If you’re purchasing a Kawasaki KX250F, or already own one, you must be wondering what the KX250F top speed is.
If that’s the case, then this article is exactly what you’re looking for, and in the following sections, you will learn all you need to know about the top speed of KX250F.
Even if you already own the bike and have had the chance to test its top speed, you will learn what factors impact it and what modifications you can make to improve its top speed and power noticeably. You can even compare our findings to what you found the top speed to be and see if they are different.
KX250F Top Speed
The Kawasaki KX250F is among the most dominant dirt bikes in its category in the world.
The KX250F top speed is 65-75 mph, but that does depend on multiple factors and modifications. Things like engine specs, gear ratios, suspension, etc., significantly impact the top speed of KX250F.
As a dirt bike, the KX250F is not designed to reach incredible top speeds, but rather has higher torque capabilities in the low RPMs.
That torque makes the bike fast off the start and at lower speeds, which is how most dirt bikes are driven on the track.
This is not to say the bikes go slow when racing on a motocross track, but that’s a bit different than a straight-drag race where top speed is the main goal.
In motocross racing, it’s not always the bike with the fastest top speed that wins the race. I’ve seen many young kids on YZ125s and KTM 125s, that are significantly underpowered, beat 450s.
Let’s look at some factors and modifications that impact the top speed of KX250F.
Four Factors That Impact the Top Speed of KX250F
The engine and fuel system
At the heart of the KX250F is its 249cc, liquid-cooled, double overhead cam (DOHC), 4-valve, single-cylinder engine, capable of outputting about 40 HP at 12,400 RPM and 25 Nm of torque at 9,400 RPM.
The single cylinder has a bore of 77 mm and a stroke of 53.6 mm, with a compression ratio of 13.8:1.
Since 2011, the bike has had a Digital Fuel Injection System (DFI), often found in bikes with larger engine displacement. Adding this system made the bike a lot more responsive and faster off the mark.
The DFI system controls and regulates the precise mixture of air and fuel to provide maximum power before injecting it into the combustion chamber. It does this by using two separate injectors that operate in two “injection stages.”
The transmission and gearbox
The gearbox and transmission significantly impact the overall top speed of KX250F. The bike has a 5-speed gearbox and 520-pitch chain-driven transmission, with power delivery from the engine by a lightweight and smooth wet clutch.
The clutch is multi-plate, and the pressure on the plates is applied using a coil spring for increased (grip) at lower and mid-range RPMs.
All the gears in the gearbox are in constant mesh, which means that all forward-spinning gears are constantly engaged.
The shift forks used to change the gears have precisely manufactured grooves for smoother shifting. This also gives the rider increased control when using the clutch to change gears or take off with the bike.
The entire gearbox and transmission assembly on the KX250F is designed to output more low and mid-RPM power rather than provide increased top speeds. Gear ratios also have a role in this, but more on that later.
The suspension can also play a role in the KX250F top speed. The bike’s front and rear suspensions are adjustable for different riding conditions.
For example, a softer suspension with a higher rebound damping value would be better for low speeds and bumps since it will provide a smoother ride.
On the other hand, the stiffer the suspension, the more acceleration, and top speed the bike can achieve. This is why many sportbikes have stiff suspensions.
So, if you adjust the KX250F suspension to be on the softer side, the bike likely won’t be able to reach the maximum capable top speed, depending on the riding conditions.
The KX250F has a 48mm telescopic fork on the front, with adjustable rebound damping and compression.
On the rear is a mono-shock suspension with low and high-speed adjustments, which means you can adjust the compression, rebound damping, and preload.
The exhaust system
The exhaust system is the last factor we’ll cover in this article that impacts the KX250F top speed and performance.
The stock exhaust that comes with the bike has a shorter resonator chamber, which lets the gasses out quickly. This results in increased lower RPM power but decreased top speed capabilities.
The muffler suppresses and reduces the engine noise to an acceptable 94 dB level. However, this is not a part that has any effect on the top speed or performance of the engine. Its other role is to reduce the levels of toxic gasses that exit the engine.
Three Modifications That Can Improve the KX250F Top Speed
Applying some or all of the following modifications to the KX250F will increase the power output by around 10-15%, which means that the KX250F top speed could be increased to upwards of 80 mph in optimal conditions.
Change the front and rear sprockets
The stock sprockets of the KX250F’s drive train are 13/48. This means that the countershaft sprocket (front sprocket) has 13 teeth, while the sprocket attached to the rear wheel (rear sprocket) has 48 teeth.
Changing the sprocket teeth number on both the front and rear sprockets will affect the KX250F top speed.
Install a custom exhaust system and turbocharger
If you replace the stock exhaust system (the one we’ve discussed above) with an aftermarket one, the bike will increase overall top speed and performance.
For example, the Racing Line (Titanium) exhaust for the KX250F by Akrapovic claims an increase in torque of 1.1 Nm at 12,500 RPM and a weight reduction of around 300 grams when compared to the stock exhaust.
The numbers may not seem like much, but combining them with other modifications can greatly increase the top speed of KX250F by 10-15%. Why does changing the exhaust system make a difference?
Because a custom exhaust system provides better and faster release of gasses, which results in less stress being applied to the combustion chamber and cylinder head. This, in turn, allows for more air intake and increased overall power of the engine.
Adjust the suspension
Adjusting the bike’s suspension’s stiffness can also slightly impact its top speed.
Since the KX250F is a dirt bike, it is factory-set to provide more damping to accommodate all the bumps on dirt tracks and motocross conditions. So, if you want more speed, you can adjust the suspension and make it stiffer.
You should also adjust the bike’s suspension to compensate enough for your weight, which is what the preload function does on the rear mono-shock.
Frequently Asked Questions About The KX250F Top Speed
A KX 250F can go about 65 to 75 miles per hour without any modifications to the bike.
A Kawasaki 250 dirt bike, the KX250F model, can go about 65 to 75 mph.
Yes, the KX250F is a race bike (motocross bike) from Kawasaki.
A 2022 KX250F makes about 40 HP.
250 4 stroke dirt bikes can usually go between 60 and 75 mph, depending on the age, model, and brand.
Yes, the Kawasaki KX250F is a good bike for motocross racing.
The F in KX250F means four-stroke (4-stroke), as the bike has a four-stroke engine.