How Fast is 70cc Dirt Bike – All You Need to Know
If you’re looking for a good dirt bike for your child to learn to ride, you’ve probably already narrowed the search down to smaller models with less powerful engines. Larger bikes are quick and fun, but are typically too big for the youngest riders, and their speed makes them difficult to control for beginners.
In this article, we’ll be looking at 70cc bikes. These small engines can be quick enough to be fun, but not so fast that a beginner will be overwhelmed by what they can do which makes them a solid choice for your child’s very first dirt bike. We’ll look at how fast these bikes go, as well as some expert tips to make sure that your junior rider’s first experience is both fun, and as safe as possible!
Table of Contents
How fast does a 70cc Dirt Bike go?
70cc dirt bikes have claimed a range of speeds from 30 mph (about 48 km/h) to as high as 58 mph (roughly 93 km/h). The general average is in the mid 40’s (about 64 km/h). This range covers bikes from the now discontinued Honda CRF70F to off-brand models not designed for serious riding.
How Fast is a 70cc Dirt Bike?
Just as with larger displacement dirt bikes, the top speed of a 70cc bike depends on a number of external factors. However, with smaller-capacity engines, the effect is much more pronounced. For a 70cc bike, there is also the brand factor to consider. As of 2022, none of the major motorcycle companies produce new 70cc bikes, with the closest you may find from companies like Yamaha or KTM being 65cc rather than 70cc. In this section, we’ll take a look at the different things that affect the speed of a 70cc dirt bike specifically.
Let’s start with what is possibly the easiest factor to identify. Familiar brands like Yamaha, Kawasaki, Suzuki, and KTM have been building dirt bikes for a very long time. These models are designed for more serious riding and are an excellent choice for kids that will eventually graduate to larger and more powerful dirt bikes or who may be interested in competition. While there are no 70cc being produced by these companies in 2022, you can still find second-hand 70cc offerings from many of these companies.
For less serious riding there are many off-brand manufacturers still producing 70cc powered models. While this class of dirt bikes can be built with decent quality, it would be unfair to consider them up against more established motorcycle companies, as the purpose behind their design is to be cost-effective rather than to be competitive.
This factor is fairly straightforward. Honda’s CRF70F was capable of speeds up to 58 mph, or 93 km/h. To compare, the Roketa AGB-21 can reach a maximum speed of 25 mph, roughly 40 km/h.
The debate between 2-stroke and 4-stroke engines has always been popular, with each side having its pros and cons. When it comes to speed, especially when talking about lower displacement bikes, the differences between 2 and 4 stroke bikes might make a noticeable impact.
A 4-stroke engine is more common in 2022, and is generally the easier option to live with since it doesn’t require premixing oil and gas. However, the factor to consider for speed is that a 4-stroke engine is typically heavier than a 2-stroke because it has more moving parts in the form of intake and exhaust valves. Because the stages of intake, compression, ignition, and exhaust are completely separate, a 4-stroke bike is also making power less frequently than a 2-stroke, which translates to a difference in torque and therefore how quickly the machine reaches its top speed.
2-stroke engines are simpler and make up for their dirtier emissions and inconvenient premixing requirements with excellent torque and lower overall weight. A 2-stroke engine combines the Intake/Compression and Ignition/Exhaust steps of operation. This means more torque at lower RPM, and, thus more off-the-line speed. These engines also do not have the intake and exhaust valves found in their 4-stroke competition which makes them lighter, and a lighter bike is typically a faster bike.
The single most influential outside factor on a dirt bike’s top speed is the amount of weight it has to carry. When in operation, the engine’s power must overcome the total weight of the bike, rider, and any cargo or gear that is weighing it down. This is even more important in low displacement bikes that may have less than 5 total horsepower.
Power-to-weight is a good way to determine exactly how much a rider’s weight will affect the bike’s performance. A 70cc dirt bike has an average wet weight of around 140 lbs. Calculating how much horsepower the bike has per pound before adding the rider will give you a base level of performance for the bike. In the case of an engine with 5-horsepower, the ratio is .03 horsepower/lb. Adding a 60 lb rider reduces that number to .02.
Remember that the higher the power-to-weight ratio is, the faster the bike will be!
Horsepower is the other side of the power-to-weight equation. In the previous example, we assumed the bike had 5-horsepower, but not all 70cc dirt bikes are the same in relation to the amount of power produced. Honda’s CRF70 and Suzuki’s DR-Z70 both make around 6-horsepower, while less serious examples, such as the Roketa, might make just over 4.
Just like with the weight of the rider, power-to-weight is key to understanding how horsepower will affect the bike’s speed. Two bikes, both weighing 140 lbs and both carrying a 60 lb rider but with different amounts of power, will have dramatically different performances. A 6-horsepower bike will have .03 horsepower per pound, while a 4-horsepower bike will only have .02 – which is a full third less usable power!
Beyond the mechanical limits of the bike, the human element is the most important factor in how fast a dirt bike might be able to go. When they first start out, very few riders will be comfortable with riding the bike as fast as it will go. The loud engine can be intimidating, and the fear of falling is difficult to overcome at first. As the bike accelerates, a lot of first-time riders will choose to back off well below the mechanical limits of the bike.
As your child gets used to riding, they will develop confidence in their ability to stay upright and become more comfortable at higher speeds. That kind of confidence only comes with experience, though, and every rider grows at their own pace.
Another important factor in how fast a dirt bike can go is the terrain it is operating on. The top speed listed on most bikes is based on a flat, even surface, representing the bike’s mechanical limits. In reality, dirt bikes aren’t designed to only operate in perfect riding conditions, and everything from loose gravel to uneven surfaces will have an effect on top speed.
Dirt bikes, naturally, are usually used on dirt tracks and trails. The loose gravel and debris found in these conditions make riding at high speed much more difficult and possibly dangerous. Even with a 70cc bike, which has a lower possible top speed than its larger relatives, it is a better idea to ride only as quickly as the rider can maintain control.
Bumpy, uneven surfaces are also important to consider, as riding too fast in these conditions can damage the bike or cause it to go out of control. In some extreme cases, the bike might even go airborne, and if the rider doesn’t know how to land properly, this can lead to a dangerous crash. To avoid these kinds of situations it is a good idea to ride more slowly on this kind of terrain.
When riding a dirt bike, the moving parts can wear down over time, reducing their effectiveness. Most often, this will result in a loss of performance. With carbureted engines like those found in dirt bikes, the carburetor will accumulate debris and buildup, which compromises its ability to deliver fuel to the engine effectively. Less fuel means less power, and less power, of course, means less speed. A dirty air filter will have a similar effect, limiting the airflow to the engine and therefore reducing the power of the engine.
Keeping parts like the air filter and carburetor clean is a matter of routine maintenance. There will be a schedule for every bike detailing how often it should be serviced in order to keep maximum performance. This also includes lubrication of the moving parts to avoid damage to the engine’s internal components, which are critical not just to performance but to operate in general.
Don’t forget the engine in itself is not the only thing that requires maintenance! While the engine produces power, the chain is what delivers that power to the rear wheel. Keeping the chain well lubricated and free of debris is important to keeping the bike in good condition and operating smoothly.
(You can find a guide to some good lubricants for the chain here)
How to make a 70cc Dirt Bike Faster
Now that we’ve explored some of the factors affecting the top speed of a 70cc dirt bike. Let’s look into how we can make these little machines even faster! While we can’t really do much about things like the terrain, and the experience level of the rider comes with time, there are plenty of mechanical tricks that we can use to improve the ability of the bike itself. From simple adjustments to improved parts and components – here are some tips to squeeze a little extra speed out of a 70cc dirt bike:
Better fuel delivery
First and foremost, let’s look at the quality of the fuel we put in the tank. The process of making power in any engine is based on the explosion that happens in the combustion chamber, so if we can increase the intensity of this explosion, we can increase the power produced by the engine. The first component we’ll look at is the fuel itself.
Carburetors or fuel injectors deliver gasoline to the combustion chamber to be compressed and ignited, and in factory form, the system is set for a specific amount to balance fuel efficiency with performance and longevity. Because the priority is balance, this factory setting is usually a compromise between power, efficiency, and longevity.
Setting the carburetor or injectors to add more fuel to the combustion chamber will result in a more potent explosion in the engine simply because there is more combustible material present. Remember, though, that this will put more strain on the internal components of the engine.
Another important thing to consider is that if there is too much fuel in the combustion chamber, not all of it will burn. Adjusting the fuel delivery should be a measured and precise process and is best handled by a professional mechanic who will be familiar with the optimal air-to-fuel ratio for the engine.
The other half of the equation in how the engine operates is air. Just like with fuel, the air is a prime component in the operation of an engine, involved in each of the four stages of power (intake, compression, ignition, and exhaust). The air mixes with the fuel during compression, helping to create an explosive reaction, which produces the energy the bike uses when we ride.
A performance air filter is designed to deliver more clean air to the engine. When paired with an increase in fuel delivered to the combustion chamber, this will produce a dramatic increase in power. We can also further enhance this effect with an exhaust system that reduces the resistance of the exhaust gasses. When properly installed, components that improve airflow are the most effective “bolt-on” solutions for increased power and performance.
Each dirt bike engine is designed to use a very specific type of oil. Your bike will specify the oil weight, or viscosity that it is meant to take, and deviating from that specification can have consequences for performance and reliability. It is important to only use the weight of oil specified in your owner’s manual, however this doesn’t mean that there aren’t options for better performance!
Synthetic oil is much more precisely controlled and resistant to breaking down. By using synthetic, rather than conventional oil, you can keep the internal components of a dirt bike’s engine better maintained and improve the overall performance and longevity of the machine.
Some oil companies have built an excellent reputation for producing lubricants with special formulas to maximize the protection of your bike’s internal parts. This example of full synthetic oil in 10w30 is recommended for bikes like the Honda CRF70, Suzuki DR-Z70, and many others!
How Fast Does a 70cc 2-Stroke Dirt Bike go?
Most examples of 70cc dirt bikes, whether from major motorcycle manufacturers or budget brands, do not use 2-stroke engines. This is because 2-stroke engines are primarily found in competition bikes to minimize weight and therefore maximize speed. There is no motocross division for 70cc bikes (they go from 65cc to 85cc); therefore, all currently produced bikes use the less maintenance-intensive and more environmentally friendly 4-stroke design.
For the sake of comparison, though, we can use the typical top speed of a 65cc 2-stroke bike from Kawasaki, KTM, and Yamaha. In these cases, the average top speed is in the mid-50 mph (80 km/h) range, with the KTM 65 SX being the fastest, topping out over 60mph.
How Fast Does a 70cc 4-Stroke Dirt Bike go?
The cleaner, easier-to-maintain 4-stroke engine design is the standard for 70cc dirt bikes. Honda’s CRF70 and Suzuki’s DR-Z70 were both 4-stroke examples, and nearly every budget-oriented bike currently available utilizes a version of the engines found in these bikes.
In the case of the 4-Stroke dirt bikes, it is much more difficult to find an average, as the difference between the motorcycles is so wide. The Honda and Suzuki dirt bikes are both reported to reach maximum speeds of around 50 to 58 mph. Other bikes like the Roketa AGB-21 report less than half of that at 25 mph, or a vague 30+ mph.
In the interest of fairness, we’ll use the Honda and Suzuki as the predictable, consistent examples of what a 4-stroke 70cc engine can accomplish, with a maximum average speed of 50 mph, or roughly 80 km/h.
Dirt Bike Safety Gear
Riding a dirt bike is a great activity, but it comes with a certain amount of risk. Falls can happen at any speed or skill level, and when they do, it’s best to make sure you’re protected! This is especially true with younger riders, who are more likely to fall when learning.
In this section, we’ve collected some examples of gear that is essential for riding as safely as possible.
This is the first and most critical piece of gear for riding safely! At no point should anyone ride without a helmet to protect their head in the event of a fall. Even a minor spill can cause catastrophic injury if the rider hits their head without protection.
Dirt bikes use a special design of a helmet that covers the whole face and head, and is designed to help deflect dirt and debris away from vents and openings in the helmet.
One thing to keep in mind when looking into a helmet is its certification. There are three major certifications: DOT, ECE, and SNELL. DOT-certified helmets are approved for use on-road in the United States. These helmets are tested by the manufacturer to ensure quality and safety.
ECE is the European standard and is more stringent than DOT. ECE-certified helmets are batch tested by an outside authority prior to public release, rather than simply relying on the manufacturer.
SNELL-certified helmets go through the most rigorous testing. There is no tougher certification in the world, and some motorsports authorities even require this certification to be present in order to pass inspection.
This helmet by Fox Racing is a typical example of a good quality helmet, carrying both DOT and ECE certifications.
Gloves are another piece of equipment that is absolutely essential for any rider but particularly important for riding a dirt bike. A good quality pair of gloves not only keeps the hands safe from flying dirt and debris, but also from painful injuries in the event of a spill. When going down, one of the first and most powerful instincts is to throw a hand out to catch ourselves, and a poor quality pair of gloves (or worse, no gloves at all!) can result in road rash that makes life difficult, even off the track.
When riding a dirt bike the last thing you should wear is a pair of tennis shoes! Special riding boots are available that stay secure when riding, and offer excellent protection against dirt and debris when riding, and in the event of a fall.
These boots are often made of thick layers of tough material and go much higher than a regular pair of shoes. They are also equipped with more secure fastening than simple laces that will not come undone in the middle of a ride.
O’Neal is a leading brand in protective equipment, and you can find just one example of their products here.
Armored pads are the final component of protective gear that can be worn to maximize safety when riding a dirt bike. These pads go on above the clothing to offer increased defense to places like the knees, elbows, chest, and back.
Pads come in a variety of different designs and configurations, although one of the most common is a jacket for the upper body and separate pads for the knees.
Jacket and these knee protectors from Alpinestars are good examples of this kind of design.
Aside from simply protecting against impacts, when riding a dirt bike supporting the neck is also of absolutely critical importance. Without proper support, the neck can roll and cause some of the most damaging injuries, including permanent nerve damage and even death in the most extreme cases.
Neck support gear helps to mitigate this risk. While it’s always a good plan not to fall in the first place, a good neck support offers protection from injury in the event of a crash.
Frequently Asked Questions
Is it safe to go fast on a 70cc Dirt bike?
Going fast in general, is always a calculated risk, but it is a risk that can be mitigated by several factors. Wearing protective equipment and riding within your experience level are just two ways to avoid injury. It’s important to know your own limits aside from just what the bike can do, and not ride beyond what you know you can handle.
How much horsepower is 70cc?
The cc rating is referring to the size of the bike’s engine and actually has very little to do with the horsepower. There are a variety of different 70cc engines, and they range from 2 horsepower to 6, although the most common horsepower for this size of the engine is just under 5.
What age is a 70cc dirt bike for?
70cc dirt bikes are intended to be the first bikes for younger riders, alongside the even smaller 50cc models. It is not uncommon to see children as young as 6 or 7 years old on the back of a 70cc bike, although shorter kids as old as 12 might start out on a 70cc bike as well. As the maximum allowable weight for these bikes is usually 100 lbs or lesser teenage riders or adults should not ride them.
Riding dirt bikes is a great hobby and one that can even be enjoyed with the entire family, thanks to smaller bikes like the 70cc offerings discussed in this article. These bikes allow young riders to enjoy the experience without reaching speeds that would be too difficult to control for their first time out.
SOMETHING TO CONSIDER: None of the major motorcycle manufacturers currently produce new 70cc dirt bikes! While there are offerings by third party companies, these bikes are designed with price in mind, and should not be considered an equivalent alternative for a more established motorcycle brand, especially if your child is interested in more serious riding or competition. Bikes like the Honda CRF70F and Suzuki DZ-R70 can be found second-hand, and 65cc options are available now from companies like Kawasaki, KTM, Yamaha, and Husqvarna.