Can Disk Brakes flip you over the handle bars?

Nate Nagel wrote:

Lots of cars didn't used to have servo assistance on the
brakes. All the force and work required to brake came from your
leg. And yet you could slow down a tonne of car from 70mph like
that.

Drum brakes used massive self servo action to achieve useful
braking. Because that effect is highly unpredictable, they had
both lock-up and fade. That is why we use disks today. You may
recall that this was discussed here at great length.

I don't understand why you consider that action "highly
unpredictable" it's simply speed dependent. Sure they lock up if
you stomp on 'em but so will boosted discs. The fade comes from
the inability of the shoes and drum to shed heat as effectively as
discs where all the parts are out in the open and in some racing
applications even have forced air ducted over them for additional
cooling.

I think you don't know the history of the drum brake. It's self
servo action is laid out about a specific friction coefficient such
that when it is a bit high, brakes lock up (even after taking the
foot off the pedal)

Which is not an issue on any automotive application, as if anything,
current non-asbestos linings have an even lower coefficient of
friction than the original linings around which the brake system was
designed. I have seen some high-performance linings made available
for various vintage drum brake setups (presumably for vintage
racing) and have not ever heard of this happening in practice.

and when it is a bit low from heating, there is essentially no brake
at all, resulting in run-aways on mountain roads.

The servo effect is what makes the drum brake respond poorly and why,
if you read the Wiki article, no RR ever used drum brakes, skidding a
wheel being a major loss.

That much is true. Of course this can also happen with discs, if you
abuse them enough, but discs cool down *much* faster than drums given
that the friction surface is in direct contact with cooling air, the
discs have a higher surface area to mass ratio, and that the calipers
and at least portions of the linings are also in closer proximity to
cooling air than in a drum brake.

It cannot happen with disks. The relation of the friction coefficient
and brake retardation is linear so the 5% change in friction that
formerly cause total brake failure, the disk sees a 5% change. It's
much like boiling engines in cars. That they don't boil today is not
because they have better radiators, but because they have a
non-leaking water pump seal and don't lose coolant.

http://en.wikipedia.org/wiki/Engine_...ere_air-cooled

Old manual drum brakes are actually quite pleasant to drive on, so
long as you're not racing or driving fast through the mountains.
IMHO they have a much better pedal feel than all but the best new
disc brakes; certainly more direct as there is a direct hydraulic
connection between foot and shoes with only a very few, simple
mechanical parts in between.

Oh nostalgia for things that weren't. Read:

http://en.wikipedia.org/wiki/Brake_f...in_drum_brakes

Seeing as I actually own and (occasionally) drive a '55 Studebaker
coupe equipped with the (excellent) factory equipment brakes, with
the only upgrade being the addition of finned drums from a later
model car, I can say that they certainly aren't anywhere near the
death-dealing devices that you seem to be making them out to be.
The three major shortcomings of drum brakes in general are 1) brakes
often undersized for the vehicle, exacerbating other problems (not
an issue on my car, but, say, the 9" front drums on an old Dart are
an insult to common sense.) 2) Cooling - drum brakes do retain heat
far more so than do discs, resulting in earlier fading. 3) single
circuit master cylinders can result in complete brake system failure
with one single hydraulic failure. Not an issue with the drums
themselves, but legal until the late 60's and therefore common on
most vehicles you'll find with four wheel drum brakes.

I take it you are saying that the auto companies of the world are
barking up the wrong tree when they dumped the drum brake. That's a
bit far fetched. Drum brakes are non-linear and unreliable.

http://tinyurl.com/jhiu

The difficult part is getting rid of all the heat that the
brakes are converting the bike's kinetic energy into.

That's why heavy trucks still use drum brakes, drums having large
surface to reject heat by forced convection. Highways have long dual
tired skid marks because the response to brake application cannot be
well controlled with drum brakes.

I believe that they still use drums because they're easier to work with
in an air brake application. They still don't shed heat nearly as well
as to discs. I suspect many of those skid marks are also the result of
air system failures, not panic stops gone bad.

You are guessing. Brakes are used for performance and disks large
enough to control a large truck will not fit inside standard truck
wheels. That's why disks are not used there.

Apparently the bicycle industry is not addressing that part of
the problem when the surface area and thermal mass their gossamer
rings of steel have. I have asked brake manufacturers why their
disks are mostly air with a thin pattern of thin steel between.
For cooling is the answer. Maybe they should tell the automotive
and railway people about their theory.

??? most automotive disc brakes are "vented," that is, the braking
surfaces are separated by a webbing of cast iron intended to have
air pass through. High-performance rotors are also cross-drilled
and/or slotted.

I think you'll find that they are not vented but rather solid disks
with no holes.

Not true at all.

OK! You keep making these claims and show no reason or reference for
them. Just inspect BMW cars and note that even their large "sport
cars"do not have holes in the disks.

The cross drilling is found only on vehicles tauted to be high
performance while no passenger sedan has cross drilling that has no
technical advantage but is a relic of the days when brake fade was
believed to be caused by out-gassing of brake shoes to generate a
gas bearing. The holes allow that imaginary gas to escape.

True, but all but very light and/or inexpensive cars still use
vented rotors, at least on the front. you are confusing
cross-drilling and/or slotting with simple venting, which is a
common feature of nearly all automotive disc brakes. Look at a disc
edge-on, you will see that it is not solid but is essentially two
solid braking surfaces connected by a webbing and with lots of air
space in between. That is what is commonly known as a "vented"
rotor.

Name a few please.

I worked in brake design with Girling and ATE in the years when the
auto industry was changing to disks and was amazed at the amount of
myth and lore surrounding brakes.

I don't mean to be insulting, but that surprises me given the
inaccuracies in your post. Although that would explain your
unfamiliarity with vented rotors, as AFAIR at least the Studebaker
applications of the first Girling brakes did in fact use solid rotors.
I would assume that other applications of those brakes did as well as
I'm not aware of any significant variations on the caliper design.

You are not trying hard enough to not be insulting. Your unsupported
claims are in themselves insulting in facer of evidence to the
contrary. The subject here was to cross drilling with holed through
the disk faces. RR disks are all internally radially vented in the
disk casting.

http://www.merriam-webster.com/dictionary/disk

Jobst Brandt

wrote:
Nate Nagel wrote:


Lots of cars didn't used to have servo assistance on the
brakes. All the force and work required to brake came from your
leg. And yet you could slow down a tonne of car from 70mph like
that.


Drum brakes used massive self servo action to achieve useful
braking. Because that effect is highly unpredictable, they had
both lock-up and fade. That is why we use disks today. You may
recall that this was discussed here at great length.


I don't understand why you consider that action "highly
unpredictable" it's simply speed dependent. Sure they lock up if
you stomp on 'em but so will boosted discs. The fade comes from
the inability of the shoes and drum to shed heat as effectively as
discs where all the parts are out in the open and in some racing
applications even have forced air ducted over them for additional
cooling.


I think you don't know the history of the drum brake. It's self
servo action is laid out about a specific friction coefficient such
that when it is a bit high, brakes lock up (even after taking the
foot off the pedal)


Which is not an issue on any automotive application, as if anything,
current non-asbestos linings have an even lower coefficient of
friction than the original linings around which the brake system was
designed. I have seen some high-performance linings made available
for various vintage drum brake setups (presumably for vintage
racing) and have not ever heard of this happening in practice.


and when it is a bit low from heating, there is essentially no brake
at all, resulting in run-aways on mountain roads.


The servo effect is what makes the drum brake respond poorly and why,
if you read the Wiki article, no RR ever used drum brakes, skidding a
wheel being a major loss.


That much is true. Of course this can also happen with discs, if you
abuse them enough, but discs cool down *much* faster than drums given
that the friction surface is in direct contact with cooling air, the
discs have a higher surface area to mass ratio, and that the calipers
and at least portions of the linings are also in closer proximity to
cooling air than in a drum brake.


It cannot happen with disks. The relation of the friction coefficient
and brake retardation is linear so the 5% change in friction that
formerly cause total brake failure, the disk sees a 5% change. It's
much like boiling engines in cars. That they don't boil today is not
because they have better radiators, but because they have a
non-leaking water pump seal and don't lose coolant.

http://en.wikipedia.org/wiki/Engine_...ere_air-cooled


a 5% change in brake friction will not cause a "total brake failure" on
any decent automotive brake system. Now it may cause more than 5% loss
on a servo-action system, but not "total."


Old manual drum brakes are actually quite pleasant to drive on, so
long as you're not racing or driving fast through the mountains.
IMHO they have a much better pedal feel than all but the best new
disc brakes; certainly more direct as there is a direct hydraulic
connection between foot and shoes with only a very few, simple
mechanical parts in between.


Oh nostalgia for things that weren't. Read:


http://en.wikipedia.org/wiki/Brake_f...in_drum_brakes


Seeing as I actually own and (occasionally) drive a '55 Studebaker
coupe equipped with the (excellent) factory equipment brakes, with
the only upgrade being the addition of finned drums from a later
model car, I can say that they certainly aren't anywhere near the
death-dealing devices that you seem to be making them out to be.
The three major shortcomings of drum brakes in general are 1) brakes
often undersized for the vehicle, exacerbating other problems (not
an issue on my car, but, say, the 9" front drums on an old Dart are
an insult to common sense.) 2) Cooling - drum brakes do retain heat
far more so than do discs, resulting in earlier fading. 3) single
circuit master cylinders can result in complete brake system failure
with one single hydraulic failure. Not an issue with the drums
themselves, but legal until the late 60's and therefore common on
most vehicles you'll find with four wheel drum brakes.


I take it you are saying that the auto companies of the world are
barking up the wrong tree when they dumped the drum brake. That's a
bit far fetched. Drum brakes are non-linear and unreliable.

http://tinyurl.com/jhiu


No, I'm saying that while discs are definitely an improvement, drums are
not nearly as dangerous and unacceptable, at least in the better
automotive implementations, as you make them out to be.

How do you explain, if the servo-action is responsible for the effects
that you claim, that some automotive drums did *not* use servo-action
brakes and still exhibited similar fade? It's the heat, plain and
simple. That was the biggest downfall of drums, and it's the biggest
advantage of discs. To a lesser extent the increased linearity of brake
torque vs. line pressure that you did mention. That is not to say that
there aren't downsides - the biggest *disadvantage* of discs is the
necessity to install a power booster on all but the lightest cars, as
you need significantly more line pressure to develop the same brake
torque as the same size drum brake. This is what I was alluding to when
I mentioned the improved pedal feel of drums - the vacuum booster
commonly used does make for a far less direct feel on the brake pedal.


The difficult part is getting rid of all the heat that the
brakes are converting the bike's kinetic energy into.


That's why heavy trucks still use drum brakes, drums having large
surface to reject heat by forced convection. Highways have long dual
tired skid marks because the response to brake application cannot be
well controlled with drum brakes.


I believe that they still use drums because they're easier to work with
in an air brake application. They still don't shed heat nearly as well
as to discs. I suspect many of those skid marks are also the result of
air system failures, not panic stops gone bad.


You are guessing. Brakes are used for performance and disks large
enough to control a large truck will not fit inside standard truck
wheels. That's why disks are not used there.

I actually *have* seen discs on heavy trucks... not nearly as many as
drums, but they are out there.


Apparently the bicycle industry is not addressing that part of
the problem when the surface area and thermal mass their gossamer
rings of steel have. I have asked brake manufacturers why their
disks are mostly air with a thin pattern of thin steel between.
For cooling is the answer. Maybe they should tell the automotive
and railway people about their theory.


??? most automotive disc brakes are "vented," that is, the braking
surfaces are separated by a webbing of cast iron intended to have
air pass through. High-performance rotors are also cross-drilled
and/or slotted.


I think you'll find that they are not vented but rather solid disks
with no holes.


Not true at all.


OK! You keep making these claims and show no reason or reference for
them. Just inspect BMW cars and note that even their large "sport
cars"do not have holes in the disks.


But they are still vented.


The cross drilling is found only on vehicles tauted to be high
performance while no passenger sedan has cross drilling that has no
technical advantage but is a relic of the days when brake fade was
believed to be caused by out-gassing of brake shoes to generate a
gas bearing. The holes allow that imaginary gas to escape.


True, but all but very light and/or inexpensive cars still use
vented rotors, at least on the front. you are confusing
cross-drilling and/or slotting with simple venting, which is a
common feature of nearly all automotive disc brakes. Look at a disc
edge-on, you will see that it is not solid but is essentially two
solid braking surfaces connected by a webbing and with lots of air
space in between. That is what is commonly known as a "vented"
rotor.


Name a few please.

Any modern car equipped with disc brakes. In my driveway, a Chevy
Impala (icky company car) a Porsche 944 and a Ford F-150. All have
vented discs, at least on the front.

The last car I saw *without* vented front discs was my mom's '86 VW
Golf. It did have solid front discs.


I worked in brake design with Girling and ATE in the years when the
auto industry was changing to disks and was amazed at the amount of
myth and lore surrounding brakes.


I don't mean to be insulting, but that surprises me given the
inaccuracies in your post. Although that would explain your
unfamiliarity with vented rotors, as AFAIR at least the Studebaker
applications of the first Girling brakes did in fact use solid rotors.
I would assume that other applications of those brakes did as well as
I'm not aware of any significant variations on the caliper design.


You are not trying hard enough to not be insulting. Your unsupported
claims are in themselves insulting in facer of evidence to the
contrary. The subject here was to cross drilling with holed through
the disk faces. RR disks are all internally radially vented in the
disk casting.

http://www.merriam-webster.com/dictionary/disk

Jobst Brandt

At this point, I can't even determine if you understand the difference
between venting and drilling. If you can't keep your terminology
straight there's no point in continuing this discussion.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

On May 2, 2:50 pm, N8N wrote:
On May 1, 7:49 pm, wrote:

Drum brakes used massive self servo action to achieve useful braking.
Because that effect is highly unpredictable, they had both lock-up and
fade. That is why we use disks today. You may recall that this was
discussed here at great length.

I don't understand why you consider that action "highly unpredictable"
it's simply speed dependent. Sure they lock up if you stomp on 'em
but so will boosted discs. The fade comes from the inability of the
shoes and drum to shed heat as effectively as discs where all the
parts are out in the open and in some racing applications even have
forced air ducted over them for additional cooling. Old manual drum
brakes are actually quite pleasant to drive on, so long as you're not
racing or driving fast through the mountains. IMHO they have a much
better pedal feel than all but the best new disc brakes; certainly
more direct as there is a direct hydraulic connection between foot and
shoes with only a very few, simple mechanical parts in between.

Nate, it sounds to me that your evaluation of "feel" is influenced
unduly by your examination of parts diagrams. You see what you think
is a "more direct connection," therefore you think drum brakes feel
better.

Drum brakes are inherently less predictable. Two personal examples:

First, I as a teenager in the '60s, I drove an old Fiat sedan. It had
drum brakes that appeared oversized for its weight. I decided to test
them to see if they would fade, by accelerating to about 60 mph and
stopping hard, repeatedly.

They did fade - but not as I imagined, by simply requiring more pedal
pressure. On about the third stop, the car suddenly swerved violently
side to side. It was barely controllable, and extremely scary.

Second, I still occasionally ride a 1972 BMW motorcycle, with double
leading shoe front drum brake. "Double leading shoe" means the built-
in servo effect works for me only in the forward direction. On a
certain steep hill with a traffic light, the front brak is barely able
to keep the bike from rolling backwards, because friction at the
braking surface acts to remove braking force.

The latter isn't particularly important, I suppose, but it does
indicate how dependent this system is on the friction coefficient.
The former indicates the same, but in a much more dangerous manner. I
assume one front brake faded before the other - that is, generated
less friction; but the sudden loss of servo effect was violent and
unpredictable. It was much different than merely "speed dependent,"
as you claim.

Drum brakes are gone from cars (at least, in front) for very good
reasons.

- Frank Krygowski

"Nate Nagel" wrote in message
...

??? most automotive disc brakes are "vented," that is, the braking
surfaces are separated by a webbing of cast iron intended to have
air pass through. High-performance rotors are also cross-drilled
and/or slotted.


I think you'll find that they are not vented but rather solid disks with
no holes.

Not true at all.

I reckon he's probably right - vented disks aren't the norm here. Faster and
bigger stuff has them, but plain old solid rotors rule for normal cars.

cheers,
clive

wrote in message
...

You are guessing. Brakes are used for performance and disks large
enough to control a large truck will not fit inside standard truck
wheels. That's why disks are not used there.

I believe trucks are moving to disks over here. Dunno if they're inboard or
not, but it's happening. Of course the USian truck industry is very
technologically conservative, so I'd not be surprised if they were a long
way behing.

cheers,
clive

"Nate Nagel" wrote in message
...

This is what I was alluding to when I mentioned the improved pedal feel of
drums - the vacuum booster commonly used does make for a far less direct
feel on the brake pedal.

You might find driving a power-braked car amusing - on a proper citroen, the
pedal doesn't move (noticably), but the braking is still proportional to how
hard you press. Coming from an over-assisted conventional car was an
interesting reminder of the difference.

Any modern car equipped with disc brakes. In my driveway, a Chevy Impala
(icky company car) a Porsche 944 and a Ford F-150. All have vented discs,
at least on the front.

Many over here don't have vented. My CX had them (all round :-) ), but
nothing else I've owned. The stuff you've just mentioned comes under "bigger
or faster than normal". Of course with the weight inflation of cars, they're
getting rather more common...

cheers,
clive

Nate Nagel wrote:

Lots of cars didn't used to have servo assistance on the
brakes. All the force and work required to brake came from
your leg. And yet you could slow down a tonne of car from
70mph like that.

Drum brakes used massive self servo action to achieve useful
braking. Because that effect is highly unpredictable, they had
both lock-up and fade. That is why we use disks today. You
may recall that this was discussed here at great length.

I don't understand why you consider that action "highly
unpredictable" it's simply speed dependent. Sure they lock up
if you stomp on 'em but so will boosted discs. The fade comes
from the inability of the shoes and drum to shed heat as
effectively as discs where all the parts are out in the open and
in some racing applications even have forced air ducted over
them for additional cooling.

I think you don't know the history of the drum brake. It's self
servo action is laid out about a specific friction coefficient
such that when it is a bit high, brakes lock up (even after
taking the foot off the pedal)

Which is not an issue on any automotive application, as if
anything, current non-asbestos linings have an even lower
coefficient of friction than the original linings around which the
brake system was designed. I have seen some high-performance
linings made available for various vintage drum brake setups
(presumably for vintage racing) and have not ever heard of this
happening in practice.

and when it is a bit low from heating, there is essentially no
brake at all, resulting in run-aways on mountain roads.

The servo effect is what makes the drum brake respond poorly and
why, if you read the Wiki article, no RR ever used drum brakes,
skidding a wheel being a major loss.

That much is true. Of course this can also happen with discs, if
you abuse them enough, but discs cool down *much* faster than
drums given that the friction surface is in direct contact with
cooling air, the discs have a higher surface area to mass ratio,
and that the calipers and at least portions of the linings are
also in closer proximity to cooling air than in a drum brake.

It cannot happen with disks. The relation of the friction
coefficient and brake retardation is linear so the 5% change in
friction that formerly cause total brake failure, the disk sees
a 5% change. It's much like boiling engines in cars. That
they don't boil today is not because they have better
radiators, but because they have a non-leaking water pump seal
and don't lose coolant.

http://en.wikipedia.org/wiki/Engine_...ere_air-cooled

a 5% change in brake friction will not cause a "total brake failure"
on any decent automotive brake system. Now it may cause more than
5% loss on a servo-action system, but not "total."

Old manual drum brakes are actually quite pleasant to drive on,
so long as you're not racing or driving fast through the
mountains. IMHO they have a much better pedal feel than all but
the best new disc brakes; certainly more direct as there is a
direct hydraulic connection between foot and shoes with only a
very few, simple mechanical parts in between.

Oh nostalgia for things that weren't. Read:

http://en.wikipedia.org/wiki/Brake_f...in_drum_brakes

Seeing as I actually own and (occasionally) drive a '55 Studebaker
coupe equipped with the (excellent) factory equipment brakes, with
the only upgrade being the addition of finned drums from a later
model car, I can say that they certainly aren't anywhere near the
death-dealing devices that you seem to be making them out to be.
The three major shortcomings of drum brakes in general are 1)
brakes often undersized for the vehicle, exacerbating other
problems (not an issue on my car, but, say, the 9" front drums on
an old Dart are an insult to common sense.) 2) Cooling - drum
brakes do retain heat far more so than do discs, resulting in
earlier fading. 3) single circuit master cylinders can result in
complete brake system failure with one single hydraulic failure.
Not an issue with the drums themselves, but legal until the late
60's and therefore common on most vehicles you'll find with four
wheel drum brakes.

I take it you are saying that the auto companies of the world are
barking up the wrong tree when they dumped the drum brake. That's
a bit far fetched. Drum brakes are non-linear and unreliable.

http://tinyurl.com/jhiu

No, I'm saying that while discs are definitely an improvement, drums
are not nearly as dangerous and unacceptable, at least in the better
automotive implementations, as you make them out to be.

How do you explain, if the servo-action is responsible for the
effects that you claim, that some automotive drums did *not* use
servo-action brakes and still exhibited similar fade? It's the
heat, plain and simple. That was the biggest downfall of drums, and
it's the biggest advantage of discs. To a lesser extent the
increased linearity of brake torque vs. line pressure that you did
mention. That is not to say that there aren't downsides - the
biggest *disadvantage* of discs is the necessity to install a power
booster on all but the lightest cars, as you need significantly more
line pressure to develop the same brake torque as the same size drum
brake. This is what I was alluding to when I mentioned the improved
pedal feel of drums - the vacuum booster commonly used does make for
a far less direct feel on the brake pedal.

When the brake application force is in the direction of drum rotation,
as it must be with drum brakes, then there is a self energising
effect. Proof of that is the rum brakes lock up at times when the
friction coefficient is slightly higher than the design level. All
deum brakes have servo effect. If you have worked on drum brakes you
should have noticed that they are designated leading shoe brakes, that
is that the activating hydraulic piston is pushing in the direction of
drum rotation.

The difficult part is getting rid of all the heat that the
brakes are converting the bike's kinetic energy into.

That's why heavy trucks still use drum brakes, drums having large
surface to reject heat by forced convection. Highways have long
dual tired skid marks because the response to brake application
cannot be well controlled with drum brakes.

I believe that they still use drums because they're easier to work
with in an air brake application. They still don't shed heat
nearly as well as to discs. I suspect many of those skid marks
are also the result of air system failures, not panic stops gone
bad.

You are guessing. Brakes are used for performance and disks large
enough to control a large truck will not fit inside standard truck
wheels. That's why disks are not used there.

I actually *have* seen discs on heavy trucks... not nearly as many
as drums, but they are out there.

You may have seen them on tractors of semi trailer rigs, but not on
the tandem dual dive axles or the semitrailer where heavy braking
occurs.

Apparently the bicycle industry is not addressing that part of
the problem when the surface area and thermal mass their
gossamer rings of steel have. I have asked brake manufacturers
why their disks are mostly air with a thin pattern of thin
steel between. For cooling is the answer. Maybe they should
tell the automotive and railway people about their theory.

??? most automotive disc brakes are "vented," that is, the
braking surfaces are separated by a webbing of cast iron
intended to have air pass through. High-performance rotors are
also cross-drilled and/or slotted.

I think you'll find that they are not vented but rather solid
disks with no holes.

Not true at all.

OK! You keep making these claims and show no reason or reference
for them. Just inspect BMW cars and note that even their large
"sport cars"do not have holes in the disks.

But they are still vented.

Look at all the high performance (BMW, Mercedes, Caddillac, Chrysler,
Cheverolet, Buick,...) cars and you will see they have no holes. You
must be assuming car companies are taking safety lightly if they sell
the largest part of their cars with, as you claim, inferior disks that
have no holes.

The cross drilling is found only on vehicles tauted to be high
performance while no passenger sedan has cross drilling that has
no technical advantage but is a relic of the days when brake fade
was believed to be caused by out-gassing of brake shoes to
generate a gas bearing. The holes allow that imaginary gas to
escape.

True, but all but very light and/or inexpensive cars still use
vented rotors, at least on the front. you are confusing
cross-drilling and/or slotting with simple venting, which is a
common feature of nearly all automotive disc brakes. Look at a
disc edge-on, you will see that it is not solid but is essentially
two solid braking surfaces connected by a webbing and with lots of
air space in between. That is what is commonly known as a
"vented" rotor.

Name a few please.

Any modern car equipped with disc brakes. In my driveway, a Chevy
Impala (icky company car) a Porsche 944 and a Ford F-150. All have
vented discs, at least on the front.

Not the new ones aold today. Exactly these are proof that there is no
benefit to the cross drillings in the disks of "sports cars".

The last car I saw *without* vented front discs was my mom's '86 VW
Golf. It did have solid front discs.

You use the term "vemnted" without definition. What do you mean?

I worked in brake design with Girling and ATE in the years when
the auto industry was changing to disks and was amazed at the
amount of myth and lore surrounding brakes.

I don't mean to be insulting, but that surprises me given the
inaccuracies in your post. Although that would explain your
unfamiliarity with vented rotors, as AFAIR at least the Studebaker
applications of the first Girling brakes did in fact use solid
rotors. I would assume that other applications of those brakes
did as well as I'm not aware of any significant variations on the
caliper design.

You are not trying hard enough to not be insulting. Your
unsupported claims are in themselves insulting in facer of evidence
to the contrary. The subject here was to cross drilling with holed
through the disk faces. RR disks are all internally radially
vented in the disk casting.

http://www.merriam-webster.com/dictionary/disk

At this point, I can't even determine if you understand the
difference between venting and drilling. If you can't keep your
terminology straight there's no point in continuing this discussion.

At this point I suggest you heed your request for definition of disk
form. I detect you are trying to make a technical educational course
about disk brake, not understanding the basic difference between disks
and drums. I am not ready to outline a course on disk brakes here.

Jobst Brandt

Clive George wrote:
"Nate Nagel" wrote in message
...

This is what I was alluding to when I mentioned the improved pedal
feel of drums - the vacuum booster commonly used does make for a far
less direct feel on the brake pedal.


You might find driving a power-braked car amusing - on a proper citroen,
the pedal doesn't move (noticably), but the braking is still
proportional to how hard you press. Coming from an over-assisted
conventional car was an interesting reminder of the difference.

Any modern car equipped with disc brakes. In my driveway, a Chevy
Impala (icky company car) a Porsche 944 and a Ford F-150. All have
vented discs, at least on the front.


Many over here don't have vented. My CX had them (all round :-) ), but
nothing else I've owned. The stuff you've just mentioned comes under
"bigger or faster than normal". Of course with the weight inflation of
cars, they're getting rather more common...

cheers,
clive

If you'd consider any of those cars "faster than normal" I have the
greatest sympathy for you. Of course Vlad the Impala and the pickup
truck are also quite large, and only one of those two has a good reason
for being so. A 944 has many redeeming qualities, but sparkling
acceleration isn't one of them.

Oddly enough, likely the fastest car I own (I don't know for sure, I
haven't fully tested its capabilities) is also the one with four wheel
drum brakes.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

wrote in message
...
Nate Nagel wrote:

Lots of cars didn't used to have servo assistance on the
brakes. All the force and work required to brake came from
your leg. And yet you could slow down a tonne of car from
70mph like that.

Drum brakes used massive self servo action to achieve useful
braking. Because that effect is highly unpredictable, they had
both lock-up and fade. That is why we use disks today. You
may recall that this was discussed here at great length.

I don't understand why you consider that action "highly
unpredictable" it's simply speed dependent. Sure they lock up
if you stomp on 'em but so will boosted discs. The fade comes
from the inability of the shoes and drum to shed heat as
effectively as discs where all the parts are out in the open and
in some racing applications even have forced air ducted over
them for additional cooling.

I think you don't know the history of the drum brake. It's self
servo action is laid out about a specific friction coefficient
such that when it is a bit high, brakes lock up (even after
taking the foot off the pedal)

Which is not an issue on any automotive application, as if
anything, current non-asbestos linings have an even lower
coefficient of friction than the original linings around which the
brake system was designed. I have seen some high-performance
linings made available for various vintage drum brake setups
(presumably for vintage racing) and have not ever heard of this
happening in practice.

and when it is a bit low from heating, there is essentially no
brake at all, resulting in run-aways on mountain roads.

The servo effect is what makes the drum brake respond poorly and
why, if you read the Wiki article, no RR ever used drum brakes,
skidding a wheel being a major loss.

That much is true. Of course this can also happen with discs, if
you abuse them enough, but discs cool down *much* faster than
drums given that the friction surface is in direct contact with
cooling air, the discs have a higher surface area to mass ratio,
and that the calipers and at least portions of the linings are
also in closer proximity to cooling air than in a drum brake.

It cannot happen with disks. The relation of the friction
coefficient and brake retardation is linear so the 5% change in
friction that formerly cause total brake failure, the disk sees
a 5% change. It's much like boiling engines in cars. That
they don't boil today is not because they have better
radiators, but because they have a non-leaking water pump seal
and don't lose coolant.

http://en.wikipedia.org/wiki/Engine_...ere_air-cooled

a 5% change in brake friction will not cause a "total brake failure"
on any decent automotive brake system. Now it may cause more than
5% loss on a servo-action system, but not "total."

Old manual drum brakes are actually quite pleasant to drive on,
so long as you're not racing or driving fast through the
mountains. IMHO they have a much better pedal feel than all but
the best new disc brakes; certainly more direct as there is a
direct hydraulic connection between foot and shoes with only a
very few, simple mechanical parts in between.

Oh nostalgia for things that weren't. Read:

http://en.wikipedia.org/wiki/Brake_f...in_drum_brakes

Seeing as I actually own and (occasionally) drive a '55 Studebaker
coupe equipped with the (excellent) factory equipment brakes, with
the only upgrade being the addition of finned drums from a later
model car, I can say that they certainly aren't anywhere near the
death-dealing devices that you seem to be making them out to be.
The three major shortcomings of drum brakes in general are 1)
brakes often undersized for the vehicle, exacerbating other
problems (not an issue on my car, but, say, the 9" front drums on
an old Dart are an insult to common sense.) 2) Cooling - drum
brakes do retain heat far more so than do discs, resulting in
earlier fading. 3) single circuit master cylinders can result in
complete brake system failure with one single hydraulic failure.
Not an issue with the drums themselves, but legal until the late
60's and therefore common on most vehicles you'll find with four
wheel drum brakes.

I take it you are saying that the auto companies of the world are
barking up the wrong tree when they dumped the drum brake. That's
a bit far fetched. Drum brakes are non-linear and unreliable.

http://tinyurl.com/jhiu

No, I'm saying that while discs are definitely an improvement, drums
are not nearly as dangerous and unacceptable, at least in the better
automotive implementations, as you make them out to be.

How do you explain, if the servo-action is responsible for the
effects that you claim, that some automotive drums did *not* use
servo-action brakes and still exhibited similar fade? It's the
heat, plain and simple. That was the biggest downfall of drums, and
it's the biggest advantage of discs. To a lesser extent the
increased linearity of brake torque vs. line pressure that you did
mention. That is not to say that there aren't downsides - the
biggest *disadvantage* of discs is the necessity to install a power
booster on all but the lightest cars, as you need significantly more
line pressure to develop the same brake torque as the same size drum
brake. This is what I was alluding to when I mentioned the improved
pedal feel of drums - the vacuum booster commonly used does make for
a far less direct feel on the brake pedal.

When the brake application force is in the direction of drum rotation,
as it must be with drum brakes, then there is a self energising
effect. Proof of that is the rum brakes lock up at times when the
friction coefficient is slightly higher than the design level. All
deum brakes have servo effect. If you have worked on drum brakes you
should have noticed that they are designated leading shoe brakes, that
is that the activating hydraulic piston is pushing in the direction of
drum rotation.

The difficult part is getting rid of all the heat that the
brakes are converting the bike's kinetic energy into.

That's why heavy trucks still use drum brakes, drums having large
surface to reject heat by forced convection. Highways have long
dual tired skid marks because the response to brake application
cannot be well controlled with drum brakes.

I believe that they still use drums because they're easier to work
with in an air brake application. They still don't shed heat
nearly as well as to discs. I suspect many of those skid marks
are also the result of air system failures, not panic stops gone
bad.

You are guessing. Brakes are used for performance and disks large
enough to control a large truck will not fit inside standard truck
wheels. That's why disks are not used there.

I actually *have* seen discs on heavy trucks... not nearly as many
as drums, but they are out there.

You may have seen them on tractors of semi trailer rigs, but not on
the tandem dual dive axles or the semitrailer where heavy braking
occurs.

Apparently the bicycle industry is not addressing that part of
the problem when the surface area and thermal mass their
gossamer rings of steel have. I have asked brake manufacturers
why their disks are mostly air with a thin pattern of thin
steel between. For cooling is the answer. Maybe they should
tell the automotive and railway people about their theory.

??? most automotive disc brakes are "vented," that is, the
braking surfaces are separated by a webbing of cast iron
intended to have air pass through. High-performance rotors are
also cross-drilled and/or slotted.

I think you'll find that they are not vented but rather solid
disks with no holes.

Not true at all.

OK! You keep making these claims and show no reason or reference
for them. Just inspect BMW cars and note that even their large
"sport cars"do not have holes in the disks.

But they are still vented.

Look at all the high performance (BMW, Mercedes, Caddillac, Chrysler,
Cheverolet, Buick,...) cars and you will see they have no holes. You
must be assuming car companies are taking safety lightly if they sell
the largest part of their cars with, as you claim, inferior disks that
have no holes.

The cross drilling is found only on vehicles tauted to be high
performance while no passenger sedan has cross drilling that has
no technical advantage but is a relic of the days when brake fade
was believed to be caused by out-gassing of brake shoes to
generate a gas bearing. The holes allow that imaginary gas to
escape.

True, but all but very light and/or inexpensive cars still use
vented rotors, at least on the front. you are confusing
cross-drilling and/or slotting with simple venting, which is a
common feature of nearly all automotive disc brakes. Look at a
disc edge-on, you will see that it is not solid but is essentially
two solid braking surfaces connected by a webbing and with lots of
air space in between. That is what is commonly known as a
"vented" rotor.

Name a few please.

Any modern car equipped with disc brakes. In my driveway, a Chevy
Impala (icky company car) a Porsche 944 and a Ford F-150. All have
vented discs, at least on the front.

Not the new ones aold today. Exactly these are proof that there is no
benefit to the cross drillings in the disks of "sports cars".

The last car I saw *without* vented front discs was my mom's '86 VW
Golf. It did have solid front discs.

You use the term "vemnted" without definition. What do you mean?

I worked in brake design with Girling and ATE in the years when
the auto industry was changing to disks and was amazed at the
amount of myth and lore surrounding brakes.

I don't mean to be insulting, but that surprises me given the
inaccuracies in your post. Although that would explain your
unfamiliarity with vented rotors, as AFAIR at least the Studebaker
applications of the first Girling brakes did in fact use solid
rotors. I would assume that other applications of those brakes
did as well as I'm not aware of any significant variations on the
caliper design.

You are not trying hard enough to not be insulting. Your
unsupported claims are in themselves insulting in facer of evidence
to the contrary. The subject here was to cross drilling with holed
through the disk faces. RR disks are all internally radially
vented in the disk casting.

http://www.merriam-webster.com/dictionary/disk

At this point, I can't even determine if you understand the
difference between venting and drilling. If you can't keep your
terminology straight there's no point in continuing this discussion.

At this point I suggest you heed your request for definition of disk
form. I detect you are trying to make a technical educational course
about disk brake, not understanding the basic difference between disks
and drums. I am not ready to outline a course on disk brakes here.

Jobst Brandt

Jobst and Nate,
Just to set some common ground - here is what I think a vented disk brake
rotor looks like:
http://images.outdoorinteractive.net/mgen/530211_oi.jpg
And here is what I think a cross-drilled disk brake rotor looks like:
http://www.camarotech.com/images/Bra...ossDrilled.jpg
Kerry

wrote:
Nate Nagel wrote:


Lots of cars didn't used to have servo assistance on the
brakes. All the force and work required to brake came from
your leg. And yet you could slow down a tonne of car from
70mph like that.


Drum brakes used massive self servo action to achieve useful
braking. Because that effect is highly unpredictable, they had
both lock-up and fade. That is why we use disks today. You
may recall that this was discussed here at great length.


I don't understand why you consider that action "highly
unpredictable" it's simply speed dependent. Sure they lock up
if you stomp on 'em but so will boosted discs. The fade comes
from the inability of the shoes and drum to shed heat as
effectively as discs where all the parts are out in the open and
in some racing applications even have forced air ducted over
them for additional cooling.


I think you don't know the history of the drum brake. It's self
servo action is laid out about a specific friction coefficient
such that when it is a bit high, brakes lock up (even after
taking the foot off the pedal)


Which is not an issue on any automotive application, as if
anything, current non-asbestos linings have an even lower
coefficient of friction than the original linings around which the
brake system was designed. I have seen some high-performance
linings made available for various vintage drum brake setups
(presumably for vintage racing) and have not ever heard of this
happening in practice.


and when it is a bit low from heating, there is essentially no
brake at all, resulting in run-aways on mountain roads.


The servo effect is what makes the drum brake respond poorly and
why, if you read the Wiki article, no RR ever used drum brakes,
skidding a wheel being a major loss.


That much is true. Of course this can also happen with discs, if
you abuse them enough, but discs cool down *much* faster than
drums given that the friction surface is in direct contact with
cooling air, the discs have a higher surface area to mass ratio,
and that the calipers and at least portions of the linings are
also in closer proximity to cooling air than in a drum brake.


It cannot happen with disks. The relation of the friction
coefficient and brake retardation is linear so the 5% change in
friction that formerly cause total brake failure, the disk sees
a 5% change. It's much like boiling engines in cars. That
they don't boil today is not because they have better
radiators, but because they have a non-leaking water pump seal
and don't lose coolant.


http://en.wikipedia.org/wiki/Engine_...ere_air-cooled


a 5% change in brake friction will not cause a "total brake failure"
on any decent automotive brake system. Now it may cause more than
5% loss on a servo-action system, but not "total."


Old manual drum brakes are actually quite pleasant to drive on,
so long as you're not racing or driving fast through the
mountains. IMHO they have a much better pedal feel than all but
the best new disc brakes; certainly more direct as there is a
direct hydraulic connection between foot and shoes with only a
very few, simple mechanical parts in between.


Oh nostalgia for things that weren't. Read:


http://en.wikipedia.org/wiki/Brake_f...in_drum_brakes


Seeing as I actually own and (occasionally) drive a '55 Studebaker
coupe equipped with the (excellent) factory equipment brakes, with
the only upgrade being the addition of finned drums from a later
model car, I can say that they certainly aren't anywhere near the
death-dealing devices that you seem to be making them out to be.
The three major shortcomings of drum brakes in general are 1)
brakes often undersized for the vehicle, exacerbating other
problems (not an issue on my car, but, say, the 9" front drums on
an old Dart are an insult to common sense.) 2) Cooling - drum
brakes do retain heat far more so than do discs, resulting in
earlier fading. 3) single circuit master cylinders can result in
complete brake system failure with one single hydraulic failure.
Not an issue with the drums themselves, but legal until the late
60's and therefore common on most vehicles you'll find with four
wheel drum brakes.


I take it you are saying that the auto companies of the world are
barking up the wrong tree when they dumped the drum brake. That's
a bit far fetched. Drum brakes are non-linear and unreliable.


http://tinyurl.com/jhiu


No, I'm saying that while discs are definitely an improvement, drums
are not nearly as dangerous and unacceptable, at least in the better
automotive implementations, as you make them out to be.


How do you explain, if the servo-action is responsible for the
effects that you claim, that some automotive drums did *not* use
servo-action brakes and still exhibited similar fade? It's the
heat, plain and simple. That was the biggest downfall of drums, and
it's the biggest advantage of discs. To a lesser extent the
increased linearity of brake torque vs. line pressure that you did
mention. That is not to say that there aren't downsides - the
biggest *disadvantage* of discs is the necessity to install a power
booster on all but the lightest cars, as you need significantly more
line pressure to develop the same brake torque as the same size drum
brake. This is what I was alluding to when I mentioned the improved
pedal feel of drums - the vacuum booster commonly used does make for
a far less direct feel on the brake pedal.


When the brake application force is in the direction of drum rotation,
as it must be with drum brakes, then there is a self energising
effect.

Actually, it doesn't matter which direction, on most brakes. The servo
effect works both ways, but the leading shoe is smaller for reasons of
even wear.

Proof of that is the rum brakes lock up at times when the
friction coefficient is slightly higher than the design level.

Ok, so? that's not generally a problem.

All
deum brakes have servo effect.

No, there are most definitely non-servo drum brakes. Early Studebaker
drums for example, or some of the odd dual wheel cylinder designs.

If you have worked on drum brakes you
should have noticed that they are designated leading shoe brakes, that
is that the activating hydraulic piston is pushing in the direction of
drum rotation.

And that is for reasons of even shoe wear. also the wheel cylinder
pushes both ways in the normal drum brake setup, so the servo action can
work in both directions.


The difficult part is getting rid of all the heat that the
brakes are converting the bike's kinetic energy into.


That's why heavy trucks still use drum brakes, drums having large
surface to reject heat by forced convection. Highways have long
dual tired skid marks because the response to brake application
cannot be well controlled with drum brakes.


I believe that they still use drums because they're easier to work
with in an air brake application. They still don't shed heat
nearly as well as to discs. I suspect many of those skid marks
are also the result of air system failures, not panic stops gone
bad.


You are guessing. Brakes are used for performance and disks large
enough to control a large truck will not fit inside standard truck
wheels. That's why disks are not used there.


I actually *have* seen discs on heavy trucks... not nearly as many
as drums, but they are out there.


You may have seen them on tractors of semi trailer rigs, but not on
the tandem dual dive axles or the semitrailer where heavy braking
occurs.


Apparently the bicycle industry is not addressing that part of
the problem when the surface area and thermal mass their
gossamer rings of steel have. I have asked brake manufacturers
why their disks are mostly air with a thin pattern of thin
steel between. For cooling is the answer. Maybe they should
tell the automotive and railway people about their theory.


??? most automotive disc brakes are "vented," that is, the
braking surfaces are separated by a webbing of cast iron
intended to have air pass through. High-performance rotors are
also cross-drilled and/or slotted.


I think you'll find that they are not vented but rather solid
disks with no holes.


Not true at all.


OK! You keep making these claims and show no reason or reference
for them. Just inspect BMW cars and note that even their large
"sport cars"do not have holes in the disks.


But they are still vented.


Look at all the high performance (BMW, Mercedes, Caddillac, Chrysler,
Cheverolet, Buick,...) cars and you will see they have no holes. You
must be assuming car companies are taking safety lightly if they sell
the largest part of their cars with, as you claim, inferior disks that
have no holes.

They may not be cross drilled, but they are all vented.

The cross drilling is found only on vehicles tauted to be high
performance while no passenger sedan has cross drilling that has
no technical advantage but is a relic of the days when brake fade
was believed to be caused by out-gassing of brake shoes to
generate a gas bearing. The holes allow that imaginary gas to
escape.


True, but all but very light and/or inexpensive cars still use
vented rotors, at least on the front. you are confusing
cross-drilling and/or slotting with simple venting, which is a
common feature of nearly all automotive disc brakes. Look at a
disc edge-on, you will see that it is not solid but is essentially
two solid braking surfaces connected by a webbing and with lots of
air space in between. That is what is commonly known as a
"vented" rotor.


Name a few please.


Any modern car equipped with disc brakes. In my driveway, a Chevy
Impala (icky company car) a Porsche 944 and a Ford F-150. All have
vented discs, at least on the front.


Not the new ones aold today. Exactly these are proof that there is no
benefit to the cross drillings in the disks of "sports cars".

Yes, all of the new ones sold today. They are vented, as I defined
above (and as is common usage.)


The last car I saw *without* vented front discs was my mom's '86 VW
Golf. It did have solid front discs.


You use the term "vemnted" without definition. What do you mean?


See above, I defined the common usage of the term when referring to brakes.


I worked in brake design with Girling and ATE in the years when
the auto industry was changing to disks and was amazed at the
amount of myth and lore surrounding brakes.


I don't mean to be insulting, but that surprises me given the
inaccuracies in your post. Although that would explain your
unfamiliarity with vented rotors, as AFAIR at least the Studebaker
applications of the first Girling brakes did in fact use solid
rotors. I would assume that other applications of those brakes
did as well as I'm not aware of any significant variations on the
caliper design.


You are not trying hard enough to not be insulting. Your
unsupported claims are in themselves insulting in facer of evidence
to the contrary. The subject here was to cross drilling with holed
through the disk faces. RR disks are all internally radially
vented in the disk casting.


http://www.merriam-webster.com/dictionary/disk


At this point, I can't even determine if you understand the
difference between venting and drilling. If you can't keep your
terminology straight there's no point in continuing this discussion.


At this point I suggest you heed your request for definition of disk
form. I detect you are trying to make a technical educational course
about disk brake, not understanding the basic difference between disks
and drums. I am not ready to outline a course on disk brakes here.

I'm afraid I don't need your "technical educational course" - not to do
the credential dick-waving thing, but I too have worked professionally
with braking systems (albeit specifically with ABS software) and
apparently quite a bit more recently than you. You're confusing venting
with cross-drilling, or you're not understanding the terminology that
I'm using which is standard and has been since the late 60's.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel