Man cycling in nature on a mountain bike

Mountain Bike Size Guide

Finding the right size mountain bike will help you in performance, comfort and safety. Get the right fit with our expert guide. 

Whether you’re new to mountain biking or simply looking for a mountain bike with a better fit, we're here to help you find the right size.

If you want to get in on the mountain trail action, the last thing you want to do is buy a bike that’s too big or too small. So, rather than having to guess your size, check out our mountain bike size guide to help you choose the right size. Even if you’re buying a bike in-store, it’s useful to know what to look for.

What are the different types of mountain bikes?

When choosing a new mountain bike, it’s important to understand the differences between the various types so you can choose the right bike for the type of riding you’ll be doing. There are two basic types of mountain bike, hardtail and full-suspension.

• Hardtail mountain bike: If this is your first mountain bike, hardtails are the simplest and most affordable. They have suspension at the front for a smoother ride on the trail, and the rear wheel is attached securely to the frame. A hardtail bike will also be lighter than similar full-suspension bikes.

• Full-suspension mountain bike: A full-suspension mountain bike features both a suspension fork at the front and a rear shock. This makes the bike smoother and faster over rocks and rough ground. This will give you more confidence and control on bumpy trails, and it will be much more comfortable and enjoyable to ride.

Hardtail and full-suspension bikes can be split into three categories: cross-country, trail, enduro and downhill. We’re going to go through the key features of each so you can choose the right mountain bike for you.

• Cross-country mountain bikes: Also known as XC bikes, these are the most common bikes you'll come across. This category includes recreational hardtail bikes as well as lightweight full-suspension and hardtail XC race bikes. They are generally lightweight and designed for speed while being efficient on the climbs. XC bikes also have lower-profile tyres compared to other mountain bikes, which means they’re quicker on smooth terrain too. They have a wide range of gears to get you up steep hills, and many are fitted with hydraulic disc brakes for good speed control when going downhill.

Man riding on mountain bike in nature

• Trail mountain bikes: This is the most popular type of bike with MTB enthusiasts. They come in hardtail and full-suspension versions, and they are built to be fast on the fun descents, as well as offer a confident ride. And trail MTBs are lightweight and efficient, making it easier on the climbs. Wide handlebars and short stems give you more control over challenging terrain, and one-by drivetrains with wide range cassettes give you plenty of gears for the climbs. For most riders, a trail bike will be ideal as they’re quick climbers and a lot of fun to ride on most trail centre tracks.

• Enduro mountain bikes: When the going gets tough, enduro bikes really shine. They are the cutting edge of modern MTB design and are built for riding the steepest and roughest descents. The forks tend to have wider tubes and the shocks often have piggy-back reservoirs and coil springs. The brakes are also more powerful to deal with the steeper gradients, though the rest of the spec is similar to what you’ll find on a trail bike. An enduro bike is a good choice if you spend most of your time pushing your limits on the most challenging trails or want to test yourself at an enduro race.

• Downhill mountain bikes:
Also known as DH bikes, these are the real specialists of the MTB world. They’re designed for riding the steepest and roughest descents, but you can’t ride these bikes uphill. Triple clamp forks help make these bikes very stable, they have wider tyres and wider rims, and the gears and frame are more durable and will hold up extremely well under pressure. Everything is bigger on a downhill bike, except for the rear cassette which is missing the big climbing cogs that you’ll find on other mountain bikes. DH bikes are great for downhill races, but you’ll need another bike if you want to ride anywhere else.

Before you hit the trails, you’ll want to ensure your suspension is correctly set up. This article will take you through the process step by step.

Why is it important to get the right size mountain bike?

Before you invest in a new bike, it’s helpful to understand why it’s so important to get one that’s the right size for your height and body shape. A bike that fits correctly and is set up properly is enjoyable to ride. You’ll be able to tackle trails faster and have more control over your bike while enjoying some much-needed comfort. Here are just a few of the issues with riding a bike that’s the wrong size:

• Poor posture: Your riding position is important with any bike and riding a frame that’s the wrong size will eventually strain your lower back. Adjusting a seat post or handlebar won’t be enough to compensate for the size of the frame.

• Wrist pain: If you spend a lot of time riding an ill-fitting bike, your wrists will begin to suffer from the added pressure. If the frame is too large, you’ll need to reach further to control the bike’s handlebars, resulting in bad body positioning.

• Fatigue: If you're planning on clocking up a fair few miles on your bike, then pedal efficiency is a major factor. When you ride the perfect sized bike, your stance and leg positioning allows you to get the most out of every pedal, without having to work harder to compensate.

• Greater risk of falls:
Having control over your bike is essential, especially when you’re riding your mountain bike on rough, uneven terrain. If you’re riding a bike that’s too big, you’ll have less control, which puts you at a much greater risk of crashing or falling off.

Man and woman on mountain bikes on rocky mountain terrain.

What size mountain bike do I need?

Mountain bike frames are usually made from steel, aluminium or carbon fibre and fitted with robust wheels and chunky tyres. Knowing how bikes are sized can help ensure you get the right size to ensure the best riding experience possible. Mountain bikes are built for off-road cycling and they usually come with 26” wheels. Though you’ll also now find larger 27.5” and 29” wheeled bikes that are better at absorbing shock and vibration, offering more speed. Here’s a little more information on wheel sizes so you can decide which will suit you best.

• 26” wheels: This is the traditional MTB wheel size, though most mountain bikes will now feature larger wheels. 26” wheels are a good option for teens and smaller adults as they can be more manageable than larger wheels.

• 27.5” wheels: This is now the most common mountain bike wheel size. The most versatile option, 27.5” wheels are playful on the trail, making for a nimble MTB. They also offer the best balance between bike handling and speed.

• 29” wheels: This wheel size is becoming increasingly popular with cross-country, enduro and downhill racers. 29” wheels accelerate slower compared to smaller sizes, but carry speed much better over rough terrain and tend to be faster and offer more grip. Though smaller riders may find them a bit difficult to handle.

Bike parts chart

What size mountain bike frame do I need?

MTB sizes are measured in inches, from the centre of the bottom bracket to the top of the seat tube. This is used to categorize these S, M or L frame sizes. MTB tubes often slope down and join the seat tube lower than road bikes, to give a rider more standover height.

To find out which size is suitable for you, you’ll need to know your height and inside leg length. Then you can use the tables below to see which size frame you need.

If you find you’re in between two sizes, choose the smaller size for easier steering (better handling and greater control) and comfort (straighter back). Or opt for the larger size for more powerful pedalling (a more stretched-out position suited to performance).

Men’s mountain bike sizing chart

Men’s mountain bike sizing chart:

Women’s mountain bikes have smaller frame sizes and tend to be shorter in length with narrower handlebars and specific saddles.

Women’s mountain bike sizing chart

Women’s mountain bike sizing chart:

These charts should be treated as a guide only, so you should always check the manufacturer’s measurements or visit a store to speak to an experienced member of staff before making a purchase.

How do I size a kids’ mountain bike?

When it comes to choosing a mountain bike for your child, you can use their age as a rough indicator. But as little riders all grow at different rates, it’s important to accurately measure their height to find out which size bike is best for your young cyclist. Kids' bikes are essentially scaled-down versions of adult bikes and are usually measured through wheel size.

Children’s MTB’s typically come in 20” and 24” wheel sizes. These tend to be lighter with a single chainring, making gear changing a breeze. Suspension on a bike can also make it more complicated and heavier, so it’s a good idea to decide whether your child needs suspension before you invest in a bike. If you’re buying a bike for your teen, you may then be moving into small-framed adult bike territory. Larger wheels do make a difference, and while you should avoid getting a bike that’s too big for your child, bigger mountain bike wheels tend to be better uphill and more comfortable over rough terrain.

Kids’ mountain bike sizing chart

Kids’ mountain bike sizing chart

When sizing a mountain bike for your child, get them to sit on it and check they can touch the ground with both feet. This will ensure the correct riding position and full control of the handlebars. You can use the size chart below as a guide.

Can I adjust the bike to make it the perfect size?

More and more of us are buying bikes online, but it’s important to check out the bike in person if you can. Getting a feel of the bike in the flesh is the best way to know if it’s the right size for you or your child. If you’ve found a bike that feels right but needs a little adjustment, there are some things you can do so that it fits you better:

• Adjust the saddle: The first thing you should do is adjust the saddle. If you can’t get it to a comfortable height then the bike could be the wrong size. The saddle is at the right height when your heel just touches the top of the lower pedal with your leg straight. And when it comes to the saddle position, start with your saddle as level as possible on the top (this is an efficient cross-county position).

• Adjust the handlebars: Some riders feel relaxed with their bars at roughly saddle height. Others (particularly cross-country racers) have them below saddle height to achieve a flat-backed streamline posture on the bike. You should go for what feels comfortable for you and the type of riding you’ll be doing.

• Control positions: Brake levers and gear shifters can be put in different positions on the bar. Some bikes will allow you to adjust lever reach and the point of contact where the brakes compress the pads. Your handlebar can also be trimmed – cutting an inch off either end of the handlebar could make a noticeable difference in comfort.

There are lots of things you can do to a bike to try and find a better set-up. But it’s important to start with a bike that fits you properly to start with and fine-tune as you go. Take your time when shopping for a new mountain bike. Do your research and ask for help in-store from one of our cycling experts so you can be confident that you’re getting a bike you can use for years to come.

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