How to adjust bike disc brakes (rotors) on a mountain bike or any bike to avoid rubbing and squealing

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BEFORE YOU START

You mainly need a set of Allen keys to adjust your bike's discs (rotors).
Adjusting the bike's brake discs and pads remains a simple intervention provided you proceed with method and patience.
This is shown on a mountain bike (MTB) but the same applies to any other type of bicycle fitted with rotors.

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Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction.
Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.

Understanding how bicycle disc brakes (rotors) work

Unlike bicycle cantilever brakes that push rubber pads on to the wheel trim, this brake system is similar to the one found in cars.
A perforated disc (also called rotor) rotates along with the wheel and is slowed down by the friction of two pads.
The mechanism is operated by the brake cable.
While using your bike, the rotor could get warped which will generate a rubbing noise and sometimes a squealing noise.
Also as a normal wear, the brake pads thickness will be reduced which requires to adjust the gap between the pads and the disc for keeping your bike's brakes responsive and efficient.

The bicycle's brake caliper is shown here. Note well:

The two bolts that fix it to the wheel fork and allow its tilting adjustment.
The pad to the cable lever side (left) which moves with and can be adjusted with the cable length.
The pad to the opposite side (right in this case) which is fixed and can be adjusted with an Allen key.

Adjusting bicycle discs and disc brake pads in 3 steps

Step 1: Tilting the brake caliper until pads are parallel to the disc.

If your bicycle's brake pads are touching the disc on part of a complete wheel turn, you might need to tilt the whole bicycle brake caliper until pads are parallel to the rotor.
Loosen the adjustment bolts of your bike's brake caliper as shown below and tilt the caliper with your hand then tighten the bolts again.

Step 2: Adjusting the bike's brake disc and the wheel as well

Having checked first the caliper tilting as explained above, and in case the bicycle's disc still touches a pad on part of the wheel turn, proceed as follows:

Rotate your bike's wheel slowly and check if it is not simply badly fitted on its seat in the bicycle fork. Check if the wheel is parallel to the bicycle frame. If needed, slacken the wheel fixing nuts, move the wheel in its seats until being equidistant to the bicycle frame, then tighten the nuts again.
Make sure to rotate the wheel with your hand slowly while looking at the brake pads for checking when exactly the disc touches the pad. Rotate the wheel so you can put your thumb on that particular point of your bicycle's brake disc and apply a strong pressure for bending the disc and correcting its warping.

Step 3: Adjusting the bicycle brake pads gap

Adjust first the fixed non moving brake pad of your bike's caliper with an Allen key. Bring it to a gap of less than 2mm with the brake disc.
Loosen the bolt that holds the brake caliper cable and pull the cable with your hand until the moving pad is at the same distance from the rotor, then tighten the cable bolt.
Try your bicycle brakes several times before riding it, and re-adjust if needed.