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Disk brakes are becomming more popular on bikes now, and I was just wondering what the advantage is of this type of brake over the older rim brakes.

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13 Answers 13

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Working backwards from how it works:

Not using the rim means the brake is unaffected by how straight the rim is, and heating the rotor doesn't affect the tyre. The rim is not worn away by braking and the rotor material can be selected entirely for its suitability for that one purpose. This also allows smaller clearance between pads and rotor, allowing:

Increased pressure between brake pad and rotor compared to rim brakes means disks are less affected by water or other contaminants. Pads can be made of harder material giving increased pad lifetime.

Having the brake caliper further away from the tyre means it's less affected by mud, and it can be made partly or fully enclosed to further sheild it. The rotor is also less likely to hit obstacles as it's further from the ground.

Being a hub brake makes unconventional designs possible. Single sided wheel mounts are the most obvious example, but some suspension systems are incompatible with rim brakes, and building a rim braked carbon composite wheel is much harder than building one to use a hub brake.

Disk brakes can also be fitted to both sides of a wheel for increased heat dissipation, and it's easier to vary the design for different characteristics (weight, heat capacity, modulation etc). Doing that with a rim brake means the brake manufacturer has to start selling wheels as well.

These combine to make disk brakes more reliable and easier to maintain.It's also somewhat easier to remove and reinstall wheels as you don't have to release the brake first.

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@e100: that is what I said.. –  Мסž Jun 2 '11 at 22:04
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Very good summary. On a side note, to my experience high-end v-brakes grip better than disk brakes when setup properly. Only seen them really used on trial bikes. –  krs1 Oct 17 '11 at 13:23
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V-brakes are still used on trials bikes because they are lighter, and trials is usually done in the dry - it has nothing to do with power. When I first switched to disc brakes (~10 yrs ago) they were noticeably less powerful than dry v-brakes. I'm now running 205mm Formula RX discs and they utterly obliterate any v-brake I have ever used (including hydraulic ones). –  cmannett85 Dec 23 '11 at 9:41
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"The rotor is also less likely to hit obstacles as it's further from the ground." - Perhaps in Australia, where they ride upside down. Every rim brake I've ever see up here in the Northern Hemisphere is mounted well above the center of the wheel. :-) –  Ross Patterson Dec 23 '11 at 13:41
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@RossPatterson the rotor for a rim brake is the rim. You're thinking of the caliper. –  Mσᶎ Jul 10 at 2:52
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I like disc brakes for these reasons:

  • they're easier to keep oil off than rims
  • bent wheels don't rub
  • easier to adjust
  • easier to get wheels in and out
  • my rims don't wear out

oh yes, they stop well too, but that's my last reason, not first!

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A number. Generally, they are unaffected by wet conditions, whereas rim brakes can get dicey in the wet. As well, for off-road bikes, they are less susceptible to mud, dust, and sand, and the attendant rim wear as well as poor braking. Also, on long descents or downhill sections, there is no danger of rim-heating and tire failure. Downside... You need purpose-made fork legs and wheel hubs to handle 'em , and the entire assembly is perhaps a bit heavier than traditional rim brakes.

You are seeing these now on even mid-level mountain bikes.

Oh, and you don't have to wrestle large-size tires through a tight-fit when remounting the wheel. Even with quick-release, some tires will just barely clear the brakes when putting a repaired flat back on.

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Actually, to use rim brakes you need purpose made forks, frames and rims too. Disk brakes require special rims and in some cases special spokes too. –  Jahaziel Oct 12 '11 at 18:21
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I have been using disc brakes on my Mountain, Cyclocross, and Road bikes for well over 10 years now. Earlier disc brake versions certainly took a while to reach excellent, smooth, and modulated braking power levels that they currently enjoy. In that context, a poorly adjusted or designed disc brake vs. a well adjusted v-brake showed less performance capabilities.

However, in recent years (5+), the technology surrounding disc brakes has increased dramatically. Particularly with hydraulic disc brake systems. Hydraulic disc systems tend to have significantly more stopping power than any rim brake system I have used. One other side effect of the additional stopping power is the ability to "modulate" that power much more smoothly. You can control how much power you use a lot more easily.

As stated above - there are different maintenance requirements with disc brake systems than with rim brake systems. However, typically they are no more onerous to learn than other maintenance protocols for any bike part.

In addition to hydraulic disc brake systems, there are mechanical versions which use your traditional cable to provide the lever to caliper clamping power on the disc rotor. These systems have the advantage of being usable with shift/brake integrated lever systems (commonly found on road bikes or bikes with "drop bars").

I have found the mechanical disc brake systems to not have as much power and modulation as hydraulic systems. In addition, they tend to require a lot more maintenance/tweaking to keep them working perfectly smoothly. The pad contact points are a lot more susceptible to making noises or dragging as they wear. Mechanical systems clamp from only one side. One pad is fixed in place, the other pad is pushed against the rotor slightly warping it into the fixed pad to provide the stopping power.

Hydraulic systems mostly have two separate calipers that push the pads from both side, (typically) providing stopping power from both sides, without warping the rotor (much).

Rim brake system tend to wear our the rim surface of the wheel if they are used in wet weather conditions. As grit gets on the rim, and you brake, the grit essentially 'sands down' the rim over time. Eventually you'll have to replace the rim as it is worn out. The thinner the rim gets, the more likely that heat transferance from the braking action can affect the rubber of the tire itself, sometimes causing catastrophic failure (exploding tire). This is fairly rare, and requires circumstances to be "just right" (i.e. well worn rims with thin side walls, possibly mis-adjusted brake pads, and long extended descents where the rider is "dragging" their brakes constantly causing heat buildup, tire casings that don't handle heat well, etc...).

Generally speaking, the maintenance requirements for rim brakes and hydraulic disc brakes tends to be about the same. Over time, you may need to have the hydraulic brake lines "bled" to keep them in good performance. However, most modern hydraulic brake systems typically don't need to be bled that often. I find my mountain bike hydraulic systems to require it only after 18 to 24 months of riding (I typically ride about 3,000 miles on my MTB in that interval).

Otherwise, it's simply a matter of replacing pads as they wear out. I do believe that disc brake pads will tend to wear out faster than rim brakes. They're simply smaller in surface area, and have a lot more heat demands placed on them. This is not true in foul weather riding conditions though - since wet/sandy conditions tend to affect rim brake pads a lot more than disc brake pads.

A lot of people will cite that disc brake systems are heavier. This is true in general. However, the majority of the 'extra weight' is non-rotational weight, which has a lot less effect on the ride quality or feeling of a bike. Since the weight is at the axle area, the weight is fairly insignificant.

Rim brake systems require thick, heavy tracks for the pads to press against. This requires that a rim brake wheel rim be significantly heavier than a disc brake rim. All of that weight is rotational mass at the outermost edges of the wheel. Any additional weight in this area is significantly increased in terms of the feeling/impact of that weight.

I often see rims made for disc brake applications that average anywhere from 100 to 250 grams lighter in weight than their rim brake counterparts. This is a significant amount of weight when it is at the worst possible location.

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A lot of good answers already - but one big disadvantage of disks is that has yet been mentioned is their (documented) ability to eject the front wheel when using a tradition QR axle. The torque generated on the axle (for a normal rear mounted disk caliper) is down - the same direction as the dropouts. Its been shown that even properly tightened axles can come loose - usually with large (200mm or greater) disks, but loose a QR can come undone very easily.

As a result, "Lawyer Lugs" are pretty much mandatory on Disk equipped front wheels (Unless a through axle is used). The problem with Lawyer Lugs is they somewhat defeat the advantages of a the QR, in that to remove the wheel, you have to unscrew the nuts quite along way.

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Since you say that it's documented, could you provide a link? I'd love to read that. –  jimirings Mar 23 '13 at 15:55
    
@jimrings: Here ... ne.jp/asahi/julesandjames/home/disk_and_quick_release –  mattnz Mar 24 '13 at 21:23
    
Interesting stuff. Thanks! –  jimirings Mar 25 '13 at 16:23
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They work even when it's wet (I think that's because rims get wetter because they're closer to the ground; and, because they have a bigger surface area, they take longer to dry).

Brakes that work when it's wet are especially useful when in traffic, or going downhill.

Good brakes might also be useful on a cycle path in the evening: it seems that small children may find a flashing front light attractive, and hurry into your path to get a better look at it.

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I'm not sure I would get disk brakes again. I used to have v-brakes, but thought disk brakes would be better.

The advantages stated are true but I've found:

  • They are harder to maintain. I was able to make simple adjustments to my v-brakes very easily, but I don't know where to start with disk brakes. (This could just be lack of knowledge on my part)
  • If you get oil on the disk and it gets on to the pads they will squeak badly and the pads may need replacing (Seems obvious now, but I just needed to be more careful when cleaning my bike and use a clean cloth for cleaning the disks)
  • The stopping power seems caparable to my old v brakes

My problems with disk brakes could probably be fixed by a little bit more knowledge, but if you're not familiar with disk brakes then these things are worth thinking about.

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So basically your "disadvantages" are down to the fact that you never bothered to learn how to setup or maintain them? –  cmannett85 Dec 23 '11 at 9:42
    
I was just trying to point out that if you're used to v brakes, disk brakes won't automatically be better. There are things you need to learn, or you may have problems. –  Richard Jan 3 '12 at 20:09
    
Oil on rim brake pads will cause them to squeak as well. –  jimirings Mar 20 '13 at 13:46
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Rim brakes are skirt-eating monsters. Disc brakes, not as much.

(Yes, there are other mitigators, but this one alone made me ask for disc brakes on the bike I'm having built. I like wearing long skirts to work.)

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I gave up skirts years ago. –  Daniel R Hicks Oct 19 '12 at 2:24
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One of the advantages given above is that a wheel that is out of true will not rub against the brake pads if using disk breaks. However I think that this rubbing with rim brakes is really the advantage precisely because it warns you that your wheel is out of true. It is not a good idea to ride in such conditions as the wheel may fail.

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A nice thing about rim brakes (any type) versus disc (any type) is the fact that they provide a guide for quick truing your wheel without taking the wheel off and putting it on the stand. Hanging my bike down on each end I can quickly true both wheels to perfection. You can't do this with a disc. And rim brakes do provide a generally cleaner look without a cable running down the fork or the rear stay. And they generally are less weight and very easy to adjust. Little things mean a lot and things do add up. Oh yeah and the pads last crazy forever which is a nicety. Fifty years of riding a LARGE number of bikes with all the kinds of brakes discussed in all conditions and my winner is a rim brake of high quality suited to your tire/riding terrain.

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I wouldn't generally agree on the "the pads last forever" argument. This will depend a lot on the type of bike and the terrain that you ride. Sandy or muddy terrain may easily consume your rim brake pads way faster than disc brake pads and concurrently weaken your rims so that you will have to replace the rims after some 1000 km. –  Benedikt Bauer Mar 21 '13 at 9:21
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One additional (rather cosmetic) advantage is that the rims stay free from grit. So you keep clean hands when changing tires.

Admittedly, thats not a reason I would invest in a disk break for; and you get the same results with ceramic-coated rims...

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Disks are way more reliable.

For example, I had a bike that had a disk in the rear of one of my bikes, in case my front brake broke.

One day it did; the whole right arm hit a tree and disabled it and the disk I was still using stopped me on the trail just fine. I then put a disk on the front since they hit stuff if you are into that type of thing.

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Welcome to Bicycles. Check out the formatting available using the icons above the answer box, to make what you write easier for others to read. I'm make an attempt at editing you answer; check it out as a guide, and make sure I have retained your meaning. –  andy256 Jul 10 at 2:30
    
Even after the edit, this is a somewhat tough post to read. –  Batman Jul 10 at 5:44
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Disc will always be better. Now there are systems lighter than v's. even a cheap set of disc brakes are better. i used traditional brakes until 2 years ago when i bought a bike with dual mechanical disc brakes and immediately felt the huge difference. its not really that they stop better but how they feel when stopping. its the same feeling from braking in a car or motorcycle. with v's braking isnt as good even if it can stop the bike just as fast. disc is more superior and dominant overall. the control you have with disc is amazing compared to v. traditional brakes will never ever have the modulation and advantages that disc will always have. facts are facts. dont care if ur a v brake fan and a weight weenie. gotta move on same day ya know? dont need them? thats fine i didnt either but they are so good i want them and i got them. never going back to traditional brakes ever again :) ya wonder why u started to see more and more disc brakes on bike eh? maybe cuz they work so dam good? try them with a professional setup not one from kmart or walmart cuz those are not adjusted correctly therefore people sometimes assume they suck. have a nice day

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I've edited out the rude portion of your answer. Per the Bicycles SE FAQ: "Civility is required at all times; rudeness will not be tolerated." Also, it's not true that discs will always be better. A couple of people, myself included, have mentioned very real disadvantages to disc brakes. The truth is that no brake (or any other component) is always better for every person in every situation. Any design has advantages and disadvantages. Which is best simply depends on what you're using it for. –  jimirings Mar 20 '13 at 13:52
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