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Btwin ST120 Kids' Mountain Bike 20" Kids 3'11" to 4'5"

Sale price: $149.00 Regular price: $199.00

To take on the first slopes, our engineers have equipped this kids' MTB with 6 speeds. This bike allows the rider to take on sloping terrain.

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Sale price: $149.00 Regular price: $199.00

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Final Sale: No returns or exchanges

Free pickup

San Francisco, 735 Market St. Options

Select an available color and size to see options.

Model: 8676047

Product Videos

Product Features

A photo of the Btwin ST120 Kids' Mountain Bike 20" Kids 3'11" to 4'5" in use

Btwin ST120 Kids' Mountain Bike 20" Kids 3'11" to 4'5" | We have designed this mountain bike for 6-to-9-year-olds (3'11" - 4'5") wanting to start mountain biking.

To take on the first slopes, our engineers have equipped this kids' MTB with 6 speeds. This bike allows the rider to take on sloping terrain.

Easy to use

Equipped with a grip shifter to easily change gears (6 speeds).

Brake control

New Easy break brake levers are sized for kids' small hands.


Tires with side lugs for good grip in the turns.

Seat comfort

A saddle with a sporty design, sized especially for kids.

Questions & Answers

Product Customer Reviews

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Btwin ST120 Kids' Mountain Bike 20
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my son likes this bike

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Good cost benefit ratio

A simpler gear control would be nice, with two levers instead of a fist. A lighter frame would be appreciated

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mountain bike

steel frame bike have a fair amount of weight but not impressed that the staff did not check the order first which the bike does not tighten the nut on the bike neck Sister brought it out to try riding at the track. The car fell over because the bike's neck fell off. Have to push it back to the staff to help tighten the bike neck lock nut again. Good thing he wasn't injured. I want the staff to check the order before delivering the product.

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The price is higher than other stores.

when comparing looks and functions that are the same as those of neighbors bought from other stores

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Affordable kid bike

the bike is great, the price is reasonable!

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Quick to learn

Quickly picked up by my 7 year old boy

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Poor fit by technician

We bought the bicycle as well as some accessories, right there at Decathlon the technician from the bicycle area made the corresponding adjustments, however, he left some loose parts that make handling difficult when using the bicycle, now I have to schedule to take it back for said adjustment…….

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Great bike

My 6 year old can handle this bike with ease and shifting gears and breaks are made for his hands

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Very good bike

very good bike, I recommend it

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The quality of the bicycle is good, however the person in charge of assembling it did not leave it well adjusted on the brakes

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Additional Product Information


Bike frame : 100.0% Steel

Frame designed for mountain biking

Our engineers have designed a new, robust steel frame. The frame's rear chainstays are short, making the bike responsive and easy to handle.

Why have we created a brake lever specifically for kids?

Because kids have smaller hands than adults, it's not always easy for them to reach the brake lever. This is why our engineers designed a brake lever that is closer to the handlebars and thus easier to hold.

Changing gear

This bike is equipped with a grip shifter to change between the 6 speeds: an easier, safer system as the kid's hands stay on the handlebars. This makes changing gears to match the terrain simple and easy!

A reinforced, ergonomic saddle

A saddle with a sporty design, designed with care to adapt to the morphology of kids. It is equipped with a plastic section on the rear (a bumper) to protect against any impacts.

Controlled braking

2 V-Brake pads for effective braking.These brakes are composed of calipers that exert more or less pressure on the rim to slow or stop the rotation of the wheels.

Storage instructions

Store the bike in a clear, dry place. Clean and grease the chain regularly. Our tips for before each ride: Inflate the tires to the pressure indicated on the sidewall.


for life (frame, stem, handlebars, rigid fork). Find out more about this bike's warranty.



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For 40 years, Decathlon has delivered the best value in the retail sports industry by offering high-quality, sustainable and cost-effective products.

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