weinmann semi automatic brakes -- what is it?
geos
does anybody know this weinmann model of "semi automatic" brakes? I
can't find any information on the net. I would appreciate any technical
details and history details, when they were produced, what was their
braking efficiency etc. can they be compared to campagnolo deltas?
any information and personal experience with this brakes would be helpful.
http://img527.imageshack.us/img527/6392/weinmann8cm.jpg
thanks,
geos
JeffWills
"Semi-automatic" refers to the adjusting mechanism, I think. It
self-adjusts the slack in the cable.
As to the brakes "efficiency", well, I dunno. I can just barely
remember seeing these brakes when they were new in the late '80's... I
think. I don't ever remember seeing them on a bike.
Jeff
jobst....@stanfordalumni.org
>> Does anybody know this Weinmann model of "semi automatic" brakes? I
>> can't find any information on the net. I would appreciate any
>> technical details and history details, when they were produced,
>> what was their braking efficiency etc. can they be compared to
>> Campagnolo deltas?
>> Any information and personal experience with this brakes would be
>> helpful.
http://img527.imageshack.us/img527/6392/weinmann8cm.jpg
> "Semi-automatic" refers to the adjusting mechanism, I think. It
> self-adjusts the slack in the cable.
> As to the brakes "efficiency", well, I dunno. I can just barely
> remember seeing these brakes when they were new in the late '80's...
> I think. I don't ever remember seeing them on a bike.
It's like the Modolo Kronos that was a forerunner to the Campagnolo
Delta-I and Delta-2, both of which had the same fatal design error of
a variable mechanical advantage. It took Campagnolo years to
discover why riders crashed with these brakes. The brake has a
variable mechanical advantage (MA) getting more aggressive as pads
wear. Beyond that, the MA increases with harder brake application as
pads bulge and brake arms flex.
Brakes must have a constant ratio of hand force to brake effect to be
controllable. This design uses a parallelogram with the brake arms
attached to two corners and the cable pulling the other two corners
together, giving a mechanical advantage that goes from zero to
infinity, mathematically: a tangent function. Note that the brake
arms are short and pivot so that the pads rise into the tire with wear
(known as cosine effect).
Observing this, It seems that these engineers never learned about the
"bell crank" or for instance, parallel universal joints on car
propeller shafts.
Note that motion in equals motion out, the two legs of the mechanism
having the same cosine error that the bell crank cancels
It's a stupid idea for several reasons and it was even worse when
Campagnolo went through two versions before giving up on the concept.
I don't know if they ever discovered why the brake is a dud. It's
like Shimano and their Octalink (also two versions) showing that they
did not understand why it fails.
Don't ride these things. Put them in your museum of failed ideas.
Jobst Brandt
diann...@yahoo.com
I just installed one on the front of my TT bike. The spring force is
noticably higher than modern dual pivot brakes. It's not easy for me to
modulate, and I don't like it's performance. But it's only my TT bike,
and I think it's aero.
Since I use a housing stop in the headset, I sawed off the adjustable
part (top 25mm or so), but I kept the rubber cover on. I can't see how
to get it off without tearing it.
geos
cheers,
geos
Jasper Janssen
>Brakes must have a constant ratio of hand force to brake effect to be
>controllable.
Why? You've stated this as an axiom numerous times, but I don't believe
I've seen the reasoning behind it. I'd think that at least small
variations in MA wouldn't make a brake uncontrollable (although probably
harder to do so).
Jasper
jobst....@stanfordalumni.org
>> Brakes must have a constant ratio of hand force to brake effect to
>> be controllable.
> Why? You've stated this as an axiom numerous times, but I don't
> believe I've seen the reasoning behind it. I'd think that at least
> small variations in MA wouldn't make a brake uncontrollable
> (although probably harder to do so).
If the MA is variable, you cannot dose braking such that you don't
crash some time or other. Today we have disc brakes on cars for that
reason. Drum brakes have a variable response because they have self
servo action, the harder you brake the greater the mechanical
advantage of actuation. You must have hear of brake lock-up. This
became so apparent in racing that the hazard to general driving was
obvious. Although disc brakes dissipation power more poorly, their
advantage in function far outweighs that problem. Just the same,
you'll note that highway trucks still use drum brakes for their
greater braking ability... and leave long dual skid marks on highways.
I think you can visualize an increasing brake effect when you pull on
the hand lever of your bicycle and how it would keep you from braking
hard for fear of a lock-up, especially on wet roads. That is what the
Delta brake did.
If you look in the RBR archives, you'll find defenders of that brake
and some rude comments.
Jobst Brandt
Dan Burkhart
Sorry Jobst, the reason trucks still use drum brakes has nothing to do
with superior performance and everything to do with reluctance to
change. In Europe, heavy trucks have pretty much converted to discs for
their lighter weight, lower maintenance, and, wait for it, superior
stopping power. Here in North America, inter vehicle compatibility is a
much greater issue than it is across the pond. Fleets with hundreds of
power units and thousands of trailers need to have the flexibility to
pull any of their trailers with any of their tractors. Mixing these
brake types on multi unit vehicles creates an imbalance that is not
only unsafe, but also illegal. Retrofitting fleets of this size is not
feasable considering the fierce competitive forces these days, and
attrition is not an option because of the reasons I have already put
forth.
Government regulation mandating stopping distances that only disc
brakes can achieve is the only way they will ever come in to common
usage, but most of the industry and goverment regulators alike remember
all too well the fiasco that was the antilock provision of FMVSS 121.
Here was a situation where an undeveloped technology was foisted on an
unsuspecting public in the name of safety. People died as a result.
Don't look for any such regulation soon.
Dan Burkhart
--
Dan Burkhart
jobst....@stanfordalumni.org
>>>> Brakes must have a constant ratio of hand force to brake effect
>>>> to be controllable.
>>> Why? You've stated this as an axiom numerous times, but I don't
>>> believe I've seen the reasoning behind it. I'd think that at
>>> least small variations in MA wouldn't make a brake uncontrollable
>>> (although probably harder to do so).
>> If the MA is variable, you cannot dose braking such that you don't
>> crash some time or other. Today we have disc brakes on cars for
>> that reason. Drum brakes have a variable response because they
>> have self servo action, the harder you brake the greater the
>> mechanical advantage of actuation. You must have hear of brake
>> lock-up. This became so apparent in racing that the hazard to
>> general driving was obvious. Although disc brakes dissipation
>> power more poorly, their advantage in function far outweighs that
>> problem. Just the same, you'll note that highway trucks still use
>> drum brakes for their greater braking ability... and leave long
>> dual skid marks on highways.
>> I think you can visualize an increasing brake effect when you pull
>> on the hand lever of your bicycle and how it would keep you from
>> braking hard for fear of a lock-up, especially on wet roads. That
>> is what the Delta brake did.
>> If you look in the RBR archives, you'll find defenders of that
>> brake and some rude comments.
> Sorry Jobst, the reason trucks still use drum brakes has nothing to
> do with superior performance and everything to do with reluctance to
> change. In Europe, heavy trucks have pretty much converted to discs
> for their lighter weight, lower maintenance, and, wait for it,
> superior stopping power. Here in North America, inter vehicle
> compatibility is a much greater issue than it is across the pond.
> Fleets with hundreds of power units and thousands of trailers need
> to have the flexibility to pull any of their trailers with any of
> their tractors. Mixing these brake types on multi unit vehicles
> creates an imbalance that is not only unsafe, but also illegal.
> Retrofitting fleets of this size is not feasable considering the
> fierce competitive forces these days, and attrition is not an option
> because of the reasons I have already put forth.
I can tell you are truly sorry. Why the cynical intro? The point is
that brakes with variable mechanical advantage are not readily
controllable and that long truck skid marks on highways are there
because their drum brakes have relatively poor control. As I
mentioned previouslt on this subject, you won't find drum brakes on
railroads, where skidding occurs more easily and has expensive
effects. I also spent a few years in the development of early disc
brakes and was involved in work to get discs to work as easily as the
drum brakes they were to replace. Today most brakes are power
assisted because disks require far greater contact force and not
having the servo effect of drum brakes.
Drums on trucks are far less expensive, less maintenance and have
greater heat dissipation surface than discs.
> Government regulation mandating stopping distances that only disc
> brakes can achieve is the only way they will ever come in to common
> usage, but most of the industry and goverment regulators alike remember
> all too well the fiasco that was the antilock provision of FMVSS 121.
> Here was a situation where an undeveloped technology was foisted on an
> unsuspecting public in the name of safety. People died as a result.
> Don't look for any such regulation soon.
I think you are confusing the issues. Drum brakes have plenty of
stopping power and good stopping distance. What they don't have is
control that is essential in operating them at the transition between
tracking and skidding, especially in curves and on wet roads. I don't
contend that the Campagnolo Delta brake did not stop the bicycle, but
that its varying mechanical advantage made it difficult to control.
Jobst Brandt
Dan Burkhart
Long skid marks are often the result of normal brake application on a
vehicle with unequally loaded axles. I should mention that anything I
offer on this issue is based not on advanced theory, but on about 4
million miles of heavy vehicle operation over a span of 34 years, with
a couple of years in the middle of that working as a driver trainer and
certified air brake instructor.
During that time, I had zero opportunity to assess disc brake
performance for myself, so all I have is anecdotal from other drivers
with the experience, manufacturers propaganda, and my own questionable
reasoning.
I don't pay too much attention to what goes on in that world anymore
as I have moved on to other pursuits, but for a while there back in the
80s and early 90s, all the heavy vehicle brake systems manufacturers
were busy developing their disc brakes in anticicpation of a wholesale
industry changeover. Some small fleets tried them out, but they were
only practical for an operation that used only their own dedicated
equipment. It would mess them up if they ever had to lease a trailer.
But anyway, I'm rambling now.
For your claim of greater heat dissipation of drums, the brake makers
counter that drums confined within the wheel are less able to dissipate
heat than a vaned rotor that is more exposed to air flow. The drum brake
is also more prone to fade when over used on long descents. The
expansion of a heated drum means a loss of mechanical advantage as the
chamber stroke, and consequently the angle of application between the
push rod and slack adjuster changes. Expansion of a disc on the other
hand reduces the application stroke.
It seems though, that the industry has pretty much given up on the
idea of converting to discs, and from anything I have read lately, most
efforts are directed at imrovements and refinements to the drum based
systems.
jobst....@stanfordalumni.org
>> mentioned previously on this subject, you won't find drum brakes on
>> railroads, where skidding occurs more easily and has expensive
>> effects. I also spent a few years in the development of early disc
>> brakes and was involved in work to get discs to work as easily as
>> the drum brakes they were to replace. Today most brakes are power
>> assisted because disks require far greater contact force and not
>> having the servo effect of drum brakes.
>> Drums on trucks are far less expensive, less maintenance and have
>> greater heat dissipation surface than discs.
>>> Government regulation mandating stopping distances that only disc
>>> brakes can achieve is the only way they will ever come in to
>>> common usage, but most of the industry and goverment regulators
>>> alike remember all too well the fiasco that was the antilock
>>> provision of FMVSS 121. Here was a situation where an undeveloped
>>> technology was foisted on an unsuspecting public in the name of
>>> safety. People died as a result. Don't look for any such
>>> regulation soon.
>> I think you are confusing the issues. Drum brakes have plenty of
>> stopping power and good stopping distance. What they don't have is
>> control that is essential in operating them at the transition
>> between tracking and skidding, especially in curves and on wet
>> roads. I don't contend that the Campagnolo Delta brake did not
>> stop the bicycle, but that its varying mechanical advantage made it
>> difficult to control.
> Long skid marks are often the result of normal brake application on
> a vehicle with unequally loaded axles. I should mention that
> anything I offer on this issue is based not on advanced theory, but
> on about 4 million miles of heavy vehicle operation over a span of
> 34 years, with a couple of years in the middle of that working as a
> driver trainer and certified air brake instructor.
When you have an empty trailer, you don't need to make heavy brake
applications, these are loaded trucks that cause these skids. I've
watched the white smoke from the tires as they brake on highways.
> During that time, I had zero opportunity to assess disc brake
> performance for myself, so all I have is anecdotal from other
> drivers with the experience, manufacturers propaganda, and my own
> questionable reasoning.
Discs are not easily cooled for high load applications. That is why
railway discs have mass to store the entire brake application and then
cool off before the next time used.
> I don't pay too much attention to what goes on in that world anymore
> as I have moved on to other pursuits, but for a while there back in
> the 80s and early 90s, all the heavy vehicle brake systems
> manufacturers were busy developing their disc brakes in
> anticicpation of a wholesale industry changeover. Some small fleets
> tried them out, but they were only practical for an operation that
> used only their own dedicated equipment. It would mess them up if
> they ever had to lease a trailer. But anyway, I'm rambling now.
Well that fell in the water when the physical and economic realities
came to bear. I doubt that you will see widespread use of discs on
heavy haul trailers. The complexities are not worth the effort.
That, however has little to do with variable ratio bicycle brakes as
you take this ever farther away from the issue.
> For your claim of greater heat dissipation of drums, the brake
> makers counter that drums confined within the wheel are less able to
> dissipate heat than a vaned rotor that is more exposed to air
> flow. The drum brake is also more prone to fade when over used on
> long descents. The expansion of a heated drum means a loss of
> mechanical advantage as the chamber stroke, and consequently the
> angle of application between the push rod and slack adjuster
> changes. Expansion of a disc on the other hand reduces the
> application stroke.
Drums are not confined to the inside of the wheel, you can see them
exposed when you follow such a vehicle. Besides, this is not a still
air zone as one is led to believe by all the wheel vents that
passenger cars have. All they do is expose how much brake dust can
accumulate on wheels. There is plenty of ventilation for those brakes
without the aerodynamic looking wheel designs.
> It seems though, that the industry has pretty much given up on the
> idea of converting to discs, and from anything I have read lately,
> most efforts are directed at imrovements and refinements to the drum
> based systems.
Yes???
Jobst Brandt
Dan Burkhart
I'll keep going as far away from the issue at hand as you care to take
it. I have crawled around under enough trucks, done enough pre-trip
inspections and hands on brake adjustments to confidently state that,
on a dual wheel application, the brake drum is almost totally enclosed
within the inner wheel. The current (gradual) shift towards wide base
single tires offers an improvement in this situation. Ventilation is a
huge issue here.
Railway brakes? Not much advancement there since the stage coach brake
design they were based on. However, in this case, the simpler the
better. Application forces are linear, and, as you say, heating the
wheel is not a problem.( Except for traction wheels.)
Dan
--
Dan Burkhart
jobst....@stanfordalumni.org
> I'll keep going as far away from the issue at hand as you care to
> take it. I have crawled around under enough trucks, done enough
> pre-trip inspections and hands on brake adjustments to confidently
> state that, on a dual wheel application, the brake drum is almost
> totally enclosed within the inner wheel. The current (gradual) shift
> towards wide base single tires offers an improvement in this
> situation. Ventilation is a huge issue here.
> Railway brakes? Not much advancement there since the stage coach
> brake design they were based on. However, in this case, the simpler
> the better. Application forces are linear, and, as you say, heating
> the wheel is not a problem.( Except for traction wheels.) Dan
Railway disc brakes are as up to date as any brakes on cars and
trucks. That freight trains use wheel shoe brakes is because stopping
a freight train is a singular event and not done with great
acceleration. Today, their brakes are pretty much adjuncts to the
dynamic braking of locomotives, used as a hand brake on a car and an
emergency brake. It is an entirely different task than a highway
vehicle that needs to alter speed often for the flow of traffic.
Passenger trains, in contrast use only discs and do plenty of
stopping. I think you should look at these brakes and see how large
and advanced in design they are.
Back to truck brakes, so where do you put discs if the drums are
entirely enclosed by dual wheels? I don't see the bearing of this on
whether drum brakes are readily controlled in brake applications.
Jobst Brandt
Ozark Bicycle
Perhaps it's a matter of what you're used to. I've been using Deltas on
one bike for 16 years and I find the "progressive" action quite
pleasant , giving excellent modulation. OTOH, I find "modern", dual
pivot brakes devoid of feel, with a kind of "on/off switch" action. In
that regard, I much prefer older, single pivot sidepulls much better
than dual pivots.
IMO, of course. YMMV, etc., etc., etc.
Jasper Janssen
>I think you are confusing the issues. Drum brakes have plenty of
>stopping power and good stopping distance. What they don't have is
>control that is essential in operating them at the transition between
>tracking and skidding, especially in curves and on wet roads. I don't
>contend that the Campagnolo Delta brake did not stop the bicycle, but
>that its varying mechanical advantage made it difficult to control.
Doesn't a brake that routinely skids the wheels have bad stopping power?
If your wheels are skidding you're not stopping with anywhere near the
theoretical maximum.. why ABS was invented.
Jasper
Helmut Springer
> If your wheels are skidding you're not stopping with anywhere near
> the theoretical maximum.. why ABS was invented.
ABS was invented to allow control which is lost once the vehicle
skids, not to improve stopping power.
--
MfG/Best regards
helmut springer
Jasper Janssen
>If the MA is variable, you cannot dose braking such that you don't
>crash some time or other. Today we have disc brakes on cars for that
>reason. Drum brakes have a variable response because they have self
>servo action, the harder you brake the greater the mechanical
>advantage of actuation. You must have hear of brake lock-up. This
>became so apparent in racing that the hazard to general driving was
>obvious. Although disc brakes dissipation power more poorly, their
>advantage in function far outweighs that problem. Just the same,
>you'll note that highway trucks still use drum brakes for their
>greater braking ability... and leave long dual skid marks on highways.
>
>I think you can visualize an increasing brake effect when you pull on
>the hand lever of your bicycle and how it would keep you from braking
>hard for fear of a lock-up, especially on wet roads. That is what the
>Delta brake did.
I can see how it would be bad to have a point where MA goes to infinity,
or too high, either as designed or after wear and/or flex are taken into
account, but I still don't see how a hypothetical brake with MA varying
from, say, 8 to 2 or 4 to 2 over the stroke which is ever seen in use
(including flex, wear, and Chalo-style or tandem riders which take an
awful lot of force to reach .6g).
If brake pad wear was not an issue, I could see a (again hypothetical)
brake which would move the shoes 1 or 2 cm with the first 5 mm of lever
travel and then go to standard MA for 1 mm away from the rim to the rest
of the stroke -- with advantages in pad clearance while changing wheels
and continuing with bent wheels. I very much doubt those advantages would
be worth the problems, though.
Jasper
G.T.
> Jasper Janssen <jas...@jjanssen.org> wrote:
>
>>If your wheels are skidding you're not stopping with anywhere near
>>the theoretical maximum.. why ABS was invented.
>
>
> ABS was invented to allow control which is lost once the vehicle
> skids, not to improve stopping power.
>
Not stopping power but stopping distance. And during a similar
discussion on rec.photo.digital.slr-systems, where it was quite
off-topic, I found several documents where the goal was to reduce
stopping distance during panic stops.
Greg
--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons
Helmut Springer
> Not stopping power but stopping distance. And during a similar
> discussion on rec.photo.digital.slr-systems, where it was quite
> off-topic, I found several documents where the goal was to reduce
> stopping distance during panic stops.
References? Bosch happens to have driven that for cars, and their
goal was control...
G.T.
Actually my part of the discussion was just about stopping distance so
I'll back off on the goals of the original designers. There never was a
consensus as to the goals but Bosch was mentioned.
This is what one other poster said but I never bothered to fact check it
(and below this are quotes from studies about stopping distances):
"This is *one* of the reasons it was invented. It was actually
developed first for aircraft, an early version being Dunlop's Maxaret
system used in the 1950's to reduce the chance of aquaplaning during
landings on wet runways.
Aquaplaning leads to *both* loss of directional control *and*
significant lowering of retardation effects of the brakes. Although
you can argue that directional control is more important, the system
was developed to solve a problem that comprises of both aspects.
So, no, it wasn't developed just to reduce stopping distances, neither
was it developed *just* to maintain directional control. It was
developed to allow aircraft to attempt landings on a runway they
usually couldn't do due to heavy rain / surface water conditions.
The first cars to have ABS (The British Jenson FF GT production car -
mid 60's, which was a first in two respects: first all wheel drive and
first ABS) used a slightly enhanced version of the Dunlop Maxaret
system too. But being a bulky, unreliable and expensive addon it then
went out of fashion for 20 years until modern electronic versions made
it a feasible option again.
Drivers of the Jenson FF have noted that the ABS could be overridden
by stamping hard on the brakes, due to it's mechanical nature - so
long as you are expecting the fibrating-foot sensation. So, it's not
much use in a panic-brake scenario.
Dunlop & Jenson are both British companies, located at the time very
close to each other. Germany's Bosch had apparently been developing
ABS since the 30's but wasn't until 1978 the first Merc's got them."
===================================================================
Stopping distance:
"During 1988-91, NHTSA performed two extensive series of stopping tests
involving vehicles with four-wheel ABS or RWAL, on various road
surfaces. The tests confirmed that four-wheel ABS was highly effective
in preventing yawing and allowing the driver to steer the car during
panic braking. Stopping distances decreased substantially with
four-wheel ABS on wet surfaces, but decreased only slightly on dry
pavement and increased on gravel."
From the US Department of Transport:
"ABS may shorten stopping distances on wet or slippery roads and most
systems may shorten stopping distances on dry roads."
http://www.nhtsa.dot.gov/cars/problems/Equipment/absbrakes/page1.html
From a small US car company called General Motors:
"Q. Does ABS reduce stopping distances?
A. Yes, in braking situations where the wheels on a non-ABS
equipped vehicle would lock up, ABS will generally provide shorter
controlled stopping distance. The amount of improvement in stopping
distance depends on many factors, including the road surface, severity
of braking, initial vehicle speed, etc."
http://www.gmfleet.com/us/products/specialized/police/safety/abs.html#2
An educational site:
"Stopping distance on many slippery surfaces will also increase with
locked wheels. Four-wheel ABS prevents wheel lock-up in situations in
which the wheels might normally lock, such as on slippery roads."
http://www.abs-education.org/faqs/faqindex.htm
A forensic company:
"In general, the real benefits of ABS are realized in straight line,
emergency braking. Under these conditions, ABS installations provide
full steering control, complete vehicle stability and shorter stopping
distances."
http://www.waltersforensic.com/articles/accident_reconstruction/vol2-...
The AAA:
"Under most conditions, a vehicle with a good anti-lock brake system
can stop in a slightly shorter distance than an average driver could
accomplish in the same vehicle without ABS"
http://www.aaafoundation.org/resources/index.cfm?button=abs#stop
Peter Cole
A front brake, being the only important brake for rapid stopping, will
usually cause a near-instantaneous crash if it locks the front wheel. On
dry roads, you have a warning when the rear wheel lifts, on wet roads or
loose surfaces you often don't. Under slippery conditions, it's critical
to be able to control the amount of braking force precisely, a
non-linear response makes that harder. This isn't noticed too often when
riding on pavement, since the coefficient of friction is pretty good,
but riding off-road in sand, gravel, mud or leaf litter is much more
challenging. Predictable brakes are much more important than gross
stopping power.
Jasper Janssen
wrote:
Well, sure, you can push much more drug^Wsafety features by claiming that
they prevent you from skidding into a ravine or 18-wheeler than you can by
claiming they'll make you stop slightly faster.
Thing is, you get a much larger decelerating force by braking until
just-before the wheel starts skidding than when it actually is skidding,
because friction coefficient for moving materials (the skidding tyre
versus the road) is much smaller than that for stationary materials (the
rolling tyre versus the road). Which is also why the front wheels stop
being able to make sure the car goes straight, or anywhere in particular,
in a skid.
Therefore, you either have to make sure you don't go over that edge
manually, back the brake off manually when it's gone over, or use ABS, to
get the best stopping distance (and if smallest stopping distance and
largest stopping power aren't the same thing in your book, that's a mighty
weird definition). Control and stopping power are directly related in the
try-not-to-skid part of automotive techniques.
Jasper
Helmut Springer
> Therefore, you either have to make sure you don't go over that
> edge manually, back the brake off manually when it's gone over, or
> use ABS, to get the best stopping distance (and if smallest
> stopping distance and largest stopping power aren't the same thing
> in your book, that's a mighty weird definition).
Interestingly skilled drivers achieve shorter stopping distances
without ABS. Most drivers are not that skilled.
Still the driver to deploy ABS was control.
That does allow the average driver to fully hit the brakes and still
have control thus coming to shorter stopping distances than not
braking powerful enough fearing to lose control...
Jasper Janssen
wrote:
>Jasper Janssen <jas...@jjanssen.org> wrote:
>> Therefore, you either have to make sure you don't go over that
>> edge manually, back the brake off manually when it's gone over, or
>> use ABS, to get the best stopping distance (and if smallest
>> stopping distance and largest stopping power aren't the same thing
>> in your book, that's a mighty weird definition).
>
>Interestingly skilled drivers achieve shorter stopping distances
>without ABS. Most drivers are not that skilled.
In controlled circumstances where the road surface is fairly regular and
when the driver in question has experimented with deliberately going into
skids on that surface, and thus knows exactly how hard he can brake
without going into one, yes. It's not that most drivers are unskilled,
it's just that they don't have any experience with going into skids,
because it's not taught and it's not advisable to try it on public roads.
>Still the driver to deploy ABS was control.
Not on this side of the ocean, it was always about shorter stopping
distances.
>That does allow the average driver to fully hit the brakes and still
>have control thus coming to shorter stopping distances than not
>braking powerful enough fearing to lose control...
Yep.
Jasper
jobst....@stanfordalumni.org
>>> Therefore, you either have to make sure you don't go over that
>>> edge manually, back the brake off manually when it's gone over, or
>>> use ABS, to get the best stopping distance (and if smallest
>>> stopping distance and largest stopping power aren't the same thing
>>> in your book, that's a mighty weird definition).
>> Interestingly skilled drivers achieve shorter stopping distances
>> without ABS. Most drivers are not that skilled.
> In controlled circumstances where the road surface is fairly regular
> and when the driver in question has experimented with deliberately
> going into skids on that surface, and thus knows exactly how hard he
> can brake without going into one, yes. It's not that most drivers
> are unskilled, it's just that they don't have any experience with
> going into skids, because it's not taught and it's not advisable to
> try it on public roads.
There you have said exactly why disc brakes with a linear response are
able to produce the best braking. They can be controlled so that the
vehicle can operate close to he limit of traction. I believe for
anyone who has been at that threshold, typically on a wet road, would
recognize the importance of linear response.
>> Still the driver to deploy ABS was control.
> Not on this side of the ocean, it was always about shorter stopping
> distances.
Maybe in your circles, flooded by safety minded PR programs that
wouldn't even hint at driving at the limit of anything. The appeal is
greatest for those least skilled in that art and that is where the
emphasis falls.
>> That does allow the average driver to fully hit the brakes and
>> still have control thus coming to shorter stopping distances than
>> not braking powerful enough fearing to lose control...
I think you should try this and I don't think you'll like it. When
riding bike over the Turini Pass in France in the summer, the road
that the Monte Carlo Rallye crosses in snow, I see where 'imitation
racers' with ABS brakes leave series of intermittent skid marks of no
better than 50% duty cycle into hairpin turns. Because an ABS system
can only tell where the limit is by exceeding it and skidding to sense
relative wheel speeds, it leaves dead zones where there is no
effective braking. With a linear brake, a good driver can approach
that threshold and hold it steady while the driver depending on ABS
gets an intermittent duty cycle with a greater stopping distance. A
good driver is analog, the ABS digital, either on or off.
Jobst Brandt
frkr...@gmail.com
Is it truly "off," or does it reduce braking to a non-zero value during
the non-skid portion of the cycle?
Wikipedia claims a decrease in hydraulic pressure, but doesn't
specifically say it reduces to zero.
http://en.wikipedia.org/wiki/Anti-lock_braking_system
http://auto.howstuffworks.com/anti-lock-brake1.htm also claims the
valve releases "some of the pressure in the brake," implying not all of
it.
If the cycle rate of the system is high enough, it seems just the
inertia of the components and fluid would prevent true _zero_ braking
during the "off" state.
- Frank Krygowski
Helmut Springer
>>Still the driver to deploy ABS was control.
>
> Not on this side of the ocean, it was always about shorter stopping
> distances.
Which is where?