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Rockrider ST900S, Full Suspension Mountain Bike, 27.5"

Sale price: $1,399.00 Regular price:

Greater efficiency and more control: ROCKSHOX 120 mm fork and air shock with handlebar lockout, single chainring, 27.5" lightened double-walled wheels, etc. Enjoy how lightweight the ST 900 S MTB is!

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Sale price: $1,399.00 Regular price:

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San Francisco, 735 Market St. Options

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Model: 8500764

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Product Features

A photo of the Rockrider ST900S, Full Suspension Mountain Bike, 27.5" in use

Rockrider ST900S, Full Suspension Mountain Bike, 27.5" | 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 and air shock with handlebar lockout, single chainring, 27.5" lightened double-walled wheels, etc. Enjoy how lightweight the ST 900 S MTB is!

Cycling comfort

Enjoy the raised position, adjustable stem, 120mm suspension, and hammock saddle

Directional control

Control your trajectory: hydraulic brakes and air fork and shock.


Smooth riding: lighter wheels, single chainring, and suspension lockout.

Easy to 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.

Product Lifestyle Image Gallery

Image Gallery

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5 

Rockrider ST900S, Full Suspension Mountain Bike, 27.5

Questions & Answers

Product Customer Reviews

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506 Reviews
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Rockrider ST900S, Full Suspension Mountain Bike, 27.5
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Rockrider ST900 S

Great bike. I've had it for several years. It has flown thousands of km, mostly in the mountains, in difficult conditions... Durable, reliable, comfortable... I only change the chain regularly. I wouldn't change.

nice mountain bike,... however.

Visually it is very aesthetic, very successful notwithstanding the numerous failures concerning the rear wheel, namely premature wear or perhaps poor quality of the latter, namely the bearings. The Decathlon warranty is effective since I had to have this rear wheel changed twice. And also to point out very poor assembly of the mountain bike. THANKS.

Bike well to resume…

Good bike for getting back into mountain biking. I changed the front and rear brake system because it was too weak and too tight after a few descents. Lack of precision in the derailleur (often goes wrong) After the suspensions the tires and comfort are good

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Lifespan after 2 years

It's beautiful when it's new. But after 2 years it's problem after problem. And the after-sales service parts don't hold up. Major repair in May, in July an HS cable (under warranty), and there 14/09, the HS cable again...

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Maximum satisfaction. Everything works, great.

A real gadget, not a mountain bike...

My son's Leclerc full-suspension mountain bike is more solid... The brakes are ridiculous (there are no marks on them) after a break-in carried out as recommended by the "manufacturer" the 2 brakes vibrate and make noise …The wheels have no marks on them either …they squeak after barely 1 week of use The paint comes off on its own …The tires mounted upside down …The grips break down under sweat hands… The rear shock absorber loses too much oil… And so on… A mountain bike at 1000€ which is not even up to the level of mountain bikes at 200€ in terms of reliability… It looks good, it is very beautiful but it's a real toy and not a mountain bike for mountain biking.

A lot of bike for little money

My bike for the ride to work. 25 km of asphalt, gravel and an approximately 10% gradient. Sure, the brakes aren't the best, nor is the gearshift - but it works perfectly. Replacement components are available for little money. I still have high-quality tires installed and high-quality pedals. So I invested around 150 euros. But it pays off. I still have two much more expensive bikes but the seating position and comfort are really unbeatable. Good work by the technicians. Summary: really a lot of bike for this price

disappointed with delivery, quality and noise

The mountain bike was given to me raw from the factory, without adjustments (the front brake disc was not aligned), no saddle setback adjustment relative to the buyer, the rear suspension loses air, 10psi, after 10 km, re-inflation obligatory) And the most annoying thing is the constant noise of the spokes (I asked to check the tension of the spokes, but the workshop does not have the device) Also, I finds that the performance is low, a 34 tooth on the chainring at the front would be much better

Excellent bike

So far, I have ridden approx. 150 km on broken terrain (roots, gravel roads, stony routes, muddy terrain and asphalt and panels) and I am completely satisfied. A single gear does not allow for very fast riding on smoother surfaces, but this bike is not designed for that. It handles uneven terrain with ease and the suspension is excellent. I'm at the limit of the load capacity of the frame, and despite that, this bike just doesn't talk and grind as you need it to. Single gear, on the other hand, is great for hills, where you don't have to worry about whether you have a large, medium or small chainring on the front drive. I struggled for a while with the optimal rear shock pressure, but finally settled on 170psi and it's a blast. When I tried Decathlon's recommended 200psi due to my heavy weight, it was too much and the bike protested with weird noises when the load changed, so lower psi solved it. I would appreciate more info when picking up the bike at the shop. Set up to take over so when I did the first 3 rides I couldn't feel the bottom - then I re-adjusted the seatpost and it was all sorted. The brakes respond great. The derailleur will need to be adjusted after a few rides, it sometimes doesn't listen in the middle gears, which is quite annoying, for example on hills, when it slows you down a lot, but that's about the adjustment, it's not a defect of the bike. Lights are also supplied with the bike. The rear is still OK, but the front seems to be missing. The handlebars are robust, so you can't place the light anywhere other than the brake and shift levers, so the light shines sideways and sideways. Still better than nothing. I will probably replace the basic heels with other ones, but they are not completely bad. Overall, this bike is a great companion. I recommend!

First driving experience

Pleasant position, accurate shifting with a good range of speeds, in my opinion, quality tires - precise guidance

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Good bike but little information

It is a very good bike that has allowed me to go out in high mountains and do positive slopes of 1000 meters, although I don't know if it was designed for this, because on stony or very irregular slopes of more than 20% downhill I don't control it too much. On the other hand, I find that in the store, although the attention has always been correct, they do not give you enough information about operation and maintenance, and the truth is that a lot is needed, especially since the bicycle manual is limited to giving technical specifications but hardly gives explanations.

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As you take care you have ;-)

I've been buying bikes for the whole family at decathlon for a long time and to be honest I'm happy, I bought the MTB ST 900 S model for my son about three years ago (he didn't spare him), the bike was used intensively and nothing serious happened, serviced once a year and maybe once a little adjustment or two and that's it. I recommend the bike, and if someone thinks that it is too weak, etc., I recommend buying the T-72 tank. Regards to Decathlon and users ;-)

extremely disappointed

Satisfied with the workshop service of the Montbéliard store BUT extremely disappointed with the quality of this VTT Vélo bought in 09/21 after months of waiting for availability and in anticipation of Christmas 03/22: exchange of the frame as a warranty pb alignment of the rear wheel with the frame. The second frame slightly improves the centering of the wheel. Question asked by the workshop department to the cycle quality department without an answer… 06/22: exchange of the REAR wheel freewheel play problem 06/23: same problem 07/23: after a few rides the play is reappearing I do without the derailleur which does not allow back-pedaling without the chain changing sprockets, behavior reported as normal in the workshop. Certainly the last mountain bike purchased from DECATHLON

poor build quality of the bike

The bike scratches very quickly, every scratch is very visible on the frame. The problem is not the use of it, but the quality of the varnish on the frame. In some places, it comes off in several centimeter patches. A year after buying the bike, the chain tensioner broke down, which was repaired in the service, but after a while it only worked halfway. After 2 years, the derailleur, crank, shifter and chain should be replaced by exploitation. The repair cost is about PLN 800. Currently, I have not done the repair yet and the derailleur does not work at all and the gears do not change. In addition, I bought shifters intended for exactly this bike, which turned out to be as tragic in quality as the bike. The levers twisted and could not be tightened. At some point, the handle turned and I fell down, then I threw them in the trash. I contacted customer service and they said there is nothing they can do about it. After my experience with this bike, I wouldn't buy it. In no way is it worth buying and spending so much money on such a tragic quality thing. The only plus is the service which is very helpful with my frequent visits. If someone is looking for a durable and quality bike, it is better to go for proven brands. For your own pocket, it is worth avoiding rockriders and btwins which, in addition, like to break.


Product of very qualitative appearance, to see in the future but I am very satisfied with my purchase value for money. I recommend
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Size Guide

Size Guide Visual

Additional Product Information


Bike frame

  • 100% Aluminium 6061

Which is the right size?

Several sizes available: M: between 5'5" and 5'9" L: between 5'9" and 6' XL: between 6'1" and 6'7" If you are at the limit between 2 sizes: Choose the smaller size for easier steering (easier to handle) and comfort (straighter back). Choose the larger size for easier pedaling with a more stretched-out position (position more suited to performance).

Unisex frame

The ST 900 S MTB has a UNISEX frame. The ST 900's frame has been carefully designed down to the smallest detail, from the top tube's relatively pronounced slope, to the wide range of sizes (M: 5'5" to XL: 6'7"). The ST 900 S MTB is not only lightweight and comfortable but UNISEX as well. To make the most of the improved comfort, the women on the RockRider team recommend the 500 Women's Sports saddle, which is specially designed for the female form.

A word from the team

The ST 900 S 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 air fork and shock to easily ride over obstacles, single chainring, and 27.5" double-walled wheels that have been lightened for greater efficiency. We've involved women mountain bikers at every stage of the design process.

A comfortable, playful frame

For less weight and more efficient pedaling, the ROCKRIDER ST 900 S 27.5" mountain bike's frame is made from 6061 aluminum (only 5.5 lbs in size M, without shock), with a "double butted" front triangle that's 7.1 oz lighter than that of the ST 540 S 27.5". Its 120 mm rear shock uses a single pivot system (more sensitive to small shocks, while staying firm for big impacts) and sealed bearings for a longer life.

Rockshox front suspension

The ROCKSHOX 30 SILVER 120 mm AIR shock is 14.1 oz lighter than the one on the ST 540 S mountain bike. Its tapered steerer tube 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.

Rear air shock

This bike has a lightweight 120 mm X-FUSION O2 air shock that has been specially adapted to fit this frame. You can easily adjust it, based on your weight, using its Schrader valve. A special "high pressure" pump is required to adjust this shock (RockRider fork and shock pump - ref: 3310286). Its quick COMBO LOCK lockout system, which you can control from the handlebar, helps prevent bobbing and loss of speed on faster sections.

Derailleur and drivetrain: a single chainring like the pros!

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

Handlebars, stem, grips

The adjustable stem brings the ST 900 S controls to your hands. The all-aluminum 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: + 0 mm, + 7.5 mm, + 15 mm, + 22.5 mm, + 30 mm. In detail: - 720 mm oversize ROCKRIDER SPORT aluminum 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 aluminum RockRider Sport seat post is lightweight and has a wide adjustment range, with a 31.6 mm diameter and 400 mm in length. Quick and easy tool-free adjustment of your saddle height using the adjustment lever on the seat post clamp.

Hydraulic disc brakes

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 aluminum brake levers are easy to grip and precise.

Wide, lightweight 27.5" wheels

Lighter wheels: With sleeved double-walled rims and lighter tires, these are 8.1 oz lighter than the wheels on the ST 540 S. With their 28 spokes, they are also stiff, and durable. The ROCKRIDER ALL CONDITIONS LIGHT (60 TPI) 27.5" tires have side knobs designed for all-terrain riding. A width of 2.2 means greater comfort and grip on technical surfaces. Tubeless Ready 23 mm rims: SCHRADER valves, TUBELESS rim tape, TUBELESS tires, and puncture-proof liquid to be added.

Platform pedals

The ST 900 S comes with RockRider Flat platform pedals with a wider pedaling surface and more pronounced dots for better grip on the pedals.

Easily transport and store your mountain bike

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 S mountain bike comes with a bell, lights, computer and GPS mount on the stem, wheel reflectors, and pedals. The frame is compatible with: -500 bottle cage (ref. 8358133) -Mountain bike mudguard set (ref. 8385291) -100 saddle bag (ref. 8347394) and 500 saddle bag (ref. 8354448)

Comfort and safety

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.



Product testing

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.

Storage instructions

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.


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

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