How Fast Does A 125cc Pit Bike Go?

Published: 29.6.23

Updated: 13.8.24

Ever wondered about the top speed of a 125cc pit bike? It's a question that often pops up among bike enthusiasts and potential buyers.

If you're interested in exploring a variety of bikes, you might want to check out the Onemoto collection.

The answer, however, isn't as straightforward as you might think.

A 125cc pit bike's top speed can range from 55 to 60 miles per hour, with the highest recorded speed being a whopping 100 miles per hour.

But how fast does a 140cc pit bike go? You can find out in this guide.

But, it's important to note that this isn't a standard speed for all riders.

On average, most 125cc pit bikes can reach a top speed of about 57.5 miles per hour.

Intrigued?

Let's dive deeper into the factors that influence these speeds.

Factors Affecting the Speed of a 125cc Pit Bike

Condition of the Track

The condition of the track can affect the top speed of a 125cc pit bike in several ways.

Some of the ways in which the condition of the track can affect the top speed of a 125cc pit bike include:

• Rough or uneven track: A rough or uneven track can slow down the bike and reduce its top speed. This is because the bike has to work harder to maintain its speed on a bumpy track.
• Smooth and well-maintained track: A smooth and well-maintained track can help the bike reach its maximum speed. This is because the bike can maintain its speed more easily on a smooth track.
• Track surface: The surface of the track can also affect the top speed of a 125cc pit bike. A track with loose dirt or gravel can slow down the bike, while a hard-packed track can help the bike achieve a higher top speed.

Related: How Fast Are 250cc Motorcycles?

Rider Experience

Rider experience is another factor that can affect the speed of a 125cc pit bike.

An experienced rider who knows how to handle the bike can push it to its limits and achieve a higher top speed.

On the other hand, an inexperienced rider may not be able to handle the bike as well and may not be able to achieve the same top speed.

Rider experience can also affect the acceleration and overall performance of the bike.

Therefore, it is important for riders to have the necessary skills and experience to handle a 125cc pit bike safely and effectively.

If you're having trouble with your dirt pit bike only running with the choke on, this troubleshooting guide might help.

Sprocket Gearing

Sprocket gearing is a critical factor that can affect the speed of a 125cc pit bike (12345). The sprocket gearing refers to the size and ratio of the front and rear sprockets.

A larger rear sprocket can increase the top speed of the bike, while a smaller rear sprocket can increase acceleration but decrease top speed (1).

Changing the sprocket gearing can also affect the bike's ability to pull high revs in top gear (2).

In a YouTube video, a speed test was conducted on an SSR 125cc pit bike with a 14-tooth and 16-tooth front sprocket, and the results showed that the sprocket size and gearing do make a difference in top speed (46).

Therefore, riders can adjust the sprocket gearing to achieve their desired balance between acceleration and top speed.

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

Rider's Weight

The weight of the rider is a crucial factor that can significantly influence the top speed of a 125cc pit bike.

The physics behind this is quite simple: the heavier the load a bike has to carry, the more power it needs to move.

A heavier rider will cause the bike to work harder to achieve the same speed as it would with a lighter rider.

This extra work can result in slower acceleration and a reduced top speed.

Conversely, a lighter rider allows the bike to accelerate more quickly and potentially reach a higher top speed.

It's not just about the rider's weight, though. The distribution of weight on the bike can also affect its handling and speed.

A rider who knows how to distribute their weight effectively can help the bike maintain stability and speed, especially in corners and on uneven terrain.

Stroke Types

The stroke type of the engine in a 125cc pit bike can have a significant impact on its top speed.

There are two main types of engines: two-stroke and four-stroke.

A two-stroke engine completes a power cycle with two strokes of the piston during only one crankshaft revolution, and it provides a high power-to-weight ratio and high acceleration.

This means that two-stroke engines can often reach higher top speeds than their four-stroke counterparts.

On the other hand, four-stroke engines complete a power cycle in four piston strokes, offering better fuel efficiency and smoother operation, but typically at the cost of lower top speed. However, it's important to note that the difference in top speed between two-stroke and four-stroke engines isn't always significant, and other factors such as gearing, rider skill, and track conditions can play a more substantial role.

Related: How to Kick Start a Dirt Bike (8 EASY STEPS)

Gear Ratios

The gear ratios of a 125cc pit bike play a crucial role in determining its top speed and overall performance.

Understanding and optimizing these ratios can significantly impact your bike's capabilities.

Calculating Gear Ratios: To calculate the gear ratio, use this formula:

$$\text{Gear Ratio} = \frac{\text{Number of teeth on rear sprocket}}{\text{Number of teeth on front sprocket}}$$

For example, if your pit bike has a front sprocket with 13 teeth and a rear sprocket with 52 teeth, the gear ratio would be:

$$\frac{52}{13} = 4:1$$

Practical Implications:

• Higher gear ratios (e.g., 4:1) provide more torque and better acceleration but lower top speed
• Lower gear ratios (e.g., 3:1) offer higher top speed but reduced acceleration and hill-climbing ability

Riding Scenarios and Optimal Ratios:

• Track Racing: A balanced ratio (e.g., 3.5:1 to 3.8:1) often works well, providing good acceleration out of corners while maintaining decent top speed on straights
• Off-Road Trails: Higher ratios (e.g., 4:1 to 4.5:1) are preferable for better low-end power and hill-climbing ability
• Flat Terrain Riding: Lower ratios (e.g., 3:1 to 3.3:1) can maximize top speed on open, flat areas

Fine-Tuning Performance:

• Changing the front sprocket by one tooth can significantly alter performance
• Increasing front sprocket size (or decreasing rear) raises top speed but reduces acceleration
• Decreasing front sprocket size (or increasing rear) improves acceleration and low-end power

Considerations for Gear Ratio Changes:

• Ensure chain length is adjusted properly after changing sprockets
• Be aware that extreme changes may affect the bike's handling and stability
• Consider the impact on engine RPM at cruising speeds to avoid overworking the engine

By understanding and optimizing gear ratios, you can tailor your 125cc pit bike's performance to suit your riding style and terrain.

Experimenting with different ratios can help you find the perfect balance between acceleration and top speed for your specific needs.

If you're looking for high-powered electric kids' ride-ons that offer a balance of speed and safety, check out this collection.

Related: Why Does My Motorcycle Backfire?

How Track Conditions Impact Speed

Rough or Uneven Track

Riding on a rough or uneven track can significantly impact the top speed of a 125cc pit bike.

When the track is bumpy or filled with obstacles, the bike's suspension system has to work overtime to absorb the shocks.

This absorption process uses up some of the bike's power, which could otherwise be used to increase the speed.

Moreover, the rider has to constantly adjust their balance and the bike's direction, which can also slow down the bike.

The bike's tyres can lose traction on a rough surface, making it harder for the bike to maintain a steady speed.

Therefore, a rough or uneven track can make it challenging for the bike to reach its maximum speed, as more energy is spent on maintaining stability rather than increasing velocity.

Smooth and Well-Maintained Track

On the other hand, a smooth and well-maintained track can help a 125cc pit bike reach its maximum speed.

When the track is smooth, the bike's suspension doesn't have to work as hard to absorb shocks, allowing more power to be directed towards increasing the speed.

The tyres can maintain better traction on a smooth surface, providing a more stable ride and enabling the bike to maintain a steady speed.

The rider can also focus more on controlling the speed and less on maintaining balance or avoiding obstacles.

Therefore, a smooth and well-maintained track can provide the ideal conditions for a 125cc pit bike to reach its top speed.

If you're wondering where you can ride dirt bikes and quad bikes in the UK, this guide might be useful.

Track Surface

The surface of the track can also play a significant role in determining the top speed of a 125cc pit bike.

Different surfaces provide different levels of traction and resistance, which can affect the bike's speed.

For instance, a track with loose dirt or gravel can slow down the bike.

The loose particles can create a layer of resistance against the bike's tyres, making it harder for the bike to move forward.

The tyres can also lose traction more easily on such a surface, reducing the bike's stability and speed.

On the other hand, a hard-packed track can help the bike achieve a higher top speed.

The compact surface provides good traction for the tyres, allowing the bike to maintain a steady speed.

The hard surface also offers less resistance against the bike's movement, enabling it to move faster.

Therefore, the type of track surface can significantly influence the top speed of a 125cc pit bike.

Related: FLAT TYRE? Fix Your Dirt Bike Tube in Minutes

How Weather Conditions Influence Pit Bike Speed

Weather conditions can significantly affect the performance and top speed of a 125cc pit bike.

Understanding these impacts can help riders adjust their expectations and riding techniques for optimal performance in various conditions.

Temperature

Ambient temperature plays a crucial role in engine performance and overall bike speed:

Cold Weather:

• Denser air can potentially increase engine power output
• Cold engines may take longer to reach optimal operating temperature
• Tire grip may be reduced, affecting cornering speeds and acceleration

Hot Weather:

• Less dense air can slightly reduce engine power
• Engines may be prone to overheating, potentially reducing performance
• Tire grip may improve due to softer rubber, but excessive heat can lead to faster wear

Humidity

The amount of moisture in the air can impact engine performance:

• High humidity reduces air density, which can slightly decrease engine power
• In extreme cases, high humidity may affect ignition system performance
• Low humidity can lead to better combustion efficiency and potentially higher speeds

Wind

Wind conditions can have a direct impact on a pit bike's speed:

Headwind:

• Increases air resistance, reducing top speed
• Can make acceleration more challenging
• May require more aggressive tucking to minimize drag

Tailwind:

• Can help increase top speed by reducing air resistance
• May improve fuel efficiency at higher speeds
• Caution needed as it can mask the sensation of speed

Crosswind:

• Can affect stability, particularly at higher speeds
• May require adjustments in riding position to maintain control

Precipitation

Wet conditions significantly impact riding performance:

Rain:

• Reduces traction, affecting acceleration and cornering speeds
• Increases stopping distances, requiring more cautious riding
• Can lead to hydroplaning at higher speeds if water accumulates on the track

Snow and Ice:

• Drastically reduces traction, making high speeds unsafe
• Requires specialized tires for any meaningful performance
• Not recommended for standard pit bike riding

Altitude

Riding at different altitudes can affect engine performance:

• Higher altitudes have less dense air, reducing engine power output
• Carbureted engines may require rejetting for optimal performance at high altitudes
• Fuel-injected engines typically adapt better to altitude changes

Adapting to Weather Conditions

To maximize speed and performance in various weather conditions:

1. Adjust tire pressure based on temperature and track conditions
2. Consider using different tire compounds for extreme temperature ranges
3. Ensure proper engine tuning for the expected weather conditions
4. In hot weather, pay extra attention to engine cooling and oil temperature
5. Use appropriate riding gear to stay comfortable and maintain focus in different weather conditions

By understanding and adapting to various weather conditions, riders can optimise their 125cc pit bike's performance and maintain safe riding practices across a range of environments.

While weather can impact top speed, skilled riders can often compensate through technique and bike setup adjustments.

Impact of Tyre Type on 125cc Pit Bike Speed

The type of tyres fitted to a 125cc pit bike can significantly influence its speed, traction, and overall performance.

Different tyre designs are optimised for specific riding conditions, and choosing the right tyre can make a substantial difference in how fast your bike can go.

Off-Road vs. Street Tyres

Off-Road Tyres:

• Feature aggressive tread patterns for better grip in loose terrain
• Provide excellent traction on dirt, mud, and gravel
• Generally have a softer compound for improved grip
• May reduce top speed on hard surfaces due to increased rolling resistance

Street Tyres:

• Have smoother tread patterns for better contact with paved surfaces
• Offer superior grip and stability on asphalt and concrete
• Usually made of harder compounds for longer wear on abrasive surfaces
• Can significantly increase top speed on paved roads compared to off-road tyres

Tyre Width and Profile

The width and profile of tyres also play a crucial role in performance:

• Wider tyres generally provide better traction but may slightly reduce top speed due to increased air resistance
• Narrower tyres can offer less rolling resistance, potentially increasing top speed on smooth surfaces
• Low-profile tyres can improve handling and cornering stability at higher speeds

Tyre Pressure

Proper tyre pressure is essential for optimal performance:

• Underinflated tyres can reduce top speed due to increased rolling resistance and heat build-up
• Overinflated tyres may provide less traction, affecting acceleration and cornering speeds
• The ideal tyre pressure varies depending on the riding conditions and tyre type

Specialised Tyres

For riders looking to maximize their 125cc pit bike's speed, there are specialised options:

• Slick tyres: Offer minimal tread pattern for maximum contact area on dry, paved surfaces, potentially increasing top speed
• Semi-slick tyres: Provide a balance between speed on hard surfaces and some off-road capability
• Dual-sport tyres: Designed to perform reasonably well both on and off-road, offering a versatile option for varied riding conditions

Choosing the right tyre type for your 125cc pit bike depends on your primary riding conditions and performance goals.

While off-road tyres excel in loose terrain, they may limit your top speed on paved surfaces.

Conversely, street tyres can significantly boost your speed on roads but may struggle in off-road conditions.

By selecting the appropriate tyre type and maintaining proper inflation, you can optimize your pit bike's performance and potentially increase its top speed in specific riding environments.

Sprocket Gearing and Speed

The gear ratios, which are determined by the sizes of the front and rear sprockets, play a pivotal role in affecting a bike's speed.

In the case of 125cc dirt bikes, a common gearing configuration includes a 14-tooth front sprocket and a 42-tooth rear sprocket.

This ratio is calculated by dividing the number of teeth on the rear sprocket by the number of teeth on the front sprocket, giving us a ratio of 3:1 in this case.

This means that for every single revolution of the front sprocket, the rear sprocket turns three times.

A higher gear ratio (more teeth on the rear sprocket or fewer on the front) will result in higher top speed but slower acceleration, as the engine has to turn more times to get the rear wheel to turn once.

Conversely, a lower gear ratio (fewer teeth on the rear sprocket or more on the front) will result in faster acceleration but lower top speed, as the engine can get the rear wheel to turn more quickly with each revolution.

Deviations from the standard 14/42 ratio can therefore impact the top speed of the bike.

For instance, if you were to increase the rear sprocket's size or decrease the front sprocket's size, you would increase the gear ratio and potentially increase the bike's top speed, but at the cost of acceleration.

If you're interested in petrol ride-ons that offer a balance of speed and control, you might want to check out this collection.

Other Factors Influencing Speed

The quality of fuel used in a 125cc pit bike can significantly impact its performance and top speed.

Higher-quality fuels, particularly those with higher octane ratings, can improve engine efficiency and power output.

Premium vs Regular Gasoline: While most 125cc pit bikes are designed to run on regular 87-octane gasoline, using premium 91 or 93-octane fuel may provide some benefits:

• Improved combustion efficiency
• Slightly increased power output
• Better protection against engine knocking

However, the performance gains from using premium fuel in a stock 125cc engine are typically minimal.

Race Fuel: Some riders opt for specialized race fuels, which can offer more noticeable performance improvements:

• Higher octane ratings (100+) allow for more aggressive engine tuning
• Increased power output, especially in modified engines
• Better throttle response and smoother acceleration

It's important to note that race fuels are significantly more expensive and may not be necessary for casual riding or stock engines.

Ethanol Content: Many pump gasolines contain ethanol, which can impact performance:

• Ethanol has a lower energy content, potentially reducing power and fuel efficiency
• Higher ethanol blends (E15, E85) are not recommended for most 125cc pit bikes
• Ethanol-free fuel may provide slightly better performance and fuel economy

Fuel Freshness: Using fresh fuel is crucial for optimal performance:

• Old or stale gasoline can lead to starting issues and reduced power
• Fuel stabilisers can help preserve fuel quality during storage
• Regular fuel system maintenance ensures clean, efficient combustion

By paying attention to fuel quality and choosing the appropriate fuel for your 125cc pit bike, you can potentially improve its performance and achieve higher top speeds.

If you're a parent with questions about junior dirt bikes and quads, this guide might help answer some of them.

Balancing Cost and Performance: Which Modifications Are Worth It?

When enhancing the speed and performance of your 125cc pit bike in the UK, it's crucial to consider the balance between cost and effectiveness.

Here's a guide to help you make informed decisions about which upgrades offer the best value for money.

High-Value, Low-Cost Modifications

These modifications typically offer the best bang for your buck:

1. Air Filter Upgrade

   • Cost: £15-£40
   • Benefits: Improved airflow, slight power increase
   • Value: High - easy installation and noticeable performance gain

2. Sprocket Changes

   • Cost: £25-£65
   • Benefits: Customized gearing for better acceleration or top speed
   • Value: High - significant impact on performance for relatively low cost

3. Performance Exhaust Tip

   • Cost: £40-£120
   • Benefits: Slight power increase, improved sound
   • Value: Medium - moderate performance gain for a reasonable price

4. Carburetor Jetting Kit

   • Cost: £15-£50
   • Benefits: Optimized fuel mixture for better performance
   • Value: High - can significantly improve engine efficiency

Medium-Cost, High-Impact Modifications

These upgrades require a bit more investment but can offer substantial performance improvements:

1. Full Exhaust System

   • Cost: £150-£400
   • Benefits: Noticeable power increase, weight reduction
   • Value: Medium to High - significant performance gain but at a higher cost

2. High-Performance Camshaft

   • Cost: £120-£250
   • Benefits: Increased power throughout the RPM range
   • Value: Medium - substantial performance improvement but requires more technical installation

3. Big Bore Kit

   • Cost: £150-£350
   • Benefits: Increased displacement and power
   • Value: Medium - significant power gain but may affect reliability if not properly installed

High-Cost, Specialized Modifications

These modifications are typically for serious enthusiasts and racers:

1. Engine Porting and Polishing

   • Cost: £250-£500
   • Benefits: Optimized airflow for maximum power
   • Value: Low to Medium - high cost for incremental gains, best for competitive racing

2. Custom ECU Tuning

   • Cost: £300-£650
   • Benefits: Optimized fuel and ignition maps for maximum performance
   • Value: Low - high cost and typically only beneficial for heavily modified engines

3. Lightweight Racing Components

   • Cost: Varies widely (£400+)
   • Benefits: Reduced weight for better acceleration and handling
   • Value: Low - high cost for minimal gains in most riding scenarios

Recommendations for Different Budgets

Low Budget (£80-£160): Focus on air filter upgrade, sprocket changes, and carburetor jetting. These offer the best performance gains for minimal investment.

Medium Budget (£250-£500): Consider a full exhaust system and a high-performance camshaft in addition to the low-budget mods. These provide a noticeable boost in power and responsiveness.

High Budget (£800+): For those seeking maximum performance, combine all the above with a big bore kit and custom ECU tuning. However, be aware that the law of diminishing returns applies – each additional pound spent yields less noticeable improvement.

Remember, proper installation and tuning are crucial for realizing the full potential of any modification.

Always factor in the cost of professional installation if you're not confident in your mechanical skills. Additionally, consider how modifications might affect your bike's reliability and maintenance requirements.

Sometimes, the best "modification" is simply ensuring your bike is in top condition through regular maintenance and high-quality replacement parts from reputable UK suppliers like Fun Bikes, Parker Racing, or Welsh Pit Bikes.

In Summary

The speed of a 125cc pit bike is influenced by a variety of factors, including the condition of the track, rider experience, sprocket gearing, rider weight, stroke types, gear ratios, and more.

While the average top speed is around 57.5 miles per hour, it can range from 55 to 70 miles per hour, and even reach up to 100 miles per hour in some cases.

However, it's important to remember that these speeds are not achievable by all riders and are dependent on specific circumstances and conditions.

So, the next time you're revving up your 125cc pit bike, remember that it's not just about the bike's specifications but also about the conditions and your skills as a rider.

Related: How Fast Does A 160cc Pit Bike Go?

FAQs

How can I increase the top speed of my 125cc pit bike?

There are several ways to potentially increase the top speed of your 125cc pit bike. One method is to modify the sprocket gearing. By increasing the size of the rear sprocket or decreasing the size of the front sprocket, you can increase the gear ratio and potentially increase the bike's top speed. However, this will likely come at the cost of acceleration. Other methods include reducing the weight of the bike, improving aerodynamics, and ensuring the engine is well-maintained and running efficiently.

Is it safe to reach the top speed on my 125cc pit bike?

Safety should always be your top priority when riding any motorbike, including a 125cc pit bike. While these bikes are capable of reaching high speeds, it's important to only ride at speeds that are safe for the current conditions and your level of experience. Always wear appropriate safety gear, follow all traffic laws, and never ride at speeds that exceed your comfort level or the bike's capabilities.

How does tyre pressure affect the speed of a 125cc pit bike?

Tyre pressure can have a significant impact on the performance and speed of a 125cc pit bike. Tyres that are under-inflated can create more rolling resistance, which can slow the bike down. On the other hand, over-inflated tyres may not provide enough traction, which can also affect speed, especially in turns or on uneven terrain. It's important to keep your tyres inflated to the manufacturer's recommended pressure to ensure optimal performance and speed.