Can Disk Brakes flip you over the handle bars?

Andrew Muzi wrote:
TBerk wrote:
Obviously I would assume they could if you clamp down fast enough.

landotter wrote:
Yes, if you don't brace yourself and are unfamiliar with the brake and
grab wildly, any powerful brake can be dangerous--but so can many
things in life. Well adjusted brakes should be easy to modulate,
provided you're not inebriated and have practiced a few panic stops,
and shouldn't necessitate the purchase of a new bicycle.
Be careful when posting questions like this, because you may attract
'bent riders, who are bearded hammers in search of nails--sometimes
with orange flippy flags!

Harry Brogan wrote:
I do NOT have orange flippy flags!!!!!! ROFLMAO

Not yet?
Tom Sherman can probably help you choose a nice flippy orange one.

I suggest a red flag with a gold "hammer & sickle" logo.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

Michael Press wrote:
In article ,
Tom Sherman wrote:

TBerk ? wrote:
On May 1, 8:31 pm, Tom Sherman
wrote:
landotter wrote:
snippage
Be careful when posting questions like this, because you may attract
'bent riders, who are bearded hammers in search of nails--sometimes
with orange flippy flags!
Since so many upright riders feel necessary to comment on the alleged
disadvantages of recumbents (often quite rudely in person), it is only
fair to do the same for uprights.
But yeah, you guys are thread-jacking though.

In other breaking news...

Thread drift is a fact of life on Usenet.

Almost all non sequiturs on recumbent bicycles
are introduced by you.

Dude, [1]

For the record, Mike Schwab first introduced recumbents into this
thread, not me. "DougC" and "landotter" also posted responses mentioning
recumbents independently of anything I posted.

You walk, or roll supine,
with `Kick Me' sign and are surprised
that you are sore? Try going a year without
a gratuitous introduction of recumbent bicycles
and see how things work out.

I did not bring up the subject in this thread, as a cursory review of
the thread would make blindingly obvious.

Change the charter of rec.bicycles.tech to exclude recumbents, and I
will not mention them without an "OT" lead to the subject line. Until
then, deal with their occasional mention.

[1] Feel free to respond "Don't call me dude".

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

TBerk wrote:
On May 1, 10:17 pm, Tom Sherman
wrote:
TBerk ? wrote:
snip
But yeah, you guys are thread-jacking though.
In other breaking news...
Thread drift is a fact of life on Usenet.

--
Tom Sherman

Sorry, forgot to include an emoticon 8])


TBerk
I'm going to be looking into replacement forks with disk brake
capacity. Stay tuned everybody...

Be sure to get a system with a through-bolt or one of the rare forks
that has the dropouts and/or caliper mounts arranged so the brake is not
trying to eject the wheel:
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/index.html.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

On May 2, 7:49 pm, Tom Sherman
wrote:
TBerk wrote:
On May 1, 10:17 pm, Tom Sherman
wrote:
TBerk ? wrote:
snip
But yeah, you guys are thread-jacking though.
In other breaking news...
Thread drift is a fact of life on Usenet.

--
Tom Sherman

Sorry, forgot to include an emoticon 8])

TBerk
I'm going to be looking into replacement forks with disk brake
capacity. Stay tuned everybody...

Be sure to get a system with a through-bolt or one of the rare forks
that has the dropouts and/or caliper mounts arranged so the brake is not
trying to eject the wheel:
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/inde....

--
Tom Sherman -


Now, see? While as yet unsubstantiated it seems like the kind of help
I started this thread for in the 1st place.


TBerk

For somebody who says they worked with ATE you should know what
'vented' means a disk brake.

Lets take a little quiz:

- What are vented disks?

- What are cross drilled disks?

- What are slotted disks?


Maybe you'd like to Google ATE Atomic disk for some help.

While youre at it, Google up the standard front brakes for, say, a VW
GTI circa 1984. (ATE being an OEM btw.)

After you have completed your homework you can get out of my thread
please sir.


TBerk
bikes, remember?

Nate Nagel wrote:
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



A vented disk is like a rotor of a radial ventilator. Maybe Jobst
understands now what you mean.

Lou

On 2008-05-02, Nate Nagel wrote:
[...]
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.

I used to have a car with four drum brakes (still have it actually long
story).

There were three distinct kinds of fade. The first was "pedal drop",
which was easily cured by pumping the pedal a couple of times. I believe
this was most likely to be caused by drum expansion. But I'd be
interested to hear other theories.

The second was fluid fade, where the fluid boils, resulting in a
distinctive "spongy" feel to the pedal. That was cured by changing the
brake fluid: modern fluid in good condition seemed more than capable of
surviving the highest temperatures that could be produced by such a
braking system.

The third kind was when you had the pedal pumped up, the fluid wasn't
boiling, but you'd find yourself pushing very hard on the pedal without
the car slowing down nearly as much as you were hoping. It didn't go
spongy or drop, just didn't seem to do much.

I took it that was some kind of reduction of friction coefficient caused
by too much heat, but don't claim to be able to explain it completely.

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.

Another downside of drums was that if you had to brake suddenly there
was a greater chance of the brake snatching on on one side before the
other.

This I took to be because they aren't "self-adjusting" in the simple way
disks are, so the pads on each side are likely to start off a more
variable distance from their target, and because of the leading-shoe
servo action which makes them snatch on as soon as they make contact.

Mine weren't self-adjusting at all, you had to keep adjusting them. Some
other cars had self adjusting mechanisms of various kinds but they
weren't as simple as the way a disk caliper works because they need
springs to retract the pads.

I don't miss drum brakes 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.

I also haven't seen a disk that wasn't vented in the way you described
for years. Cross-drilled disks are rarer. You see them on Porsche 911s.

On 2008-05-03, Nate Nagel wrote:
wrote:
[...]
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.

Just to clarify he means the servo effect of leading shoes, not of a
manifold vacuum operated brake servo or "power booster".

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.

No Jobst is right about that: it is for the servo action.

also the wheel cylinder pushes both ways in the normal drum brake
setup, so the servo action can work in both directions.

Front drums usually have two cylinders because they're twin leading-shoe
for best braking going forwards.

Rear drums often have one cylinder with a piston coming out of each end
to give you one leading and one trailing shoe. That's so you have some
braking in reverse. Also because you might park facing up a hill.

On 2008-05-03, Tom Sherman wrote:
aka Jobst Brandt wrote:
[...]
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.[...]

Herr Brandt must not have driven a 2002-2005 Honda Civic, which has rear
drum brakes but exhibits none of the ills that Brandt claims are
inherent to drums.

Drums are fine on the back. The back brakes do very little in normal
driving, and are mostly useful for when you're parked, for which the
drum is a good design as it shrinks "on" when it cools.

You don't want drums on the front.

A cable operated parking brake on rear disks is possible but you usually
get a self-adjusting threaded oddity in the rear slave cylinders which
is a bugger when you come to change the pads because you have to twist
it back in.

Some cars with rear disks have little drums as well, just for the
parking brake.

On 2008-05-03, TBerk wrote:
On May 2, 7:49 pm, Tom Sherman
[...]
Be sure to get a system with a through-bolt or one of the rare forks
that has the dropouts and/or caliper mounts arranged so the brake is not
trying to eject the wheel:
http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/inde....

--
Tom Sherman -


Now, see? While as yet unsubstantiated it seems like the kind of help
I started this thread for in the 1st place.

The wheel ejection problem is correct in theory but in practice it
doesn't happen if you do your QRs up reasonably tight.