Brake fade (mtb)

Discussion in 'Cycling Equipment' started by Andrew Cooke, Jan 22, 2003.

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  1. Andrew Cooke

    Andrew Cooke Guest

    Hi,

    Are there are any simple, low-cost ways of reducing/managing brake fade during (cautious) downhills?
    Any riding style (apart from not braking) better than another? Some kind of pad that might be better
    than another?

    I have a Raleigh M50. Alloy wheels (black anodized with the rims ground back to silver). Tekpro
    brakes. I realise this isn't the most sophisticated bike in the world, but it's what I've got
    (actually, for the price, I think it's pretty good - but I've no experience of anything fancier).
    I'm not at all keen (money, appearance and a suspicion of anything new/fancy) to get disc brakes.

    Thanks, Andrew

    PS When i last cycled off-road, maybe 6 or 7 years ago, I don't remember this problem. That was on a
    similar quality bike - hence my wondering if there's something "obvious" that could help. In both
    cases I'm in dry, dusty country (Chile, S America).
     
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  2. David

    David Guest

    "andrew cooke" <[email protected]> wrote in message
    news:[email protected]...
    > Hi,
    >
    > Are there are any simple, low-cost ways of reducing/managing brake fade during (cautious)
    > downhills? Any riding style (apart from not braking) better than another? Some kind of pad that
    > might be better than another?

    Yes, but if your pads are old, just getting new ones might help, or maybe just sanding odd a bit of
    old rubber. If that doesn't do it, try the salmon-colored Kool-Stops (good braking but tend to be
    noisy in V-type brakes).

    If that doesn't work, switch to a disc brake in front.

    David
     
  3. David Ornee

    David Ornee Guest

    "David" <emrich.doesn'[email protected]> wrote in message
    news:[email protected]...
    >
    > "andrew cooke" <[email protected]> wrote in message
    news:[email protected]...
    > > Hi,
    > >
    > > Are there are any simple, low-cost ways of reducing/managing brake fade during (cautious)
    > > downhills? Any riding style (apart from not braking) better than another? Some kind of pad that
    > > might be better than another?
    >
    > Yes, but if your pads are old, just getting new ones might help, or maybe just sanding odd a bit
    > of old rubber. If that doesn't do it, try the
    salmon-colored
    > Kool-Stops (good braking but tend to be noisy in V-type brakes).
    >
    > If that doesn't work, switch to a disc brake in front.
    >
    > David
    >
    As others suggested, keep the pads clean by carefully sanding or filing them. I suggest cleaning the
    braking surface of the rims as well. Scotch pads and a little water works well. When you take the
    tires off to check your wheels, you can also carefully use some Acetone to clean the braking
    surfaces. Be especially careful with Acetone, as it is extremely volatile, flammable, and can
    dissolve rubber products like tubes and tires.

    David Ornee, Western Springs, IL
     
  4. Kinky Cowboy

    Kinky Cowboy Guest

    "andrew cooke" <[email protected]> wrote in message
    news:[email protected]...
    > Thanks for the all the suggestions. People have mentioned:
    >
    > - Sanding/cleaning pads
    > - Cleaning rims
    > - Replacing calipers
    > - Replacing pads
    > - Getting discs
    >
    > However, I'm not clear how most of these are going to solve my problem. The brakes are fine
    > normally - it's only when I'm on a long, slow downhill that they become less and less responsive.
    > So I'm not sure how cleaning pads or rims would change this (and with all the dust here I think
    > I'm sanding pads every time I use them). Also, I don't see how calipers flexing is going to affect
    > braking (never mind how it can only become a problem when the rims are hot) - surely the force
    > between pad and rim is the same, whether calipers flex a lot or a little (the only difference I
    > can see is that if they flex more, the levers move more for the same amount of force, zo you
    > might, with very flexy calipers, run out of movement ).
    >
    > I'm not trying to be ungrateful - I just want to think things through to avoid going on a
    > wild-goose chase.
    >
    > Thanks, Andrew
    >
    > [email protected] (andrew cooke) wrote in message
    news:<[email protected]>...
    > > Hi,
    > >
    > > Are there are any simple, low-cost ways of reducing/managing brake fade during (cautious)
    > > downhills? Any riding style (apart from not braking) better than another? Some kind of pad that
    > > might be better than another?
    > >
    > > I have a Raleigh M50. Alloy wheels (black anodized with the rims ground back to silver). Tekpro
    > > brakes. I realise this isn't the most sophisticated bike in the world, but it's what I've got
    > > (actually, for the price, I think it's pretty good - but I've no experience of anything
    > > fancier). I'm not at all keen (money, appearance and a suspicion of anything new/fancy) to get
    > > disc brakes.
    > >
    > > Thanks, Andrew
    > >
    > > PS When i last cycled off-road, maybe 6 or 7 years ago, I don't remember this problem. That was
    > > on a similar quality bike - hence my wondering if there's something "obvious" that could
    > > help. In both cases I'm in dry, dusty country (Chile, S America).

    That's what I like to see; sound reasoning on r.b.t, not a frequent occurrence. The only suggestions
    which might cure your brake fade are those which address the problem, viz: your current friction
    material has a coefficient of friction which is acceptable when cold but too low when hot. Of the
    proposals put forth, changing the brake pads or changing both the pad and the braking surface (i.e.
    switching to discs) both have the possibility of addressing the problem. Since you don't want discs,
    this leaves changing the pads. Look for recommendations of pads which either have a higher
    coefficient of friction than your current ones at elevated temperatures or which are designed with
    better heat dissipation in mind so that the pads stay cooler. Of course, this problem is the one
    discs were introduced to solve, and they do it very well, so if you really want the best downhill
    brake you need to overcome your Luddite tendencies.
     
  5. David

    David Guest

    "andrew cooke" <[email protected]> wrote in message
    news:[email protected]...
    > Thanks for the all the suggestions. People have mentioned:
    >
    > - Sanding/cleaning pads
    > - Cleaning rims
    > - Replacing calipers
    > - Replacing pads
    > - Getting discs
    >
    > However, I'm not clear how most of these are going to solve my problem. The brakes are fine
    > normally - it's only when I'm on a long, slow downhill that they become less and less responsive.

    I had a couple of occurrances of severe fade that were solved with better pads. One one of the
    descents (>40MPH down a lightly gravelled road) I had a minor crash when I ran out of brakes
    approaching a corner. On a 19% grade road descent (same bike, but with road tires), a heat-related
    flat (a patch seperated in my front tire) accompanied the severe fade. I don't think the new pads
    are going to help much with that part.

    I do the same stuff in my bike with a front disk with no brake fade.

    David
     
  6. Jobst Brandt

    Jobst Brandt Guest

    Andrew Cooke writes:

    > Thanks for the all the suggestions. People have mentioned:

    > - Sanding/cleaning pads
    > - Cleaning rims
    > - Replacing calipers
    > - Replacing pads
    > - Getting discs

    > However, I'm not clear how most of these are going to solve my problem. The brakes are fine
    > normally - it's only when I'm on a long, slow downhill that they become less and less responsive.

    From the description, these are otherwise properly functioning brakes. Brake fade comes from thermal
    effects on brake pad material. None of the metal parts are measurably affected at these temperatures
    so the only reasonable suggestion in the above list is "Replacing pads".

    That is to say, the problem lies in the brake pad material... and of course, the situation that
    causes high brake temperatures. Therefore, get a set of Kool-Stop Salmon colored pads. Details at:

    http://sheldonbrown.com/harris/brakeshoes.html

    Jobst Brandt <[email protected]> Palo Alto CA
     
  7. In article <[email protected]>, <[email protected]> wrote:
    >Andrew Cooke writes:
    >
    >> Thanks for the all the suggestions. People have mentioned:
    >
    >> - Sanding/cleaning pads
    >> - Cleaning rims
    >> - Replacing calipers
    >> - Replacing pads
    >> - Getting discs
    >
    >> However, I'm not clear how most of these are going to solve my problem. The brakes are fine
    >> normally - it's only when I'm on a long, slow downhill that they become less and less responsive.
    >
    >From the description, these are otherwise properly functioning brakes. Brake fade comes from
    >thermal effects on brake pad material. None of the metal parts are measurably affected at these
    >temperatures so the only reasonable suggestion in the above list is "Replacing pads".
    >
    >That is to say, the problem lies in the brake pad material... and of course, the situation that
    >causes high brake temperatures. Therefore, get a set of Kool-Stop Salmon colored pads. Details at:
    >
    >http://sheldonbrown.com/harris/brakeshoes.html

    Does anyone have any experience using salmon pads with Mavic ceramic rims (vs. using the green
    pads)? Are they hard enough to avoid getting eaten?
     
  8. Bluto

    Bluto Guest

    "Kinky Cowboy" <[email protected]> wrote:

    > the pads. Look for recommendations of pads which either have a higher coefficient of friction than
    > your current ones at elevated temperatures or which are designed with better heat dissipation in
    > mind so that the pads stay cooler. Of course, this problem is the one discs were introduced to
    > solve, and they do it very well, so if you really want the best downhill brake you need to
    > overcome your Luddite tendencies.

    I recently got my first bicycle disc brake in service (Avid Mechanical, stock on Van Dessel Buzz
    Bomb). It seems to have improved braking power once the pads warm up, just like the brakes on my
    motorcycle. Unlike the brakes on my motorcycle, the flimsy little disc seems to warp in a new and
    different way every time it gets hot.

    On the plus side, the pads don't rub any worse now that the dished front wheel has gone all
    wobbly. :(

    Chalo Colina
     
  9. Kronk

    Kronk Guest

    On 20 Dec 2002 04:37:18 GMT, "Alexander Grekhov" <[email protected]> wrote:

    >You may need to adjust your riding position -- your weight should not be "all on the front". Lower
    >your seat, slide back. Rise your handlebars if necessary (stem/handlebar with more rise).

    My first ten speed had drop bars and extension levers for the brakes so that I could brake from
    either the uppers or lowers. Rear wheel liftoff happened much easier when my hands were on the
    uppers. I'm pretty sure raising the bars would not improve anything here, and might make
    matters worse.

    Kronk
     
  10. [email protected] wrote:

    > ... Because the aluminum rim in rim braking is the heat (energy) sink, coating it with an
    > insulator is a bad idea because that causes the pad to overheat and the rim to cool poorly once it
    > warms up.

    Anonymous trolls and snipes:

    Aside from the actual brake track were a good thermal connection is required, the rims and spokes
    should be aluminum and black. Black bodies radiate (and absorb) heat better than anything other
    "color." That's why the Al heat sinks for electrical equipment is most often black. The "aero" rim
    is best because it provides the largest surface area. So rims should be aero and anodized black and
    should not have stainless steel eyelets because these will not transmit heat sufficiently to the
    spokes. Brass or Al nipples should be used (because of good heat conduction), and the spokes should
    also be anodized black and they should be bladed for the purpose of increasing the surface area.
    All this will help get rid of the heat generated from braking. Also, riders should only ride at
    night or in overcast conditions because this will mitigate the effect of sun loading on the heat
    dissipating surfaces.

    This makes perfect sense.

    Thanks, Pom-Pom
     
  11. Ajames54

    Ajames54 Guest

    On Fri, 20 Dec 2002 02:12:14 GMT, [email protected] wrote:

    >Paul Southworth <[email protected]> writes:
    >
    >>>http://sheldonbrown.com/harris/brakeshoes.html
    >
    >> Does anyone have any experience using salmon pads with Mavic ceramic rims (vs. using the green
    >> pads)? Are they hard enough to avoid getting eaten?
    >
    >Get ceramic specific pads. Ceramic being an insulator, it overheats most common pad materials.
    >Because the aluminum rim in rim braking is the heat (energy) sink, coating it with an insulator is
    >a bad idea because that causes the pad to overheat and the rim to cool poorly once it warms up. In
    >its effort to prevent rim wear it degrades thermal energy dissipation from braking.
    >
    >Jobst Brandt <jobst.br[email protected]> Palo Alto CA

    FWIW I built a pair of wheels from the 217 Ceramics when they first came out ('93? '94?) and since
    there was no such thing as a ceramic specific pad at the time I used the Scott Mathauser pads that I
    had sworn by (at?) for years. If anything they were quieter than on most other rims... and they
    lasted and lasted and lasted..

    in all honesty though it is only since I had to switch to the newer pads that I've noticed anything
    like what I would call brake fade

    I've been told that the kool-stop salmon pads are the same material as the mathausers but nobody
    around here sells them...
     
  12. Jobst Brandt

    Jobst Brandt Guest

    Anonymous trolls and snipes:

    >> ... Because the aluminum rim in rim braking is the heat (energy) sink, coating it with an
    >> insulator is a bad idea because that causes the pad to overheat and the rim to cool poorly once
    >> it warms up.

    > Aside from the actual brake track were a good thermal connection is required, the rims and spokes
    > should be aluminum and black. Black bodies radiate (and absorb) heat better than anything other
    > "color." That's why the Al heat sinks for electrical equipment is most often black.

    As the old saying goes, "a little knowledge can be dangerous" and applies here because at the
    temperatures of bicycle brakes, all bodies are "black bodies" regardless of color, thermal radiation
    being in the long infrared wave lengths.

    Jobst Brandt <[email protected]> Palo Alto CA
     
  13. Terry Morse

    Terry Morse Guest

    The Pomeranian wrote:

    > Aside from the actual brake track were a good thermal connection is required, the rims and spokes
    > should be aluminum and black. Black bodies radiate (and absorb) heat better than anything other
    > "color." That's why the Al heat sinks for electrical equipment is most often black.

    Note that something that looks black to the eye may not be a good infrared emitter. Anodized
    aluminum is an excellent infrared emitter, but black chrome is terrible.
    --
    terry morse Palo Alto, CA http://www.terrymorse.com/bike/
     
  14. Jobst Brandt

    Jobst Brandt Guest

    Jon Isaacs writes:

    >> From the description, these are otherwise properly functioning brakes. Brake fade comes from
    >> thermal effects on brake pad material.

    >> None of the metal parts are measurably affected at these temperatures so the only reasonable
    >> suggestion in the above list is "Replacing pads".

    > Serious question:

    > I wonder how much the characteristics of the rim affects the temperature of the pad, would a rim
    > with a larger surface area or better heat transfer help in a situation like this???

    In a friction pair, heat is generated by deformation of the softer material (the one that wears and
    deforms) and in bicycle rim brakes, that is almost entirely the brake pad. Rim wear from hard
    particle contamination (road grit) of the interface, the stuff that causes rim wear is the
    exception. Therefore, because the pad is an excellent thermal insulator, braking heat can escape
    only when transmitted from the pad surface to the rim for dissipation to the atmosphere. From this
    it should be evident that an insulating rim will cause conventional pads to melt and wear rapidly
    while producing poor retardation.

    Anything that results in a more rapid cooling rim is preferred in this respect although some methods
    are impractical for bicycling.

    > Not serious section:

    > Anyone thinking black anodized here?? (<g>)

    > Of course one could always rig up to spray the brakes with water from a Camel Back, that would
    > cools them but might cause other issues with the coefficient of friction... <g>

    This is part of the above question and, yes, anodizing is a ceramic, and yes it insulates. But then
    long time readers of this newsgroup have heard this discussion often. Water cooled brakes work but
    the friction surface must remain dry. As I said, "some methods are impractical for bicycling."

    Jobst Brandt <[email protected]> Palo Alto CA
     
  15. Jobst Brandt

    Jobst Brandt Guest

    Per Löwdin writes:

    >> Are there are any simple, low-cost ways of reducing/managing brake fade during (cautious)
    >> downhills? Any riding style (apart from not braking) better than another? Some kind of pad that
    >> might be better than another?

    > The rims are of course also an important factor. Ceramic rims fade less and last longer.

    Brake fade is cased by thermal softening of brake pad material. Rims do not change physical
    characteristics significantly below glowing red temperatures. Ceramic rims raise surface
    temperatures of the pad significantly, thereby causing more rapid fade and wear.

    From what do you draw the conclusion that ceramic rims prevent brake fade?

    Jobst Brandt <[email protected]> Palo Alto CA
     
  16. Terry Morse

    Terry Morse Guest

    [email protected] wrote

    > As the old saying goes, "a little knowledge can be dangerous" and applies here because at the
    > temperatures of bicycle brakes, all bodies are "black bodies" regardless of color, thermal
    > radiation being in the long infrared wave lengths.

    Even at the long infrared wavelengths, some bike parts are blacker than others. Emissivity of
    anodized aluminum is 0.82-0.86. Highy polished aluminum, however, has an emissivity of about 0.05,
    about 17 times worse than anodized. Even highly oxidized aluminum's emissivity is only about 0.25.
    --
    terry morse Palo Alto, CA http://www.terrymorse.com/bike/
     
  17. Terry Morse

    Terry Morse Guest

    Jobst Brandt wrote:

    > Terry Morse wrote:
    > > Even at the long infrared wavelengths, some bike parts are blacker than others. Emissivity of
    > > anodized aluminum is 0.82-0.86. Highly polished aluminum, however, has an emissivity of about
    > > 0.05, about 17 times worse than anodized. Even highly oxidized aluminum's emissivity is only
    > > about 0.25.
    >
    > That is not the way I recall measuring emitted energy from a polished and matte aluminum plate

    Here are some reference emissivity ranges for some materials:

    http://www.electro-optical.com/bb_rad/emissivity/matlemisivty.htm

    > Even if black anodized were a better emitter, I don't see that, for mechanical durability reasons,
    > aluminum should be anodized.

    If durability is an issue, a very thin anodized coating is enough to raise aluminum's emissivity to
    over 0.8. The color doesn't matter. I doubt thin anodizing has much impact on durability, since
    cracks in the thin surface are too small to propagate. If anodizing's not possible, a thin gel coat
    can produce 0.7 or higher. But gel coats are not as durable as anodizing.

    Back when I was doing aerospace heat transfer work, measured emissivities were invariably lower than
    the published figures by as much as 10%. This messed up the cooling models, until we started using
    the more conservative numbers.
    ---
    terry morse Palo Alto, CA http://www.terrymorse.com/bike/
     
  18. "terry morse" <[email protected]> wrote in message
    news:[email protected]...
    > Terry Morse wrote:
    >
    > Oops. Make that "clear coat", not "gel coat". I must have been thinking of sailing when I wrote
    > that. Clear coats for bikes, gel coats for boats.
    > --

    I didn't know that much money existed in one spot anymore. Abike AND a boat!!!! I am agast at anyone
    that has the where-with-all to have both of these hobbies. I am also just kidding and very jealous.

    Mike
     
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