Brake fade (mtb)

"andrew cooke" <[email hidden]> wrote in message
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Quoted message said:

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

"David" <[email hidden]> wrote in message
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Quoted message said:

"andrew cooke" <[email hidden]> wrote in message

"]news:[email hidden]...

Quoted message said:

Quoted message said:

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

Quoted message said:

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

"andrew cooke" <[email hidden]> wrote in message
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Quoted message said:

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 hidden] (andrew cooke) wrote in message

news:<[email hidden]>...

Quoted message said:

Quoted message said:

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.

"andrew cooke" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

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

Andrew Cooke said:

Thanks for the all the suggestions. People have mentioned:

Quoted message said:

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

Quoted message said:

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:

sheldonbrown.combrakeshoes.htmlOpen ↗

Jobst Brandt <[email hidden]> Palo Alto CA

In article said:

Andrew Cooke said:

Thanks for the all the suggestions. People have mentioned:

Quoted message said:

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

Quoted message said:

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:

sheldonbrown.combrakeshoes.htmlOpen ↗

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?

Kinky Cowboy said:

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

Alexander Grekhov said:

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

Quoted message said:

... 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

Quoted message said:

Paul Southworth said:

Quoted message said:

sheldonbrown.combrakeshoes.htmlOpen ↗

Quoted message said:

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 <[email hidden]> 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...

Anonymous trolls and snipes:

Quoted message said:

Quoted message said:

... 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.

Quoted message said:

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 hidden]> Palo Alto CA

The Pomeranian said:

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 terrymorse.combikeOpen ↗

Jon Isaacs said:

Quoted message said:

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

Quoted message said:

Quoted message said:

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

Quoted message said:

Serious question:

Quoted message said:

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.

Quoted message said:

Not serious section:

Quoted message said:

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

Quoted message said:

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 hidden]> Palo Alto CA

Per Löwdin said:

Quoted message said:

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?

Quoted message said:

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 hidden]> Palo Alto CA

[email hidden] wrote

Quoted message said:

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 terrymorse.combikeOpen ↗

Jobst Brandt said:

Terry Morse said:

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:

electro-optical.commatlemisivty.htmOpen ↗

Quoted message said:

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 terrymorse.combikeOpen ↗

"terry morse" <[email hidden]> wrote in message
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Quoted message said:

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