27.5 Inch Mountain bike Rockrider ST 520 - Black


This mountain bike has been designed and developed by us to best suit mountain-bike rides on hilly and rolling terrain.

With this bike you can go faster while controlling your trajectory. The mechanical disc brakes on the ST 520 mountain bike allow you to confidently take on descents, winding trails and obstacles.

Size: size guide


Product benefits

Cycling comfort

Enjoy touring: raised position, 80 mm suspension, hammock saddle, FLEX seat post

Directional control

Control your trajectory: mechanical disc brakes, tyres with side knobs.


Smooth riding: light aluminium frame, 24 speeds and fast rolling tyres.


An ultra-strong MTB: welded saddle, double-wall rims.

Lifetime warranty

Rockrider offers a lifetime warranty on the frame, handlebar and stem.

Technical information


Several sizes available:

S: 1.50 m to 1.64 m
M: 1.65 m to 1.74 m
L: 1.75 m to 1.84 m
XL: 1.85 m to 2.00 m.
To fit the bike to your height and weight, try these tips:
1/ Sitting on the saddle, you should be able to touch the ground with the tips of your toes.
2/ To adjust the saddle height, your knee should be slightly flexed with your foot on the pedal in the lowest position.
3/ If you're trying to decide between two sizes, choose the larger size.


With a heavily sloped top tube and a wide range of sizes (from S: 1.50 m to XL: 2.00 m).

The ST 520 mountain bike frame is UNISEX.

The ST 520 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 520 mountain bike was fully designed and developed by our passionate MTB team at the B'Twin Village in France (Lille).

Mountain bikers we talked to expressed their need for control so they can take more risks and continue to improve their technical skills. With that as a starting point, we designed and tested the ST 520 mountain bike, involving MTB riders at every stage.


Our designers created a frame that's easy to get onto.

The CGF frame (Comfort Geometry Frame) EVO is made of 100% aluminium for greater comfort. Its slope was carefully designed to keep your back straighter.


The 80 mm front suspension helps you get started with overcoming obstacles on slightly uneven trails easily.

Easily adjust the hardness using U-Fit technology (weight adjuster). Simply set the number to your weight using the dial on the fork.


This mountain bike has no rear suspension. It is a "semi-stiff" mountain bike: perfect for beginners getting started with their first mountain bike rides. Compared to a full suspension mountain bike (with rear suspension), it has the following advantages: the bike is lighter; you can pedal faster on flatter ground.


3 x 8 speeds, 24 speeds total!
2 shifters on the handlebar.
Left (chainrings): control ascents/descents.
Right (speeds): more precise control over your pedalling.

In detail:
-ROCKRIDER FC ATB 500 triple chainring - 22/32/42 teeth
-SHIMANO ALTUS front derailleur
-MICROSHIFT RD-M46-L rear derailleur
-MICROSHIFT TS39 shifters
-SHIMANO 8-speed cassette (11-32 teeth)
-KMC Z7 wide and sturdy chain


The adjustable stem on the ST 520 S allows you to position the levers so they're easy to grip. The all-aluminium ROCKRIDER stem is 70 mm (size S), 80 mm (size M/L), or 90 mm (size XL) and can be raised in 5 adjustment intervals: + 0 mm, + 7.5 mm, + 15 mm, + 22.5 mm, + 30 mm.
In detail:
- 680 mm oversize ROCKRIDER SPORT aluminium handlebar
- ROCKRIDER SPORT "soft touch" ergonomic grips for good grip and a comfortable feel.


The ST 520 saddle is welded to prevent any saddle movement as you cycle.

Because your comfort is our top priority after your safety, we've added an exclusive Rockrider Ergofit saddle that is wider and hammock shaped.

Easily adjust the height of your saddle with the Flex steel seat post (either 350 mm or 400 mm long, depending according to the bike size). Its reduced diameter (27.2 mm) provides your seat with natural flexibility, 30% more than a standard solution.


The Tektro TKD 68 160 mm double disc brakes provide powerful, progressive braking at the front and rear. The aluminium Tektro brake levers are light, precise, and easy to hold. You can brake with just two fingers.

We recommend that you have your brakes checked at least once a year.


The 27.5" wheels of the ST 520 are tolerant and sturdy, with 19 mm double-walled rims with 28 spokes. Fearlessly get started with riding over obstacles, small rocks, roots, holes and bumps!
Because your first rides will be on dry terrain, the DRY 27.5 x 2.0 tyres are the most suitable. They have higher performance thanks to a smooth and fast central section, whilst the side lugs provide good grip on turns.


The Rockrider ST 520 mountain bike comes with flat mountain bike pedals made from hard resin for lighter weight and greater safety.
If your feet can slide off the pedals when needed, there's less risk of injury.

The pedals on the ST 520 are compatible with toe clips.


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


Your ST 520 mountain bike is supplied 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 your bike's components last longer, we recommend a maximum load of 120 kg (rider plus fully equipped MTB).


Lifetime (frame, stem, handlebar). Availability of spare parts: 2 years.


S - 150-164cm : 14.35 kg
M - 165-174cm : 14.45 kg
Weight without pedals.

Product concept & technology

Product Composition

Frame 100% Aluminium 6061


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.

User Directions

Not suitable for XC, All Mountain, Enduro and BMX.


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.


To have more informations about this product, consult the notice


27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black
27.5 Inch Mountain bike Rockrider ST 520 - Black


Q:How to assemble your bike?

A: Everything you need to know about making sure your bike is comfortable, secure and ready to ride.

Q:Do you offer a Cycle To Work scheme?

A: Find out everything you need to know about way of getting to work that’s for good you and the environment. Check Here
Products sold and shipped by Partners are not eligible for Cycle to work Schemes

Customer reviews