Start with the quick visual check

Before you touch any tools, spin each wheel by hand and watch the brake pads. They should sit evenly on both sides of the rotor — the metal disc attached to the wheel — with a gap of roughly 1 to 2 millimetres between pad and rotor. If one pad is rubbing the rotor while the wheel spins, or if both pads are dragging, the caliper (the part that holds the pads) is misaligned and needs adjustment.

Stop the wheel and squeeze the brake lever. The pads should clamp the rotor smoothly without the lever traveling more than halfway to the handlebar. If the lever goes nearly to the bar before the brake engages, your pads are worn or the system needs bleeding — a separate job covered later. If the lever feels spongy or soft, air is trapped in the brake line and the system needs bleeding before any other work.

Key Takeaways

  • Disc brake adjustment usually means moving the caliper sideways so both pads sit evenly on the rotor, not replacing parts.
  • Most hydraulic disc brakes self-adjust as pads wear, so if one pad is dragging, the caliper itself is out of position.
  • Mechanical disc brakes have a barrel adjuster on the lever or cable that lets you pull the pads closer without moving the caliper.
  • A soft or spongy brake lever means air is in the line and requires bleeding, not caliper adjustment.
  • Rotor rub that happens only when you brake hard usually means the rotor is bent, not the caliper.

Adjust a hydraulic disc brake by moving the caliper

Hydraulic disc brakes use fluid pressure to push the pads, and they automatically move the pads closer as they wear. If one pad is rubbing while the wheel spins freely, the caliper itself has shifted out of alignment. You will need a 5 mm Allen key (hex wrench) and sometimes a T25 Torx key, depending on your brake model.

Locate the two bolts that hold the caliper to the frame or fork. These are usually on the back of the caliper, facing away from the rotor. Loosen both bolts by one or two turns — do not remove them completely. Spin the wheel again and watch which pad is closer to the rotor. Gently push the caliper toward the side that is rubbing until both pads sit evenly. Once they are centered, hold the caliper in place and tighten the bolts in a cross pattern: tighten the top bolt, then the bottom, then the top again. This prevents the caliper from twisting as you tighten.

Spin the wheel one more time to confirm the rub is gone. If the pads still drag on one side, loosen the bolts again and make a smaller adjustment. Hydraulic calipers are sensitive — a 1 or 2 millimetre shift often makes the difference.

Adjust a mechanical disc brake using the barrel adjuster

Mechanical disc brakes use a cable to pull the pads toward the rotor, and they do not self-adjust. As the pads wear, you need to pull the cable tighter to keep the pads close. Most mechanical brakes have a barrel adjuster — a threaded collar — on the brake lever or where the cable enters the caliper.

Spin the wheel and watch for rub. If both pads are dragging evenly, the cable has stretched and you need to tighten it. Turn the barrel adjuster counterclockwise (away from you) by half a turn. Spin the wheel again. Repeat in half-turn increments until the pads sit 1 to 2 millimetres away from the rotor on both sides. Do not turn the adjuster more than two full rotations — if you reach that point and the pads are still dragging, the cable needs replacement.

If one pad is rubbing while the other is not, the caliper itself is misaligned. Loosen the two caliper bolts slightly, center the caliper the same way you would on a hydraulic brake, and retighten. Then use the barrel adjuster to set the pad gap.

Fix a bent rotor that rubs only under braking

If the rotor rubs only when you squeeze the brake lever hard, the rotor is bent, not the caliper. A bent rotor will not rub when the wheel spins freely because the pads are not pressing against it. Spin the wheel without braking and watch the rotor pass through the caliper. If it runs straight, the rotor is true and the caliper is fine.

To straighten a slightly bent rotor, you can use a rotor truing tool or an adjustable wrench. Place the tool on the rotor where it is closest to the caliper, and gently bend the rotor back into line. Work slowly — a quarter turn at a time — and check your progress after each adjustment. If the bend is severe or if the rotor has cracks, replacement is safer than repair.

Bleed a hydraulic brake if the lever feels soft

A spongy or soft brake lever means air has entered the hydraulic line. This is not a caliper alignment problem — it is a system problem that prevents proper braking. Bleeding removes the air and restores firm lever feel. The process varies by brake model: some use a syringe and hose, others use a lever bleed kit, and a few use a catch bottle.

Check your brake manual for the exact steps for your model — Shimano, SRAM, and Magura all have different procedures. In general, you will attach a syringe or hose to a bleed port on the caliper, push fresh fluid through the system, and watch for air bubbles in the hose. Once the fluid runs clear and bubble-free, you close the port and test the lever. Bleeding usually takes 15 to 30 minutes and requires the correct hydraulic fluid for your brake — using the wrong fluid can damage seals.

Replace brake pads when they stop working

Brake pads wear down over time and eventually stop clamping the rotor effectively. If you have adjusted the caliper and barrel adjuster but the brake still feels weak, or if the pads are visibly thin (less than 1 millimetre of friction material left), replacement is the next step.

Remove the wheel and locate the pad retention pin or clip. Most pads slide out sideways or downward once you remove this pin. Slide the new pads in, making sure the friction material faces the rotor. Reinstall the retention pin and spin the wheel to confirm the pads sit evenly. Squeeze the brake lever several times to bed the new pads to the rotor — this helps them grip properly. The first few rides may feel slightly less powerful until the pads fully bed in.

Frequently Asked Questions

Why does my brake rub on one side even after I adjust the caliper?

If the rub returns after adjustment, the rotor may be bent or the caliper bolts may not be tight enough. Spin the wheel without braking and watch the rotor. If it wobbles side to side, the rotor is bent and needs straightening or replacement. If the rotor runs straight, tighten the caliper bolts firmly — they may have loosened during riding.

Can I adjust my brakes without removing the wheel?

Yes. You can loosen the caliper bolts and adjust alignment, and you can turn the barrel adjuster on a mechanical brake, all without removing the wheel. However, you should spin the wheel by hand to check your work, which is easier with the wheel off the frame.

How often should I adjust my disc brakes?

Hydraulic brakes rarely need adjustment because they self-adjust as pads wear. Mechanical brakes may need a barrel adjuster turn every few months as the cable stretches. If you are adjusting more than once a month, the pads are probably worn and need replacement.

What is the difference between a rotor rub and a caliper rub?

A caliper rub happens when the caliper is misaligned — one pad drags while the wheel spins freely. A rotor rub happens when the rotor itself is bent — the rub appears only when you brake and the pads press against the rotor. Caliper rubs are fixed by moving the caliper. Rotor rubs are fixed by straightening or replacing the rotor.

Do I need special tools to adjust disc brakes?

You need a 5 mm Allen key for most hydraulic calipers and a T25 Torx key for some models. Mechanical brakes need only your fingers to turn the barrel adjuster. A rotor truing tool helps straighten bent rotors but is not required for basic adjustment. Most adjustments can be done with tools you already have.