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ROCKRIDER ST 900 Mountain Bike, Black/Red- 27.5"

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was £599.99 -%


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£599.99 -%
This price includes a recycling fee for electrical equipment and batteries DecathlonDeeeTaxMentionAfterPrice / Since

* From To

* Sales from to Until end of stock
* From and limited stock
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This 27.5" MTB is designed for MTB rides lasting over 3 hours, all year round. Greater efficiency and more control: ROCKSHOX 120 mm fork with handlebar lockout, single chainring, lighter 27.5" double-walled wheels. You'll love how light the ST 900 mountain bike is!
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Due to high demand, we are currently suspending online delivery for bikes. We are now increasing the availability of our bikes in our store showrooms while continuing with our Click and Collect service. This is a temporary measure and we thank you for your patience and understanding.

Product benefits

Cycling comfort Enjoy the raised position, adjustable stem, 120mm suspension and hammock saddle
Directional control Control your trajectory: hydraulic fork and brakes, tyres and a wide handlebar.
Efficiency Smooth riding: lighter wheels, single chainring and fork lockout.
Ease of use Change speeds or lock your fork with a single motion on the handlebar.
Lifetime warranty ROCKRIDER offers a lifetime warranty on the frame, handlebar and stem

Technical Information


Several sizes available:
S: between 1.50m and 1.64m
M: between 1.65m and 1.74m
L: between 1.75m and 1.84m
XL: between 1.85 m and 2.00 m
If you are between 2 sizes:
Choose the smaller size for easier steering (easier to handle) and comfort (straighter back).
Choose the larger size for easier pedalling with a more stretched-out position (position more suited to performance).


With a heavily sloped top tube and a wide range of sizes (from S: 1.50 m to XL: 2.00 m).
The ST 900 mountain bike frame is UNISEX.
The ST 900 mountain bike is available with the same frame in a WOMEN'S version: fitted seat, narrower handlebar, shorter stem, fork with a more flexible spring, and brake levers that are closer together.
As a WOMAN, if you choose the MEN'S model, we recommend at least purchasing the WOMEN'S SPORT 500 saddle which is fitted to the female form.


The ST 900 mountain bike was fully designed and developed by our passionate MTB team at the B'Twin Village in France (Lille).
A comfortable, efficient mountain bike: 120 mm ROCKSHOX fork to easily ride over obstacles, fork with handlebar lockout, single chainring and, 27.5" double-walled wheels that have been lightened for greater efficiency.
Women mountain bikers were involved at every stage of the design process.


For less weight and more efficient pedalling, the Rockrider ST 900 frame is made from 6061 aluminium (only 1.6 kg in size M). It is 500g lighter than the ST 540 frame, thanks to its double butted front triangle.
Our designers created this bike to be comfortable and easy to manoeuvre. Its slope has been designed to keep your back straighter. The lower bottom bracket helps keep you more stable during turns.


The 120 mm Rockshox 30 Silver hydraulic fork is 400g lighter than that on the ST 540 MTB. It is conical and offers even more stiffness and precision when steering.
Easily adjust the fork's bounce and stiffness. Its quick COMBO LOCK lockout system, which you can control from the handlebar, helps prevent bobbing and loss of speed on faster sections.


This mountain bike has no rear suspension. This is a "semi-rigid" mountain bike.
Compared to a full suspension mountain bike (with rear suspension), the advantages are clear: lighter weight, less loss of energy on flatter terrain. If however your primary concern is comfort and manoeuvrability, the ST 900 is available in a full suspension version with suspension at the rear.


The single chainring is easy and efficient to use.
1 chainring and 11 speeds: accelerate on the flat and take on climbs with no compromise.
1 single shifter on the handlebar: adapt your speed instantly like the pros as the terrain changes!
In detail:
-SRAM X1000 32-tooth single chainring
-MICROSHIFT M665 11-speed rear derailleur
-MICROSHIFT M8515 right shifter
-MICROSHIFT H113 11-cog 11 to 46 teeth cassette
-KMC X11 chain


The adjustable stem brings the ST 900 controls to your hands. The all-aluminium ROCKRIDER stem is 70 mm (size S), 80 mm (size M/L), or 90 mm (size XL) and can be raised to 5 adjustment intervals: + 0mm, + 7.5mm, + 15mm, + 22.5mm, + 30mm.
In detail:
- 720mm oversize ROCKRIDER SPORT aluminium handlebar
- ROCKRIDER ergonomic grips for good grip and a comfortable feel.


Our teams designed and created an exclusive ROCKRIDER ERGOFIT Pro saddle. Designed for all hip widths, its hammock shape is very comfortable for long, athletic rides. The Flex 27.2mm diameter aluminium seatpost also contributes to its increased level of comfort.
Quick and easy tool-free adjustment of your saddle height using the adjustment lever on the seat post clamp.


No matter what conditions you ride in (dry/wet), the Rockrider by Tektro 180 mm (front) and 160 mm (back) double hydraulic disc brakes will come through for you, even in the mud.
Hydraulic braking adds more power and progressive braking and requires less powerful use of the brake levers.
The aluminium brake levers are easy to grip, lightweight, and precise.


Lighter wheels: with sleeved double-walled rims and lighter tyres, these are 230g lighter than the wheels on the ST 540.
With 28 spokes, they are lightweight, stiff, and durable.
The exclusive ROCKRIDER ALL CONDITIONS LIGHT (60 TPI) 27.5"x2.2 tyres have side knobs designed for all terrain riding. A width of 2.2 means more grip on technical sections.
Tubeless Ready 23 mm rims: you will need rim tape, Schrader valves, and puncture sealant.


The ST 900 comes with Rockrider Flat platform pedals with a wider pedalling surface and more pronounced dots for better grip on the pedal.


We added a quick release system for easily removing/reattaching the front wheel.
Our advice: a bike rack is an easy way to transport your mountain bike without dirtying your car.


Your ST 900 mountain bike is fitted with a bell, lights, wheel reflectors and pedals.
The frame is compatible with:
- Front and rear mudguards
- Stand
- Bottle cage
- Saddle bag
- Rear pannier rack
- Child seat


Your bike's fittings (chain, derailleur, brakes, etc.) will adjust over time. Take advantage of a free servicing within 6 months after purchase. Our technicians will carry out a 13-point check of your bike. Just come to your nearest Decathlon workshop with your Decathlon card and/or receipt.


To ensure components last longer, we recommend a maximum load of 120 kg (rider and MTB included).


S - 155-164cm: 12.85 kg
M - 165-174cm: 12.95 kg
L - 175-184cm: 13 kg
XL - 185-200cm: 13.1 kg
Weight without pedals.

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Composition / advice

100.00% Aluminium 6061
Stock advice After washing, rub with a dry cloth to remove all traces of moisture. Store your mountain bike in a cool, dry place, away from corrosive products and salty air.
Restricted use : Not suitable for XC, All Mountain, Enduro and BMX.
Legal notice To ensure components last longer, we recommend a maximum load of 120 kg (rider and MTB included).

Our commitments

Test Product Our engineers always have real riders test all our products in real conditions. These tests round out our lab tests and let us validate all our products before they hit store shelves.
Guarantee : Lifetime (frame, stem, handlebar). Availability of spare parts: 2 years.


Q : How to assemble your bike?
Everything you need to know about making sure your bike is comfortable, secure and ready to ride.
Q : How do you adjust your brakes?
Having properly functioning brakes is vital when out on the road. Check out how to get them working to your liking.
Q : How to replace a brake lever on a bike?
Having properly functioning brakes is vital when out on the road. Here’s a video to show you how to make sure your new brake level is working nicely.
Q : How to replace a disc brake?
Having issues with your disc brake? Then this video is for you.
Q : How to adjust your bike handlebar?
A suitable handlebar height is essential to your cycling safety and comfort. Find out how to adjust it to your liking with our video.
Q : Do you offer a Cycle To Work scheme?
Find out everything you need to know about way of getting to work that’s good you and the environment.Check Here

Your reviews

Reviews by our Team Members

Our services

Maintenance and repair
Maintenance and repair
27.5" MTB ST 900 - Red/Black
Because you look after your own health, we look after that of your products: tips for initial settings, maintenance and repair advice, video tutorials, FAQs, instructions...
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