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

Sale price: $179.00 Regular price:

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: $179.00 Regular price:

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San Francisco, 735 Market St. Options

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Model: 8676047

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.

Product Customer Reviews

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9 Reviews
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Btwin ST120, Kids' Mountain Bike, 20
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Affordable kid bike

the bike is great, the price is reasonable!

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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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Thanks for taking the time to leave a review Ben, we are glad to hear your son is enjoying his new bike!

Don't forget about the first free tune up within one year of the purchase!

Decathlon Calgary

Buena relación costo beneficio

Estaría bien un control de cambios más simple, de dos palancas en vez de puño. Se agradecería un cuadro mas ligero

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Mal ajuste del técnico

Compramos la bicicleta así como algunos accesorios, ahí mismo en decathlon el técnico del área de bicicletas le hizo los ajustes correspondientes sin embargo dejó algunas piezas flojas que al usar la bicicleta dificulta el manejo, ahora tengo que programar llevarla nuevamente para dicho ajuste…….

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La calidad de la bicicleta buena, sin embargo el encargado de armarla no la dejo bien ajustada en frenos

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Rapide a prendre en main

Rapidement pris en main par mon garçon de 7 ans

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Merci pour votre commentaire, Jérome!

Nous sommes heureux d'entendre votre réponse sur notre vélo de montagne enfant, et encore plus heureux de savoir qu'il est à votre satisfaction !

Au plaisir de vous revoir dans notre magasin Décathlon Brossard.

Passez une bonne journée,

Chloé, Team fitness

Tres bon velo

tres bon velo, je le recommande

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จักรยานโครงเหล็ก มีน้ำหนักพอควร แต่ไม่ประทับใจตรงที่เจ้าหน้าที่ไม่ตรวจเช็คความเรียบร้อยให้ก่อน ซึ่งจักรยานไม่ได้ขันน๊อตที่คอจักรยาน น้องเอาออกมาลองขี่ที่สนาม รถล้มเพราะคอจักรยานหลุด ต้องเข็นกลับไปให้เจ้าหน้าที่ช่วยขันน๊อตล็อกคอจักรยานให้อีกครั้ง ดีที่น้องไม่ได้รับบาดเจ็บ อยากให้เจ้าหน้าที่ตรวจสอบความเรียบร้อยก่อนที่จะส่งมอบสินค้า

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เมื่อเปรียบเทียบรูปลักษณ์ และฟังก์ชั่นที่เหมือนกันกับของเพื่อนบ้านที่ซื้อจากห้างอื่น

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Additional Product Information


Bike frame

  • 100% 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.

Riding position

When mountain biking, it is important to control your path. To make it easier for kids to learn, our engineers installed a handlebar and stem that are combined into a single steering block. This eliminates the needs for adjustments, so they can stay focused on the road!


The new chainset has a 140 mm crank that is designed for a kid's leg length. This chainset allows you to start pedaling more easily. The crank is covered to prevent the kid from coming into contact with the metal part. The double chain guard prevents the chain from derailing.

20" wheels and mtb tires

The tires are designed for mountain biking. The lateral lugs provide good grip on turns. The recommended tire pressure is indicated on the side of the tire (2 to 3.5 bars). 20" inner tube, 1.7" to 2.2" Schrader valve.

Mtb fittings

This MTB is equipped with a bell, lighting, wheel reflectors, and platform pedals. The frame is also compatible with other B'Twin accessories: - front and rear mudguards - stand - bottle cage - saddle bag - stabilizers:

Dimensions of the bike ready to use

Length: 140 cm. Height: 80 cm. Width: 54 cm.

Frame dimensions

Top tube length: 431.6 mm Seat tube length: 285 mm Chainstay length: 360 mm Seat post length: 300 mm Head angle: 68.8°



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.

Superior quality. Unbeatable prices.

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

Decathlon makes the difference
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    Research and development

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    Minimal retail footprint

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Size Guide Visual