What are the negative consequences of not bedding in disc brakes?

Question

It's common knowledge that disc brakes need to be bedded in. But I've never heard or found a description of what happens if you don't bed them in.

Given the number of BSO's that now have disc brakes, and the likelihood that 99% of those never get bedded in, I'm guessing that the consequences can't be too incredibly dire.

But what are those consequences? Reduced braking power? Uneven braking power? Squealing brakes? Reduced lifespan of pads and/or rotors? Are those consequences long term? Or do the brakes "naturally" bed in with regular use and the consequences are only short term?

Answer 1

I think your last comment is the operative point - it will happen anyway sooner or later.

The technology here is basically the same as with automobiles. You start off with new pads and a clean rotor. The bedding in process involves the deposit a small layer of pad onto the rotor (mixed in with a little frictional heat).

Until you have that layer on the rotor, braking could be less powerful and uneven.

You don't ask this, but for completeness, the rotor should be cleaned whenever the pads are changed, using isopropyl alcohol. And, once the rotor is clean, the bedding-in process will start over.

You don't see an awful lot on this subject if you look on the web at bike pages, but as I say if you start looking in the context of cars, there's lots out there and it is definitely not new technology.

Answer 2

Since there has been a lot of discussion on comments on this question, I'll restate the salient points that need to be answered, though the OP stated most of them in his original question:

What are the consequences of failing to "bed in" a bicycle disc brake rotor?

The consequences of failing to bed in a rotor include reduced braking power, uneven braking power, noisy brakes, reduced lifespan of pads, though not typically the rotors.

In the main, these consequences are long term, though permanent might be an over reach. Though many people feel that a brake rotor "naturally" beds in with regular use, this is a fallacy born of a misunderstanding of the term.

Thus, I will first define the term.

Bed in, rotor: The process of transferring material, either resin or metal, from a brake pad to the surface of a brake rotor, through heat transfer, specifically depositing an even, continuous layer of pad material on the rotor, for the purpose of increasing braking friction.

While normal braking does transfer some pad material to the rotor, regardless of whether the appropriate procedure is followed, that does not mean the brake is automatically bedded correctly, or that the procedure has no point. Bedding in the rotor is intended to apply pad material to the rotor in a continuous and even layer.

This is best achieved by bringing a bike up to speed, and then applying the brake smoothly and consistently to slow the bike, releasing the brake without actually stopping.

Normal braking, which for most people does include actually stopping, if done on a fresh rotor that has not been bedded in, will apply pad material in an uneven layer. Stopping during the bed in period creates a patch of material on the rotor which can cause the brake to pulse or grab during braking. Uneven braking is the second consequence of failing to bed in the brake. This is relatively long term, lasting at minimum until the rotor is cleaned of the pad material, new pads are installed, and the bed in procedure is performed.

The first consequence, which is short term, is the lack of braking power and control. On a new set of Shimano Ultegra hydraulic discs, until the brake bed in procedure is performed, the brakes essentially fail to stop the bike. While they create some drag, the wheels do not lock up, and there is no modulation. After the mechanic installing the brake performs the bed in procedure, their performance is quite good. The difference is quite obvious to anyone who has ridden these brakes in both states. This is unlikely to be an issue in the long term, unless the bike is ridden in a location or at a speed which puts the rider at risk, prior to bed in.

The third consequence, reduced pad/rotor life, is minor, and not typical, though it is mentioned by the manufacturer as a possibility.

One additional benefit of bedding in a brake is that it "trues" the mating of pad and rotor, causing the alignment of the pad to the rotor to be more precise. This has 2 primary benefits, that of silencing the brake, as the "squeal" that is typical on a new disc brake is usually caused by vibration due to the minor misalignment between pad and rotor causing "chatter" between the 2 surfaces. This portion of the bed in process does also occur through natural braking, and is the source of the fallacy that bed in will happen naturally.

The second benefit, increased brake modulation, is the result of this trued mating allowing finer contact between brake pad and rotor, due to finer tolerances in the mating of pad and rotor.

This is not to say that bedding in a brake is a life or death issue. Many people have ridden new brakes without setting them up correctly, and been just fine. But that doesn’t mean that their experience with their brakes gives them the best possible performance that they could have gotten, with just a bit more care and time during setup.

As for the idea that a BSO with disc brakes not being properly set up should set the standard that all bikes are built to, that’s a false argument. In fact, I guarantee you that the owner’s manual for that BSO says that the bike must be assembled and tuned by a professional before riding, and that the professional in question must follow the manufacturers’ recommendations when building the bike, including those for brake setup.

The fact that it is not cost effective to have a professional spend $100 worth of his or her time on a bike sold for $100, doesn’t mean that it shouldn’t happen.

Answer 3

Take SRAM for example

All new brake pads and rotors should be put through a wear-in process called ‘bed-in’. The bed-in procedure, which should be performed prior to your first ride, ensures the most consistent and powerful braking feel along with the quietest braking in most riding conditions. The bed-in process heats up the brake pads and rotors which deposits an even layer of brake pad material (transfer layer) to the braking surface of the rotor. It is this transfer layer that optimizes braking performance.

They clearly express the benefits:
consistent and powerful braking feel along with the quietest braking in most riding conditions

If normal riding achieved that SRAM would not have a specific procedure. For one they warn not to lock up the brakes.

If you deposit an uneven layer I would suspect the consequences to be permanent.

I don't get your logic on if BSO does not do it then it cannot be dire. I don't want my bike to perform like a BSO.

Service Manual
Bed In Procedure