rider height.

X-Factors - rider height, style bike/e-bike weight, component availability

There is one genetic human attribute that affects the mountain bike wheel size choice and that is rider height. Since we were toddlers learning to ride we've increased wheel size to fit our proportions. A 27.5-inch bike is more proportioned for shorter riders and 29-inch wheels for taller riders. Luckily, there is a wide crossover in the middle-from about 5'5" to 6'2" is where a rider can comfortably choose either wheel size. Under 5'5" is generally 27.5 jurisdiction and above 6'2" is fit by 29-inch bikes best. You'll see this in many manufacturers as their extra small sizes are only available in the 27.5 sizes.

When it comes to riding style, mountain bikers who love to play and pop over rocks, roots, and other trail features will find that 27.5-inch wheels are a better fit. A bike with smaller wheels is generally easier to throw around and requires less effort to change directions. For the riders who like to go fast, maintain speed and plow over things, a bike with 29-inch wheels is a very willing partner.

Mountain bike wheel size is a tool that can be harnessed to make an ebike more nimble.

Wheel size is a tool that can be harnessed to make an ebike more nimble.​

As far as e-bikes are concerned, the motor usually takes up some chainstay real estate, resulting in slower handling. And an extra 15+ lbs of motor and battery weight hinder the agility of the bike as well. So a 27.5 wheel, especially in the rear, helps e-bikes regain some of the lost handling and agility.

Keep in mind that these are rough guidelines to help you get started and that there are exceptions to every rule.

Related: How to Service Santa Cruz Suspension Linkages

On one of our ebikes, we experimented with a mullet 27.5 rear and 29er front setup to see which mountain bike wheel size works best.

On one of our ebikes, we experimented with a mullet 27.5 rear and 29er front setup.​

29 front and 27.5 rear, aka, "mullet setups"

Some bike brands are experimenting with 29-inch front wheels paired with 27.5-inch rear wheels. These mixed wheel size bikes fill a void and offer a novel solution. If the 29 excels in speed and 27.5 in style, how about a combo platter that provides speed and style? Front end composure and rollover, good rear end agility, and less rotational weight, as well as some additional butt clearance when the suspension bottoms out, are some of the benefits of mixed wheel size mountain bikes.

Does it really work? Indeed it does, but careful engineering is required to optimize this configuration. Head and seat angles as well as the bottom bracket heights need to be accounted-just swapping in a 27.5-inch rear wheel into a 29er won't provide the best mix of both. The chainstays need to be made specifically for the 27.5 wheel to take advantage of the agility the smaller wheel offers.

As mentioned above with 27.5 wheels, the mullet configuration can be a solution for e-bikes, which are typically less agile and more difficult to change direction with. The motor and battery add about 15+ lbs of bottom bracket weight. Also, the motor often takes up valuable real estate that results in longer chainstays.

When it comes to mountain bike wheel size, the choice these days is between a 27.5 and a 29 inch wheel.

The choice for a mountain bike these days is between a 27.5 and a 29 inch wheel​

What about my 26er?

If you're upgrading from a bike that is at least 10 years old, you may have a 26-inch bike. That wheel size has mostly been abandoned and is now seeing duty in kids bikes and dirt jump bikes. The latest forks, wheels, and tires are no longer available for the 26er wheel size, so one must upgrade to either 27.5 or 29. But have no fear, the new mountain bike wheel sizes are better in every aspect described above compared to the trusty 26er. But one has to choose which direction to go with.

During the Lenzerheide UCI MTB World Cup stop in Switzerland.​

Bottom Line

Hopefully, we've armed you with some of the key considerations in making a decision on mountain bike wheel size. The 27.5-inch wheel is ideal for popping over stuff, changing speeds and direction, and playing with the trail. The 29er is best for going fast and winning races. It covers ground well, stays planted, and plows over obstacles.

These baseline attributes serve as a starting point and the rider can make a personal choice and make either wheel fit their style and preference.

What is your current wheel size choice and what is the size for your next bike?