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When installing new brake pads for disc brakes, manufacturers recommend to "bed in" the pads. For example, Magura recommends to go 30kph then brake hard and repeat this process 30 times.

What is exactly achieved by doing this? And what would be the risk if it's not done?

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    If you don't mind, I changed seating in the title to bedding in. The latter is the standard English term.
    – Weiwen Ng
    Commented Oct 30, 2023 at 19:58
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    @WeiwenNg sure I changed the text as well, thanks!
    – Rеnаud
    Commented Oct 30, 2023 at 20:35

3 Answers 3

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I think it is the same principle as for road cars and has the following reasons:

  • Wearing off contamination (even though a responsible mechanic should clean the rotors/pads during installation) but there might be some coating/residue.
  • Pad transfer: Getting brake pad material on the rotor will improve stopping performance and reduce squealing and noise. Brake pad against brake pad material has more traction than against the pristine rotor. A bit of "micro-wear" probably means that the pad has better contact with the rotor, too.
  • Organic pads (for example according to Rose) require an additional step of "heating up" the pads so that resin material in the pads can evaporate.

The risk is just getting into your first rides with less than optimal braking performance. I could also imagine that "conditioning" may play a role, too... for example overheating fresh discs/pads on a long descent might impair on overall performance and lifespan of disc/rotors in general.

All of this doesn't mean that brakes don't work without bedding in. Perhaps, many riders won't even notice that their brakes are not as good as they are supposed to be. So, the stopping power might be sufficient for a controlled stop but might be not when you have to go hard. This means, you should take your time for an easy ride after changing pads/rotors and perhaps don't hit a big descent right away - unless you can safely perform the procedure before it gets technical...

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    One issue is the evenness of the braking: if with new pads, or especially rotors, you do some really abrupt stops from low speeds (as you might when riding away from the bike shop in traffic), you don't get that even deposition of material on the rotors, but instead it's patchy, and you can feel that. It's worse if the whole experience is new and you lock the brakes on your early stops, as I did at the back the first time I got mechanical discs, and again the first time I got hydraulics.
    – Chris H
    Commented Oct 30, 2023 at 14:24
  • @ChrisH It seems there is more room for error than just on rim brake bikes and while some riding profiles might be a good enough break-in without thinking about it, others may not, hence, the recommendations. That being said, I was always cautious on my first rides on new pads and will definitely consider this when my gravel bike arrives next year.
    – DoNuT
    Commented Oct 30, 2023 at 14:47
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    How often do you need full braking force right out of the gates? On a mountain bike ride in properly mountainous areas, your ride will often start with 300 m - 600 m of climbing (so no braking). Once you’re at the top, the descending trail is often quite steep (2x - 4x) steeper than the climb) with short-radius turns and challenging features. In other words, if you didn’t bed-in new pads, you’re going to have a bad time and probably ruin the pads. To be clear, this describes a typical mountain bike ride for me.
    – Paul H
    Commented Oct 30, 2023 at 15:58
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    @DoNuT I actually post the question because I didn't notice a difference when changing the pads. But this bike could do very well enough with much less powerful brakes... (4-piston brakes with 57mm gravel tires, but live in a country that is almost as flat as a pancake).
    – Rеnаud
    Commented Oct 30, 2023 at 16:43
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    @Renaud In my experience, if you swap for identical pad material from the same brand, you’re already halfway there. Though I might be wrong about that and I just got lucky. In your case, you bring up a good point: 4-piston brakes are likely “overpowered” for the tires you have (depending on tread pattern and riding surface).
    – Paul H
    Commented Oct 30, 2023 at 16:46
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The main risk is that at the beginning the brake action is much weaker than the final braking force after the break in period. By accelerating the breaking in by repeatedly accelerating and braking you allow the braking surfaces to get into the right surface condition from the friction against each other.

If you do not do the accelerating break-in procedure, you will reach the strong braking action in some time anyway, but you will spend significant time riding with weak brakes. Shimano, for example, just states in the manual that the brakes have a burn-in period and that the breaking force will gradually increase during this period.

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  • Also: bedding in from scratch is needed after deep clean (e.g., if you remove pads and sand off the surface, and clean and possibly sand the rotor). Commented Oct 31, 2023 at 18:51
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The goal is to maximize braking performance.

I never do this, but my performance requirements are not that high(normal weight, non-aggressive riding, fairly flat roads).

Secondly, I only replace one part at a time, so a minor temporary drop in the performance of one set of brakes is no issue for me. I will admit that new brake pads sometimes feel worse than the old ones initially, but I think they would be able to lock my wheels whether old or new so it's not the limiting factor (tire/ground interface is limiting).

A heavy rider, with brand new rotors and pads front and back, racing down a steep hill on his first ride might get into serious trouble. So the risk depends on who you are, how you ride and what parts you replaced. The first ride after doing changes to your bike should always be done with some extra care/caution anyway IMO.

For me the risk by not doing it is negligible, for others it might be significant.

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