How to Adjust Disc Brakes on a Bike

Disc brakes are excellent right up until something rubs, and then they are maddening — a faint tick-tick-tick every wheel revolution that you cannot un-hear. The good news is that the fix is almost always one of three things, and all three take a couple of minutes once you know which one you are dealing with.

Mechanical or hydraulic?

Look at what runs into the caliper. A thin steel cable in a housing means mechanical. A sealed hose, usually with a banjo fitting, means hydraulic. This determines almost everything about what you can adjust.

Centring the caliper — fixes most rub

The lever-squeeze method

1. 1

   Spin the wheel and confirm the rub

   Look through the caliper from behind. You will usually see which pad is touching, and whether it rubs all the way round or only at one point.

2. 2

   Check the axle is properly seated

   A wheel sitting crooked in the dropouts will always rub. Re-seat it first — the method is in removing a front bike wheel.

3. 3

   Loosen both caliper bolts a quarter turn

   The caliper should be able to slide sideways but not rattle around freely.

4. 4

   Squeeze the lever hard and hold it

   Both pads clamp the rotor, which pulls the caliper into perfect alignment with it.

5. 5

   Retighten while holding the lever

   Alternate between the two bolts, a little each, so the caliper does not twist as it clamps down. Around 6–8 Nm is typical.

6. 6

   Release and spin

   If it still rubs faintly, repeat — it commonly takes two goes. If it rubs only at one point in the rotation, the rotor is bent, not the caliper misaligned.

Setting mechanical disc brakes

Most mechanical disc calipers move only one pad; the other is fixed and set by a dial or an Allen key adjuster on the inboard side. If you skip this, cable tension can never give you a good result — you are asking one pad to do all the travel.

Straightening a bent rotor

A rotor is a thin steel disc and it bends if the bike falls over, if it catches on something during transport, or occasionally from heat. Spin the wheel slowly and watch the rotor pass between the pads — you will see the wobble. Mark the high spot with a marker.

• Use a rotor truing fork if you have one. In a pinch, an adjustable wrench opened to just over 1.8 mm works.
• Bend gently and re-check constantly. Steel moves more than you expect and overcorrecting is easy.
• Never touch the braking surface with bare fingers — skin oil contaminates it. Handle by the spider arms.
• If the rotor is visibly warped over a wide area or worn below its minimum thickness, replace it. Minimum thickness is usually stamped on the rotor itself.

What hydraulic brakes need instead

There is no cable to tension, so the adjustment list is short: centre the caliper, keep the rotor straight, keep everything clean. If the lever feels spongy or pulls further than it used to despite good pads, air has got into the system and it needs bleeding — a job with brake-fluid-specific kit that many people reasonably hand to a shop.

For rim brakes the whole approach is different — pad height and toe-in matter far more. That is covered in adjusting bike brakes, and symptom-led diagnosis for either type is in fixing bike brakes.