Trail bike sizing. How to choose the right wheel size

Mountain Bike Buying Guide: How to Choose the Right MTB

A mountain bike is a bicycle designed for off-road riding. Although this definition is adequately descriptive of what a mountain bike is, the world of modern mountain biking is wonderfully diverse and varied in terms of riding disciplines and the types of mountain bikes designed for various styles of riding and varieties of terrain.

A quick look at the history of cycling will remind us that when the bicycle was first invented, smoothly paved roads were the exception, not the rule. That being said, modern mountain biking as we know it traces its roots back to the 1970s in Marin County, California where the “klunker” movement emerged. Back then, off-road cycling enthusiasts used heavily modified road bikes to race down Mt. Tamalpais. From there, interest in the sport progressively increased within the United States and beyond.

Choosing the right mountain bike can often be a daunting task, especially for those who are new to the sport. JensonUSA offers a vast selection of mountain bikes so to help you decide which is best for you, we present a concise mountain bike buying guide covering essential topics including:

Types of Mountain Bikes

The modern categorization of mountain bikes is broadly done according to riding disciplines within the sport. Keep in mind that as mountain bike design and technologies evolve, some of the lines between some categories are blurred. We will talk about how you can go about picking the mountain bike that best suits your needs if your riding style combines elements of more than one type of mountain biking.

Cross Country Mountain Bikes

Cross country bikes (often known as XC bikes) are designed to prioritize efficient, fast pedaling and long-distance riding over a variety of terrain. If your riding is all about covering big distances that go over changing terrain, with your home tails going up, down and everything in between, you probably want the lightweight build and efficient pedaling character of a typical XC bike. The main downside of many (yet not all) XC mountain bikes is that they will not excel in technical and super steep descending.

Trail / All-Mountain

The best way to think of most trail bikes is that they are the perfect compromise of the mountain biking world. They won’t climb as efficiently as pure XC machines, and they won’t descend with the same prowess of purpose-built downhill sleds, but they will do everything with enough competence to make them, arguably, the funnest and the most versatile category of mountain bikes to ride.

A trail bike might be for you if you want to do the same kind of riding you would do on a cross country bike, but have built up the riding skills and confidence to start tackling bigger and more technical terrain when the trail points down. There is a reason they’re often called “all-mountain” bikes. It comes from the desire to ride all of the mountain, without having to dismount and walk the bike down the more gnarly sections.

Enduro Mountain Bikes

Enduro racing is a type of mountain bike racing that has exploded in popularity in recent years. Perhaps much of the popularity of enduro is owed to the fact that it embodies some of the best things about mountain biking, drawing on elements from disparate riding disciplines.

Enduro bikes come with even slacker geometry, even chunkier tires and even longer suspension than trail bikes. You can still climb on an enduro bike, but it is only a means to the end of enjoying the high-speed descent on rock-strewn trails with technical features on which trail bikes might be out of their depths.

Downhill Mountain Bikes

Downhill (DH) bikes are made for a single-purpose: descending at high speeds on aggressive and technical terrain. Everything on a downhill bike – from the super long suspension travel to the robust construction of the frame to the descending-optimized geometry – is designed for trails that point down only.

If your riding is all about for lift-assisted descending, there is a strong case for considering a DH bike as your next bike.

Electric Mountain Bikes

Electric mountain bikes are better described as pedal-assist bikes. There is no separate throttle. Rather the electric motor only kicks in to boost your own human-powered pedaling. The electric assist enables you to go further, longer and faster, which all make an already fun sport extra fun.

The motor assist allows you to do more climbs to earn the fun descents without having to completely drain your energy on the first couple of laps. Additionally, the added power helps you tackle technical features with more confidence than you would otherwise or be hesitant to do on a normal bike. Last but not least, electric mountain bikes are a great equalizer when it comes to allowing people of various fitness levels to enjoy group riding together.

How to measure yourself for sizing a mountain bike

Picking the right frame size is often not as straightforward as it initially seems. After all, all reputable bike manufacturers provide extensive geometry charts and even some size recommendations based on general body measurements.

There are two main challenges that make the process of picking a frame size puzzling for a beginner mountain biker: 1) there are no concrete sizing standards used between manufacturers (so what might be a medium in one brand may fit like a large in another, etc.). 2) Attempting to understand geometry tables and charts can be bewildering if you don’t know what all the numbers and terms mean.

Short of getting a bike fit session with a professional bicycle fitter, there are two things you can easily do to figure out what the size that fits you:

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  • Learn how to read bike frame geometry charts: Because there is no standard reference, you will have to consider the specific numbers provided for each bike you are interested in. The good news is that the fundamentals of understanding bicycle frame geometry are not difficult to learn.
  • Measure yourself: There are a few key body measurements that you will need to take. Having a friend to help with taking the measurements makes the process easier. These measurements include:
  • Your height: Stand against a wall and place a pencil level with the top of your head. Make a small mark there, and measure from the mark down to the ground. Your height is a general indicator of an approximate frame size range. It is useful, but this measurement on its own is an imprecise frame size selection method.
  • Your inseam (inside leg): Another key point to note on mountain bike frame sizing is that reach (which is the horizontal distance from the center of the headtube to the center of the bottom bracket) is the basis for modern bike sizing. Reach has more of an impact on the riding position than any other frame geometry metric. The old method of determining your optimal size was based on seat tube length, which has lost its relevance in the age of sloping top tubes and dropper posts. This should also account for the type of bike you are planning to buy (e.g. XC bikes typically have a more outstretched riding position compared to trail and enduro bikes).

Another key point to note on mountain bike frame sizing is that reach (which is the horizontal distance from the center of the headtube to the center of the bottom bracket) is the basis for modern bike sizing. Reach has more of an impact on the riding position than any other frame geometry metric. The old method of determining your optimal size was based on seat tube length, which has lost its relevance in the age of sloping top tubes and dropper posts. This should also account for the type of bike you are planning to buy (e.g. XC bikes typically have a more outstretched riding position compared to trail and enduro bikes).

Another tip on bike fit and frame size: a great way to research mountain bike sizing is to use the known geometry of the bike you previously owned as a reference. If you were generally happy with the fit of a bike you have used before, you already have a range of geometry numbers to use as a guide.

Our mountain bike frame size guide

Below is a very approximate mountain bike frame size chart using height and inside leg measurement.

How to measure a mountain bike frame

Manufacturers have made buying mountain bikes which are the correct size relatively straight forward. Most manufacturers provide a sizing and geometry chart for each specific model. Sizing and geometry charts are sufficient for the vast majority of riders to pick the right size bike for them.

The two key frame measurements on the geometry chart are seat tube length and top tube length.

  • Seat tube length — This can affect how much stand-over clearance there is between you and the bike. This is important for new riders as you may well need to stop and get your feet on firm ground quickly. However, some bikes — such as those with longer suspension travel — can have zero standover clearance, and still be the correct size.
  • Top tube length — This determines the comfort, fit and handling of your bike to a large extent. Ideally, you should aim not to feel either cramped or stretched.

The difference between road bike and MTB sizes

For road bike riders looking at MTBs, sizing can be confusing because MTBs tend to have a smaller seat tube and longer top tube length than their road bike cousins.

As mentioned above, manufacturers assist customers through simplifying the sizing process using the ‘catch-all’ sizing (Extra Small through to Extra Large). For more details, see the example chart above.

You can read our in-depth road bike size guide here.

How MTB geometry affects the ride

MTB geometry is important. The angles at which the tubes are joined to form the frame have a profound impact on how the bike will ride.

The ideal geometry largely depends on what type of riding you do. Cross-country-style MTBs tend to have steeper geometry (for example, they may have a 73.5-degree seat tube and a 71-degree head tube) whereas enduro and trail bikes, tend to have slacker geometry (for example a 71-degree seat tube and 67-degree head tube).

Fork Offset

Some­times, short­er is bet­ter. Instead of the typ­i­cal 51 mm off­set, the new Rip­ley uses a 44 mm off­set. This gives you the sta­bil­i­ty of a slack­er head angle, while retain­ing the BMX like feel of, well, a Ripley.

We pio­neered the wide rim rev­o­lu­tion a few years ago and inspired a new crop of wider 2. 4 ” — 2. 6 ” tires. When paired togeth­er, this com­bo can be run at ultra low pres­sures that pro­duce elbow-drag­ging cor­ner­ing trac­tion with­out sac­ri­fic­ing speed.

Ripley Geometry

130mm Fork (544mm axle to crown)

Sizing Guide (Rider Height)

Ripley Specific FAQs

All our manuals are available here. You can also find the Quick Setup guide for the Ripley in the ‘Setup’ tab on the right.

There are two different tunes for the Ripley shock. Our standard tune and a light tune.

Since August of 2019, we have been shipping small and medium Ripleys with the light tune. To identify the light tune, find the four digit code on the shock. Here are the light tune codes: DZGP, DZGN or DZGM. The standard codes are DXBC, DWSL and DWRC.

Nearly everyone under 160 pounds should use the light tune. Above that and you will want the firmer tune.

Some lighter riders may prefer the standard tune if any of these describe your riding:

  • Your riding style has a lot of jumping and you want more rebound control on landings
  • You have a lot of really long downhills and don’t want to overheat the shock
  • You are a Semi Pro or above DH racer

Fox, or an authorized Fox service center can revalve your shock for you if you want to go with a different tune.

The dual eccentrics offered an efficient pedaling platform and supple suspension feel, but they took up valuable real estate in the seat tube. To make the Ripley compatible with the new crop of long dropper posts, we’ve transitioned to an all new Ripmo inspired chassis. In the process, we’ve significantly reduced the frame weight and increased stiffness.

How Do You Size A Dirt Bike For A Child?

Getting the right size dirt bike is not only important for your child but for anyone intending to take up dirt bike riding!

This is even more important if the person is just beginning, and this will be their first dirt bike. Here are the main reasons that a bike of the right size is beneficial to your child or anyone else.

  • Starting. Many dirt bikes still use the kickstart method to get the engine going. It is very difficult to kickstart a bike that is too big for you.
  • Balance. If the bike is too tall for the person, they will have trouble pulling off and stopping the bike.
  • Confidence. If the person or child feels comfortable on the bike, they will have more confidence, and their ability to learn to ride and negotiate the terrain will progress at a more Rapid pace.
  • Control. If the dirt bike is too big for the person, not only in physical size but also the power of the motor, then the person will struggle to control the bike and could develop a fear for the machine.
  • Safety. Safety should always be a top concern in dirt bike riding, especially for kids, and all the previously mentioned points could result in a compromise of the safety of the child on the bike.

The temptation may be to buy a bike that is slightly too big for the child so that they can grow into the bike. This may be a good strategy when you buy your kid a pair of jeans, but not when it comes to dirt bikes!

Yes, kids do grow fast, and they will outgrow their dirt bikes. but it is not worth compromising their safety by buying too much bike for them to handle. Dirt bike riding is a growing outdoor activity, and as such, there will always be a market for second hand bikes.

Once your child outgrows the bike, sell it and put the funds towards buying a bike another size up for your kid.

Size UP or DOWN? What To Do If You’re in BETWEEN Bike Sizes

How To Size A Dirt Bike For Your Kid

The standard way to size a bike is by the person’s height and what seat height of the bike is appropriate for that particular bike.

Generally, the power of the motor will increase along with the increased height of the bike until you get to a certain seat height, where you will get a number of different sized motors in that range of bikes.

With the younger generation kids in the 3 to 7-year age group, the bike could last the child a good few years before you need to upgrade. We will cover this aspect when we discuss individual bikes.

The best way to judge the right size bike for your child is to use the following guidelines to establish a baseline size bike.

These guidelines should help you to find the right size dirt bike for your kid, but you also need to take into account the boldness and personality of your child, especially when choosing the engine size of the bike. Some kids show no fear, and others are a little more conservative and reserved.

Let your child progress in dirt bike riding at their own pace, and don’t push them to ride a bike that is too powerful for their level.

What Size Dirt Bike Should A 5-Year Old Ride?

Many children start dirt bike riding at a young age, some even as young as 3-years old. Children that are younger than 5-years would probably start on a bike with training wheels to help them balance since they are unlikely to even be able to ride a bicycle yet.

When it comes to children that are about 5-years old, you would need to get a bike that is suited to the height of your child, and in the smaller-sized bikes, this is often determined by the wheel size.

A 50cc bike would be the recommended engine size for a bike for a 5-year old, but you would need a 50cc with a wheel size of between 14 and 16-inches to cater to the height of your child.

What Age Is A PW50 For?

PW50 bikes are a great entry-level bike for the younger generation of dirt bike riders. These bikes are so popular that they come in a range of sizes. The size can be adjusted as the child grows by increasing the size of the wheels on the bike, which would make the bike a better fit for your child as they grow.

This means that a PW50 can be suitable for a child from the age of 3-years all the way to 7-years old. The popularity of these bikes also means that there is a great secondhand market for these bikes.

Another bike that fits well into this age group is the KTM50, which is also popular and has a little more of a rugged look to it than the Yamaha PW50.

How Old Should Your Child Be To Ride A 250?

When you get to the bikes with the larger engines, the dynamic changes quite substantially. These bikes may only be 125 or 250cc, but they are very powerful machines that should be treated with respect and responsibility.

trail, bike, sizing, choose

125cc bikes are generally more than enough for most teenage riders. Many adults ride the 125cc class motorcycles as well, which is an indication of the power of these bikes.

The 250cc is a big jump from the 125cc and is a lot of bike for a teenager to handle. This is especially true if your child is a smaller framed person and is not tall enough or does not have the physical strength to handle the bike.

It is recommended that only teenagers from the age of 16-years upward consider riding a 250cc dirt bike. Even so, you should only consider this bike for your kid if they are tall for their age and have the experience and strength to be able to tame a 250cc dirt bike.

Are you riding the right size bike? | Bike Geometry Explained


The right size dirt bike for your kid is a crucial aspect not only for their safety on the bike but also for their enjoyment of the bike and being able to ride it in the dirt with confidence.

Another important part regarding the safety of your child on the bike is for them to have the right safety gear. This includes quality riding protection in the way of a helmet, goggles. chest, back, elbow, and knee protection, gloves, boots, and clothing.

These items are not to make your kid look cool when they ride their bike but serve to protect them from injury. Looking cool is just a bonus side-effect of the gear!

trail, bike, sizing, choose

At Risk Racing, we can offer you a wide range of gear, not only for your child to wear but also gear for the bike that will make life easier.

Our innovative magnetic dirt bike stand is one such item among many, so take a look at what we have to offer to make dirt bike riding a fun-filled activity for the whole family!

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