Dirt Bike Top Speed: How Fast Can Motocross Bikes Really Go?

For motocross and off-road riding enthusiasts, few things beat the adrenaline rush of flying across rough terrain on a high-performance dirt bike. But just how fast can these specialized motorcycles actually go?

The top speed of a dirt bike depends on several key factors, especially the engine size and strokes. A 50cc bike may only reach 40 mph, while a 450cc machine can exceed 100 mph under the right conditions.

In this in-depth guide, we’ll cover everything you need to know about dirt bike top speeds, including:

Typical top speeds by engine size
Factors that determine acceleration and max velocity
The fastest dirt bike models available
Tips for increasing your bike’s speed
The pros and cons of high speed riding
Buying considerations for speed-focused bikes
Maintenance tips to get the most from your machine
Answers to frequently asked questions

Let’s get started!

Typical Top Speeds by Dirt Bike Engine Size

One of the biggest determinants of how fast a dirt bike can go is its engine capacity, measured in cubic centimeters (cc). Here are the typical top speeds based on dirt bike engine sizes:

50cc

Max Speed: 25-40 mph
Best for young kids just starting out

50cc dirt bikes have small, low-power engines designed for new riders. Top speeds are very limited, but this makes them easy to control.

65cc

Max Speed: Up to 62 mph
Ideal for teenagers and smaller adults

Slightly larger than 50cc models, 65cc dirt bikes provide moderate speed capability perfect for novices.

80cc

Max Speed: 45-55 mph
Manageable for young teens

80cc engines offer decent acceleration while remaining very controllable. Top speeds exceed 50 mph on some tuned models.

100cc

Max Speed: 50-80 mph
Intermediate rider bikes

100cc dirt bikes are fast enough for older teens and smaller adults to enjoy trail riding. Advanced tuning can push speeds over 80 mph.

110cc

Max Speed: 50-55 mph
Ideal for younger teens

Offering a balance of speed and stability, 110cc bikes are well-suited for younger teenage riders moving up from 85cc models.

125cc

Max Speed: 55-70 mph
Common choice for older teens and adults

With moderate power and good handling, 125cc 4-stroke engines can reach 60 mph for exciting recreational trail riding.

150cc

Max Speed: 50-60 mph
Beginner to intermediate bikes

150cc dirt bikes provide controllable power for new adult riders, with top speeds similar to 125cc models.

200cc

Max Speed: 60-90 mph
High performance for experts

200cc engines make these bikes fast enough for motocross racing. Top speeds exceed 85 mph for highly modified machines.

250cc

Max Speed: 60-80 mph or some models can reach 90 mph
Common motocross racing class

High revving 250cc 2-stroke engines allow elite riders to compete at 70+ mph. They require experience to control.

450cc

Max Speed: Up to 80-120 mph
Expert motocross bikes

The most powerful dirt bike class, 450cc 4-strokes reach over 123 mph in the right conditions. Traction control aids acceleration.

As you can see, dirt bike speed capability rises sharply with engine size. But there are other important factors that determine velocity too.

Factors That Determine a Dirt Bike’s Top Speed

While engine size plays a major role, these other elements also impact how fast a dirt bike can ultimately go:

Engine Strokes – 2 Stroke vs 4 Stroke

2 stroke engines generate more raw power from a given displacement than 4 strokes. Their lighter weight also aids acceleration.
But 4 stroke engines make more usable power across a broader rpm range. They also have emissions controls and require less maintenance.

Tuning and Modifications

Performance parts like exhaust systems, air filters, and engine tuners can add substantial horsepower.
Gearing changes to suit specific tracks optimize acceleration and max speed.

Rider Weight

Heavier riders will make a dirt bike slower compared to a very light rider. Power-to-weight ratio is important.

Terrain

Wide open dirt areas allow higher top speeds than tight, technical tracks with hills and jumps.

Now let’s look at some of the specific makes and models with the fastest top speed capabilities.

Fastest Dirt Bike Models

Here are 5 of the quickest motocross bikes available from major manufacturers:

KTM 450 SX-F

With a 449cc single-cylinder 4-stroke engine, the KTM 450 SX-F is considered one of the fastest production dirt bikes available. In optimal conditions, it can exceed 123 mph thanks to its 63 horsepower output. No wonder Ryan Dungey has taken it to multiple supercross wins.

Yamaha WR450F

Yamaha’s high performance WR450F features a 449cc 4-valve DOHC engine. Weighing under 258 lb pounds, it can hit 99.4 mph in the right hands. The WR450F is street legal in some states too.

Honda CRF450R

The CRF450R’s 449cc Unicam engine gives it a huge 92 mph top speed for closed course use. It’s also incredibly nimble thanks to an aluminum chassis and suspension designed for Supercross tracks.

Beta 450RS

Beta’s 449cc single-cylinder 4-stroke Enduro bike reaches a max of 110.9 mph. It’s street legal across the US, with mirrors that can fold in for off-road riding. The SOHC engine produces 48hp for a great power-to-weight ratio.

Suzuki RM-Z450

Suzuki’s RM-Z450 has a 449cc fuel-injected DOHC engine tuned for massive midrange power. Top professionals like Eli Tomac ride it to over 111 mph on the motocross circuit. It’s also an incredibly popular amateur racing bike.

Tips for Increasing Your Dirt Bike’s Speed

While caution should be exercised when pushing a dirt bike to its limits, there are some modifications that can safely raise top speed:

Engine tuning – Getting your engine optimized by a professional can find hidden horsepower.
Exhaust system upgrades – A less restrictive aftermarket system increases power. But check noise regulations.
Weight reduction – Shedding pounds with a lighter seat, wheels, and accessories aids acceleration.
Suspension adjustments– Proper sag and damping settings let you carry more speed through rough sections.
Gearing changes – Taller sprockets or smaller rear pulleys bring higher top speeds at the cost of some acceleration.

Of course, safety gear and rider skill should also increase alongside any power gains.

Pros and Cons of High Speed Dirt Bikes

Riding a high velocity dirt bike can be an incredibly fun and exciting experience. But it does come with some trade-offs:

Pros

Huge adrenaline rush from high speeds
Increased passing power for racing
Ability to ride more advanced terrain
Cool factor of owning a powerful machine

Cons

Higher risk of crashes and difficulty controlling
More expensive purchase and maintenance costs
Not suitable for beginners
Possible noise complaints
Decreased low-end power

Buying Considerations for Speed-Focused Dirt Bikes

If you want a dirt bike capable of high speed riding, keep these factors in mind:

Rider skill – Match the bike to your experience level so you can safely control it at speed. Don’t exceed your abilities.
Riding goals – Focus on competition requires a faster bike than just recreational trail use.
Budget – The most powerful bikes carry higher price tags. Factor in mods/maintenance too.
Riding terrain – Rocky vs. smooth, trails vs. tracks, and elevation changes impact target top speed needs.
Size/weight – Ensure the bike suits your height and strength to manage it physically.

Test ride different bikes and gear them towards your specific needs. An expert 450cc motocrosser isn’t the ideal choice for a child learning to ride!

Maintenance Tips for High-Performance Dirt Bikes

To keep your speed machine running in peak condition:

Change oil regularly – engines work hard at high rpms
Inspect and replace the air filter – prevent dirt damaging the motor
Keep suspension components serviced – handling suffers with bad shocks
Check tire pressures/wear – prevent flats or loss of control
Adjust valve clearances – maintain compression and performance
Lubricate the chain – reduces friction and prevents premature wear
Check spoke tightness – loose spokes can damage the wheels
Inspect controls and cables – fix loose handlebars, sticky throttles, etc.
Replace spark plugs – ensure full combustion and optimal timing
Check engine mounts – tighten any that are loose to avoid damage
Clean the radiator – prevent overheating problems
Fix any oil or coolant leaks immediately
Keep fasteners tightened – vibration can loosen bolts over time

With intense speeds on rough terrain, dirt bikes take a beating. Staying on top of maintenance helps maximize performance and safety when riding your machine to its limits. Investing in regular service from a qualified motocross mechanic can extend the life of your bike’s high performance components too.

FAQs About Dirt Bike Top Speeds

If you’re new to high performance dirt bikes, chances are you have plenty of questions. Here are answers to some of the most frequently asked ones:

What’s the fastest dirt bike in the world?

The KTM 450 SX-F is currently considered the fastest production dirt bike, with a tested top speed of 123 mph. But heavily modified bikes have gone even quicker in specialized land speed trials.

How fast can a beginner dirt bike go safely?

Beginners should stay under 50mph until they’ve developed proper control and technique. Starting on a 50-125cc bike allows you to gradually build speed capability as your skills improve.

Can you make a dirt bike street legal?

Some dirt bikes like the Yamaha WR450F come equipped for street legality from the factory. Others require headlights, taillights, mirrors and other modifications to become street legal – but it varies by state.

Do motocross riders actually reach top speeds during races?

Rarely, since most tracks have tight turns, jumps and other obstacles. But on long straightaways or open desert terrain, the fastest bikes can approach their maximum speed.

Does engine size affect acceleration too?

Yes, larger engines typically have more low-end torque for faster acceleration, in addition to higher maximum speeds. But factors like gearing and tuning make a big difference too.

Final Thoughts on Choosing a Fast Dirt Bike

When it comes to dirt bike top speed, bigger engines clearly equal faster bikes – but consider your riding skills and needs too. Novices should stick to controlled speeds under 60mph until developing more experience.

On the other hand, expert riders seeking an adrenaline pumping motocross or desert racing machine need 450cc-class engines capable of speeds over 100 mph.

Just remember to put proper safety gear first whenever pushing your dirt bike’s limits. And invest in regular maintenance to keep your high velocity machine in peak riding condition. The right bike matched to your ability will deliver huge thrills on the track or trail.

Ride safe out there!