Brake fade (mtb)  

Re: Brake fade (mtb)

"David" <emrich.doesn'tlikespam@bigfoot.extrastuff.com> wrote in message
news:6y1M9.723$UE3.60420254@newssvr13.news.prodigy.com...
>
> "andrew cooke" <andrew@acooke.org> wrote in message
news:aef33705.0212180748.5d8f800@posting.google.com...
> > 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

Re: Thinking about this [Was: Brake fade (mtb)]

"andrew cooke" <andrew@acooke.org> wrote in message
news:aef33705.0212190349.43ca4e2@posting.google.com...
> 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
>
> andrew@acooke.org (andrew cooke) wrote in message
news:<aef33705.0212180748.5d8f800@posting.google.com>...
> > 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.

Re: Thinking about this [Was: Brake fade (MTB)]

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 <jobst.brandt@stanfordalumni.org> Palo Alto CA

Re: Thinking about this [Was: Brake fade (MTB)]

In article <uHpM9.55682$Ik.1699452@typhoon.sonic.net>, <jobst.brandt@stanfordalumni.org> 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?

Re: Thinking about this [Was: Brake fade (mtb)]

"Kinky Cowboy" <kinkySPAMKILLERcowboy_uk@excite.com> 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

Re: Thinking about this [Was: Brake fade (MTB)]

jobst.brandt@stanfordalumni.org 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

Re: Thinking about this [Was: Brake fade (MTB)]

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 <jobst.brandt@stanfordalumni.org> Palo Alto CA

Re: Thinking about this [Was: Brake fade (MTB)]

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 <jobst.brandt@stanfordalumni.org> Palo Alto CA

Re: Brake fade (mtb)

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 <jobst.brandt@stanfordalumni.org> Palo Alto CA

Re: Thinking about this [Was: Brake fade (MTB)]

"terry morse" <tmorse@spamcop.net> wrote in message
news:1d7ea2f8.0212221856.120d4768@posting.google.com...
> 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