What mountain bike frame size do I need?

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what mountain bike frame size do I need?

It is essential that you buy the correct mountain bike frame size for you. If your mountain bike frame size is incorrect, you are setting yourself up for a whole host of problems.

A poorly fitting mountain bike will cause unnecessary pressure on your body, which will eventually cause pain and maybe injury. However, you will instantly know if your bike is the wrong size if it is difficult, dangerous, or unentertaining to ride.

So in this post, we will answer the question of “what mountain bike frame size do I need?”.

We will also highlight what an ill-fitting mountain bike frame feels like and how you can make it better. By the end of this article, you will be confident in buying a new bike that fits you correctly.

How to choose the correct mountain bike frame size?

Riding a mountain bike that doesn’t fit you is incredibly unpleasant. This will put you off riding it or make you want to replace it, wasting money.

Your mountain bike frame needs to fit your body’s measurements. They come in varying sizes, so here are the things you need to know before buying your new mountain bike.

Learn how mountain bike brands size their bike frames

Mountain bike manufacturers have size charts. You should be able to find these charts on the manufacturer’s website.

Most mountain bike brands label their frame sizes as XS, S, M, L, and XL, while others will indicate their bike frame’s size in inches. Each sizing chart will give you a range of measurements corresponding to your body and the manufacturer’s suggested frame sizes.

One of the most critical measurements is the mountain bike’s standover height. When you stand with your legs on either side of the bike with your feet flat on the floor, you should have a gap between you and the top tube.

You need about 2″ clearance for a hardtail mountain bike, but if you have suspension, you will get away with 1 to 2″. This is because the suspension will compress when you sit on the saddle or stand on the pedals.

Determining the clearance is tricky without actually standing over the bike. So if you are buying your new mountain bike online, you will need to take some measurements.

Measure the distance between your crotch and the ground. This measurement is commonly known as your inside leg or inseam. You need to take this measurement with no shoes on and your legs slightly apart.

Use this measurement to compare it with the standover height on the manufacturer’s sizing chart. Doing this will ensure that your mountain bike frame size will be correct for you.

This doesn’t mean your bike will be perfect, but it isn’t the end of the story. After a few rides, you will get a feel for the size and geometry of your new mountain bike.

You can fine-tune certain aspects of your bike. For example, change the saddle height, raise or lower your handlebars, or change the handlebar stem. All this will allow you to customize your riding position, but we will go into this in more detail later in this article.

How your new mountain bike frame should feel

Another mountain bike frame measurement you need to take note of is its reach. The reach makes a big difference to your riding position and how your bike feels when you ride, especially when standing on the pedals.

If you like to ride long distances, you may benefit from a bike with a more extended reach. However, if you are a novice mountain biker, you may prefer a shorter reach.

Mountain bikes with shorter reach measurements put the rider in a more upright position. Sitting more upright is more comfortable and confidence-inducing, as you have a great field of view when riding.

A mountain bike with the perfect reach measurement for you gives you a balanced and comfortable riding experience, but it also gives you more control and makes your pedaling more efficient.

The ideal reach will put your shoulders in a relaxed position while having a slight bend in the elbows.

Problems to expect from riding an ill-fitting mountain bike frame

Hip pain

You can easily adjust your saddle height, but if you don’t set it correctly, you could start to experience hip pain. This can also be caused by your saddle angle being set incorrectly.

If you experience hip pain while riding your mountain bike, you can quickly remedy it by setting your saddle up to suit you. Of course, your bike frame needs to be the correct size, or you will still experience discomfort.

Pain in your upper body

Many mountain bikers that ride the wrong sized bike suffer pain in their upper back, neck, and shoulders. This pain boils down to an incorrect riding position. They may find that they are sitting too far forward or backward, negatively affecting how they hold on to the handlebars.

You can often fix this problem by tweaking the handlebar and seat post height and the length of the stem. You can even fit handlebars with a different rise to alter your riding position.

Back pain

Some mountain bikers complain that they get back pain when out on the trails. The most common cause of this is the ride having a weak core. Therefore, adding a core session into your workout routine will go a long way to reducing back pain.

Your handlebar height can also cause back pain, so this may be worth looking into too. You need to get your saddle height perfect for comfort, and so you can pedal as efficiently as possible.

However, your knee pain could stem from your clipless pedal setup. If you ride with clipless pedals, you may need to change your cleats for ones with more float.

How to set your mountain bike up perfectly

Play with your cockpit

Your mountain bike’s cockpit is made up of everything attached to your handlebars. Your mountain bike rides will be more comfortable and enjoyable when your cockpit is set up perfectly.

Some mountain bikers feel pain in their hands pretty quickly during a ride. The good news is that if you experience this, it may be an easy fix.

All you need to do is fine-tune the position of your brake levers and gear shifters. You can twist and slide them inwards and outwards to find the perfect setup. This goes a long way to improving your comfort, so you may want to take a multi-tool with you during your rides to tweak them until you have their positions perfected.

Consider the length of your cranks

The length of your mountain bike’s cranks will affect your comfort and pedaling efficiency. This is especially the case if you are taller or shorter than the average person.

Most mountain bikes are fitted with cranks that measure 170mm to 175mm. But shorter riders may find that shorter cranks are better. The problem with your bike’s cranks being too long is that your knees bend too much at the top of your pedal stroke.

Also, if your cranks are too long, you won’t benefit from the full range of motion as you pedal. If your cranks are the correct size for you, you will have a slight bend in your knee at the bottom of the pedal stroke.

Experiment with your saddle height

When you get your new mountain bike, you will need to set your saddle height correctly for all the reasons we have already mentioned. 

By experimenting with your saddle height, you will be able to find the sweet spot between pedal efficiency and comfort. 

If you set your saddle too high, your hips will move from side to side as you pedal. This motion wastes energy, and it can get in the way when riding technical terrain.

But if you set your saddle too low, you can’t put enough power into your pedals when seated, and you will be very uncomfortable.

To find the saddle height sweet spot, sit on the saddle and fully extend your leg with your heel on the pedal. This position means that when you put your foot on the pedal correctly, your knee won’t lockout at the bottom of the pedal stroke.

Even with this ideal seat post position, it won’t suit every eventuality. Therefore, you may want to fit your bike with a dropper seat post. 

A dropper seat post allows you to change the saddle height as you ride with the push of a button. Set it high for riding along flats and climbing, but drop it out of the way for steep descents.

Dropper seat posts are expensive and sound unnecessary to people who haven’t tried one. However, you won’t want to go back to a regular Seat post after using a dropper.

Final thoughts; choose the correct mountain bike frame size

There is no substitute for sitting on a bike and riding it to see if it fits you correctly. But, paying close attention to the mountain bike manufacturer’s size chart will make the process of buying one (online) much more straightforward.

As we have highlighted, even if your new bike isn’t the perfect fit, there are several things you can do to make it more comfortable.

You may benefit from booking a session with a professional bike fitter. Most good bike shops will be able to use formulas and measurements to ensure your bike fits you as well as it can.

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Geert is a marathon mountainbiker who is also a bike maintenance graduate. Besides mountain biking he likes going on hikes and he loves an occasional trail run.

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