What is the Lightest Adult Dirt Bike on the Market?

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Dirt biking is a riot of fun. If you’re new to the sport (or remember when you first learned) the easiest bike to ride will be the lightest bike for your weight.

Overall, the lightest dirt bike out there is the FX5 Mountain Moto. Current 2019 models weigh about 132 pounds to 136 pounds depending on the specific model.

There is a lot to this bike, so lets dive right into it!

What Makes FX5 Mountain Moto Bike so Light?

The FX company uses a combination of components from motocross, mini-motocross, trial motorcycles, pit bikes, and Enduro. As such, the FX5 Mountain Moto is a fantastic combo of powerful trail dirt bikes and agile mountain bikes.

Of course, this bike isn’t as powerful has some of its heavier counterparts, and that makes sense. If you are looking for a light bike, then this is obviously number one, but if you are looking for speed then I would look elsewhere.

The type of person that would own this bike is somebody who wants something between a mountain bike and a dirt bike. You aren’t going to set any speed records, but the bike is so light that it can handle a lot of really interesting situations that other dirt bikes or mountain bikes can’t.


FX5 Mountain Moto Models:

For the FX5 Mountain Moto, three models are available. The three models each have a 125 cc 4-stroke engine, a chrome molybdenum steel chassis, and a four-speed auto clutch.

Beyond this basic, important similarities, each model has the same quality and similar lightweight but a few different features.


The steel model of the FX5 Mountain Moto weighs about 136 lbs (62 kg) ready-to-ride, which is by far one of the lightest bike weights I have ever seen for a dirt bike.

This model also sports an Ollé Shock, steel coil spring. And has a standard level trial fork.

This model, which is still amazing, only has one seat/bike color option. But if you’re not too picky, this may be the bike for you, being the most economical (at $4,395 from the company or less if bought used) of the three models.


The Gold model of the FX5 Mountain Moto bike has a ready-to-ride weight of 134 lbs (61 kg), which is an astounding weight for a dirt bike.

This model functions with an Ohlins Shock, steel coil spring and a “racing” level trials fork.

This model has three options for seat/frame coloring, a stainless steel fastener set, and an FX-Works engine upgrade. these extra features do hike up the price a little more, making this model $7,995. But if these extra features float your boat, the price may well be worth spending.


The Titanium model is, by far, the lightest of the three models or any other bike out there. It weighs about 132 lbs (60 kg) ready-to-ride.

It has an Ohlins Shock, Titanium coil spring, and a formula/tech factory trials fork. This model also features an FX-Works engine upgrade, and a titanium fastener set for quality replacement and modification needs. Carbon fiber handlebars (which is one of the lightest materials used for dirt bike products) are sported on this particular model.

At $11,995, this model is the most expensive version of the FX5 Mountain Moto. If you are looking for the lightest, highest performing bike, this model will give you the bang for your buck.

Pros and Cons of the FX5 Mountain Moto:


Besides being the lightest bike on the market, the FX5 Mountain Moto can take you places that bulkier, heavier bikes can not go.

Because of their lightweight, this bike is easy to move over obstacles such as logs or fences when needed, giving you a straighter, focused path for your adventure without having to take a detour.

This bike is also easy to control. As shown in the review video below, if you need to stop the bike immediately because of an unexpected obstacle, you can easily put your feet on the ground and stop the bike sooner rather than chasing after it.


The biggest cons with this bike that I can see is that this bike doesn’t go as far or as fast as other bikes with higher cc engines.

If you’re looking for a bike that you can ride for longer and/or on flatter terrain that you want to accelerate on, the FX5 Mountain Moto going to perform the way the best compared to other bikes for this purpose.

Why would you want a lighter bike?

If you’re a beginner…

If you are newly starting out in the dirt biking sport, lighter bikes are the way to go, because they are easier to control. Lighter dirt bikes allow you more flexibility and reaction time to the obstacles that you will come across as you’re out riding. Heavier bikes are more difficult to turn and to stop because of their weight.

If you’re a new dirt biker, stick with bikes between the 125cc and 250cc ranges until you have gained some more experience.

If you’re a smaller person…

Generally speaking, if you are a smaller, lighter person, you’re going to want a smaller, lighter bike. Not only will this help you control the bike and have an awesome time, but you won’t have to expend all your energy early in your ride.

Think of it this way, is it easier to run with a heavy backpack or without one? My suggestion is that you avoid any unnecessary weight on your bike’s build or supplies. If you’re wondering what bike size you should get for your size, here’s some helpful height and bike information.

If you’re going trail riding…

If you are the kind of person who is focused less on motocross and more on backcountry trail riding, a lighter bike will serve you better on your adventures.

Trails can be rough, especially those that are less traveled. You will most likely come across logs, boulders fences and so many other obstacles. But, the good news is, lighter bikes allow you to maneuver around these major bumps in the road with greater ease than a heavier bike could manage.

Some riders might find it necessary to lift their bike over a log or a fence in order to continue on their journey. Although lifting a bike over tons of obstacles throughout the ride could become exhausting, a lighter bike will contribute to less strain and more trail freedom for those of us who aren’t Dwayne the Rock Johnson.

If you’re looking for speed…

Lighter bikes are generally faster than other bikes. Referring to our backpack analogy, imagine you’re running a race. Would you want to be geared up in bulky, heavy training shoes or in sleeker, lighter spike shoes?

Of course, there are other components to consider, such as if the engine is 2-stroke or 4-stroke and how many cubic centimeters (cc) it is, when it comes to speed. But if your engine is carrying less weight, it won’t have to strain as hard to get your machine up to top-notch speed.

Lighter Bikes with Larger Engines:

When it comes to speed, you might want to look into bikes with higher cc ranges than the FX5 Mountain Moto. It’s the lightest bike out there, but there are various dirt bikes that are still light while carrying bigger engines.

Of course, it’s important to keep in mind that your weight can have an effect on how light your bike is. You want a bike that can support you without a problem. Here’s some more information about important aspects you might want to consider when you’re a heavier or bulkier rider.


Husqvarna FC 250:

A light 250cc dirt bike is the Husqvarna FC 250. It weighs 217.8 lbs (98.8 kg). This bike is heavier than the FX5 Mountain Moto, but it has more power and speed than a 125cc making it ideal for more experienced rider’s who want a lighter bike.

Yamaha YZ250F

The Yamaha YZ250F has a wet weight of 231.5 lbs and a powerful engine. This makes it about a hundred pounds heavier than the FX5 Mountain Moto, but gives it the opportunity to support a 250 cc 2-stroke engine.

This bike is a powerful accelerator that makes up its weight with speed. It’s one you might want to look into if you’re considering buying a bike that is light weight but full of power.


Honda Montesa 4 Ride

The Honda Montesa 4 Ride is a particularly light 300cc bike. It weighs about 178.6 lbs (81.0 kg), making it only 42-46 lbs heavier than the FX5 Mountain Moto. This is still quite a bit heavier than the lightest bike talked about above but is certainly light, impressive weight for the size of its engine.

This bike is a great option for more experienced riders who are looking for bikes that have more power and speed while still keeping it light.

Beta Evo 300 Sport

The Beta Evo 300 Sport is a crazy machine with a surprisingly light weight at just 149 lbs dry weight. This bike’s sleek aerodynamics and 2-stroke engine give it the vibe of being built for speed.

If you’re looking for a lightweight bike that has a larger engine than a 250cc but less bulk than a 450cc, this just might be the bike for you.


KTM 450SX-F:

The KTM 450SX-F has been considered one of the lightest 450cc bikes in motocross. It has a weight of 220.9 lbs (100.2 kg), which is certainly a lot heavier than the FX5 Mountain Moto, but much lighter than other 450cc bikes such as the Suzuki RM-Z450 which is 240 lbs (108.9 kg).

For heavier riders who are looking for a bike that can support them up a hill and various terrain, this bike is a good match for speed and strength.

Kawasaki KX450

The Kawasaki KX450 has a total curb weight of 242.4 lbs with the fuel levels above 90% capacity. For a 450cc engine, this machine is a slim, light bike that’s sure to give you the speed you’re looking for without being too bulky.

Plus, who said you have to have every possible gear and tool on this bike? A good way to keep the weight down is to be more selective about what you choose to carry with you while you’re riding.

How can you make the bike you already have lighter?

There are several ways that you can decrease the weight of your bike. Of course, depending on how much you’re willing to spend on modifications, you can shrink the overall weight by a lot. But there are some adjustments you can make that won’t totally break the bank.

Unsprung vs. Sprung Weight:

When it comes to figuring out how to make your own dirt bike lighter, it’s better to focus on lowering unsprung weight than sprung weight.

Unsprung Weight:

Unsprung weight includes everything below the bike’s suspension’s springs. This consists of not only the tires but also the fork legs, brake calipers, rims, spokes, rotors, hubs, linkage, tubes, swingarm, and rim locks.

Unsprung weight plays the biggest part of the extra weight and drags your bike can take on while riding. While riding, your unsprung weight will go up into the chassis when you hit the ground. If your unsprung weight is lighter, your suspension will have a faster reaction time because it won’t be strained by the extra weight.

The heavier the moving parts in your unsprung weight can have a big impact on how fast your engine can move them. The heavier they are, the harder your engine has to work. That’s why lowering the unsprung weight as much as you can ultimately benefit you when riding.

Lightening Unsprung Weight:

You can start removing unnecessary unsprung weight by getting lighter tires that will still be suitable for your riding needs. Another good note is to consider using thin tubes instead of heavier, thicker ones. It’s the little things that can make a big difference when there are a lot of them that are attached to your bike.

Sprung Weight:

Sprung weight is the weight of the upper part of the bike above the suspension’s springs. It includes the engine, upper fork tubes, controls, frame, shock body, plastic, and saddle. In short, the sprung weight is everything that’s part of the chassis of your dirt bike.

Your sprung weight doesn’t have as much impact on the total weight of the bike during the performance as the unsprung weight does. This is because the sprung weight of your bike is supported by your suspensions springs. Therefore, when you’re out riding, the springs absorb the impact of the trail before the chassis is affected.

Lightening Sprung Weight:

If you are looking to remove even more weight after you’ve taken care of the unsprung weight, you can look into modifications for your sprung weight. The biggest thing is to avoid bling unless you need it.

When you’re adding things like handguards or skid plates, consider picking ones that are made of a lighter material. I would even look into carbon fiber materials, which might not even be that expensive compared to other heavier materials like alloy.


The FX5 Mountain Moto is a uniquely light performance and trail bike, but there are also several great options to consider when looking for a lighter bike. Not only are there lighter bikes available for each engine size, but you can also take your own measures to decrease the sprung and unsprung weight of your bike without having to fork out too much money. Whatever you choose to work toward, soon you’ll be riding free of extra weight.

Jim Harmer

I'm the co-owner of Dirt Bike Planet. I live in Star, Idaho and enjoy dirt biking with my wife and two boys throughout the Idaho mountains.

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