Ref: 8746784

CERES 5.3 27.5 MTB"


This 27.5" mountain bike is designed for you to enjoy two- to three-hour rides all year round.

With your CERES 5.3 mountain bike, accelerate and brake very quickly to adapt to the hazards of the terrain! The single chainring and hydraulic disc brakes will transform your mountain bike rides.

First use

Inflating your tyres

The recommended average tyre pressure is 1.8 bar.

If you're looking for more comfort and grip AND/OR if you weigh under 70kg, you can reduce the pressure by 10% but without dropping below 1.6 bar (the minimum recommended pressure). On abrasive terrain, however, this will increase the risk of punctures.

You should check the pressure of your tyres regularly.

Adjusting the height of your handlebars

Your handlebar is set to the most raised position, which is the most comfortable position for riding.

For improved aerodynamics and more efficient pedalling, you can lower your handlebar so that your body leans forward and adopts a more racing-like position.

Follow the steps in this video to move the headset spacers below the stem and lower the handlebars on your bike.

Aligning your handlebar

Check out this video to learn how to align your handlebars.

Adjusting the height of your saddle

Your ST 540 bike frame is fitted with a quick-release lever.

Stand next to your saddle. Tilt the quick-release lever to unlock it. Pull the saddle up or push it down to bring it level with your pelvis.

Tilt the lever again to lock it.

To make sure you get it right, take a look at our tutorial video.

Adjusting the tilt of your saddle

Check out this video to learn how to adjust the tilt of your saddle.

Bedding in your brakes

When you first get your bike from the store, the brake pads and discs are brand new and therefore the initial braking performance is very low (weak). A sharp prolonged braking action (for example, during a descent) with brakes that have never before been used can cause the pads to overheat and "glaze over".

To ensure that your brakes perform well, we recommend you bed them in. This takes about 10 braking actions per brake. For each braking action: apply a single brake to slow the bike down from about 25 km/h to 5 km/h without fully blocking the wheel. Repeat with the other brake.

Positioning your brake levers

Check out this video to learn how to orient your brake levers.

Changing your pedals

Check out this video to learn how to replace your pedals.


The right equipment in case of a hiccup

You need to have the right equipment with you when you're out and about on your mountain bike so that you can take care of a puncture, a broken chain or any other type of setback. Here's a selection of products that can get you out of a tight spot or two.

Have a problem?

A wheel is bent

When you take your new bike out for a ride for the first time, a lot of parts can shift and fall into place.
You'll hear the spokes on your wheels creak because of the residual torsion in them.
Your bike is equipped with sturdy double-walled rims (on the inside of the wheel), so your wheels should be straight and not bent.
In the unlikely event a wheel is or becomes slightly bent or twisted, please bring your bike to any Decathlon workshop and they will make the adjustment free of charge as part of the free tune-up available within 6 months of the date of purchase of the bike.

Message for parents: Some technical moves performed by young riders (wheelies, skids, jumping etc.) can result in play in the rear hub or warping of the wheels if performed too often.If your child performs these tricks on a regular basis, speak to them and let them know the problems they can cause.

wheelies and buckling of the ROCKRIDER ST 100 mountain bike's wheels
Repairing a flat

Unfortunately, a flat tyre is something that can happen to any of us.

- The terrain (thorns, brambles, glass, nails, etc.)

- Or the way the bike is used (jumping over obstacles such as: stones, steps, kerbs, potholes, etc.)are often the cause of, respectively, perforation punctures (small holes) or pinch punctures (small slits close together).If there are multiple punctures, this may instead be explained by:

- Incorrect assembly of the wheel in our factory causing a spoke head to pierce the inner tube

- A faulty inner tube or tyre (with holes)

- A poorly repaired puncture and a foreign body (spike, glass, metal shard, etc.) left in the rim or tyre.It's important to correctly diagnose the puncture and remove any foreign bodies before repair.Don't know how to remove/put back a tyre, or how to repair or replace an inner tube?

1- The simplest thing is to not even touch your wheel. Instead, get yourself out of trouble using a puncture repair spray:

Screw the end of the sealant tube onto the valve of the flat tyre (valve should be in the lower position) and squeeze and hold to inject the foam into the inner tube. The tyre should become full and firm once more, allowing you to get back home safely.

2- To repair or replace the inner tube yourself, please refer to one of the video tutorials which you'll find below.

Rockrider ST 100 MTB Tyre Puncture
Rear gears don't shift properly

There are several things you can do to ensure your rear gears shift properly:
1. Check the position of the housing ends:

1a. Housing ends that are out of position can obstruct the derailleur cable when it is being pulled and prevent the gears from shifting smoothly. If a housing end is out of position, push it back into place.

1b. If the derailleur is not moving even after you have engaged and disengaged the grip shifter, it probably means that the cable and its housings have seized up. You will need to have the cable and housings replaced.

You can opt to replace them yourself by watching this video, or bringing your mountain bike to a Decathlon workshop.

2. Check that the derailleur dropout isn't bent:
A bent hanger causes the derailleur to be out of alignment and therefore unable to function correctly. Stand behind your bike and check the alignment of the derailleur.
If the hanger is bent or broken, please visit your nearest Decathlon workshop to have the derailleur hanger replaced. You can also replace it yourself by following the instructions in this video tutorial in the "BROKEN HANGER" section

REMEMBER: You can have all the settings on your bike checked for free in the first six months following the date of purchase.

NB: If you regularly ride your MTB in wet or muddy conditions, or if you regularly wash your bike with lots of water, then your cables and cable housing will need to be replaced more frequently. Washing your bike using a high pressure hose is highly discouraged as it can push dirt and dust into the cable housing.

The brake lever touches the handlebar too easily before braking starts

If your brake lever feels spongy and/or touches the handlebar before your bike starts to slow down: You need to bleed the brake system.

Visit one of our Decathlon workshops to get our technicians to do this for you.

Your derailleur hanger is bent

A bent hanger causes the derailleur to be out of alignment and therefore unable to function correctly.

Stand behind the bike and check the alignment of the derailleur.If the hanger is bent or broken, please visit your nearest Decathlon workshop to have the derailleur hanger replaced. You can also replace it yourself by following the instructions in this video tutorial.

Your chain has broken

Did your chain break? You have two options:

1- You can repair it yourself using our video tutorial. You'll need a quick-link and a chain tool. 

2- Visit a Decathlon workshop to have the operation done by one of our technicians.

Video tutorials

The following tutorial videos tell you everything you need to know to repair or replace certain parts on your bike.

- Installing/removing a rear wheel                                            - Repairing a flat tyre

- Changing an inner tube                                                       - Adjusting the handlebar height

- Repairing a chain                                                                   - Replacing the derailleur hanger

You'll find more helpful video content on our YouTube channel. Check it out!







Maintaining your mountain bike

Cleaning your mtb

To clean your bike properly, you'll need some bike cleaner, a sponge, and a brush.

Rinse off the bike with a hose and apply the bike cleaner.

Next, use the sponge and brush to apply the cleaner effectively.

It's essential to give the bike cleaner some time to act before rinsing the bike off.

When hosing the bike off, make sure you do so from a few steps away so as not to damage the mechanical components.

Lastly, dry your bike using a cloth that is dry, clean and soft.

Cleaning and lubricating your drivetrain

To clean and lubricate your drive train, you will need a degreaser spray, a soft bristled brush and a lubricant.

The first step involves covering the brake disc with a clean cloth to prevent any lubricant from getting on to it.

Next, spray the degreasing agent onto the entire drivetrain, scrub the cassette, the chain, and the rollers on the derailleur with the brush.

Let it sit for a few minutes before rinsing with a hose from a moderate distance.

Wait a little while to let the drive train dry before moving on to the greasing step.

For greater effectiveness, shake the can of bike lubricant and spray on the inner side of the chain.

Replacing a drivetrain cable

Is your drive train cable dirty, rusty, damaged, or do you find changing speeds to be difficult or unreliable? 

If so, you need to replace your drive train cable. To do so you'll need a pair of pliers, a screwdriver, a wirecutter, an Allen key, and a new set of derailleur cables and cable housing.

First, remove the cable from its housing. Remove the hood from the gear shifter, move the indicator to the last gear and cut the cable. This will allow you to remove all of the cable and then the housing.

Cut the housing to size and fit the end caps on the end of the cable, which is now ready to fit.

Install the cable on the shifter and pull it through the housing. Once done, put the cover back on the shifter and attach the cable to the derailleur. To adjust the drive train, tighten the cable if you have a hard time shifting to higher gears, and loosen it if you have a hard time shifting to lower gears.

Once adjusted, cut the cable and put a cap on the extremity using a pair of pliers.

Removing your rear wheel

Check out this video to learn how to remove your rear wheel.

Repairing a flat tyre

To repair a flat tyre, you will need: a bicycle pump, a basin with water, a dry cloth, and an inner tube repair kit.

Partially inflate the inner tube. Submerge the inner tube into the water to locate the puncture by the source of the bubbles.

Once you have located the puncture hole, dry off the inner tube with the cloth and rub the spot to be repaired using the sandpaper included in the inner tube repair kit.

This prepares the inner tube for glueing and ensures that the patch sticks to the inner tube as securely as possible.

Generously apply glue to the inner tube around the hole and wait 3 to 5 minutes.

Then apply the patch to the hole and hold it in place for a few minutes.

You can then fit your inner tube back into the tyre.

Replacing the brake pads on mechanical disc brakes

To do this, you will need: brake pads, a flat head screwdriver, and a 3 mm Allen key.

First, remove the wheel. Next, use a large flat head screwdriver to separate and remove the pads, and put the pistons back into their original position.

Next, remove the pin that holds the pads, and remove the pads from their casing. Prepare the new brake pads by placing the return spring between them.

Insert the new pads in the brake calliper and then put the pin back in place to complete the process.

Put the wheel back on and do a visual inspection to check that the brake pads are in their proper place and do not rub against the disc.

Replacing your derailleur hanger

To do this operation you will need a new derailleur hanger that fits your bike (see the section on "SPARE PARTS"), and a 5 mm Allen key.

Remove the bike wheel as well as the damaged derailleur hanger using suitable tools.

Position the new hanger on the frame.

Remove the old hanger from the derailleur before installing the new hanger using the 5 mm Allen key.

Then install the derailleur onto the new hanger and check that you can change gears properly.

Replacing the chain

To do this, you will need: a chain tool, a new chain, and a quick-link.

Put the chain on the cog and on the smallest chainring. 

Remove the quick-release link using the quick-release chain tool and then remove the chain from the drive train.

Put the new chain on the last of the cogs and on the smallest chainring. This makes it easier to determine its optimal length.

Pull the chain down, pass it under the upper pulley of the derailleur.

Once you've defined the correct length, use the chain tool to cut the chain.

Lastly, install the quick-link onto the chain, turn the pedal so as to position the quick-link on the upper part of the chain, and use your hand to apply pressure and ensure it is firmly locked in place.


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User guides


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Our commitments

Rockrider provides a lifetime warranty on your MTB's frame, handlebar and stem (under normal conditions of use).

All other parts have a 2-year warranty.

When you start riding your bike, some components will move slightly. This is why we offer a free tune-up of your mountain bike within six months of purchase.