Disc brakes squeal due to loose pads?



jim beam <[email protected]> writes:

> david, you are correct that when the brakes are fully
> effective, maximum braking is defined in terms of the
> above. but it is incorrect to assume that all brakes are
> effective to this level in all conditions. foreign
> material [mud] between the brake pad & the braking surface
> has a substantially negative impact on their friction
> coefficient and can easily cause the brake to not be able
> to approach the above limit.

Mud, perhaps, but not just water as in rain on the road.

> please also remember that not everyone lives in flat
> country like you.

Have you ever been to England? It's not exactly Holland-like
in its terrain. San Francisco type hills are not hard to
find in England.

> in my case, 210lbs [15 stone?] of lard contending with
> several miles of gradient 6" deep in winter effluent are
> not optimum conditions for rim brakes. next time you're in
> the san francisco bay area, you're welcome to borrow my
> guest bike and see what i mean. you'll enjoy it -
> california rain is much warmer than british rain.

You should try Minnesota's winter riding conditions... ;-)
 
Michael Press <[email protected]> writes:

> Jobst, I'm having some trouble understanding exactly what
> you're saying here, so please indulge some (possibly
> obvious to you) clarifications. I believe that you're
> agreeing with my subjective impressions of rim brakes
> becoming ineffective in the presence of lots of water, and
> are stating that you have done some studies to validate
> those theories.
>
> [email protected] wrote:
>
>> I have had the opportunity to brake in water deep enough
>> to submerge the rim and found that there was practically
>> no brake effect during the immersion.
>
> By "No brake effect during immersion" you mean that
> braking was completely ineffective during immersion?

Think of it as a water film between the brake pad and the
rim. Riding through a deep puddle, the water competely coats
the rim and is constantly resupplied. Once you're out of the
puddle, the rim dries off rapidly when the brakes are
applied. Riding in the rain, water gets onto the rim in a
random pattern from falling raindrops and splashing from the
road surface, so the film is not as fully coating the
surface of the rim and is not as constantly resupplied, so
the brake pads have the chance of drying off the water and
getting more friction against the rim (I think this is what
David D. was referring to).

>>Subsequently I rode in snow so there was a snow pack on
>>the inner periphery of the rim. On braking, this snow
>>melts supplying a continuous flow of water to the braking
>>surface. Braking came back to typical wet weather effect
>>as the snow was gone and shortly after that full
>>effectiveness returned.
>
> So by "Braking came back to typical wet weather effect"
> you're stating that when the melting snow supplied a flow
> of water on the rim, the effect was the same as during
> immersion, that is little or no braking ability?

Yup, that's how I read it. If it's cold enough, the layer of
water on the rim will freeze and then you've really got no
brakes. This is common here in Minnesota for winter riders
as the temperatures are below the freezing point for about 7
months out of the year. An outlying town recorded an
overnight low of 33 deg F last night... We haven't had
summer yet and may not, at the rate things are going.

In really cold weather I either find something else to do,
or I ride a bike with some kind of hub brake (a coaster
brake wheel on my track bike, in my case). It's way too
dangerous to be riding in an urban area- chock full of
oblivious latte-sipping cell-phone-talking SUV drivers-
without any damn brakes. Life's too short to be stupid.
 
"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...
> jim beam <[email protected]> writes:
>
> > david, you are correct that when the brakes are fully
> > effective, maximum braking is defined in terms of the
> > above. but it is incorrect to assume that all brakes are
> > effective to this level in all conditions. foreign
> > material [mud] between the brake pad & the braking
> > surface has a substantially negative impact on their
> > friction coefficient and can easily cause the brake to
> > not be able to approach the above limit.
>
> Mud, perhaps, but not just water as in rain on the road.

The roads I've ridden have enough grit on them that the
rain splashes up an unpleasantly abrasive-sounding mixture
onto the rims.

One good reason for having hard brake pad material is that
the grinding sound of wet braking goes away once the grit
washes or scrapes out of the pads.

With soft pads, it embeds permanently and the scraping never
seems to go away....

> > please also remember that not everyone lives in flat
> > country like you.
>
> Have you ever been to England? It's not exactly Holland-
> like in its terrain. San Francisco type hills are not hard
> to find in England.

I had a laugh over this comment by "jim beam". It's not
unusual to find roads in England with gradients of more
than 1 in 7.

> > in my case, 210lbs [15 stone?] of lard contending with
> > several miles of gradient 6" deep in winter effluent are
> > not optimum conditions for rim brakes. next time you're
> > in the san francisco bay area, you're welcome to borrow
> > my guest bike and see what i mean. you'll enjoy it -
> > california rain is much warmer than british rain.
>
> You should try Minnesota's winter riding conditions... ;-)

In fact, rain is always at slightly above freezing temp. The
difference is in the ambient temperatures of the air you
experience with it.
--
Mark South: World Citizen, Net Denizen
 
Tim McNamara wrote:
> jim beam <[email protected]> writes:
>
>
>>david, you are correct that when the brakes are fully
>>effective, maximum braking is defined in terms of the
>>above. but it is incorrect to assume that all brakes are
>>effective to this level in all conditions. foreign
>>material [mud] between the brake pad & the braking surface
>>has a substantially negative impact on their friction
>>coefficient and can easily cause the brake to not be able
>>to approach the above limit.
>
>
> Mud, perhaps, but not just water as in rain on the road.
>
>
>>please also remember that not everyone lives in flat
>>country like you.
>
>
> Have you ever been to England? It's not exactly Holland-
> like in its terrain. San Francisco type hills are not hard
> to find in England.

yup! and i've been to cambridge too, which is where dd
lives. it is indeed very holland-like. fewer canals
perhaps...

>
>
>>in my case, 210lbs [15 stone?] of lard contending with
>>several miles of gradient 6" deep in winter effluent are
>>not optimum conditions for rim brakes. next time you're in
>>the san francisco bay area, you're welcome to borrow my
>>guest bike and see what i mean. you'll enjoy it -
>>california rain is much warmer than british rain.
>
>
> You should try Minnesota's winter riding conditions... ;-)
 
Mark South writes:

> The roads I've ridden have enough grit on them that the
> rain splashes up an unpleasantly abrasive-sounding mixture
> onto the rims.

This is how riders discovered their rear brake was dragging
with dual pivot brakes and moved them to climb with the rear
brake QR open. Since the QR was often not closed again
before the descent, they had no rear brake. In response,
Campagnolo made a single pivot 4:1 brake for the rear so
this would not recur.

> One good reason for having hard brake pad material is that
> the grinding sound of wet braking goes away once the grit
> washes or scrapes out of the pads.

> With soft pads, it embeds permanently and the scraping
> never seems to go away...

Not so with Kool-Stop salmon red pads. That they do not do
this is one of their main features. They do not pick up
gouging grit that eats rims and degrades braking. If there
is road grit in the pad, pumping the brake a couple of sharp
times expels these and allows good braking. That is how I
got to these pads in the first place.

Jobst Brandt [email protected]
 
jim beam <[email protected]> or "tux lover" or whatever sock puppet he's using
this week wrote:
>that all brakes are effective to this level in all
>conditions. foreign material [mud] between the brake pad &
>the braking surface has a substantially negative impact on
>their friction coefficient and can easily cause the brake
>to not be able to approach the above limit.

This is not an issue in road riding - grit and muck, sure,
but not the thick mud that makes disc brakes a more sensible
choice when riding offroad.

>please also remember that not everyone lives in flat
>country like you.

I don't. I have been fairly consistently too lazy to update
my Web page since circa 1997.

>in my case, 210lbs [15 stone?] of lard contending with
>several miles of gradient 6" deep in winter effluent are
>not optimum conditions for rim brakes.

You simply cannot beat someone who rides in the UK in terms
of filthy weather conditions - and while multiple-mile hills
are a rare enough affair, steep ones certainly are not. With
full panniers I have quite a bit more than 210 pounds to
stop, let alone the addition of a trailer (which does not
change the CoG much, being well-balanced on its own wheels,
but does increase the work to be done in braking.)
--
David Damerell <[email protected]> flcl?
 
<[email protected]> wrote:
>David Damerell writes:
[That rim brakes work well in the wet]
>I disagree on your assessment of rim brakes on wet rims.
>I have performed tests on wet braking that conclusively
>show that it doesn't work the way most riders visualize.
>I have had the opportunity to brake in water deep enough
>to submerge the rim and found that there was practically
>no brake effect during the immersion. Subsequently I rode
>in snow so there was a snow pack on the inner periphery
>of the rim.

Hang on; I am perfectly willing to grant that rim brakes do
not work well when the bottom of the rim is underwater, or
in heavy snow that coats the rim; I've done both.

I'm not _too_ worried about that, however, because I can't
ride very quickly in such conditions.

However, what is being said is that rim brakes cannot lift
the rear wheel when simply riding in the rain; and that is
manifestly false.
--
David Damerell <[email protected]> flcl?
 
Tom Sherman <[email protected]> wrote:
>David Damerell wrote:
>>Then your rim brakes are incompetently adjusted or
>>designed. A good rim brake will lift the rear wheel. You
>>cannot have more braking than that....
>While the above is true theoretically, in the real world a
>brake that provides better control of its modulation will
>allow the rider to apply a force closer to the theoretical
>maximum than a brake with poorer modulation would.

True, but I know well enough that I can get the rear wheel
to unload momentarily in emergency braking situations -
thankfully a rare occurrence, but they happen.

Now, if you want to say that some V-brakes do not modulate
well, I'm not going to argue with that.
--
David Damerell <[email protected]> flcl?
 
David Damerell wrote:

> <[email protected]> wrote:
>> David Damerell writes:
> [That rim brakes work well in the wet]
>> I disagree on your assessment of rim brakes on wet rims.
>> I have performed tests on wet braking that conclusively
>> show that it doesn't work the way most riders visualize.
>> I have had the opportunity to brake in water deep enough
>> to submerge the rim and found that there was practically
>> no brake effect during the immersion. Subsequently I rode
>> in snow so there was a snow pack on the inner periphery
>> of the rim.
>
> Hang on; I am perfectly willing to grant that rim brakes
> do not work well when the bottom of the rim is underwater,
> or in heavy snow that coats the rim; I've done both.
>
> I'm not _too_ worried about that, however, because I can't
> ride very quickly in such conditions.
>
> However, what is being said is that rim brakes cannot lift
> the rear wheel when simply riding in the rain; and that is
> manifestly false.

I can lift my rear wheel in heavy rain too. However, I've
still found there to be an increase in stopping distance;
the brakes don't start grabbing as quickly. It hasn't had a
large enough effect to make me want to rush out and buy disc
brakes, but it's quite noticeable.

--
Benjamin Lewis

Base 8 is just like base 10, if you are missing two fingers.
-- Tom Lehrer
 
Benjamin Lewis <[email protected]> wrote in
news:[email protected]:

> I can lift my rear wheel in heavy rain too. However, I've
> still found there to be an increase in stopping distance;
> the brakes don't start grabbing as quickly. It hasn't had
> a large enough effect to make me want to rush out and buy
> disc brakes, but it's quite noticeable.

That's why I'm leaning toward disc brakes on a new town
commuter/light trail bike. It's more about quick response
than the degree of stopping power, when a car or a dog pulls
out in front of you. I live in the Pacific Northwest, and
the roads are sloppy and wet for about half the year. I've
never loved the way rim brakes work in the rain, so I
thought I'd try disc brakes with this project.

On the other hand... I remember reading someplace (maybe
here?) that the slower reaction time with wet wheels and rim
brakes is a better match for a wet/slippery road surface. I
think the idea was that if you couldn't instantly lock the
wheel, you'd be less likely to skid on a wet road. Or
something like that.

I'm not sure that makes sense, but I'm curious what everyone
else here thinks about it. It seems to me that if you have
good modulation and an experienced rider, it's always an
advantage if the brakes are immediately available, instead
of having a delay to wipe water off the rim. But I don't
know (never having used disk brakes). Maybe there is a kind
of automatic safety factor in the balance between reduced
tire grip on wet roads, and delayed response with a wet
wheel and rim brakes?

--
Mike Barrs
 
David Damerell <[email protected]> wrote in message news:<Yom*[email protected]>...
> Michael Press <[email protected]> wrote:
> >David Damerell <[email protected]> wrote:
> >>Michael Press <[email protected]> wrote:
> >>Then your rim brakes are incompetently adjusted or
> >>designed. A good rim brake will lift the rear wheel.
> >>You cannot have more braking than that. What part of
> >>this escapes you?
> >The "wet" part seems to escape you.
>
> A good rim brake will lift the rear wheel in the wet. You
> cannot have more braking than that. What part of this
> escapes you?

A good disk brake will stop nearly equally well in either
set of conditions, limited only by the friction of the tire
against the road surface. In addition the predictability of
the amount of lever force needed to accomplish a certain
amount of braking likewise nearly equal.

The theoretical limit of braking capacity is a nice red
herring, but doesn't address the real, functional
differences between the two systems.

> >>>applied, in all conditions; the rim brakes lose
> >>>modulation in the wet, where you pretty much have to
> >>>mash them to get any stopping power.
> >>This sounds more like the days of steel rims than modern
> >>equipment.
> >Again, discounting others' experiences...
>
> That is not true. I am not disputing that your brakes do
> not perform well; I am merely pointing out that, since rim
> brakes can work perfectly well in the wet

Not all rim brakes work "perfectly well" in the wet. Some
require more effort and care, and some are just not well-
designed or set up.

One of the great benefits of disk brakes is the ease
of set-up.

> Obviously one can equally well obtain an inferior disc
> brake; that would not imply that no disc brake works well.

Actually, not. There are a very few, ultra-low-end
mechanical disk brakes that are a pain in the neck to
install and set up, but they are not nearly as finicky as
mediocre rim brakes in their operation. The "equally well"
part of your statement doesn't fly.

> >>>This is my experience. Others may have different
> >>>experiences, but unlike other posters, I won't discount
> >>>their experiences with blanket generalities.
> >>Unfortunately the "blanket generality" I am using is
> >>elementary applied mathematics.
> >Uh huh. Oh yeah, NOW I remember learning "disc brakes
> >suck" in math class.
>
> Evidently you didn't learn anything, or you would be able
> to see how the position of the CoG relative to the front
> contact patch informs maximum braking.

> >Just so you know, I won't be responding any more to
> >your posts.
>
> Of course not; you don't have an argument, merely a set
> of vague insinuations. This is an attempt to conceal
> that fact.

The fact that *you* make statements that are patently false
doesn't help your case. Such as misrepresenting the OP's
comments about not being able to lift his rear tire with his
brake set up to mean that the OP is claiming it's not
possible to do so with any given rim brake set up. A lovely
strawman, however.

Of course, I have long said I don't get the point of disk
brakes on a road bike, considering the fork strength and
potential ejection issues, but maybe there is a place for
them on an all-weather commuter/tourer, and that I have been
mistaken about my preconceived bias.
--
Jonesy
 
"Mark South" <[email protected]> writes:

> "Tim McNamara" <[email protected]> wrote in message news:m23c4m9af2.fsf@Stella-
> Blue.local...
>> jim beam <[email protected]> writes:
>>
>> > david, you are correct that when the brakes are fully
>> > effective, maximum braking is defined in terms of the
>> > above. but it is incorrect to assume that all brakes
>> > are effective to this level in all conditions. foreign
>> > material [mud] between the brake pad & the braking
>> > surface has a substantially negative impact on their
>> > friction coefficient and can easily cause the brake to
>> > not be able to approach the above limit.
>>
>> Mud, perhaps, but not just water as in rain on the road.
>
> The roads I've ridden have enough grit on them that the
> rain splashes up an unpleasantly abrasive-sounding mixture
> onto the rims.
>
> One good reason for having hard brake pad material is that
> the grinding sound of wet braking goes away once the grit
> washes or scrapes out of the pads.
>
> With soft pads, it embeds permanently and the scraping
> never seems to go away....

I use Mathauser or Koolstop salmon pads, which do not seem
to get grit imbedded in them, for this very reason. Brake
pads should be one smooth chunk of material with no grooves
or whatever- all those do is entrap grit.

>> > please also remember that not everyone lives in flat
>> > country like you.
>>
>> Have you ever been to England? It's not exactly Holland-
>> like in its terrain. San Francisco type hills are not
>> hard to find in England.
>
> I had a laugh over this comment by "jim beam". It's not
> unusual to find roads in England with gradients of more
> than 1 in 7.

Like 1 in 4... :-o

>> > in my case, 210lbs [15 stone?] of lard contending with
>> > several miles of gradient 6" deep in winter effluent
>> > are not optimum conditions for rim brakes. next time
>> > you're in the san francisco bay area, you're welcome to
>> > borrow my guest bike and see what i mean. you'll enjoy
>> > it - california rain is much warmer than british rain.
>>
>> You should try Minnesota's winter riding
>> conditions... ;-)
>
> In fact, rain is always at slightly above freezing temp.
> The difference is in the ambient temperatures of the air
> you experience with it.

Rain? Minnesota winter? Bwahh-haah-hah! Not much rain falls
at 20 below F. ;-) Although the last few winters have been
very mild with very little of this, allowing more winter
time riding in above-freezing temps (and greater likelihood
of cold rain). Once the water bottles freeze up on a ride, I
park the bike and wait for warmer weather. I admit it, I
ride 6,500 miles a year but I pretty much am a fair weather
rider. I see no reason to be miserable in the pursuit of
having fun.
 
foldedpath <[email protected]> writes:

> Benjamin Lewis <[email protected]> wrote in
> news:[email protected]:
>
>> I can lift my rear wheel in heavy rain too. However, I've
>> still found there to be an increase in stopping distance;
>> the brakes don't start grabbing as quickly. It hasn't had
>> a large enough effect to make me want to rush out and buy
>> disc brakes, but it's quite noticeable.
>
> That's why I'm leaning toward disc brakes on a new town
> commuter/light trail bike. It's more about quick response
> than the degree of stopping power, when a car or a dog
> pulls out in front of you. I live in the Pacific
> Northwest, and the roads are sloppy and wet for about half
> the year. I've never loved the way rim brakes work in the
> rain, so I thought I'd try disc brakes with this project.

Well, not only is the water an issue but anodized sidewalls
on rims also adversely affect wet braking. With bare
aluminum braking tracks on the rims and Koolstop salmon
pads, wet weather braking is pretty good (relatively
speaking).
 
Tim McNamara writes:

>> With soft pads, it embeds permanently and the scraping
>> never seems to go away....

> I use Matthauser or Kool-stop salmon pads, which do not
> seem to get grit embedded in them, for this very reason.
> Brake pads should be one smooth chunk of material with no
> grooves or whatever- all those do is entrap grit.

It is not grooves that embed grit in the brake pad. The
damaging effect is that the pad so securely holds a piece of
grit that it becomes a cutting tool without dislodging. If
you inspect such a brake pad, you'll find that the major
component is oxidized aluminum shavings that have created a
pocket in the pad. Kool-Stop salmon pads are not immune to
grit entrapment but pumping the brake will dislodge any
particle that gets between pad and aluminum rim.

Jobst Brandt [email protected]
 
Tim McNamara <[email protected]> wrote:
>Well, not only is the water an issue but anodized sidewalls
>on rims also adversely affect wet braking. With bare
>aluminum braking tracks on the rims and Koolstop salmon
>pads, wet weather braking is pretty good (relatively
>speaking).

Unfortunately, we ask ourselves what's the best way to
wear the anodisation off so we can brake more readily
in the rain... and the answer is, of course, to ride in
the rain. :-(
--
David Damerell <[email protected]> flcl?
 

Similar threads