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Rockrider ST100, Mountain Bike, 20'', Kids 3'11" to 4'5"

Sale price: $149.00 Regular price: $249.00

A sturdy, single-speed, 20" white bike that's simple to ride. Equipped with a bell, it can be ridden around town as well as on trails.

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Sale price: $149.00 Regular price: $249.00

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San Francisco, 735 Market St. Options

Select an available color and size to see options.

Model: 8549158

Product Features

A photo of the Rockrider ST100, Mountain Bike, 20'', Kids 3'11" to 4'5" in use

Rockrider ST100, Mountain Bike, 20'', Kids 3'11" to 4'5" | Designed for 6 to 8 year old children who are beginning to learn to ride a bike.

A sturdy, single-speed, 20" white bike that's simple to ride. Equipped with a bell, it can be ridden around town as well as on trails.

Easy to learn

Single-speed, simple and efficient bike. Bike weight 24.3 lbs.

Bike safety

V-Brakes provide powerful and easy braking.

Lifetime warranty

B’Twin offers a lifetime warranty on the frame, stem, handlebar and rigid fork.

Product Customer Reviews

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29 Reviews
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Rockrider ST100, Mountain Bike, 20'', Kids 3'11
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Great bike for kids!

This bike is great! Simple for my son to work the brakes. Great quality. Super easy to put together. Customer service is also fantastic.

Great Bike Kids (Beginner)

Rockrider ST100 bike is sturdy with easy adjustable seat that's comfortable and suitable for my kids (ages 9-11) who just started to learn cycling without the supporting wheels. They pickup cycling less than 15minutes :)

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Dear Mahzura, thank you for your time in leaving us with a 5-Star rating on our product/service. We are glad that we managed to delight you with the standards of our product/service. We really appreciate your loyalty with Decathlon. Please let us know if there is anything else we can improve on in the future. Thank you once again for your time and we hope to serve you again soon!

Mohd azman
20’’ Bicycle

Need to check on this as front wheel seems to be loose.

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Dear Mr. Mohsin,

thank you for taking the time to write the review! We are truly sorry to hear that our product and service did not meet your expectations. We have read your feedback and will take note of these points into improving ourselves to better satisfy your needs. Thank you once again for your time and we hope to serve you again soon!

Khairil Hafiq

Kids' Mountain Bike RR 20" ST 100 B'TWIN

my son loves it

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Excellent price and service

I went to Decathlon to buy a bike for my 8 y.o. son. without any particular preference other than to get an affordable solution. Once in the store, I was pointed to the bike I ended up buying. The staff advised me on size, which I would have possibly guessed wrong, and price. This was the last piece in the store at the lowest price. They set up everything very quickly and I left the store quite satisfied with the bike and the service.

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The Chain Is Too Loose

The Chain Will Come Out Many Times A Day, Very Frustrated

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Hi Patrick,

Thanks for taking the time to leave a review of the ST 100 RR 20 inch Kids Bike! I'm sorry to hear about your difficulty with the chain coming off.

It sounds like the locknuts for the rear wheel may have worked loose and thus there is not enough tension to keep the chain on the sprocket or chainring.

Our Workshop Leaders will be more than happy to help you sort it out - you will just need to make an online booking here.

I will feed back to our Cycling and/or Production teammates about this - please rest assured that we take such feedback seriously and will work to improve our processes in the future. Thanks and have a great day!


Digital Sport Leader

Cycling & Roller Sports


my 7 year old son's first bike. he likes it.

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Kids' Mountain Bike

My daughter enjoys cycling on this bike so far

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kids bicycle

good, the kids love it

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Good quality budget upgrade

Our upgraded from 14" to 20", They're just almost reaching 120cm and once on the move, they're enjoying riding noon stop, Perfect for them for probably another 3 to 4 years use?

kids Mountain Bike RR20 ST 100 BTWIN

Right size for kids. handlebars stability and ease in control.

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Sturdy and nice design. Delivery was fast as came 3 day of order

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Formative years cycling experience!

To get the confidence level up for a 5/6 yr old I switched from a training cycle to this 20” and she just loved it. A father-daughter Saturday morning cycling and jogging ritual.

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Hi Tejas,

Thank you for taking the time to write a review on the Kids' Mountain Bike RR 20" ST100. I am glad that this product has been working well for you and that you love it.

At Decathlon, our mission is to make sports accessible for the many. It is our responsibility to ensure that our products are made to satisfy our users. 

Feel free to write a review on other Decathlon products and I hope to see you in our store soon!

Stay Healthy, Be Sporty!


All items r vry greatful

I have no comment for it's coz everything ur products, material, quality everything r really2 the best n vry gd servers too. Tq fully for it

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Hi Rosni,


Thank you for your review and honest feedback. We are glad that you enjoy shopping with us, and hope we are your preferred stop & shop for your essential sports equipment and leisure wear!


We, in Decathlon, always strive to make sports available to everyone via our products at affordable prices, and we hope you are amongst those that have benefitted from this objective. Thank you for your support and I wish you a pleasant week ahead! :)

Skate safe! Skate fast!

Guo siong

Bedok Oxelo Sports Leader

Excellent bike for kids 6-7 years old

Good sturdy bike for kids about 120-130cm. My kids love it. More importantly the after service is great! Went back to adjust the height after buying online and the staff was very friendly and helpful

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Hi Tze Yong,

Thank you for taking the time to review our products. We are pleased to hear that the child enjoys using this ST 100 20" kids bike!

We look forward to more of your reviews and sharing! Plus, the new Decathlon app has been launched and you can now purchase all your favourite sports goods with just a few clicks on your smartphone! Yes, it's now available both in the App store and Google Play Store! Download now and happy shopping!

Thank you for your support and stay safe! :)

Sport on safely!


CSM Digital Leader

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Additional Product Information


Bike frame

  • 100% Steel


The chainwheel anti-derailment device and low step-through frame make it easy to get on and off.

Accessories / equipment

Fully equipped for use on public roads (bell, reflectors). The rear derailleur guard protects the derailleur from damage in the event of an impact.



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
  1. product-research

    Research and development

    delivers high-quality cost-effective products

  2. State-of-the-art production processes

    minimize manufacturing costs

  3. Optimized supply chain

    reduces retail prices

  4. laptop-checkout

    Minimal retail footprint

    lowers overhead and indirect costs


Size Guide Visual