How Fast Does a 140cc Pit Bike Go?

Published: 15.5.23

Updated: 13.8.24

So, How Fast Does a 140cc Pit Bike Go?

A question often asked in the world of motocross is, "How fast does a 140cc pit bike go?" 

The answer isn't as straightforward as it might seem, as there are several factors to consider. But let's dive into the nitty-gritty of pit bike speed.

Understanding Pit Bikes

What is a Pit Bike?

A pit bike, often known as a mini-moto or small dirt bike, is a small off-road, two-wheeler motorcycle.

Originally designed for traversing pits (hence the name), these bikes have gained popularity among racers and enthusiasts alike for their agility and versatility.

The 140cc Pit Bike

When we talk about a 140cc pit bike, we're referring to the engine size of the bike.

A 140cc engine is a mid-range size, offering a balance between power and control.

The top speed of a 140cc pit bike can vary depending on the model, year, and conditions it is ridden in.

According to various sources, a 140cc pit bike can go anywhere from 45 to 55 mph on average.

Related: How Fast Does A 125cc Pit Bike Go?

Factors Influencing Pit Bike Speed - Extended

Note: These factors are crucial when considering how to optimize your pit bike's speed. Always take into account the overall balance between speed and safety.

Several factors can affect the top speed of a 140cc pit bike. As we've previously discussed, rider and bike factors, as well as riding conditions, are significant influencers. Let's expand on these:

Bike Modifications

Modifications made to the bike can greatly influence its top speed.

These could be changes to the engine, the exhaust system, or the gear ratio, primarily via the sprocket setup.

Surface and Tyres

The surface on which the pit bike is being ridden also plays a role. Hard, flat surfaces allow for higher speeds compared to uneven or soft terrains.

Additionally, the type of tires equipped on the bike can impact the speed, with certain tread designs better suited for specific surfaces.

Weather and Temperature Conditions

The weather and temperature conditions can also affect a pit bike's top speed.

For instance, cold weather can result in denser air, which could increase air resistance and potentially decrease speed.

Elevation and Location

Elevation and location can affect the bike's performance as well.

For example, riding at a higher altitude where the air is thinner might reduce the engine's efficiency, thereby impacting the top speed.

Related: How Fast Are 250cc Motorcycles?

Comparing 140cc Pit Bike Speeds - Extended

When compared to other engine sizes, a 140cc pit bike typically falls in the middle of the speed range.

For instance, a 125cc dirt bike can reach a top speed of up to 100 MPH, while the average top speed for 400cc-450cc dirt bikes is around 96.67 miles per hour.

140cc Pit Bike Specifications

A 140cc pit bike typically has an 11-hp engine and a four-speed transmission.

This mid-range engine size offers a balance between power and control, making it a popular choice for many riders.

These points should give you a more comprehensive understanding of what influences the top speed of a pit bike and how a 140cc pit bike compares to other engine sizes.

Remember, while speed can be thrilling, safety should always come first.

If you're interested in what size dirt bike you should get, you may be interested in this article.

Weight

A rider's weight can significantly influence the speed of a pit bike.

Heavier riders may find that their bikes don't reach the same top speeds as those ridden by lighter riders.

Experience and Skills

A rider's skills and experience also play a role in how fast a pit bike can go.

Experienced riders can manipulate the bike's controls more efficiently, potentially achieving higher speeds.

Bike Factors

Gearing

The bike's gearing, particularly the sprocket gearing, can affect its top speed.

The gear ratio, or the relationship between the drive sprocket and the rear sprocket, can be adjusted to favor either speed or acceleration.

Modifications

Aftermarket parts and engine work can also influence a pit bike's top speed.

These modifications can enhance the bike's performance, allowing it to reach speeds that wouldn't be possible with stock parts.

Riding Conditions

The terrain, climate, and elevation where the bike is ridden can all impact its speed. For example, a bike may go slower on rough terrain or at higher elevations due to thinner air.

Increasing Pit Bike Speed

Upgrading the Sprocket

One of the most common modifications to increase a pit bike's speed is 

upgrading the sprocket. A smaller front sprocket or a larger rear sprocket can increase acceleration, while the opposite can increase top speed.

Remember, changing the sprocket gearing impacts not just speed but also the bike's overall performance.

Engine Work for Increased Performance

Enhancing a pit bike's speed through engine modifications is a popular approach among enthusiasts.

However, these alterations should only be undertaken by experienced individuals or professionals to prevent potential engine damage and ensure optimal results.

Carburetor Tuning

Proper carburetor adjustment can significantly improve engine performance:

• Jet Sizing: Replacing the stock jets with larger ones can increase fuel flow, potentially boosting power output. For a 140cc pit bike, moving from a #38 to a #40 main jet might yield noticeable improvements.
• Air/Fuel Mixture: Fine-tuning the air/fuel mixture screw can optimize combustion efficiency. A typical starting point is 1.5 turns out from fully closed, with adjustments made in quarter-turn increments.
• Float Bowl Height: Adjusting the float bowl height affects fuel delivery. Raising it slightly (about 1-2mm) can increase fuel flow for better top-end performance.

Exhaust System Upgrades

Improving the exhaust system can enhance engine breathing and power output:

• High-Flow Exhaust: Replacing the stock exhaust with a high-flow system can reduce back pressure and increase horsepower. Gains of 2-3 hp are not uncommon for a 140cc pit bike.
• Expansion Chamber: Installing an expansion chamber can improve exhaust scavenging, potentially increasing power across the RPM range.

Engine Displacement Increase

Increasing engine displacement can significantly boost power:

• Bore Kit: Installing a larger bore kit (e.g., from 140cc to 150cc) can increase power output by 10-15%, potentially adding 1-2 hp.
• Stroker Crankshaft: A longer stroke crankshaft can increase displacement without changing the cylinder, potentially yielding similar power gains to a bore kit.

Compression Ratio Adjustment

Raising the compression ratio can improve engine efficiency:

• Head Shaving: Removing material from the cylinder head can increase compression. A 0.5mm reduction might raise compression by 0.5-1 point, potentially adding 1-2 hp.
• High-Compression Piston: Aftermarket pistons with higher compression ratios can significantly boost power. A jump from 9:1 to 11:1 compression could add 2-3 hp.

Camshaft Upgrades

Installing a performance camshaft can optimize valve timing for increased power:

• High-Lift Cam: A cam with increased lift and duration can improve high-RPM performance. Gains of 1-2 hp are typical for a 140cc engine.
• Adjustable Cam Sprocket: This allows fine-tuning of cam timing for optimal power across the RPM range.

While these modifications can significantly enhance a 140cc pit bike's performance, it's crucial to consider that they may affect reliability and require more frequent maintenance.

Always consult with experienced mechanics and consider the intended use of the bike before making substantial modifications.

Comparing 140cc Pit Bike Speeds

When compared to smaller engine sizes, such as a 50cc pit bike, a 140cc bike offers a noticeable increase in top speed. However, it's crucial to remember that with greater speed comes the need for enhanced control and skill. Always prioritise safety over speed.

On the higher end, some sources suggest that with modifications such as changing the sprocket, a 140cc pit bike can reach speeds of up to 100 km/h (62 mph) or even 160 km/h (99 mph).

But again, modifications should be made with caution and understanding.

Comparing 140cc Pit Bike with Other Off-Road Bikes in the UK Market

To better understand the capabilities and positioning of 140cc pit bikes in the UK, it's helpful to compare them with other popular off-road bike sizes. This comparison will focus on speed, cost, and usability across different engine capacities, tailored to the UK market.

Speed Comparison

While 140cc pit bikes offer similar top speeds to 125cc models, they typically provide more low-end torque and acceleration. The 250cc bikes, however, offer significantly higher top speeds and overall performance.

Cost Comparison

• 125cc Pit Bikes: Generally range from £600 to £900
• 140cc Pit Bikes: Typically cost between £700 to £1,100
• 250cc Dirt Bikes: Usually priced from £2,500 to £7,000 for new models

The 140cc pit bikes offer a slight performance increase over 125cc models for a relatively small price difference, making them an attractive option for many UK riders.

Usability and Riding Experience

• 125cc: Lightweight and easy to maneuver, ideal for beginners and intermediate riders. Suitable for tight trails and compact tracks common in the UK.
• 140cc: Offers a noticeable increase in power over 125cc models, especially in low-end torque. Better suited for more experienced riders and varied terrain found in UK off-road areas.
• 250cc: Significantly more powerful, requiring more skill to handle. Ideal for experienced riders, racing, and diverse off-road conditions in the UK's motocross and enduro scenes.

Weight Considerations

The weight difference between 125cc and 140cc pit bikes is minimal, usually less than 2.5 kg. However, 250cc dirt bikes are considerably heavier, often weighing 14-23 kg more than their smaller counterparts.

Power Characteristics

• 125cc: Typically have a peaky power band, requiring frequent gear changes to maintain optimal performance.
• 140cc: Offer a broader power band than 125cc models, with more usable low-end and mid-range power, beneficial for UK trail riding.
• 250cc: Provide substantial power across the entire RPM range, with explosive acceleration and high top speeds, suitable for UK motocross tracks.

Maintenance and Reliability

140cc pit bikes generally require similar maintenance to 125cc models. Both are relatively simple to maintain compared to larger 250cc bikes, which often demand more frequent and complex servicing due to their higher performance capabilities.

UK Legal Considerations

• 125cc: Can be ridden on public roads with a CBT (Compulsory Basic Training) certificate by riders aged 17 and over.
• 140cc: Generally not road legal in the UK without significant modifications and individual vehicle approval.
• 250cc: Requires a full motorcycle license to ride on public roads.

In conclusion, 140cc pit bikes offer a balanced compromise between the accessibility of 125cc models and the performance of larger dirt bikes. They provide a noticeable performance boost over 125cc bikes without the significant jump in cost and complexity associated with 250cc models, making them an excellent choice for UK riders looking to progress their skills or enjoy more versatile off-road experiences in the diverse British countryside.

Safety Considerations When Increasing Pit Bike Speed

When exploring the speed capabilities of a 140cc pit bike, it's crucial to prioritise safety.

Increasing the speed of your pit bike comes with inherent risks that riders must be aware of and prepared for.

Maintaining Control at Higher Speeds

As pit bikes reach higher speeds, maintaining control becomes increasingly challenging.

Riders must develop advanced skills to handle the increased momentum and reduced reaction time.

It's essential to practice proper body positioning, smooth throttle control, and precise braking techniques to ensure stability and maneuverability at higher speeds.

Potential Risks of Modifications

While modifications can enhance a pit bike's performance, they can also introduce new safety concerns:

• Engine modifications may lead to increased heat and stress on components, potentially causing mechanical failures.
• Suspension alterations can affect the bike's handling characteristics, requiring adjustment to riding style.
• Aftermarket parts may not meet the same quality standards as original equipment, potentially compromising safety.

Always consult with experienced mechanics and use reputable parts when modifying your pit bike to minimize these risks.

Importance of Protective Gear

As speeds increase, the potential for injury in the event of an accident also rises. Proper protective gear is non-negotiable for pit bike riders:

• DOT-approved helmet to protect against head injuries
• Goggles or a face shield for eye protection
• Sturdy boots that cover the ankles
• Gloves for improved grip and hand protection
• Knee and elbow pads to guard against impacts
• Chest protector for additional torso safety

Wearing appropriate gear can significantly reduce the severity of injuries in case of a fall or collision.

Environmental Awareness

Higher speeds require greater awareness of your surroundings. Always ride within your skill level and the limitations of your riding environment.

Be mindful of obstacles, changes in terrain, and other riders or vehicles that may be present.

By prioritising safety and taking these considerations into account, riders can responsibly explore the speed capabilities of their 140cc pit bikes while minimising risks and maximising enjoyment.

In Summary

So, how fast does a 140cc pit bike go? On average, anywhere from 45 to 55 mph. However, factors such as the rider's weight and experience, the bike's gearing and modifications, and the riding conditions can all impact this speed.

And with the right modifications, a 140cc pit bike can hit astonishing speeds of up to 99 mph. But remember, speed isn't everything. It's also about enjoying the ride.

FAQs

How can I increase the top speed of my 140cc pit bike?

You can increase the top speed by upgrading the sprocket, modifying the engine, or improving the exhaust system. However, any modifications should be made with a good understanding of mechanics or by a professional.

Does a rider's weight affect a pit bike's speed?

Yes, a rider's weight can influence the speed of a pit bike. Generally, heavier riders may not reach the same top speeds as lighter riders.

What is the average speed of a pit bike with a smaller engine size, like a 50cc?

A 50cc pit bike typically has a top speed of around 25-30 mph, though this can vary based on various factors.

How does the gear ratio affect a pit bike's speed?

The gear ratio, determined by the front and rear sprockets, can be adjusted to favour either speed or acceleration. A smaller front sprocket or a larger rear sprocket increases acceleration, while the opposite increases top speed.

Are there any risks associated with modifying a pit bike to increase its speed?

Yes, there are risks. Improper modifications can cause engine damage and can also impact the control of the bike, increasing the risk of accidents. It's recommended to seek professional help for modifications.