How to Adjust Bike Brakes

Brakes generate three complaints and they have three different causes: a pad rubbing (the caliper is off-center), a lever pulling to the bar (there is cable slack), and a squeal (alignment on a rim brake, contamination on a disc).

All three are fixable in a few minutes with a hex key. One safety note before anything else: test at walking pace before you ride properly. If a brake does not feel right after adjustment, do not go and find out at speed.

What you need

• A 5mm hex key for most caliper bolts, and often a 4mm and 3mm
• Your fingers, for the barrel adjuster
• A torque wrench, if the bike has any carbon parts
• Isopropyl alcohol and a clean rag, for disc rotors

Problem 1: the lever pulls too far

If the lever comes close to the handlebar before the bike slows, there is slack in the system — from pads that have worn thinner, or a cable that has stretched.

The fix

1. Find the barrel adjuster. On road bikes it is usually at the caliper; on flat-bar bikes at the lever.
2. Turn it counterclockwise one full turn. This lengthens the housing, which effectively shortens the cable and moves the pads inward.
3. Squeeze the lever and check. You want firm resistance with the lever roughly halfway to the bar.
4. Repeat one turn at a time until it feels right.
5. Spin the wheel to confirm the pads are not now rubbing.

If the adjuster runs out of thread: wind it back in almost all the way, loosen the cable pinch bolt at the caliper with a hex key, pull a few millimeters of cable through with pliers, and retighten. Park Tool publish around 4 to 5 Nm for a brake cable pinch bolt — firm, not heroic. Then fine-tune with the barrel adjuster again.

If the lever feels spongy rather than merely long: on a rim or mechanical disc brake that is usually a frayed cable or compressed housing. On a hydraulic brake it means air in the system, and that is a shop job.

Problem 2: a pad is rubbing

Spin the wheel and listen. A regular scrape once per revolution is a buckled wheel, not a brake. A constant scrape is the caliper sitting off-center.

Rim brakes

1. Check the wheel is properly seated first. A wheel not sitting square in the dropouts is the most common cause and takes ten seconds to rule out: open the quick-release, push the wheel fully home, close it.
2. Loosen the caliper mounting nut slightly— the bolt that passes through the frame or fork.
3. Hold the caliper centered over the rim so the gap is equal on both sides.
4. Retighten while holding it there. Park Tool’s published figure for a dual pivot mounting nut is typically 6 to 7 Nm.
5. Spin and check. Many calipers also have a small centering screw on the side for fine adjustment.

Disc brakes

This is the standard procedure and it works remarkably well:

1. Loosen the two caliper mounting bolts about half a turn each — enough that the caliper can shift, not enough that it falls off.
2. Squeeze the brake lever and hold it. The caliper self-centers over the rotor.
3. Still holding the lever, retighten both bolts evenly, a little at a time, alternating between them.
4. Release and spin the wheel. Repeat if it still rubs.

If it still rubs after several attempts, the rotor may be slightly bent. Spin the wheel and watch where the rotor moves sideways — a rotor truing fork straightens it, and a shop will do it in minutes.

Problem 3: squealing

On rim brakes: usually toe-in

Loosen the pad-fixing bolt, angle the pad so the front edge contacts perhaps half a millimeter before the back, and retighten. Park Tool publish approximately 6 to 8 Nm for a pad-fixing bolt.

While you are there, check the pad hits the braking surface of the rim squarely— not overlapping the tire (which will cut it) and not below the rim edge (which will let it dive into the spokes).

On disc brakes: almost always contamination

Any oil on a disc rotor causes squeal, and that includes fingerprints. Chain lube overspray is the usual culprit.

1. Clean the rotor with isopropyl alcohol and a clean rag. Never with a general degreaser, which leaves residue.
2. Handle rotors by the edge from now on.
3. If it persists, the pads are contaminated and they are porous, so they do not clean. Replace them.

Note that new disc brakes squeal until they are bedded in. Ten to twenty firm slowdowns from moderate speed, without coming to a complete stop, transfers a layer of pad material onto the rotor and usually quietens them.

When to check pad wear

• Rim pads: most have wear grooves molded in. When the grooves are gone, so are the pads. Also check for grit embedded in the surface, which cuts the rim.
• Disc pads: look through the caliper. Manufacturers generally specify replacement when the friction material is down to around 0.5mm above the backing plate.
• Both: uneven wear side to side means the caliper is off-center. Fix that first, or the new pads will wear the same way.

If the pads turn out to be the problem rather than the adjustment, the brake pad guide covers the replacement thresholds and how to work out which shape your caliper takes — which is the part that trips people up, because a pad fits a caliper rather than a bike.

What to leave to a shop

• Hydraulic bleeding. Needs a brand-specific kit, and the failure mode is brakes that do not work.
• Anything that came loose without explanation. A caliper bolt that worked itself out has a cause worth finding.
• A rotor that is visibly bent or a rim with a cracked braking surface. Both are replacements, not adjustments.
• A bike you have adjusted and still do not trust. Brakes are the wrong component to be uncertain about, and twenty dollars of shop time is a good trade for confidence.