How to Bed In New Brake Pads

How to Bed In New Brake Pads

New pads don’t reach their full braking power until they’ve been bedded in. If you take a fresh set straight to a steep descent, you’ll either be alarmed at how weak the brakes feel, or you’ll glaze the pads in the first 30 seconds and ruin them before they ever performed properly.

Bedding takes about 5 minutes and it’s the easiest brake job in this whole series. Skip it at your own risk.

What bedding actually is

Two things happen during the bed-in process:

  1. Pad material transfers to the rotor. A thin, even layer of pad compound deposits onto the rotor surface, filling its microscopic pores. Most braking force comes from this pad-on-pad-material contact, not from pad-on-bare-steel.
  2. The pad surface conforms to the rotor. New pads have tiny irregularities (asperities) on the friction surface. Bedding wears those flat against the rotor, giving you full contact area.

Once both are done, the brakes are at full strength and the lever feel sharpens up noticeably.

The opposite of good bedding is glazing. Glazing happens when you generate too much heat in one spot, usually by dragging the brake or by panic-stopping with brand new pads. Glazed pads have a shiny, hardened friction surface that doesn’t bite. You can sometimes sand them back to life, but often they need to be replaced.

The procedure

You’ll need:

  • A flat or gently sloped road, gravel path, or empty parking lot
  • No traffic
  • A few minutes

The basic version:

  1. Get the bike up to about 25 km/h (15 mph).
  2. Apply one brake firmly but smoothly. Slow down to about walking pace. Don’t lock the wheel. Don’t come to a complete stop.
  3. Release the brake and accelerate back up to speed.
  4. Repeat 15-20 times for that brake.
  5. Then do the other brake the same way.

If you’ve got a long gentle descent available, you can do both brakes at once, using long even drags down to walking pace. Then turn around, climb back up (letting the rotors cool on the way), and do another pass.

The rules

  • One brake at a time if you’re on flat ground. Doing both at once on a flat road means you have to pedal hard to get back up to speed between every stop. Single-brake bedding gives the other brake time to cool while you work the first one.
  • Never lock the wheel. A locked wheel doesn’t deposit pad material evenly. It dumps a big patch in one spot, which causes vibration and pulsing forever afterwards.
  • Never come to a full stop on a hot rotor. If you stop with the pad pressed against a hot rotor, you’ll print a pad-shaped patch into the rotor surface that you can never grind out. Always slow to walking pace, then release the brake before fully stopping.
  • Let things cool between passes. If you’ve done 5-6 hard stops in a row and you can smell the brake, give it a minute. Hot pads on a hot rotor are how glazing happens.

The parking lot variation

If you don’t have a long open road and you’re stuck in a flat parking lot, you can speed up the bedding process with water.

Pour a thin stream of water onto the rotor as you do the slowing drags. The water plus the abraded pad material forms a slurry between pad and rotor, which acts a bit like a sharpening stone: it abrades both surfaces more aggressively than dry bedding. This gets the pad surface conformed to the rotor faster, in less space.

Still apply the same rules. No lockup, no full stops, smooth pressure.

How do you know when they’re bedded?

Two signs:

  1. The rotor surface looks darker and more uniform. A new shiny rotor will pick up a slight grey tint across the braking surface as pad material deposits onto it.
  2. The lever feels firmer and the brakes bite harder. You’ll notice the moment the pads “come in.” It’s a clear step up in stopping power, not a gradual change.

Once both are happening, you’re done. The pads will continue to settle in over the first few real rides, but they’re at usable strength immediately.

When to re-bed

Any time you change pads, change rotors, or contaminate a rotor and clean it. Each combination of new components wants its own bed-in. Sintered pads on a previously-resin-bedded rotor will need a re-bed, for example.

If you’ve ridden new pads without bedding them and you’ve ended up with weak or noisy brakes, you can sometimes recover by bedding properly now. If they’ve fully glazed, sand them flat with 80-grit sandpaper (on a flat surface, not by hand) and re-bed, or just replace them. Fresh pads here if it’s gone too far.

This article is based on Park Tool’s video How to Bed In Disc Brake Pads.

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