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I've owned a couple of department store bicycles in the past with caliper brakes and I set the brakes up properly so when I squeezed the brakes the bike stopped pretty quickly.

I test-rode a bicycle from a bike shop a couple of days ago which had disc brakes, and it was just so slow to stop the bike, it seemed like the brakes were so weak. I checked the brakes on the spot by standing next to the bike and squeezing the front brake and pushing the bike forward, and there was no slippage, and same with the rear wheel. So I think the brakes were set up correctly, they just seemed to have no stopping power.

I asked the clerk about it and he said they would need to be "bedded in". I couldn't understand what he was talking about, but is it normal? And why can't I get a bike that's ready to go from when I buy it. Do I just buy a bike with weak brakes and use it for a while and after a few days the brakes will work better after it grinds a groove in or something like he said? Or were the brakes not set up correctly?

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Bedding-in is a common process with new disc brake pads. Disc brakes were developed much earlier for motorcycles and cars, from which the technology and the terminology has been transferred to MTBs: see https://ebcbrakes.com/articles/motorcycle-bed-in/ and http://www.centricparts.com/files/White%20Paper%20Revisions%204-2012/Centric%20White%20Paper%20C3-2012-Bed-In%20Stock.pdf

Bedding-in is a process in which both the pad surface microstructure but also the surface composition of the rotor is affected. During the run-in a very thin layer of material is transferred from the pads to the rotor. This surface deposit increases the brake power significantly.

However, even when the brake pads are not yet bedded-in, a disc brake should have more stopping power than a rim brake. So I wonder whether the surface of the rotor or possibly the pads have inadvertently been poisened by a lubricant. Ask the seller to clean the rotor with alcohol.

  • It should be said that if your pads have become contaminated then they should be replaced immediately; cleaning the rotor won't help. Also, bedding-in should be done in a way to prevent the pads' surface from glazing over.. i.e. try to stop as abruptly as possible rather than doing long, slow stops. – James Mar 21 '18 at 13:48
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    @James having recently faced this cleaning the rotors and replacing the pads helps a huge amount. Even if it doesn't quite get you to back to peak performance it will get you to as good as rim brakes. – Chris H Mar 21 '18 at 21:52
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I just searched and found this: https://www.sram.com/sites/default/files/techdocs/gen0000000004358_rev_a_avid_brake_pad_advancement_product_installation_update_0.pdf

This is from SRAM's website. They are a prominent disc brake manufacturer:

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 seem to think that if you accelerate to a moderate speed and then brake down firmly to walking speed about 20 times, then accelerate to a faster speed and brake down firmly to walking speed again a further 10 times, that this will be enough.

From my own experience, brand new disc brakes are not as strong as you'd want them to be, but after a ride or two they pick up in performance and are a lot stronger than they were at the start.

To answer the second part of your question (why can't I buy a bike that is ready to go): Because it would cost more. With modern manufacturing techniques being so consistent, the bike probably hasn't actually been fully assembled before you do it or get it done at the store and ride it. They would have to fully assemble it and either take it for a ride or mount it in some specialised machine in order to bed the brakes in which all takes time and money. This might cost an extra $20 on the bike price. For something which is really only a minor inconvenience it's not really worth it to most people. Bedding in of brakes is also just generally something that's accepted, even for car disc brakes.

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    If "bedding in" requires riding the bike, how is one supposed to do it "prior to your first ride"? – phoog Mar 21 '18 at 17:02
  • @phoog I would say "prior to first ride with possible dangers", it's a bit too short-cut there. – yo' Mar 21 '18 at 17:15
  • It's also pretty difficult to bed in the brakes according to their method if the bike shop is in the city centre on a busy road and you have to ride it away. Making the first few stops firm but controlled and from a respectable speed makes a massive difference, and that's close to city riding anyway – Chris H Mar 21 '18 at 21:49
  • Maybe they say "prior to your first ride" because it's not really a real ride if you're on the bike for the sole purpose of getting it working correctly. I think the meaning is clear enough. – WhatEvil Mar 21 '18 at 21:56
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Why can't I get a bike that's ready to go from when I buy it?

I would say you can. Ask your LBS to bed the brakes before you'll buy it, that is the service that your bike store is in the position to provide over a department store or online retailer.

You didn't specifically mention, in your post, if the disc brakes were hydraulic or cable. One of my kids has a bike with a cable disc brake and it does not brake nearly as well as a similar bike with a cable rim brake and far worse than the bikes I have with hydraulic discs.

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I believe bedding means letting the brakes wear out slightly so it sits perfectly on the disc because the disc is not completely flat and neither are the brake pads.

  • I'm just confused because there's nothing about "bedding" in the 50-page owner's manual from the manufacturer's website, even though it has an extensive and detailed section on how brakes work and how to adjust them effectively. – user37012 Mar 21 '18 at 7:57
  • Is this the owners manual from the brake manufacturer or from the bike manufacturer. Most likely the owners/technical manual of the brake will highlight this point. – nollak Mar 21 '18 at 8:38
  • True, it's from the bike manufacturer, so I'll check out the brake manufacturer's manual. – user37012 Mar 21 '18 at 9:28
  • Just slight off topic but if your discs "squeal" usually after they get wet you need to bed them in again. I also slightly abrade the rotor surface with fine emery paper to improve/speed up the process. – Bonzo Mar 21 '18 at 10:53
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    @Bonzo getting disc brakes wet does not necessitate re-bedding them in – Paul H Mar 21 '18 at 16:16

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