A clear age and size guide for parents - and why engine size alone won't tell you which dirt bike your child needs.
- Engine size is not the whole story - how the bike is built matters more than the cc sticker.
- Most 50cc kids bikes are 2-strokes: oil premixed into every tank, more noise, more upkeep.
- A 40cc 4-stroke like the FRP Moto FX40 runs on straight pump gas - with full suspension and dual disc brakes. From $279.99.
- FRP Moto's whole kids line - dirt bike, mini bike, and ATVs - is 40cc 4-stroke by design. Choose by the rider's age, size, and confidence.
Why Engine Size Isn't the Whole Story
Most 40cc-vs-50cc guides assume a bigger engine means a bigger, faster, more advanced bike. With real kids' dirt bikes, that is often wrong. A beginner bike is built around the rider, so two bikes with similar engines can be worlds apart in wheel size, suspension, and brakes. There is also a difference most guides skip: nearly every 50cc kids bike on the market is an older-style 2-stroke that needs oil premixed into every tank, while a modern 40cc like the FRP Moto FX40 is a 4-stroke that runs on straight pump gas. That is why FRP Moto builds its entire kids line on the 40cc 4-stroke platform. So the real question is not "40cc or 50cc?" but "which bike fits my child, and how is it built?"
40cc vs 50cc by Age and Size
As a general guide, match the bike to the rider this way. Always size by fit first: the child should touch the ground with their feet and reach the handlebars comfortably.
| Rider | What fits | FRP Moto option |
|---|---|---|
| Ages 5-8 (small / first-timer) | Low seat, light, simple controls | FRP Moto MB40 (40cc mini bike) · or FX40 + training wheels |
| Ages 8-11 (ready for trails) | 40cc trail bike — suspension, bigger wheels | FRP Moto FX40 (40cc) |
| Ages 11-14 (confident) | 40cc trail bike, speed limiter opened up | FRP Moto FX40 (40cc) |
A cautious, smaller, first-time rider does well starting light and low - that is the MB40's job, or the FX40 with its bolt-on training wheels. A taller or more confident child who is ready to leave the flat yard for real trails benefits from suspension and bigger wheels - which is where the 40cc FX40 earns its place. Prefer four wheels? The same 40cc 4-stroke formula powers the Sahara 40 and FA40-NEO kids ATVs.
FRP Moto FX40 (40cc) vs the Typical 50cc Starter: Head to Head
Here is how the 40cc FX40 compares against the typical 50cc kids bike sold today - most of which are 2-stroke starters:
| Spec | Typical 50cc starter (2-stroke) | FRP Moto FX40 (40cc) |
|---|---|---|
| Engine | 50cc 2-stroke - oil premixed into fuel | 40cc 4-stroke - straight pump gas, no mixing |
| Upkeep | Premix every tank; more engine service | Fuel up and ride; simpler maintenance |
| Noise | Louder, smokier 2-stroke | Quieter, cleaner 4-stroke |
| Top speed | ~20-25 mph, varies by brand | 20 mph with adjustable limiter |
| Suspension | Varies - often rigid or basic | Full front & rear |
| Brakes | Varies by brand | Front & rear disc |
| Training wheels | Rarely supported | Bolt-on training wheels available |
| Parts & support | Varies by importer | Stocked FRP parts + US support |
Full suspension · dual discs · training-wheel ready
Low seat · light · easiest first step · ages 6+
Which Should You Choose?
Choose the 40cc FX40 if your child is ready for real riding: full suspension, front and rear disc brakes, and a 4-stroke engine that runs on regular gas with no oil mixing - with bolt-on training wheels for the youngest riders. Choose the MB40 mini bike if your rider is smaller and wants the lowest, simplest start on two wheels. Prefer four wheels? The 40cc Sahara 40 and FA40-NEO ATVs run the same easy 4-stroke formula. And if you are set on a 50cc: most are 2-strokes that need premixed fuel - before buying one, check the suspension, the brakes, and whether replacement parts are actually stocked. Every FRP 40cc is EPA approved, runs beginner-friendly speeds, and is backed by stocked replacement parts so the bike keeps running as your rider grows.
The FRP Moto Rider Journey
The right first bike is the start of a path: a young rider gets going easily on a right-sized 40cc, grows into the style and speed of trail riding, and - because parts and upgrades are supported - the family keeps a bike they can maintain and pass down rather than replace. Start with the bike that fits today - and when they outgrow it, the FX125 and FX140 are the next steps on the same path.
Frequently Asked Questions
Is a 40cc or 50cc dirt bike better for a child?
For most first-time riders, a modern 40cc 4-stroke is the better choice: no oil mixing, quieter running, and less upkeep - at the same beginner speeds. Most 50cc kids bikes are older-style 2-strokes that need premixed fuel. That is why FRP Moto builds its entire kids line - the FX40 dirt bike, MB40 mini bike, and its 40cc ATVs - on 4-stroke 40cc engines.
What age is a 40cc dirt bike for?
Roughly ages 6-12, sized by fit rather than age alone: feet touching the ground and a comfortable reach to the bars. For the smallest beginners, the FX40 supports bolt-on training wheels, and the low-seat MB40 mini bike is the easiest first step.
Is a 50cc dirt bike faster than a 40cc?
Barely, and for a first bike it should not matter. Both classes run beginner speeds around 20 mph - the FX40 has an adjustable limiter. What actually separates kids bikes is the build: suspension, brakes, wheels, and how easy the engine is to live with, not the 10cc on the sticker.
Should my child's first dirt bike be 40cc or 50cc?
Go 40cc 4-stroke unless you have a specific reason not to. There is no fuel premixing, less noise, and easier upkeep - and the FX40 adds full suspension and front-and-rear disc brakes, equipment most 50cc starters skip.
Is a 2-stroke 50cc or a 4-stroke 40cc better for a kid?
The 4-stroke, for almost every family. A 2-stroke 50cc needs oil mixed into every tank and runs louder; a 4-stroke 40cc like the FX40 or MB40 starts with a pull, runs on straight pump gas, and needs far less service between rides.
What 40cc bikes does FRP Moto make for kids?
Four: the FX40 Ogemaw dirt bike (full suspension, dual disc brakes, training-wheel compatible), the low-seat MB40 mini bike, and two 40cc kids ATVs - the Sahara 40 and FA40-NEO. All are 4-stroke, EPA approved, run beginner-friendly speeds, and have stocked replacement parts.
Still deciding? See the complete kids dirt bike age and size guide or browse the full kids dirt bike lineup.
