Bedding In process for brakes

Question

A few days ago, someone asked a question which touched upon the bedding-in process for their new disc brakes. Because the question did not have any answer already, I wrote one in which I said that bedding-in would happen in any case with use. I kept track of this question and, later, saw a second answer in which the responder said that there was a specific process that you have to follow, otherwise the brakes would not work properly. And I was surprised to see that this answer had several upvotes.

So my question, basically, is, Is there a specific bedding-in process which should be followed? If so, what is it and why is there a process over and above just riding the brakes in? Is it different between disc and rim brakes? Is this process different between one brake and the next? Some concrete examples would be great.

Answer 1

Proper "Bed-in" Procedure assuming pads and rotor are brand new per manufacturer's instruction (SRAM, Shimano, etc all recommend this method with slight variations).

This should be done prior to the first ride of the bike, shop employees should do this after assembly and prior to it being on the sales floor. 95% of Big box stores to do not.

1. Clean the rotor with alcohol, this is not the most important step, but it is recommended by SRAM as well as some others, but is more of a perfectionist approach as is #2.
2. Visually inspect brake pads for debris, dust, contaminants etc from shipping.
3. Select a large flat area where you can safely ride at approximately 20MPH (30 kph)
4. Begin by riding about 10-15mph (15-25kph) and firmly apply brakes until walking speed is achieved DO NOT COME TO A COMPLETE STOP Repeat this process approximately 20 times.

- Coming to a complete stop builds excess material in the spot the pad comes to rest, imagine pushing a dry erase eraser over a white board full of black marker, where it stops it leaves a build up of the ink it has removed, the physics are similar.

5. Now repeat this process but at a higher speed, around 20+ MPH (30+ kph), and very firmly apply the brakes until a walking speed is acheived, DO NOT STOP, repeat this process 10 times.

NEVER LOCK THE BRAKES UP DURING THE BED IN PROCESS for the reason described above.

-This is why casual riding does not do the job, as stopping or having to stop can ruin the entire process.

Allow the brakes to fully cool before additional riding.

The bed in process works by heating the pads and rotor which helps to apply a smooth and consistent transfer layer to the rotor. Locking the wheels up while braking during this process cause one area to be slightly heavier in deposit than others, which after every pass and stop in that position more is deposited in that one spot which eventually leads to shuddering of the brakes due to the microscopic varying of thickness.

Rim brakes do not require this procedure as the interaction between rubber and metal is much different than metal to metal (or organic) compounds. Rubber brake pads do not require as smooth as surface and are much more forgiving with surface imperfections. Thus is the reason they don't squeel and squeek nearly as bad as disc brakes.

Rubber is also a lot easier to transfer to the rim surface because of it's pliable nature, and it requires less heat to achieve this, the heat that is gained by following the above procedure is instrumental in transferring metallic substrates.

Any extra rubber that builds up on the rim surfaces will be quickly worn away in the next several passes of the wheel, metallics that have been heated, transferred and then allowed to cool (it happens quick) are a lot harder to remove as they have formed a stronger bond.

This can be explained as such: melt a piece of rubber and allow it to drip onto a piece of sheet metal and allow it to cool, now do the same with metal and try and remove both... you get the idea.

Some people also douse the calipers with cool distilled water afterwards to help the cooling process, but i personally am not a fan of this nor do i recommend it.

Sources include:

• years of industry experience on the distribution side

Related Reading: - SRAM - Village Cycle

Answer 2

For disk brakes I would follow the recommendations of the manufacturer, for example Hope have section on bedding in the pads on their disk brakes here. So before riding the bike in anger they recommend riding a short distance with the pads just scuffing on the disc followed by pulsing the brakes repeatedly so as to slow down but not stop.

With rim brakes I've never come across any requirement to bed these in - the materials and surfaces involved are very different.