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Rockrider ST900, Kids' Mountain Bike, 20"

Sale price: $399.00 Regular price:
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Sale price: $399.00 Regular price:

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Model: 8549160

Product Features

A photo of the Rockrider ST900, Kids' Mountain Bike, 20" in use

Rockrider ST900, Kids' Mountain Bike, 20" is designed for

20-inch bike with 6 speeds, front suspension, double disc brake

Easy to use

6 speeds, quick-release saddle, quick-release front wheel

Bike safety

Double disc brakes provide powerful and easy braking.

Shock absorption

Suspension fork.

Lifetime warranty

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

Product Lifestyle Image Gallery

Image Gallery

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20 

Rockrider ST900, Kids' Mountain Bike, 20

Product Customer Reviews

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Rockrider ST900, Kids' Mountain Bike, 20
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Great bike

Very nice children's bike. Unfortunately, the size specification from Decathlon is not exactly appropriate. It is only correct if the child should reach their feet to the floor on the seat. Like us adults, my son rides on the pedal with his knee straight. This makes this bike just enough for children with 125cm. It went back and was swapped for the same one in 24 inches. That fits from 125cm and drives great.

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Actually a nice bike

I bought this bike for our daughter in the branch in Kiel because our daughter got along with it straight away and urgently needed a bigger bike. Unfortunately, I noticed at home that the rear derailleur protection bar was missing, which is important for a child's bike that is sometimes robust. I immediately called Decathlon, but got the announcement that I could come back to Kiel, then they would grow this for me there. For me as a Flensburg native, this is of course not a sensible option. Here I would have liked the part to be sent to me in the interests of customer service. Hopefully the bike won't take any damage until the part is somehow with me. In addition, the online images also show bicycle lamps and spoke reflectors, which my son's bike (online purchase) was also equipped with. It's a shame, but I don't get any benefit from buying it in a store if the bike is incomplete.

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Great color, great handling. My son likes it and we've done long tours together. So far nothing to complain about for the price.

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Size Guide

Size Guide Visual

Additional Product Information


Bike frame

  • 100% Aluminium 6061


Aluminum frame designed by B'Twin. The lowered frame geometry makes it easier to get on and off the bike.


6 speeds. Ultra-soft grip shifter for children: change gears using a grip shifter, which is easier and safer (the child doesn't have to let go of the handlebar to change gears). B'Twin chose this shifter as it is extra soft and specially sized for children's hands.

Handlebar / stem / steering

Mid-rise stem and handlebar. Quick-release saddle. Comfortable, reinforced (plastic shell) saddle that provides a comfortable position. Fast, tool-free saddle adjustment. B'Twin selected this reinforced saddle for its tried-and-tested durability (should the bike fall over, for instance).


Very reliable double disc Brakes. B'Twin chose to equip this bike with a double disc Brake system for its ease of use, easy maintenance, and greater braking power.




Lifetime warranty (frame, stem, handlebars). Details on Spare part availability : 2 years

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