From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: History of Campy Delta Brakes
Date: 30 Sep 1996 21:52:40 GMT

Tom Kunich writes:

> Campy built the Delta brakes in the Record and C'd'Aune line. The
> cheaper versions had an external return spring and were very
> unpopular. The Record version sold poorly due in great part to their
> price.

> As brakes they were only so-so. They look great.

> Eventually they were proclaimed as mechanically dangerous by Jobst
> Brandt who is/was working strictly from a theoretical point of view.

The first to do so were the sponsored pro's who refused to use them
after enough riders crashed and others had spooky experiences.

I am working from riding experience and from standard brake technology
in which variable ratio brakes known to be useless.  I worked in brake
design for several years at Porsche KG.  I reviewed the Delta brake
in the 1970's when it was the Modolo Chronos.  It should be
mechanically obvious that a regular-parallelogram when at extreme
extended position (cable fully extended) has zero mechanical advantage
and at the other extreme (the cable corners together) has an infinite
mechanical advantage.  This is not a logical range in which to operate
a brake, nor is even a part of that range.

Such a characteristic is unconscionable for any brake manufacturer to
offer as a brake, and even more so for one who sponsors racers who
descend mountain roads or ride criteriums.  The avocational bicyclist
may probably not notice the effect because he does not stand the bike
on its nose, so to speak, as he enters curves.  Self energizing
cantilever brakes that have been offered have a similar effect that is
not even brake stroke dependent.  They are also dangerous.

> Is the actuation mechanism design good? No. Were they good brakes?
> No. Were they as bad as Jobst seems to think they were? No. In
> practice they seem about as good as Super Record brakes, a design
> that most people were satisfied with until Shimano (and then Campy)
> developed the dual pivot brakes.

Oh, please explain what makes the dual pivot brake better than
previous brakes.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: History of Campy Delta Brakes
Date: 30 Sep 1996 15:19:52 GMT

Kristan Roberge writes:

> Garry Lee wrote:

>> The longest thread of all time ran about these.  Apparently the
>> brakes are a dangerous design as when the pads wear beyond a
>> certain amount your braking disappears suddenly. Read the
>> instructions if you can get them. For the above reason, they were
>> taken off the market.

It's the opposite.  The mechanical advantage of the brake caliper goes
from zero to infinity through its stroke, it is flat and at a 1:1
ratio only at the middle of its short stroke.  As the brake pads wear,
the mechanism moves into the high leverage region where it locks up
the wheel, the hand lever falling against the handlebar.  This is the
reason the brake is no longer made.

> Really?  And here I thought they were taken off the market because 
> Campy perfected their own dual-pivot brakes which offered most of
> the power of the Delta's but with easier setup and less weight...

What does a dual pivot brake have to do with the demise of the
"beautiful" Delta brake?  I hope you realize that there is no power
brake and leverage cannot be created.  Either the hand lever travel
increases or you don't get more brake force.  Leverage is a constant
product of travel and force.  You can't change one without the other.

The sole purpose of the dual pivot brake is to guarantee centering,
nothing more.  The dual pivot is half centerpull and half sidepull and
has the problem that the short arm sweeps up into the tire as
centerpulls do, requiring pad adjustment as they wear.  You may have
noticed that dual pivot brakes always remain centered and cannot track
a wheel with a broken spoke.  This is an advantage?

Of course, road bikes today, with 2mm tire clearance can't be ridden
with a broken spoke.  You call a tow truck if that happens (in the
middle of nowhere).  The people who only cruise the main with their
flashy bikes don't care about that anyway, so as a result you can't
buy a bike with clearance.  It's gotta be tight.

> Jobst maintains the brakes were dangerous but that doesn't stop
> alot of happy owners from using them even today. I know one local
> who uses them on all his bikes, and as he buys a new $3-4000 bike
> every year, its certainly not because he can't afford better.

There are many people who never consider braking in a turn, slowing
down with hard deceleration or braking in the wet.  Any of these
exercises is extremely hazardous on the Delta.  I also look at bikes I
see on the road an have seldom seen a worn brake pad, so I can imagine
there are people for whom the smooth lines of the Delta may be
preferable.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: History of Campy Delta Brakes
Date: 11 Oct 1996 04:52:53 GMT

Tom Kunich writes:

>> Forget it.  A brake that has a variable mechanical advantage is out
>> of contention for any consideration by brake or controls people.

> And yet normal sidepull brakes have a mechanism that varies it's
> leverage with pad wear. I suppose that there is some level of
> non-linearity in which you consider yourself an expert at judging
> which is more than you consider kosher and which then becomes
> dangerous.

Oh?  Explain that will you.  There is essentially no change in radius
as the pad wears from new to nothing.  I have a sack of pads worn to
the metal that were never adjusted after installation.  You'll have to
do more than make claims like that to make it stick.  You may have
noticed that the pivot point on a sidepull brake is directly over the
center of the wheel and has arms of about 50mm.  With a rim width of
22mm that gives an angle of about 12.5 degrees that has a Cosine of
0.98.  That means that when 10mm of pad wears away, the change in
position on the rim is about 0.2mm lower.  That doesn't constitute a
variable ratio brake to me.

>> I don't understand what you mean by this.  Are you suggesting there is
>> a discrete threshold at which the brake characteristic is irrelevant?

> Excuse me?  Perhaps you aren't aware than MOST bikes don't have
> brakes that even WORK?  If most people can get away using brakes
> that cannot even stop their bicycles you are telling me that the
> Delta's non-linearity at extremes is significant? I think that you
> are loosing perspective of the problems.

I'm sorry, your hyperbole escapes me.  What means this... so to speak?
We are talking about professional racers that were under contract to
use the brake and that these riders crashed or had scary incidents
with it.  What klutzes do with their carbon fiber parade machines is
not relevant to the quality of the brake.

>> These brakes were dangerous at any speed, however, people who ride
>> with a huge safety margin may not crash, but their riding is
>> influenced just the same by the odd response of the brake.  As a
>> result they ride with even more margin to avoid the spooky condition.

> Yes, we have all seen the absolute wealth of injured riders who were
> 'done in' by Campi Deltas.  Well, since there aren't any, I suppose
> that you are the only rider on the net who doesn't ride with a "huge
> safety margin".

The way you say that, you must have been there when various pro racers
took a dive.  I heard it from reliable sources and I believe them just
as I believe that Umma Gumma tires caused crashes on wet roads.  My
knowledge of brakes indicates that the Delta should cause crashes.  As
I said, I predicted this would occur when Modolo offered the brake
years before Campagnolo chose to pick up the design.

> As I said, I have Deltas on my Graftek. They work OK. They aren't
> dangerous in any manner that I've detected. I'm not impressed by
> their operation either. They are somewhat heavier than a brake need
> be and they are extremely expensive to build. That is what killed
> the brake and not your imaginary non-linear response. To listen to
> you one would think that bicycles were operated above the speed of
> sound.

I wouldn't make such an issue of your sedentary riding style for which
a brake as bad as the Delta is fine.  This is not a sign of superior
skill, because skill will not change its characteristic, but is a sign
that you don't need a high performance brake.  You keep harping on it
so I'm taking you up on it this time.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: History of Campy Delta Brakes
Date: 19 Oct 1996 01:21:42 GMT

Stephen Judice writes:

> Maybe I am misled, but I have noticed that it does not take that
> much to lock up the wheels of a bicycle; even when it is going fast.
> I do not see any reason that either single or dual pivot could not
> reach this point.  After this, the thing that regulates braking is
> the friction between the pavement and the tire.  Everything else
> kind of doesn't play a role....No, I am not saying that I mosh on the
> brakes and lock up my wheels every time I stop, but when I am hard
> pressed to stop in a hurry, it sometimes happens, sometimes even to
> the front wheel on wet pavement.

Some people might suspect you as a paid lackey of mine to raise
unraised issues, knowing that I generally don't initiate a thread here
on the net.  However, that not being the case...

From what you say, I take it you are skidding your rear wheel because
locking up the front wheel, if you position yourself for strong
braking, is not easily done with most bicycle brakes.  That is if the
rim is not brand new and sticky, and brake pads are worn in.  Skidding
the rear wheel is not where "it's at" in the vernacular.  Slowing down
at the limit of raising the back wheel is the requirement.  This takes
a brake with good modulation and suitable mechanical advantage.

In recent years, many new riders joined the ranks of bicyclists,
including many less than athletic people who took up the sport to
change that facet of their lives.  Not only did they discover that
sitting on a bicycle saddle causes soreness for the beginner, but that
braking is more difficult than they had imagined.  The push was on for
a brake that had a higher mechanical advantage than the classic 4:1
brake lever and the 1:1 caliper.  This ratio did not come about by
accident.  For bicycle racers, this was an optimal design that also
allowed a non fatal quick release.  Campagnolo Record brakes, if
properly adjusted, could be used in the open position, and could
survive a race in the rain on dirt alpine roads without adjustment.

The only way to get more braking force was to raise the mechanical
advantage.  This was not possible with the existing design without
power assist.  There being no power assist available on bicycles as
there is on cars leaves only changing the ratio and this used up the
lever travel.  Putting the pads closer to the rim caused brake drag,
the bane of all older brakes after a period of use.

Two solutions for this come to mind.  A variable ratio brake that
makes contact with the rim at low mechanical advantage and then
applies braking force at a higher mechanical advantage.  This had been
tried for years in the automobile industry and never got past the
research lab and test cars.  They finally tossed in the towel and went
to power assist brakes that today are more than 50% power.  Stopping a
car with the motor off or at full throttle (with no vacuum) is barely
possible.  I believe Campagnolo tried the variable ratio Delta brake
to achieve what others had considered unfeasible.  It did not, as
people in the automotive brake business could have told them.

The alternative is to reduce pad clearance and take a bigger cut at
the mechanical advantage.  This requires a brake that does not drag by
drifting off center with use.  The forerunner of such a design were
the self centering centerpull brakes in the late 1960's.  However the
centerpull was discredited for its excessive much sponge and large
cosine error (pad sweeping off the rim in an arc), almost as bad as a
cantilever but without the benefits of a cantilever.  It died on the
vine as side pull brakes made stiffer arms and re-established their
leadership.

The dual pivot brake needs its two pivots because it takes two points
to determine a line of action.  This basis allows precision tracking
and adjustment of the pads to practically touching a true wheel.  With
this proximity a higher caliper ratio is achieved at the expense of
two small losses.  The shorter (off center pivoted) arm has cosine
error (the sweep of the arm rises into the tire) with pad wear, and
the brake cannot track a wobbly wheel.  A wobbly wheel, one with a
broken spoke, will not turn as it could with single pivot side pulls.
The hand levers remained standard and only the caliper changed.  This
is not what the V-brake did and it is an unfortunate departure whose
reason I have not yet discovered.

Jobst Brandt      <jbrandt@hpl.hp.com>