Hide Filters
Filters 0
Sort by :
Filters 0
27.5+ Inch Electric Mountain Bike E-ST 900 - Grey



27.5+ Inch Electric Mountain Bike E-ST 900 - Grey

VAT included
Size :
Not available online

Store Availability

This electric mountain bike is designed for MTB rides in the mountains.



Head for the summit powered by a 250W motor with 70Nm torque

Battery life

Ride for around 3 hours at a sporty pace thanks to the 500Wh battery.

Smooth pedal stroke

The built-in motor automatically assists you when needed. Perfect for MTBing.

Cycling comfort

Enjoy: raised position, 120 mm suspension, very wide tyres, Ergofit saddle.

Directional control

Control your trajectory: ROCKSHOX Judy fork, extra wide HUTCHINSON tyres




Which is the right size?

Several sizes available:
S: 1.55 m to 1.64 m
M: between 1.65 m and 1.74 m
L: between 1.75 m and 1.84 m
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).


You have to pedal to go forward!

The electric assistance boosts your pedalling by 320%, helping you ride over obstacles.
You'll get to enjoy longer MTB rides.
The motor stops when you stop pedalling.
The walking mode compensates for the weight of the bike when you need to put your feet down.


Our team of mountain bike enthusiasts created this E-ST 900 electric mountain bike at our B'Twin Village in Lille, France.
We designed and tested the E-ST 900 MTB by involving MTB riders at every stage of the project.


The frame of the Rockrider E-ST900 electric MTB is made of 6061 aluminium with hydroformed tubes. Why? The battery sits snugly on the frame to improve the robustness of this electric mountain bike.
The forged aluminium parts make it compatible with the new 27.5"+ tyre format (wider than the 27.5") in the rear, while remaining easy to manoeuvre. We've kept a frame geometry with short bases for easier steering.


The BROSE T Aluminium central motor is specially designed for high altitude mountain biking:
- 70 Nm torque to handle large obstacles and steep gradients
- metal housing for maximum durability
- belt for an ultra-quiet motor
- sealed bearings to hold up to tough environments while mountain biking


Our battery is equipped with SAMSUNG SDI cells, renowned for their high level of reliability and safety.
Our battery supplier sources its minerals responsibly and sustainably, and is part of the "Responsible Minerals Initiative".


Our Rockrider mountain bike team has designed a battery that locks in place with a simple lever. Child's play!
This locking system prevents the battery vibrating when riding on rough terrain.
A key lock is also installed if you want to protect your battery from theft. For example, if you park your bike in the street.


A discreet LCD control screen. The screen is right next to your left grip so you don't have to let go of the handlebar to choose from the 4 assistance modes available: Eco+, Economy, Standard, Boost.You'll also find a host of useful information:

-Assistance level
-Battery level
-Speed (current, average, maximum)
-Remaining battery life
-Distance covered (total and trip)


Mode 0 - Deactivated
The battery is not used.

Mode 1 - Economy +40%:
Extend your rides while conserving battery life. Ideal when you want a little push on small gradients.

Mode 2 - Economy +80%:
Gain power. A perfect helping hand for keeping up with other mountain bikers.

Mode 3 - Standard +160%:
This is the most versatile mode. Climb any slope without getting too tired and without using too much power.

Mode 4 - Boost +320%


Ride over obstacles (roots, pebbles, stones, etc.) easily thanks to the Rockshox JUDY fork with 120 mm of travel.
This fork has:
- a thru axle and conical pivot for more durability.
- pneumatic spring for optimal adjustment based on your weight
- rebound adjustment and lockout for better control, depending on the terrain.


The E-ST900 electric bike is equipped with a single chainring and ChainFlow 3D anti-drop technology to prevent chain drops.
A single shifter on the right handlebar makes it easy to shift between the 10 speeds.

In detail: - ChainFlow anti-derailment 34-tooth chainring
- SHIMANO DEORE M6000 Shadow+ 10-speed rear derailleur with long cage
- SHIMANO DEORE M6000 right shifter
- MICROSHIFT 10-cog cassette (11-42 teeth)
- KMC E10 Turbo special e-bike chain

27.5+ Sunringle Duroc 40 Wheels

These wheels were specially designed for this mountain bike:
- 36 mm rims (width between brackets) and 32 spokes at the front and rear for greater durability and a good hold on wide (2.8") tyres.
- BOOST format thru axles (12x148 rear, 15x110 front) for greater durability
- Aluminium hubs with sealed bearings.

- TUBELESS READY rims: you will need valves and puncture sealant to convert to tubeless


So you feel safe on any terrain, and to provide traction suited to your motor, the E-ST900 mountain bike is equipped with Hutchinson Taipan Koloss 27.5+ tyres with a 2.8" cross-section. Our test riders particularly liked these tyres for their grip on the ground. Mounted on wide rims, these tyres ensure grip, traction, and comfort on any terrain.


No matter the conditions you ride in (dry, muddy, wet), the Tektro TKD32 hydraulic disc brakes on the front and rear provide powerful, progressive braking. Oversized 180mm diameter discs provide even more power.


The adjustable stem brings the E-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 SPORT "soft touch" ergonomic grips for good grip and a comfortable feel


Since your mountain bike rides will get longer and longer, it is important to sit comfortably. So our teams designed the exclusive ROCKRIDER Ergofit Pro saddle. It fits all hip sizes and has a curved shape that is particularly good for sport trail rides.

The 31.6 mm aluminium seat post ensures compatibility with most adjustable and suspended seat posts on the market.

Platform pedals

The bike comes with 520 Grip MTB platform pedals (ref. 8487130) with a wider pedalling surface and more pronounced dots for better grip on the pedal.However, if you are looking for improved performance when pedalling and better control of the bike when cycling, we recommend replacing them with clipless pedals with platforms or wide aluminium platform pedals.


Your E-ST900 mountain bike is fitted with a bell, lights, wheel reflectors and pedals.

The frame is compatible with:
- front and rear mudguards
- stand
- bottle cage (on the horizontal tube)
- saddle pouch
- rear pannier rack (fixed onto the seat stays or special mounts for wide bikes, 148 mm gap for the rear wheel & 2.8" fat tire)
- child seat


Tip no.1
When mountain biking, there is always the risk of a fall: don't forget to wear a helmet.

Tip no. 2
A puncture could happen at any time, so always remember to take a repair kit and a 6 mm Allen key for removing your wheels.

Tip no.3
If you don't want to stop to drink, bring water in a bottle or water bladder to access it while riding.

Care advice

Leave your battery on the bike when washing using a hose. This will protect the connectors from rusting.

Tips for storage and maintenance

Storage tips

Store it in a warm, dry place away from corrosive products and salty air. Never store with the battery flat, and remember to recharge it at least once every six months.

Restrictions on use

Don't forget to remove the battery to handle the chain.


Agree by

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.

Parts guarantee

Lifetime (frame, stem, handlebar). Availability of spare parts: 2 years.Guaranteed for 500 charges.