Started by the Pedalwise team from official manuals, support pages and repair videos

A brake rotor is the thin metal disc bolted to the hub that the pads clamp to slow the wheel. A bent, worn or contaminated rotor causes rubbing, noise and weaker braking.

What it's used for

Small bends can often be trued. Park Tool says a rotor is true enough when the wobble is smaller than a business card's thickness (Park Tool rotor truing). It says to replace a rotor that is badly bent, especially from an impact, or one that shows no improvement after a few minutes of work, and to replace it if you are unsure (Park Tool).

What to look for

• The same size and mount as the original. Your bike's manual or the brake maker's site lists them.
• Pad compatibility. Park Tool notes some rotor and pad combinations are incompatible, so check the markings on the rotor and the pad packaging (Park Tool pad guide).
• Wear limits. For a worn rotor, the brake maker's manual gives the minimum thickness. Use that figure rather than a guess.

Using it safely

• Rotor edges are sharp and can cause serious cuts when the wheel spins (Park Tool).
• Keep the rotor free of oil and grease. Park Tool lists a dark surface that smears as a sign of contamination (Park Tool).
• Loose mounting bolts or a loose lockring can stop a rotor seating on the hub (Park Tool). Tighten to the maker's value with a Torque wrench.
• Rub can also come from caliper misalignment (Park Tool caliper alignment).

Guides that use it

• Clean and true brake rotors
• Replace disc brake pads
• Bed in disc brakes
• E-bike brakes

Sources

• Disc brake rotor truing, Park Tool
• Disc brake pad removal and installation, Park Tool
• Hydraulic disc brake alignment, Park Tool