Mountain bike wheel size is one of the most hotly debated topics on the trails. If you’re new to the sport though, the whole subject can be quite confusing.

How can a couple of inches here and there make such a difference? Why does mountain bike wheel size matter so much? Well, there are actually quite a few reasons.

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There are three sizes of wheel predominantly in use in mountain biking; 26 inch, 27.5 inch, often called 650B, and 29 inch, and put simply, the size of wheel you choose will alter everything from your riding position to your riding style and how you feel on the bike.

That’s why we’ve put together this easily digestible guide to everything you need to know before picking your wheel size, buying your first mountain bike and joining the argument.

Why Exactly Does Mountain Bike Wheel Size Matter?

why wheel size matters decathlon 26 27.5 29 650B inch

Despite what you might have been telling yourself all of your life, size does matter – at least it does when it comes to mountain biking.

The size of your wheel determines the level of rolling resistance you will get on the trails. Having a bigger wheel base allows you to overcome bigger obstacles.

The science behind this is called the “angle of attack", and revolves around the point at which the tyre will strike the obstacle in question, and the angle at which that strike will occur.

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Imagine you’re riding along on a 26 inch bike and you come across a log in the middle of the trail. The log will meet your bike at a higher point on the wheel than it would on a 27.5 or 29 inch bike, and at a steeper angle as well. Subsequently, more force will reverberate back against the wheel, making it harder to maintain control, stability and forward momentum on the bike.

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When you’re flying down a trail at however-many-miles-per-hour, those inches make a difference.

That’s why monster trucks can pretty much destroy anything in their path, and why you could probably send a tricycle flying by putting a stiff loaf of bread in its path.

26 inch Mountain Bike Wheels

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Now, when mountain biking first started, the 26 inch wheel was the only option. The 26 incher is lighter than the 27.5 or 29 inch, largely because, well, there’s less of it.

Being smaller, lighter and more agile, bikes with 26" wheels offer much better acceleration than their larger counterparts, making it great for short, steep climbs and fast-flowing, quick-turning trails.

The old timer’s choice is incredibly responsive and gives the rider a lot of freedom on the saddle, but it can struggle and become tough to control on rough terrain – particularly given the speed at which it sets off.

The riding position of the 26 inch mountain bike also places the saddle and the handlebars closer to each other, and while this is one of the key factors in the agility and responsiveness of the bike, it also makes it harder for the rider to maintain their balance.

This has lead a lot of the mountain biking market to favour a larger wheel in recent years, as the stability, reliability, and predictability of the ride is so significantly higher.

Bikes designed for dirt jumping will still traditionally feature 26 inch wheels or even smaller though, and downhill bikes will also often have 26 inch or 27.5 inch wheels.

29 inch Mountain Bike Wheels

29 inch wheels mountain bike why wheel size matters

So, what’s the big deal with big wheels? Well, as we’ve already established, the bigger the wheel, the smoother the ride and the easier it’ll be for your bike to flow over whatever you come across on the trails – hence the 29er.

The 29 inch bike is also longer than a 26 inch ride, and as such offers a lower centre of gravity. This means the rider has a much steadier feel on the bike, but it can take a while to readjust to the new riding position.

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The improved levels of control, strength and stability while riding are unquestionable. The top speed of the bike will also be higher and easier to maintain with the bigger tyres, though the acceleration levels will have fallen.

On the down side, even though the 29er can reach a higher top speed than a 26 inch wheel, the riding doesn’t feel quite as fast, and many do find the bikes overly rigid and tough to manoeuvre, particularly if they are used to riding on a 26 inch wheel.

27.5 inch/650B Mountain Bike Wheels

27.5 inch wheels mountain bike why wheel size matters

The 650B/27.5" wheels appeared on mountain bikes around 2007 as a compromise to the problems raised by both 26 inch and 29 inch wheels, though they didn’t really take off until the past few years.

Now that they’ve got going though, it’s hard to see the 650B boom slowing down anytime soon. Many say the bike is the perfect in between point, providing a notably smoother ride than the 26 inch bike while also riding much more nimbly than the 29er.

The 27.5" wheels don’t bend as much as the big 29ers and handle a lot better in terms of manoeuvrability and durability. They’re faster, stronger and more agile than the bigger wheels and also ride much more fluently than the smaller. The best of both worlds.

Cross country and enduro/all-mountain bikes will commonly feature 27.5 or 29 inch bikes as they are more focused on control and grip than responsiveness.

The Verdict

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At the end of the day, only you’re going to know which wheel size is right for you. The best way to find out is to test ride one of each and see how you like it.

If you’re just getting started in mountain biking though, there’s no reason why you shouldn’t join the revolution and get a ride with 650B/27.5" tyres. You’ll have the speed, the control, the stability and the smoothness. If nothing else, you’ll soon find out what your favourite feel is on the bike and can build from there!

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