Disk Brakes vs. V Brakes??

Discussion in 'Road Cycling' started by Chris_MdR@gmx.net, Oct 9, 2006.

  1. Hi,

    I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
    for the first time, and would appreciate your input on my impressions:

    - On the first bike I tried, it was not possible to block the wheel
    with the disk brake. I checked and found that the disk was oily. On
    another bike (same brake) I was able to get the wheel to block, but
    with application of extreme force to the brake handle, MUCH more than
    required by any V brake I ever tried.

    Question: Are Hydraulic Brakes really weaker than V brakes, or was this
    bike just assembled by monkeys?

    - I noticed that the hydraulic disc brakes have a much 'spongier' feel
    than the cable actuated V brakes. This I guess was related to the
    hydraulic hose / brake line expanding under pressure, because it was ok
    on the front brake (1/2 of the brake lever way until full braking), and
    not acceptable no the rear brake (had to pull the brake lever almost up
    to the handle bar to get full breaking power)

    Question: Is this again a problem of monkey assembly (not enough
    fluid?, air in the lines?, what else? ...), or cheap brake lines, or
    both? And are there better brake lines that expand less than the stock
    ones?
    Or ARE hydraulic disc brakes just spongier? If yes, that much
    spongier??

    - After playing with the brakes for a few minutes, I noticed that the
    discs get noticeably warm, around 170F. Are there ever heating issues
    with disc brakes on longer downhill segments? Seems a stupid question,
    but they did get quite warm just by playing around on level ground for
    about ten minutes.

    Thanks a lot!

    PS: All the monkey references are founded on an employee there telling
    me that 'there are no electrical brakes' when I asked for differences
    between hydraulic and cable actuated. When I asked her that about the
    front fork maxing out, i.e. hitting the limit of it's travel hard, she
    replied with 'many people like their forks soft'. (I found out how they
    can be adjusted later.) When I showed her that the (later found to be
    well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
    So monkeys or Neanderthals are definitely a possibility in that store.
    But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I

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    Tags:


  2. Group: rec.bicycles.misc Date: Tue, Oct 10, 2006, 12:04am (EDT-2) From:
    Chris_MdR@gmx.net

    >Hi,
    >      I tried a bike with hydraulic disk
    >brakes (Hayes Sole V6) yesterday for the
    >first time, and would appreciate your
    >input on my impressions:


    >  - On the first bike I tried, it was not
    >possible to block the wheel with the disk
    >brake. I checked and found that the disk
    >was oily. On another bike (same brake) I >was able to get the wheel to

    block, but
    >with application of extreme force to the
    >brake handle, MUCH more than required
    >by any V brake I ever tried.


    >Question: Are Hydraulic Brakes really >weaker than V brakes, or was

    this
    >bike just assembled by monkeys?


    Disk brakes are definitely not weaker than V's, especially better
    hydraulic brakes (I am not counting the $#!^ usualy found on dime-store
    bikes). Many things can cause bad brake performance, many of which you
    guessed. Without actually examining the brakes, though, I cannot tell
    you which.

    Disk brakes are vulnerable to contaminates, especially oily ones, just
    like rim brakes (any type). if there was oil on the disks, you might
    have them checked for leaks. Oil on the disk is bad, Oil leaking from
    the lines is bad.

    >  - I noticed that the hydraulic disc >brakes have a much

    'spongier' feel than
    >the cable actuated V brakes. This I
    >guess was related to the hydraulic hose /
    >brake line expanding under pressure,
    >because it was ok on the front brake (1/2
    >of the brake lever way until full braking),
    >and not acceptable no the rear brake
    >(had to pull the brake lever almost up to
    >the handle bar to get full breaking power)
    >Question: Is this again a problem of
    >monkey assembly (not enough
    >fluid?, air in the lines?, what else? ...), or
    >cheap brake lines, or both? And are
    >there better brake lines that expand less
    >than the stock ones?
    >Or ARE hydraulic disc brakes just
    >spongier? If yes, that much spongier??


    I have Hayes mechanical disks on my MTB and V's on my road tourer, and
    there is a difference in "stiffness" regarding the lever feel there too.
    Both stop great so I put the "sponginess" feeling down to increased
    mechanical advantage in the disk, and yes, the rear is spongier than the
    front due to extra cable length. Although the things you mentioned will
    also create this feeling. the real factor to go by is performance. Does
    the bike stop without too much [lever] effort?

    >  - After playing with the brakes for a few
    >minutes, I noticed that the discs get
    >noticeably warm, around 170F. Are there
    >ever heating issues with disc brakes on
    >longer downhill segments? Seems a
    >stupid question, but they did get quite
    >warm just by playing around on level
    >ground for about ten minutes.
    >
    >Thanks a lot!


    Disk brakes will get hot. that is a given. all brakes work by the same
    principle; turning kinetic energy (motion) into heat. Hayes even warns
    users not to touch the disks, especially after long periods of braking,
    because they can get hot enough to cause burns. This is normal. disk
    brakes get a lot hotter that rim brakes because they are a lot smaller,
    there is not as much metal to absorb the heat. The pads are made
    specially to work under these conditions,

    Rim brakes, on the other hand, use rubber pads that do not work as well
    when hot. But as noted before, a rim has a lot more mass to absorb all
    that heat. the main worries with rim brake heating is too much heat
    expanding the air in the tires leading to blow-off.

    This ability to continue working (and not blow the tires) even when very
    hot is one of the main reasons disk brakes are popular on tandems.

    - -
    Compliments of:
    "Your Friendly Neighborhood Wheelman"

    If you want to E-mail me use:
    ChrisZCorner "at" webtv "dot" net

    My website:
    http://geocities.com/czcorner
     
  3. Smokey

    Smokey Guest

    Chris_MdR@gmx.net wrote:
    > Hi,
    >
    > I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
    > for the first time, and would appreciate your input on my impressions:
    >
    > - On the first bike I tried, it was not possible to block the wheel
    > with the disk brake. I checked and found that the disk was oily. On
    > another bike (same brake) I was able to get the wheel to block, but
    > with application of extreme force to the brake handle, MUCH more than
    > required by any V brake I ever tried.
    >
    > Question: Are Hydraulic Brakes really weaker than V brakes, or was this
    > bike just assembled by monkeys?
    >
    > - I noticed that the hydraulic disc brakes have a much 'spongier' feel
    > than the cable actuated V brakes. This I guess was related to the
    > hydraulic hose / brake line expanding under pressure, because it was ok
    > on the front brake (1/2 of the brake lever way until full braking), and
    > not acceptable no the rear brake (had to pull the brake lever almost up
    > to the handle bar to get full breaking power)
    >
    > Question: Is this again a problem of monkey assembly (not enough
    > fluid?, air in the lines?, what else? ...), or cheap brake lines, or
    > both? And are there better brake lines that expand less than the stock
    > ones?
    > Or ARE hydraulic disc brakes just spongier? If yes, that much
    > spongier??
    >
    > - After playing with the brakes for a few minutes, I noticed that the
    > discs get noticeably warm, around 170F. Are there ever heating issues
    > with disc brakes on longer downhill segments? Seems a stupid question,
    > but they did get quite warm just by playing around on level ground for
    > about ten minutes.
    >
    > Thanks a lot!
    >
    > PS: All the monkey references are founded on an employee there telling
    > me that 'there are no electrical brakes' when I asked for differences
    > between hydraulic and cable actuated. When I asked her that about the
    > front fork maxing out, i.e. hitting the limit of it's travel hard, she
    > replied with 'many people like their forks soft'. (I found out how they
    > can be adjusted later.) When I showed her that the (later found to be
    > well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
    > So monkeys or Neanderthals are definitely a possibility in that store.
    > But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I
    >
    > --

    I haven't worked on any hydraulic bicycle disc brakes, but have
    worked on many motorcycle ones and that sure sounds like there is some
    air in the lines that needs to be bled out.

    Smokey

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  4. Chris_MdR@gmx.net wrote:
    > Hi,
    >
    > I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
    > for the first time, and would appreciate your input on my impressions:
    >
    > - On the first bike I tried, it was not possible to block the wheel
    > with the disk brake. I checked and found that the disk was oily. On
    > another bike (same brake) I was able to get the wheel to block, but
    > with application of extreme force to the brake handle, MUCH more than
    > required by any V brake I ever tried.
    >
    > Question: Are Hydraulic Brakes really weaker than V brakes, or was this
    > bike just assembled by monkeys?


    Number 2..rotors and pads must be free of any contamination.
    >
    > - I noticed that the hydraulic disc brakes have a much 'spongier' feel
    > than the cable actuated V brakes. This I guess was related to the
    > hydraulic hose / brake line expanding under pressure, because it was ok
    > on the front brake (1/2 of the brake lever way until full braking), and
    > not acceptable no the rear brake (had to pull the brake lever almost up
    > to the handle bar to get full breaking power)
    >
    > Question: Is this again a problem of monkey assembly (not enough
    > fluid?, air in the lines?, what else? ...), or cheap brake lines, or
    > both? And are there better brake lines that expand less than the stock
    > ones?
    > Or ARE hydraulic disc brakes just spongier? If yes, that much
    > spongier??


    Brakes need to be bled. Lines don't flex or expand, poor setup.
    >
    > - After playing with the brakes for a few minutes, I noticed that the
    > discs get noticeably warm, around 170F. Are there ever heating issues
    > with disc brakes on longer downhill segments? Seems a stupid question,
    > but they did get quite warm just by playing around on level ground for
    > about ten minutes.


    Temp no big deal.>
    > Thanks a lot!
    >
    > PS: All the monkey references are founded on an employee there telling
    > me that 'there are no electrical brakes' when I asked for differences
    > between hydraulic and cable actuated. When I asked her that about the
    > front fork maxing out, i.e. hitting the limit of it's travel hard, she
    > replied with 'many people like their forks soft'. (I found out how they
    > can be adjusted later.) When I showed her that the (later found to be
    > well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
    > So monkeys or Neanderthals are definitely a possibility in that store.
    > But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I


    Typical of bike shop, USA..peopled by the untrained. Think that if they
    ride a bike, they know something about them(no electric brakes, that is
    amazing that she would say such a thing. I guess she has not heard of
    'mechanical' disc brakes)
    >
    > --
    > rec.bicycles.off-road is moderated by volunteers. To find help solving
    > posting problems, or contact the moderators, please see http://rbor.org/
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  5. jim beam

    jim beam Guest

    Chris_MdR@gmx.net wrote:
    > Hi,
    >
    > I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
    > for the first time, and would appreciate your input on my impressions:
    >
    > - On the first bike I tried, it was not possible to block the wheel
    > with the disk brake. I checked and found that the disk was oily. On
    > another bike (same brake) I was able to get the wheel to block, but
    > with application of extreme force to the brake handle, MUCH more than
    > required by any V brake I ever tried.
    >
    > Question: Are Hydraulic Brakes really weaker than V brakes, or was this
    > bike just assembled by monkeys?


    no, just assembled badly. hydraulic brakes are highly effective, more
    so than rim brakes in off-road conditions.

    >
    > - I noticed that the hydraulic disc brakes have a much 'spongier' feel
    > than the cable actuated V brakes. This I guess was related to the
    > hydraulic hose / brake line expanding under pressure, because it was ok
    > on the front brake (1/2 of the brake lever way until full braking), and
    > not acceptable no the rear brake (had to pull the brake lever almost up
    > to the handle bar to get full breaking power)
    >
    > Question: Is this again a problem of monkey assembly (not enough
    > fluid?, air in the lines?, what else? ...), or cheap brake lines, or
    > both? And are there better brake lines that expand less than the stock
    > ones?
    > Or ARE hydraulic disc brakes just spongier? If yes, that much
    > spongier??


    no, they're firm. sponginess means air in the line.

    >
    > - After playing with the brakes for a few minutes, I noticed that the
    > discs get noticeably warm, around 170F. Are there ever heating issues
    > with disc brakes on longer downhill segments? Seems a stupid question,
    > but they did get quite warm just by playing around on level ground for
    > about ten minutes.


    they get warm because of the friction - that's what all brakes do.
    you'll have no problem with heating issues on a disk braked bike - once
    set up correctly, use with complete confidence.

    >
    > Thanks a lot!
    >
    > PS: All the monkey references are founded on an employee there telling
    > me that 'there are no electrical brakes' when I asked for differences
    > between hydraulic and cable actuated. When I asked her that about the
    > front fork maxing out, i.e. hitting the limit of it's travel hard, she
    > replied with 'many people like their forks soft'. (I found out how they
    > can be adjusted later.) When I showed her that the (later found to be
    > well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
    > So monkeys or Neanderthals are definitely a possibility in that store.
    > But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I
    >
    > --
    > rec.bicycles.off-road is moderated by volunteers. To find help solving
    > posting problems, or contact the moderators, please see http://rbor.org/
    > Please read the charter before posting: http://rbor.org/rbor_charter.txt
    >


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  6. Dion Dock

    Dion Dock Guest

    > When I showed her that the (later found to be
    > well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
    > So monkeys or Neanderthals are definitely a possibility in that store.
    > But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I


    I would strongly suggest you _run_ from a shop that is trying to sell a bike
    with oiled braking surfaces. What else have they mis-assembled?

    If you have to pay someone to get the bike to work, you're going to lose any
    money you would save from their "sale" price. If you can do all the work
    yourself, you don't need answers from rec.bicycles.tech.

    -Dion


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  7. jim beam wrote:
    > Chris_MdR@gmx.net wrote:
    > > Hi,
    > >
    > > - After playing with the brakes for a few minutes, I noticed that the
    > > discs get noticeably warm, around 170F. Are there ever heating issues
    > > with disc brakes on longer downhill segments? Seems a stupid question,
    > > but they did get quite warm just by playing around on level ground for
    > > about ten minutes.

    >
    > they get warm because of the friction - that's what all brakes do.
    > you'll have no problem with heating issues on a disk braked bike - once
    > set up correctly, use with complete confidence.
    >


    Regarding the heating issue, I came across a couple on a tandem who had
    a hydraulic disk brake in back, instead of a drag brake. They said
    that on long downhills the brake heating transfers heat to the fluid,
    the fluid expands and they end up with the brake applied without any
    lever action. They have to stop and let the fluid cool.

    A tandem drag brake and a downhill ATB are not the exact same situation
    but both can expect to sometimes apply the brake for 20-30 minutes on a
    very long downhill. Does this ever occur on an ATB?

    Tom

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  8. Matt O'Toole

    Matt O'Toole Guest

    On Tue, 10 Oct 2006 00:04:56 -0600, Chris_MdR wrote:

    If they're working properly, either brake should be able to lock the rear
    wheel or send you over the handlebars. Disk brakes offer more precise
    modulation and better performance in wet conditions, but their extra power
    is really unnecessary because other kinds of brakes are more than powerful
    enough. Most mountain bikes with decent forks and other equipment come
    with disk brakes anyway, so that's what you'll get. Just make sure the
    disks are clean and nothing is leaking, and you'll be fine. The same
    applies to rim brakes, whether V-brakes, traditional cantilever, or caliper.

    Matt O.

    >
    > Hi,
    >
    > I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
    > for the first time, and would appreciate your input on my impressions:
    >
    > - On the first bike I tried, it was not possible to block the wheel
    > with the disk brake. I checked and found that the disk was oily. On
    > another bike (same brake) I was able to get the wheel to block, but
    > with application of extreme force to the brake handle, MUCH more than
    > required by any V brake I ever tried.
    >
    > Question: Are Hydraulic Brakes really weaker than V brakes, or was this
    > bike just assembled by monkeys?
    >
    > - I noticed that the hydraulic disc brakes have a much 'spongier' feel
    > than the cable actuated V brakes. This I guess was related to the
    > hydraulic hose / brake line expanding under pressure, because it was ok
    > on the front brake (1/2 of the brake lever way until full braking), and
    > not acceptable no the rear brake (had to pull the brake lever almost up
    > to the handle bar to get full breaking power)
    >
    > Question: Is this again a problem of monkey assembly (not enough
    > fluid?, air in the lines?, what else? ...), or cheap brake lines, or
    > both? And are there better brake lines that expand less than the stock
    > ones?
    > Or ARE hydraulic disc brakes just spongier? If yes, that much
    > spongier??
    >
    > - After playing with the brakes for a few minutes, I noticed that the
    > discs get noticeably warm, around 170F. Are there ever heating issues
    > with disc brakes on longer downhill segments? Seems a stupid question,
    > but they did get quite warm just by playing around on level ground for
    > about ten minutes.
    >
    > Thanks a lot!
    >
    > PS: All the monkey references are founded on an employee there telling
    > me that 'there are no electrical brakes' when I asked for differences
    > between hydraulic and cable actuated. When I asked her that about the
    > front fork maxing out, i.e. hitting the limit of it's travel hard, she
    > replied with 'many people like their forks soft'. (I found out how they
    > can be adjusted later.) When I showed her that the (later found to be
    > well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
    > So monkeys or Neanderthals are definitely a possibility in that store.
    > But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I


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  9. Matt O'Toole

    Matt O'Toole Guest

    On Tue, 10 Oct 2006 12:46:37 -0600, treynolds@my-deja.com wrote:

    > jim beam wrote:


    >> Chris_MdR@gmx.net wrote:


    >> > - After playing with the brakes for a few minutes, I noticed that
    >> > the
    >> > discs get noticeably warm, around 170F. Are there ever heating issues
    >> > with disc brakes on longer downhill segments? Seems a stupid
    >> > question, but they did get quite warm just by playing around on level
    >> > ground for about ten minutes.


    >> they get warm because of the friction - that's what all brakes do.
    >> you'll have no problem with heating issues on a disk braked bike - once
    >> set up correctly, use with complete confidence.


    > Regarding the heating issue, I came across a couple on a tandem who had
    > a hydraulic disk brake in back, instead of a drag brake. They said that
    > on long downhills the brake heating transfers heat to the fluid, the
    > fluid expands and they end up with the brake applied without any lever
    > action. They have to stop and let the fluid cool.


    I'm not surprised. Tandems have double the weight and therefore double
    the energy to be dissipated while braking. If the brake components are
    not upgraded to compensate it's likely they'll overheat. There are
    tandem-specific disks for this reason. But because it's a smaller
    market they may not be as well-developed as single MTB brakes -- which
    also had overheating problems in their early days.

    > A tandem drag brake and a downhill ATB are not the exact same situation
    > but both can expect to sometimes apply the brake for 20-30 minutes on a
    > very long downhill. Does this ever occur on an ATB?


    Yes. As I said, overheating was common with the first generation of
    MTB disks.

    The best "disk" is your rim, but overheating it can cause tires to blow
    off, which is the reason for drag brakes at the hub on tandems.

    Matt O.

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  10. Marz

    Marz Guest

    treynolds@my-deja.com wrote:
    > jim beam wrote:
    > > Chris_MdR@gmx.net wrote:
    > > > Hi,
    > > >
    > > > - After playing with the brakes for a few minutes, I noticed that the
    > > > discs get noticeably warm, around 170F. Are there ever heating issues
    > > > with disc brakes on longer downhill segments? Seems a stupid question,
    > > > but they did get quite warm just by playing around on level ground for
    > > > about ten minutes.

    > >
    > > they get warm because of the friction - that's what all brakes do.
    > > you'll have no problem with heating issues on a disk braked bike - once
    > > set up correctly, use with complete confidence.
    > >

    >
    > Regarding the heating issue, I came across a couple on a tandem who had
    > a hydraulic disk brake in back, instead of a drag brake. They said
    > that on long downhills the brake heating transfers heat to the fluid,
    > the fluid expands and they end up with the brake applied without any
    > lever action. They have to stop and let the fluid cool.
    >
    > A tandem drag brake and a downhill ATB are not the exact same situation
    > but both can expect to sometimes apply the brake for 20-30 minutes on a
    > very long downhill. Does this ever occur on an ATB?
    >


    I've never had heat cause the brakes to apply through heat expansion.
    What I do experience is dot4 brake fluid boiling (or the water in the
    fluid boiling) and I loose all braking power. And I have to wait until
    it cools before continuing down hill. On the same hill with v-brakes I
    had a front tire blow because the rim got too hot.

    My make of disk brake is not compatible with dot5 fluid, which if I
    could use it, would help.

    Here's a question, which action produces the most heat, keeping the
    brakes on to control speed on a steep hill or letting the bike go and
    then jamming on the brakes at the last second to kill the speed?
    Laters,

    Marz

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  11. Matt O'Toole

    Matt O'Toole Guest

    On Tue, 10 Oct 2006 13:45:38 -0600, Marz wrote:

    > Here's a question, which action produces the most heat, keeping the
    > brakes on to control speed on a steep hill or letting the bike go and
    > then jamming on the brakes at the last second to kill the speed?


    Believe it or not it's the latter. The amount of energy to be dissipated
    is a product of the mass of bike and rider and the height of the hill,
    which remains the same whether you go fast or slow. But at higher speeds
    there's more airflow over the rims or brake disks, so more heat is
    transferred to the air.

    Matt O.

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  12. Per treynolds@my-deja.com:
    >A tandem drag brake and a downhill ATB are not the exact same situation
    >but both can expect to sometimes apply the brake for 20-30 minutes on a
    >very long downhill. Does this ever occur on an ATB?


    I've had my front brake (Hope C2) lock up in that manner when descending a very
    steep hill.

    Somebody who knows can chime in, but my suspicion is that phenom is limited to
    closed-system hydraulic brakes.

    I also think it's aggravated by having fluid that needs changing bc after I bled
    the brake, it stopped happening.
    --
    PeteCresswell

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  13. In article
    <1160505867.555025.85930@i42g2000cwa.googlegroups.com>,
    "Marz" <marzjennings@gmail.com> wrote:

    > Here's a question, which action produces the most heat, keeping the
    > brakes on to control speed on a steep hill or letting the bike go and
    > then jamming on the brakes at the last second to kill the speed?
    > Laters,


    Depends. If it is a fast road descent, you brake very
    hard for a short time, then run up to speed again
    whereupon the air flow cools the rim before much heat
    gets to the tire. On a long slow descent, road or
    trail, nothing works. You need to stop and let the
    system cool.

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  14. Bart Bailey

    Bart Bailey Guest

    In Message-ID:<8b4oi2hpg4v758oddn9c8mfkb2rs9hujpi@4ax.com> posted on
    Tue, 10 Oct 2006 16:45:44 CST, (PeteCresswell) wrote: Begin

    >Per treynolds@my-deja.com:
    >>A tandem drag brake and a downhill ATB are not the exact same situation
    >>but both can expect to sometimes apply the brake for 20-30 minutes on a
    >>very long downhill. Does this ever occur on an ATB?

    >
    >I've had my front brake (Hope C2) lock up in that manner when descending a very
    >steep hill.
    >
    >Somebody who knows can chime in, but my suspicion is that phenom is limited to
    >closed-system hydraulic brakes.
    >
    >I also think it's aggravated by having fluid that needs changing bc after I bled
    >the brake, it stopped happening.


    That might suggest bubbles
    that expanded with prolonged application heating
    causing the lockup
    and would no longer be an issue after bleeding them out

    You might think that those bubbles would tent to migrate upward toward
    the hand lever and away from the source of heat however, unless there's
    a slight leak at the connection to the hydraulic applicator and the
    bubbles were forming there as you rode then subsequently heating before
    their chance to float away.

    --

    Bart

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  15. Smokey

    Smokey Guest

    Marz wrote:
    > treynolds@my-deja.com wrote:
    > > jim beam wrote:
    > > > Chris_MdR@gmx.net wrote:
    > > > > Hi,
    > > > >
    > > > > - After playing with the brakes for a few minutes, I noticed that the
    > > > > discs get noticeably warm, around 170F. Are there ever heating issues
    > > > > with disc brakes on longer downhill segments? Seems a stupid question,
    > > > > but they did get quite warm just by playing around on level ground for
    > > > > about ten minutes.
    > > >
    > > > they get warm because of the friction - that's what all brakes do.
    > > > you'll have no problem with heating issues on a disk braked bike - once
    > > > set up correctly, use with complete confidence.
    > > >

    > >
    > > Regarding the heating issue, I came across a couple on a tandem who had
    > > a hydraulic disk brake in back, instead of a drag brake. They said
    > > that on long downhills the brake heating transfers heat to the fluid,
    > > the fluid expands and they end up with the brake applied without any
    > > lever action. They have to stop and let the fluid cool.
    > >
    > > A tandem drag brake and a downhill ATB are not the exact same situation
    > > but both can expect to sometimes apply the brake for 20-30 minutes on a
    > > very long downhill. Does this ever occur on an ATB?
    > >

    >
    > I've never had heat cause the brakes to apply through heat expansion.
    > What I do experience is dot4 brake fluid boiling (or the water in the
    > fluid boiling) and I loose all braking power. And I have to wait until
    > it cools before continuing down hill. On the same hill with v-brakes I
    > had a front tire blow because the rim got too hot.
    >
    > My make of disk brake is not compatible with dot5 fluid, which if I
    > could use it, would help.
    >
    > Here's a question, which action produces the most heat, keeping the
    > brakes on to control speed on a steep hill or letting the bike go and
    > then jamming on the brakes at the last second to kill the speed?
    > Laters,
    >
    > Marz
    >
    > --
    >There is a higher temp grade of DOT fluid called DOT 5.1. Despite it's numerical designation, it IS NOT the same as DOT 5 fluid, it's a grade of DOT 4 developed specifically for high temp braking (wonder why they didn't call it 4.1?). Some of the motorcycle road racing teams are using it. Speaking of brake fluid, when I worked in a motorcycle shop, this was the second most neglected item of maintenance (changing the fluid). The most neglected was checking tire pressure.


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  16. jlee

    jlee Guest


    > I'm not surprised. Tandems have double the weight and therefore double
    > the energy to be dissipated while braking.


    It will be more than double - significantly more as the double weight
    going downhill only experiences the air resistance of a single rider.
    As any rider knows from experience, the heavier rider will descent
    faster (handling aside) than a lighter rider.

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  17. Matt O'Toole

    Matt O'Toole Guest

    On Wed, 11 Oct 2006 00:58:40 -0600, jlee wrote:

    >> I'm not surprised. Tandems have double the weight and therefore double
    >> the energy to be dissipated while braking.


    > It will be more than double - significantly more as the double weight
    > going downhill only experiences the air resistance of a single rider.


    This is true.

    Matt O.

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  18. unas

    unas Guest

    Chris_MdR@gmx.net a écrit :

    > Hi,
    >
    > I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
    > for the first time, and would appreciate your input on my impressions:
    >
    > - On the first bike I tried, it was not possible to block the wheel
    > with the disk brake. I checked and found that the disk was oily. On
    > another bike (same brake) I was able to get the wheel to block, but
    > with application of extreme force to the brake handle, MUCH more than
    > required by any V brake I ever tried.
    >
    > Question: Are Hydraulic Brakes really weaker than V brakes, or was this
    > bike just assembled by monkeys?
    >
    > - I noticed that the hydraulic disc brakes have a much 'spongier' feel
    > than the cable actuated V brakes. This I guess was related to the
    > hydraulic hose / brake line expanding under pressure, because it was ok
    > on the front brake (1/2 of the brake lever way until full braking), and
    > not acceptable no the rear brake (had to pull the brake lever almost up
    > to the handle bar to get full breaking power)
    >
    > Question: Is this again a problem of monkey assembly (not enough
    > fluid?, air in the lines?, what else? ...), or cheap brake lines, or
    > both? And are there better brake lines that expand less than the stock
    > ones?
    > Or ARE hydraulic disc brakes just spongier? If yes, that much
    > spongier??
    >
    > - After playing with the brakes for a few minutes, I noticed that the
    > discs get noticeably warm, around 170F. Are there ever heating issues
    > with disc brakes on longer downhill segments? Seems a stupid question,
    > but they did get quite warm just by playing around on level ground for
    > about ten minutes.
    >
    > Thanks a lot!
    >
    > PS: All the monkey references are founded on an employee there telling
    > me that 'there are no electrical brakes' when I asked for differences
    > between hydraulic and cable actuated. When I asked her that about the
    > front fork maxing out, i.e. hitting the limit of it's travel hard, she
    > replied with 'many people like their forks soft'. (I found out how they
    > can be adjusted later.) When I showed her that the (later found to be
    > well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'
    > So monkeys or Neanderthals are definitely a possibility in that store.
    > But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I
    >
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    the model that you use?


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  19. Werehatrack

    Werehatrack Guest

    On Tue, 10 Oct 2006 00:04:56 CST, Chris_MdR@gmx.net wrote:

    >
    >Hi,
    >
    > I tried a bike with hydraulic disk brakes (Hayes Sole V6) yesterday
    >for the first time, and would appreciate your input on my impressions:
    >
    > - On the first bike I tried, it was not possible to block the wheel
    >with the disk brake. I checked and found that the disk was oily.


    Well, that would explain it. BTW, a brake which locks the front wheel
    when the bike is actually being ridden can be an unpleasant thing to
    have. If you get one, I suspect that you will discover this at some
    point.

    > On
    >another bike (same brake) I was able to get the wheel to block, but
    >with application of extreme force to the brake handle, MUCH more than
    >required by any V brake I ever tried.
    >
    >Question: Are Hydraulic Brakes really weaker than V brakes, or was this
    >bike just assembled by monkeys?


    In my experience, most v-brakes require far less finger pressure to
    produce a given amount of stopping power than a disc brake.

    > - I noticed that the hydraulic disc brakes have a much 'spongier' feel
    >than the cable actuated V brakes. This I guess was related to the
    >hydraulic hose / brake line expanding under pressure, because it was ok
    >on the front brake (1/2 of the brake lever way until full braking), and
    >not acceptable no the rear brake (had to pull the brake lever almost up
    >to the handle bar to get full breaking power)


    Cable-operated disc brakes often have similar results. This is not
    unusual for disc brakes as a class of unit, but results vary wildly
    between setups; it is foolish to infer anything about a specific
    brake's probable operating characteristics on the basis of other
    brands or models. The only way to reliably establish what a given
    brake does is to try it and see.

    >Question: Is this again a problem of monkey assembly (not enough
    >fluid?, air in the lines?, what else? ...), or cheap brake lines, or
    >both? And are there better brake lines that expand less than the stock
    >ones?


    To each: Possibly.

    >Or ARE hydraulic disc brakes just spongier? If yes, that much
    >spongier??


    Any brake can be made to work poorly. Some can't be made to work
    well. Each must be evaluated on its own merits.

    > - After playing with the brakes for a few minutes, I noticed that the
    >discs get noticeably warm, around 170F.


    Gosh, you had a contact thermometer available? I'm impressed.

    >Are there ever heating issues
    >with disc brakes on longer downhill segments? Seems a stupid question,
    >but they did get quite warm just by playing around on level ground for
    >about ten minutes.


    Yes, it is possible to get disc brakes hot enough on a long descent
    (especially with a heavy rider or on a steep grade) to discolor the
    disc. Whether this is a problem depends on other factors that vary
    from brake to brake.

    >PS: All the monkey references are founded on an employee there telling
    >me that 'there are no electrical brakes' when I asked for differences
    >between hydraulic and cable actuated.


    Correct: there are no electric brakes. If you used the term "cable
    actuated" they should have known you were talking about something that
    was not electrically operated, how did you manage to get them to think
    that an electrical connection was involved?

    >When I asked her that about the
    >front fork maxing out, i.e. hitting the limit of it's travel hard, she
    >replied with 'many people like their forks soft'. (I found out how they
    >can be adjusted later.)


    What does this have to do with brakes?

    >When I showed her that the (later found to be
    >well oiled) disk didn't stop the bike, she said 'Oh. Eh? Uh?'


    Oil contamination of disc brakes has been an issue with motorcycles as
    well, for much longer. It happens. When the pads get oiled, you
    generally have to replace them; if they're getting oiled by a leaking
    fork, then you need a better fork. In the case of bicycles, the best
    solution is often to go back to V-brakes, but not always.

    >So monkeys or Neanderthals are definitely a possibility in that store.
    >But the bike is on sale, so I might still buy there. Uh. Uh. Uh. I


    I think I'd shop for something else.
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  20. Tosspot

    Tosspot Guest

    Werehatrack wrote:
    > On Tue, 10 Oct 2006 00:04:56 CST, Chris_MdR@gmx.net wrote:
    >


    <snip>

    >>- After playing with the brakes for a few minutes, I noticed that the
    >>discs get noticeably warm, around 170F.

    >
    >
    > Gosh, you had a contact thermometer available? I'm impressed.


    IR Thermometer. Every cyclist should have one.

    http://www.webbikeworld.com/r2/digital-infrared-thermometer/digital-infrared-thermometer.htm

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