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Mountain bike wheel sizes: 27.5in. vs. 29in.

In the mountain biking world, wheels seem to have settled on two main sizes – 27.5in. and 29in. – and each of them have benefits that may or may not match your riding style. To help you choose which wheel size is right for you, we’ll take a look at the following:

  • Comparing 27.5in. vs. 29in. wheels: Differences to consider for weight, acceleration, attack angle, traction and manoeuverability.
  • How does wheel size affect bike fit?
  • Which wheel size is more fun?

It’s important to know that wheel size is only part of the story, and that a bike’s design likely has more to do with how a bike feels than wheel size alone. That being said, if you’re comparing two bikes with similar geometry, then the size of the hoops can make your bike feel nimbler, faster or provide better traction.

Wondering why 26in. wheels aren’t included? Most mountain bike manufacturers have adopted 27.5 and 29in. as the new norm and moved away from 26in. wheels.

Head to head comparison: 27.5 vs 29er

29in. wheels have been around for a while. They were originally used mainly on cross-country or XC bikes, since they helped XC racers squeeze as much efficiency as possible from their bike. In recent years, a new breed of 29er bikes has emerged and they’re more well-suited to steep, gnarly technical descents.

27.5in. wheels, also known as 650b, started to appear after 29ers were on the scene, and became more common after 2010. Riders saw this size as the sweet spot since they were nimble yet were still able to roll over challenging terrain easily.

Weight differences

It’s not surprising that bigger wheels have more material and therefore are usually heavier. For comparable set-ups, the weight difference between a 29in. and 27.5in. wheelset with tires is usually around 500g more for the 29er. Longer spokes, bigger rims and bigger tires all come into play. Since the weight is distributed all around the rim and tire, it’ll have a greater impact on the feel of the bike than if that extra weight was distributed evenly all over the frame. If you’re looking to shave weight, then 27.5in. wheels get the point in this category.

Acceleration differences

With everything else being equal, a wheel with a smaller diameter will accelerate faster, partly due to the fact that wheel weight is also rotating mass. Since 29in. wheels are generally heavier, getting 29in. wheels up to speed can take longer than getting smaller, lighter wheels up to speed. The good news is that once you get to cruising speed, you’ll be able to keep your momentum going much easier. When it comes to comparing wheel size and acceleration, 27.5 wheels will generally be easier to get up to speed, but 29in. will carry that speed when the trails get a bit rough.

Attack angle differences

Diagram showing different in attack angle for wheel sizes

The larger the wheel’s diameter, the more easily it rolls over obstacles. For example, think about how skateboard wheels can get caught on small bits of gravel on the road as opposed to bike wheels that roll over the same gravel. The same idea applies to 27.5 and 29in. wheels. The 29ers have a smaller attack angle that allows them to roll over rough sections of trails more easily and they’ll be able to carry speed better over jutting roots and bumpy rocks.

Traction differences

Good traction between the trail and your bike can mean the difference between walking or riding steep technical sections. Traction is based on how much tire is in contact with the ground. As you can imagine, fat bikes have the best traction because of the massive tires that they use. If you look at regular mountain bike tires that are the same width, then the 29in. tires would have more surface in contact with the ground (and thus more traction) than equivalent 27.5in. tires.

If your bike allows for wider tires, 27.5in+ (sometimes called plus size tires) are wider tires that you can run at lower pressures. The extra width and lower tire pressure helps increase the contact between your tire and the trail and provides amazing traction at a 27.5in. wheel size.

Manoeuverability differences

Generally speaking, bigger wheels require more space in a bike’s frame. This also changes a bike’s geometry; this is especially important to note when it comes to the length of the chainstays. Most bike manufacturers are trying to get chainstays as short as possible to create a bike that’s playful and corners well. 27.5in. wheels have the advantage over 29in. wheels on this front, but development in bike geometry makes the gap between these two options smaller and smaller every year.

How does wheel size affect bike fit?

It seems logical to think that taller riders would feel more comfortable on larger bikes, and the opposite would also make sense, wouldn’t it? But it’s not as black as white as that – we’ve heard plenty of shorter riders says that they love 29ers, and some taller riders that prefers 27.5in. bikes. While this challenge in fitting smaller and taller riders on specific bikes may exist, how a bike fits and feels mostly comes down to preference in the end.

The biggest takeaway is to get on the bike and take it on a demo ride. You may be surprised at how larger or smaller wheels sizes feel once you’re on the bike – when you’re bike shopping, don’t eliminate a certain wheel size just because you assume it’ll be too big or small for you.

Which wheel size is more fun?

You guessed it: there’s no definitive answer to this question. Now that you understand some of the benefits of each wheel size, take the bike you’re eyeing for a spin and to see how it rides. Ideally you can try a 27.5in. and its 29in. equivalent to get a real feel of which one fits your riding style best.

Go to a trail you’re familiar with and ride a line you’ve ridden a hundred times before so you can compare it to what you already know. If you’re new to biking, visit the trail network where you expect to be riding most. Most importantly, don’t forget that wheel size is only part of the answer when evaluating how a bike feels.