How Fast Does a 70cc Dirt Bike Go? Speeds and Performance

Have you ever wondered just how fast one of those buzzing 70cc dirt bikes can really go? When you’re first getting into the world of dirt bikes, it’s tempting to want to go as fast as possible and really open up the throttle. However, 70cc bikes have their limits, especially in stock form.

So how fast can a 70cc dirt bike actually go? Most stock 70cc dirt bikes can reach top speeds of 45-60 mph depending on the specific model and various factors. With some basic performance modifications like an aftermarket exhaust, sprocket change, and air filter, top speeds of 65+ mph are possible.

In this detailed blog post, we’ll explore everything you need to know about 70cc dirt bike speeds, including:

• The top speeds of stock and modified 70cc dirt bikes
• Factors that affect 70cc dirt bike acceleration and top speed
• The best 70cc dirt bike models for achieving high speeds
• Tips for safely riding your 70cc dirt bike at faster speeds
• Whether it’s worth modifying a 70cc bike for more speed vs upgrading to a larger engine

So whether you’re a new rider looking to go faster or a worried parent concerned about safety, read on to get the full scoop on how fast those screaming 70cc dirt bikes can really go.

What Is The Top Speed Of A 70cc Dirt Bike?

When buying a dirt bike, one of the key specs riders want to know is the top speed. For 70cc dirt bikes, top speeds can vary quite a bit depending on the specific model and version. Here’s a look at the top speeds you can expect:

Stock 70cc dirt bikes: Most stock 70cc dirt bikes with no modifications can reach top speeds of 45-60 mph. More specifically:

• Mid-level 70cc bikes like the Honda CRF70F or Yamaha TT-R70E can reach around 45-50 mph in stock form.
• High performance 65cc motocross bikes like the KTM 65 SX or Kawasaki KX65 can hit 55-60 mph from the factory.

Modified 70cc dirt bikes: By adding some basic bolt-on performance upgrades to a 70cc dirt bike like an aftermarket exhaust, different sprocket ratio, and an upgraded air filter, top speeds of up to 65 mph are possible.

With more advanced internal engine work, some highly modified 70cc bikes with expert riders can exceed 65 mph. But this requires significant engine work and money.

Rider weight impacts speed: Top speed is also dependent on rider size. A lightweight kid or smaller rider may reach higher speeds compared to a full grown adult on the same 70cc bike. The engine has less mass to accelerate.

So while stock 70cc dirt bikes are certainly not sluggish, their top speed capabilities are limited compared to larger displacement 85cc, 125cc, and 250cc dirt bikes. But adding some basic mods can still provide a fun boost in speed for thrill-seeking young riders.

Factors That Impact 70cc Dirt Bike Speed And Acceleration

When it comes to dirt bikes, there are many factors that influence either the top speed or the acceleration. Here are some of the main factors that impact how fast your 70cc dirt bike can go:

Engine Size

• One of the biggest factors determining the speed capabilities of a dirt bike is the engine displacement or cc rating.
• 70cc dirt bike engines are smaller and less powerful than larger 85cc, 125cc, or 250cc engines.
• More engine power equals a higher top speed potential.
• 70cc dirt bikes are usually 4-stroke engines, which have less power and torque than 2-stroke engines of the same size.
• A 2-stroke engine can reach higher speeds faster, but a 4-stroke engine has more consistent power delivery and fuel efficiency.

Gearing

• The gearing on a dirt bike – meaning the size of the front sprocket and rear sprocket – has a big impact on acceleration and top speed.
• Smaller rear sprockets provide higher gear ratios which allow a bike to reach a higher top speed in each gear.
• Larger rear sprockets give more low end torque for acceleration.
• Gear ratios are the relationship between the number of teeth on the front and rear sprockets.
• A higher gear ratio means that the engine turns faster for each revolution of the rear wheel, resulting in a higher top speed.
• A lower gear ratio means that the engine turns slower for each revolution of the rear wheel, resulting in more torque and acceleration.

Rider Weight

• A dirt bike will reach a higher top speed when carrying a lighter rider compared to a heavier rider.
• This is simple physics – less mass on the bike means the engine can accelerate to higher speeds more quickly.
• So lighter kids will go faster compared to a 200 pound adult on the same 70cc bike.
• The rider’s position and aerodynamics also affect the speed of the bike.
• A rider who leans forward and tucks in their elbows and knees reduces wind resistance and increases speed.
• A rider who sits upright and spreads out their limbs increases wind resistance and decreases speed.

Terrain And Surface Conditions

• The terrain and surface the bike is being ridden on impacts speed as well.
• Hard packed dirt or gravel surfaces provide more traction to apply the engine power resulting in higher speeds.
• Deep soft sand or mud significantly reduces speed due to lack of traction.
• The tire pressure and tread also affect the traction and speed of the bike.
• A higher tire pressure reduces rolling resistance and increases speed on hard surfaces, but decreases traction and stability on soft surfaces.
• A lower tire pressure increases rolling resistance and decreases speed on hard surfaces, but increases traction and stability on soft surfaces.
• A tire with a knobby tread provides more grip on loose terrain, but less grip on smooth terrain.
• A tire with a smooth tread provides more grip on smooth terrain, but less grip on loose terrain.

Riding Style And Throttle Control

• An aggressive riding style with fast throttle twisting to fully open the throttle quickly will result in higher top speeds versus a more conservative, smooth riding technique.
• But it takes skill to control the power.

Taking all of these factors into account allows riders to understand why 70cc dirt bike speed can vary and how modifications, rider size, surfaces, and riding style all play a role.

how to safely increase the top speed of a 70cc dirt bike?

Gearing Changes

One of the easiest ways to increase top speed is by changing the sprockets to alter the gearing. Installing a smaller rear sprocket or larger front sprocket increases the gear ratio, which gives more top end speed. Just be careful not to sacrifice too much low end power. Go up 1-2 teeth on the rear sprocket for a noticeable difference.

Exhaust System

Replacing the stock exhaust with an aftermarket high performance exhaust system allows more engine power to be produced. This can add several mph to the top speed. Make sure to get an exhaust made specifically for your bike model.

Air Filter Upgrade

A clean, high-flow air filter allows the engine to breathe better and increases power. Clean the stock air filter regularly or install a performance air filter kit. Avoid oiled filters which can damage a bike.

Engine Modifications

More complex internal engine mods like porting the cylinder head, installing a performance camshaft, or a big bore kit can significantly increase power and top speed. But these mods start getting more costly and time consuming to properly do.

Remove Restrictors

Many stock 70cc bikes have power restricting inserts in the exhaust and airbox to meet regulations. Removing those restrictors can unlock some extra power. But check local laws first.

Tune Carburetor

Properly tuning and jetting the carburetor to match the mods on the bike can optimize air/fuel mix for best performance. May require some trial and error testing.

When modifying a bike, it’s best to consult with experts and make changes gradually, testing the results safely. Avoid pushing the bike too far beyond its capabilities with excessive mods. Take it slow and have fun!

How Quickly Do 70cc Dirt Bikes Accelerate?

In addition to top speed, the acceleration of a dirt bike is important for quick maneuvers and getting out of tricky situations on the track or trail. Here’s a look at the acceleration capabilities of 70cc dirt bikes:

• Stock 70cc dirt bikes: A completely stock 70cc dirt bike with no performance modifications will accelerate from 0 to 30 mph in about 4-6 seconds depending on the specific model. This is decent acceleration but lagging behind larger bikes.
• Modified 70cc bikes: By adding a performance exhaust, new air filter, and adjusting the gearing, a modified 70cc dirt bike can accelerate from 0 to 30 mph in approximately 3-4 seconds.
• Rider weight impacts acceleration: Just like with top speed, a lighter rider will experience quicker acceleration compared to a heavier rider on the same 70cc bike and setup.
• Proper clutch and throttle use: Employing smooth, progressive clutch releases and controlled throttle inputs will allow riders to get the most from a 70cc bike’s acceleration capacity. Learning proper throttle control takes practice.

While their smaller 70cc engines limit overall acceleration potential, properly set up bikes ridden by skilled riders can still offer lively acceleration for motocross tracks and trail riding fun. Upgrading to a larger engine size is needed for truly explosive acceleration.

What Are The Best 70cc Dirt Bikes For Speed?

While all stock 70cc dirt bikes are limited in their speed capabilities compared to larger displacement bikes, some stand out as the fastest models able to reach the highest top speeds:

KTM 70 SX

The KTM 70 SX is considered one of the fastest custom 70cc dirt bikes. It is a modified version of the KTM 65 SX, which has a 64.9cc engine. The KTM 70 SX has a big bore kit that increases the displacement to 70cc and the power output to 19.5 hp. In stock form it can reach a top speed up to 60 mph, giving it an edge over competitors. As a race-ready motocross bike, it’s designed for maximum performance.

Honda CRF70F

The legendary Honda CRF70F has been around for decades and is known for being easy to modify. With some basic performance upgrades like an exhaust and carburetor work, it’s possible to get a modified CRF70F up to 50 mph.

Yamaha TT-R70E

Yamaha’s high revving TT-R70E can reach speeds up to 47 mph in stock form making it one of the fastest for its class. It responds well to engine modification allowing it to reach 60 mph.

Suzuki RM70

While not the fastest top speed bike, the lightweight Suzuki RM70 is known for having a potent power band and excellent handling allowing skilled riders to accelerate and ride it at pace beyond its rivals. It is also a custom 70cc dirt bike, based on the Suzuki RM65, which has a 64.8cc engine. The Suzuki RM70 has a big bore kit that increases the displacement to 70cc and the power output to 18 hp.

If speed and riding fast motivates you or your child, these 70cc models provide the most thrill-seeking potential to have a need for speed safely on the dirt.

Tips For Safely Riding A 70cc Dirt Bike At Higher Speeds

While kids eagerly want to pin the throttle and go as fast as possible, excess speed also brings increased risk. As a responsible parent, here are some tips to keep safety in mind while still allowing your child to enjoy riding a 70cc dirt bike within reason:

• Start slowly and spend time mastering riding skills at slower speeds first before increasing speed. Learning proper clutch, throttle, steering, and braking control should come before speed.
• Use all proper protective riding gear like a quality DOT helmet, goggles, gloves, and boots every ride. This gear protects in a crash.
• Consider bike size – smaller bikes like a 70cc are best suited for smaller riders. Match bike size to the child’s size, strength and skill level.
• For fast riding, pick open areas with smooth terrain and good visibility. Avoid big hills, mud, or tight technical sections.
• Throttle use requires self-control. Remind kids to be careful with the throttle and resist going full throttle at first. Gradually work up to faster speeds safely.
• Supervise kids closely and set reasonable speed limits appropriate for their skill level. Periodically check-in on their riding and progress.

By setting some ground rules and smartly managing progression, 70cc dirt bikes can be ridden at pace while prioritizing safety. Take time to instill good habits and discipline.

Is it Worth Modifying a 70cc Dirt Bike for More Speed?

With kids eager to go as fast as possible, a common question is whether it’s worth modifying a 70cc dirt bike to increase the speed through engine performance parts or power mods. Here are some considerations:

• It depends on the rider’s size, skill level, and budget – smaller or beginner riders won’t necessarily benefit from added speed they can’t safely control.
• It may be better to save up for a larger displacement 85cc or 125cc dirt bike which offer more power and speed from the factory. They cost a little more up front but avoid ongoing mod costs.
• Basic bolt-on mods like a slip-on exhaust, different gearing, and air filter cleaning kit can gain 5-10 mph top speed for a couple hundred dollars. This may be worth it. (Note: these numbers are rough estimates and may vary depending on the type and quality of the mods, the condition of the dirt bike, and the riding environment.)
• More complex engine modifications like head porting, cam upgrades, and stroker kits can increase speed 15+ mph but the costs add up quickly in the $1000+ range. (Note: these numbers are approximate and may vary depending on the type and quality of the mods, the labor involved, and the availability of parts.)

For many kids, staying with mostly stock 70cc bikes and focusing on building proper skills is recommended. Then they can eventually move up to larger, faster bikes when ready. But some basic mods can offer measurable gains without breaking the bank.

The thrill of speed is addicting on a dirt bike at any age. Just remember to balance that desire for speed with the proper care and maturity needed to ride safely within your limits. So take it slow at first, gear up, and practice, practice, practice!

With some guidance from parents and mentors, 70cc dirt bikes can continue to serve as a perfect entry into the fun of dirt biking that can last a lifetime. Enjoy the ride!