How Fast is a 125cc Dirt Bike?

Dirt bikes have been popular for a while now. Their popularity began in the 1960s. From that time, however, their use has become more and more widespread. People are slowly starting to relegate their attention to dirt bikes.

Dirt bikes are different from regular bikes. Regular bikes do not have an engine or power source of any kind. They just work with the mechanism of pedaling and drivetrains.

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With dirt bikes, however, there is an engine and a motor. The dirt bikes are described using different engines like 50cc, 125cc, etc.

One of the most common versions is the 125 cc. If you’re thinking to yourself, how fast is a 125cc dirt bike? Read this article to learn more.

Manufacturers have only recently started to manufacture dirt bikes. Before the 20th century, people were using regular street motorbikes to meet difficult terrain.

More and more people are accepting dirt bikes as a professional sport. People are also investing in dirt bikes to take the bike off roads and have some adventures of their own.

Dirt bikes present many opportunities for those seeking an adrenaline rush. However, the speed, motor power, and engine capabilities tell much about how the dirt bike will perform.

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In the article below, we’ll discuss what a dirt bike is, how it functions and how fast a 125 cc Dirt Bike can go.

What Is a Dirt Bike?

A dirt bike falls within the motorcycle category since it has a motor and engine, which provide it the power to move. It’s also clear that motorcycles and dirt bikes look very similar.

But a dirt bike is most important for off-road excursions. There’s no one specific track that dirt bikes follow. They have special breaks, tires, motors, engines, and hydraulic breaks because these bikes are used on dirt roads.

Each type of bike has its unique style, based on the needs of the rider. However, the dirt bikes you see in the market that you can buy have some general differences when comparing them to a regular bike or even a motorbike. 

A regular motorbike will not have the same capabilities as a dirt bike, and neither will a regular bicycle.

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Types of Dirt Bikes Available

We know that there are many models of dirt bikes available in the market. We also know that the different CCs depend on the kind of motor and engine which the dirt bikes have.

We have listed some of the different dirt bikes you can choose from when making your next purchase.

1. Motocross Dirt Bike

This bike is not ideal for trails. You can only use it for racing since it’s difficult for you to use it on the road. It has a 2-stroke and a 4-stroke engine.

2. Enduro Dirt Bikes

These bikes are built for long distances. If you’re looking to compete in longer trails, these bikes could be the perfect fit for you. They also do considerably well with road conditions which are less than ideal.

3. Dual Sport Dirt Bikes

These dirt bikes are road-compliant, so you can also run your errands with them. These bikes are excellent for trails but not that great for motocross.

4. Adventure Dirt Bikes

These dirt bikes are perfect for long-distance trails. They have a lot of capacity for gear and are fully road-compliant.

5. Supermoto/Motard

These dirt bikes are excellent for street riding and are manufactured as street bikes. They have a 2 stroke and 4 stroke engine.

6. Trials Dirt Bike

These Dirt bikes are only for obstacle climbing. They have the most limited use as you can not use them for motocross, trails, or street riding.

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How Does a Dirt Bike Function?

To know how fast a 125 cc dirt bike can go, we first need to know how it works. Most modern-day engines in a dirt bike work in a similar way to that of a car engine. Most dirt bikes have a 4 stroke engine. However, some dirt bikes have a 2-stroke engine.

The Components of a Basic Dirt Bike Engine

The basic components of a dirtbike engine, whether it’s 2 strokes or 4 strokes, are similar. The basic components of an engine include the following components:

  • Pistons- They form the combustion engine.
  • A cylinder block and head- This houses the pistons.
  • Fuel Inlets or Ports- They allow for the fuel to charge into the pistons.
  • Exhaust Outlet or Port- These are required to remove the gaseous materials from the engine.
  • Crankshaft- It connects the piston shaft and drives the power via the clutch.

The pistons move up and down inside the cylinder block in all engines, even those of a dirt bike. The pistons can move because there are explosions of an air-fuel mixture ignited by the spark.

The spark is provided by a spark plug, which is on top of the engine. The spark plugs are screwed into the cylinder head.

The pistons move up and down, turning the crankshaft. The lateral motion, which creates an up and down movement of the piston, is transformed into a rotary motion of the crankshaft.

The rotary motion is then transferred through the crankshaft via the clutch and transmission through the sprockets and chain to the rear wheel of your bike.

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How are Engines of Dirt Bikes Classified?

Most dirt bikes tend to be classified by the size and stroke of your engine. The capacity of the combustion chamber is in CCs, and people generally classify engines using this method.

The capacity of the cylinder is the greatest amount of volume it can have when the piston is in a complete downward position on the cylinder block called the Bottom Dead center.

If a dirt bike has a 250 cc engine, the 250 cc is a quarter of one liter in the cylinder capacity. The other way to define an engine is in terms of the engine strokes or cycles. So there can either be a two-stroke cycle engine or a four-stroke cycle engine.

Another final classification of an engine is the number of cylinders and the shape of these cylinders. If you think about car engines, they also follow the same process. Many cars have a V8 engine.

The 8 represents the number of cylinders, and “V” means that they’re in a shape of a V. Dirt bike engines are also similar.

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How Fast Is a 125CC Dirt Bike?

Dirt bikes with an engine capacity of 125 cc are known to have high top speeds. For a 125 cc dirt bike, the top speeds can go up to 60 mph.

The road features and riders’ physique inform the operating speed at which the bike can travel. The speed range of these dirt bikes goes above these speeds.

However, manufacturers recommend that riders shouldn’t go above this speed. The reason for this is that they shouldn’t do anything that may cause them significant harm.

With dirt bikes, you must be aware of the precautions you must take to prevent any injuries to speed.

Most dirt bikes have an engine capacity of 125CC. Their horsepower is in the range between 5.9 horsepower and 7.8 horsepower, with a maximum of 7500 revolutions per minute or rpm.

The bikes are equipped with single cylinders of a 4-stroke engine. The 4-stroke engine is a relatively novel technology. These engines also use four major categories.

These phases include processes of intaking, compressing, power, and exhausting. The way they can achieve the highest speeds depends on this.

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Determinants of the Speed of a 125cc Dirt Bike

We’ve talked about why a 125cc engine has the capacity that it does. However, other factors affect a 125 cc dirt bike’s speed, and you should know about them when making the purchase.

These factors are ones which we have mentioned below:

1. Engine Size

Different dirt bikes have different engine sizes. The size factor plays a very significant role in the speed, capacity, and horsepower of a dirt bike.  Regular dirt bikes have engines that go from 50cc to 140cc.

Some manufacturers also go as far as 175cc and 250cc. However, these capacities are much greater than the requirements of a dirt bike.

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Dirt bikes must also reach a maximum rpm that increases with the gear increases. When you ride your dirt bike on shorter sections, you’ll use lower gears and thus will be able to reach lower speeds. However, on longer rides, you can reach the highest speed of 50 mph.

If we’re talking about the 125 cc dirt bike, you can hope to attain a speed of 70 mph with the highest gear on good days and with the top speed. Hence, the engine size is an indispensable factor in determining the speed you can travel at.

2. Sprocket Gearing

In the front, a dirt bike has a smaller drive sprocket, while it has a larger rear sprocket gearing in the back. These two features may create the base ratio gear in your dirt bike.

Manufacturers do this so they can target a larger number of consumers of all kinds in the market. They achieve the base gear ratio by setting up a sprocket gear combination that can provide you with overall performance.  

Most often, the regular gearing in sprockets is usually set up as 14/42. This modification means that a 14-tooth drive version of a sprocket gear is on the front of your bike while the 42-tooth version sprocket is present on the rear end.

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The engine rpm and the red line on the speedometer can help you understand that the average speed of a 50 CCc dirt bike falls in the range of 22-25 mph.

If you apply the regular average speed to a 125  dirt bike, then the speed is going to increase the average velocity to 35 mph. The sprocket gearing on a 125 cc dirt bike drives the bike and informs you about its speed.

3. Modifications

You must make the correct modifications if you want to increase or decrease the speed of a dirt bike. Regarding this, most people prefer increasing the speed of dirt bikes rather than reducing it.

The modification for this is by replacing the dirt bike’s stock sprockets. This technique does not reduce the torque acceleration in the lower end when increasing average speed.

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You can also change the bike’s stock 14 tooth drive sprocket completely so that it can be a  sprocket with 15 teeth instead.

Similarly, if you switch a 42 tooth sprocket gearing in the rear end with a 32-tooth sprocket gearing, you’ll have a greater speed but a lower low-end torque acceleration.

If you understand how sprocket gearing functions, you can think to increase your bike’s average speed in a way that you don’t diminish the torque acceleration for your bike.

If you understand torque acceleration, you will also know how to get maximum speed in a short time with your bike.

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Modifications on your dirt bike can be the difference between you winning and losing a race.

4. Time Trials

If you’re wondering about the average speed of your 125 cc dirt bike, you can find it out by timing your bike’s laps. This type of trial is necessary for helping riders establish the maximum speed at which the bikes will go.

The way this works is pretty simple. Initially, you designed a course for your bike.

Then, enlist a regular biker, someone to keep the time, and an experienced biker. Each rider will go for three laps, and you can calculate the average speed which the ride offers.

These trials can also help you establish that the average top speed of your 125 cc dirt bike is one that riders can reach regardless of their degree of expertise.

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Final Thoughts

Dirt bikes can reach a range of speeds depending on the type of engines they use. Many different factors depend on how fast a 125 cc engine would go. However, we can establish that the regular speed that a dirt bike with this engine is about 65-70 mph.

The different factors that affect the bike’s speed are its engine, the sprocket gearings, and the modifications we make on the bike. We must use all of these in combination to achieve our required speed on a dirt bike. Most dirt bike riders want exceptions to speeds. However, it’s necessary to maintain the required safety.