From: chumpychump@hotmail.com (Chalo)
Newsgroups: rec.bicycles.tech
Subject: Re: 6 or 8 inches front disc?
Date: 5 Nov 2003 20:05:02 -0800
Message-ID: <8b4b7de4.0311052005.51ffc38b@posting.google.com>

"Matt O'Toole" <matt@deltanet.com> wrote:

> Any brake has enough power to either lock the front wheel or flip you over
> the handlebars.

Hello?  No it doesn't.  Folks say this as if it will somehow become
true through repetition.

There are conditions under which, say, a single-pivot caliper brake
will deliver nose-wheelie quality braking:

- the bike must have a short wheelbase
- the bike must be of the upright type
- the bike must be for a single rider
- the rider must be of average or smaller size and weight
- the rider must be using a forward-leaning body position
- the rider must have abundant grip strength
- the bike must carry no heavy cargo
- the wheels must be clean, dry, and true
- the brakes must be well adjusted
- the brake pads must be of good quality and in good condition

If all these conditions do not apply, the braking will be less than
optimal.  Because of the rider size, weight, and positioning issues, I
am unable to get the kind of braking you describe on 16 of my 17
bikes.  It ain't because I don't squeeze the bejeebers out of them,
either.

I had to make my own brakes for the other bike!  They give me all the
stopping power I can use.

In my experience, nothing short of a loose, wet, or otherwise slippery
surface will allow a bike of conventional layout to skid the front
tire.

If you and Jobst are happy with weak brakes, great.  You can have
them; they don't work for me.  They fail to work well for a lot of
other people too.

Chalo Colina

From: chumpychump@hotmail.com (Chalo)
Newsgroups: rec.bicycles.tech
Subject: Re: 6 or 8 inches front disc?
Date: 6 Nov 2003 20:32:55 -0800
Message-ID: <8b4b7de4.0311062032.5cfa4df5@posting.google.com>

I wrote:
> I had to make my own brakes for the other bike!  They give me all the
> stopping power I can use.

Carl Fogel very kindly posted a couple of photos of my brake to his
webspace:

My thanks go to Carl for the favor.

The brake in the pictures is the strongest I have ever seen attached
to a bicycle.  It outperforms boosted Self Energizing cantilevers, any
and all V-brakes, Magura rim brakes, and every disc brake I have ever
had occasion to try.  8" Hayes hydraulic discs do not approach the
braking torque this brake provides.

I made the brake to replace a set of Avid Tri-Align brakes that I had
broken.  The fork was a pair of Bontrager legs stuck in a deep-arch
magnesium crown I made in order to accept the 700c wheel because the
legs were for 26".  When I decided to invest the effort of making my
own brakes, I sought out some suspension fork legs.  The ones I got
were Specialized Future Shock Carbon legs, because they were available
cheap, legs only, at a local shop.  They've since been heavily
reworked to shorten and stiffen the travel and to reinforce the
bushings.

I made a new fork brace, both to clear the 700c tire and to provide a
new location for the brake pivots.  Those pivots are 12.7mm (1/2") in
diameter rather than the usual 8mm, and they fit more closely than the
studs do in most cantilever or V brakes.  They are brass for its
improved bearing qualities against aluminum.

I made a booster arch that holds the fork arch at three points. The
former brake pivots were used to anchor the booster to the fork legs
for more extra additional bonus redundancy.

The brake arms are longer overall than regular V-brakes, but have
lower
mechanical advantage due to the relocated pivot points.  The pads are
Kool-Stop Thinline.  When I used the brake levers shown in these
pictures (Snafu Ultimate Levers), I was able to switch from
linear-pull leverage to cantilever leverage, and either one worked
just fine.  The feel was different, but either ratio gave plenty of
braking without running out of travel.

I had not seen Shimano V-brakes at the time I made these.  I used
Marinovative Cheap Trick brakes as a design guide, but the box brace
was my
own invention.  I had already observed that booster arches helped me
get strong braking, and I had seen that boosters tended to flex
forward visibly during hard stops.  I chose to bolt the booster to the
fork brace at top, and I provided a more mechanically rigid interface
at the pivots.

I am convinced that all the improvement in power over an ordinary
brake (and it is quite a bit) is attributable to the lack of flex in
the system.  Neither cable force nor pad frictional force can twist
the brake into a less effective configuration.  It takes a relatively
small force at the lever to get lots of braking, which I believe
supports my impression that flex is the primary source of most brakes'
inability to directly proportion lever force to braking force.  There
is nothing else so different about these brakes as to account for the
improvement in braking force over commercially available brakes.

After making this brake, I soon had to make a new fork crown, because
the enhanced braking bent the steerer and caused the fork stanchions
to crawl up in their clamps.  I made a stem and fork crown to match
each other, so that they could be joined with a rod to resist bending
loads on the steerer.  At one point I attempted to swap this front end
onto a lugged steel frame, but the braking forces bent the frame (!)
and I was obliged to switch back.

Chalo Colina

From: chumpychump@hotmail.com (Chalo)
Newsgroups: rec.bicycles.tech
Subject: Re: 6 or 8 inches front disc?
Date: 7 Nov 2003 18:59:31 -0800
Message-ID: <8b4b7de4.0311071859.7704133@posting.google.com>

carlfogel@comcast.net (Carl Fogel) wrote:

> Chalo's brake  may weigh less than you and I both
> thought at first glance.
>
> If you look at the front view carefully, the massive
> front U-arm appears to have a deep, smoothly-machined
> U-shaped indentation, making it more of a girder
> than a solid billet bent into a U.

I machined the front arch into a channel shape and the rear one into
an I-beam shape.  I arbitrarily chose .125" as a decent section
thickness, and wherever solid metal was not required for threads or
clamped areas, I machined reliefs into the sections until the
remaining webs were .125" thick.

I think the weight of this brake compares to that of a bicycle drum
brake-- it's lighter than an Arai drum, for instance.  But it's safely
heavier than any caliper, cantilever, or V-brake ever made.  It
performs well for me on a braking-energy-per-gram basis, though.

> It's still a substantial chunk of metal.

Oh yes.

The rear brake on that bike is a last-generation Pedersen Self
Energizing cantilever.  It provides more than half the braking potency
of the front brake, while weighing less than half as much.  It is much
more demanding to set up and much more temperamental than the big
brake, though.

Chalo Colina

From: chumpychump@hotmail.com (Chalo)
Newsgroups: rec.bicycles.tech
Subject: Re: 6 or 8 inches front disc?
Date: 7 Nov 2003 13:31:12 -0800
Message-ID: <8b4b7de4.0311071331.6fc3f875@posting.google.com>

Tim McNamara <timmcn@bitstream.net> wrote:

> chumpychump@hotmail.com (Chalo) writes:
>
> > The brake in the pictures is the strongest I have ever seen attached
> > to a bicycle.
>
> Good grief!  What does it weigh?

I don't know.  The bike it's attached to, which has similarly uprated
wheels, crank, BB, stem, bars, seat, etc., weighs 37 lbs ready to
ride.

That's without my special stainless steel pump, which weighs 2.2 lbs.

Chalo Colina

From: chumpychump@hotmail.com (Chalo)
Newsgroups: rec.bicycles.tech
Subject: Re: 6 or 8 inches front disc?
Date: 10 Nov 2003 17:24:19 -0800
Message-ID: <8b4b7de4.0311101724.64d77f89@posting.google.com>

carlfogel@comcast.net (Carl Fogel) wrote:

> Mark Hickey <mark@habcycles.com> wrote:
>
> > chumpychump@hotmail.com (Chalo) wrote:
> >
> > >That's without my special stainless steel pump, which weighs 2.2 lbs.
> >
> > Hefty steer tubes for a 360 pound guy, I understand...
> >
> > A custom-made brake that would stop a Harley, I understand...
> >
> > But a 2.2 pound air pump?

> B) Would you like to be an ordinary hand-pump in
>    Chalo's paws? He can probably be quite delicate,
>    but it's easy to get carried away when pumping
>    up tires. Recall his cheerful phrase about
>    squeezing the bejeebers out of a front brake
>    lever and spend a moment in silent sympathy
>    for any equipment that he gives a workout.

It would be nice to think that my one-off frame pump answered some
serious shortcoming of normal frame pumps, but that's not exactly it.

The frame pump in question (I'll call it Mr. Pump out of respect for
its mass) came from an idea I had many years ago, during my period of
routine 300-mile weeks in city traffic.  I had a classmate in art
school named Irwin "Trip" Franke, who was a sculptor, a militant vegan
and inveterate pedestrian.  He was somewhat irascible, and often
defended his personal space against cars by applying one of the
formidable walking sticks of his own making that he always carried
with him.  (Sometimes he got arrested as a result, because many cops
see it as their solemn duty to serve and protect all cars.)

Despite the fact that I enjoyed personal harmony more than Trip did, I
nonetheless could see the useful qualities of a baton that was always
close at hand.  I was inspired by my Silca frame pump to cook up a
similar appliance with a bit more structural integrity, which could be
used for the purposes of:

1) inflating tires

2) teaching dogs tricks, e.g. "roll over", "play dead"

3) cleaning windows for drivers who are having difficulty seeing
clearly

At the time I was thinking maybe 1/8" walled aluminum tubing for the
body and plunger, and a Campy metal head.  Unfortunately my
metalworking skills at the time ran to silversmithing rather than
thread-cutting, and there was no one I knew who could instruct me.
Also, I was completely unaware of the simplicity of one of those pump
heads, and thought I would have to make some kind of valving, which I
found intimidating.

Years later, by which time I had a much lower mileage routine, a much
more generous physique, and a gentler disposition, I decided to make
good on my earlier plans to build Mr. Pump.

Here is a semi-crude cross-sectional diagram adapted from my working
drawings:

Thanks again for hosting, Carl.

I used .065 wall stainless, partly because it was handy, parly because
it seemed more formidable, and partly because it was a better bore
size match for the Silca leather washer I chose to use as the one-way
plunger valve.  I machined the head out of a cylindrical chunk of
solid stainless, the better to approximate a hammer.  I used Delrin to
make the pump head internal features, a guide bushing on the plunger,
and the pump handle.  I used 7075 aluminum for the plunger rod and
yellow brass for the main bushing on the pump body.  I modified a
stainless SAE hydraulic plug fitting to house the Silca rubber grommet
at the output end.  there is a Buna-N o-ring seal there, and another
o-ring that serves as a "top out" bumper between the guide bushing and
the fixed bushing.

I built in about 2.5" of bushed overlap between the plunger shaft and
outer tube, so that the first time it was called upon to whack
something would not necessarily be the last.  This feature also makes
for smoother and stabler pumping than with a Silca Impero, which is
what the pump is in principle.

I will see what I can do about getting a photo up on the web.

Chalo Colina

From: jobst.brandt@stanfordalumni.org
Subject: Re: 6 or 8 inches front disc?
Newsgroups: rec.bicycles.tech
Message-ID: <wGGqb.4581$Wy2.51879@typhoon.sonic.net>
Date: Fri, 07 Nov 2003 06:09:32 GMT

Chalo Colina writes:

>> I had to make my own brakes for the other bike!  They give me all
>> the stopping power I can use.

> 

> 

> My thanks go to Carl for the favor.

> The brake in the pictures is the strongest I have ever seen attached
> to a bicycle.  It outperforms boosted Self Energizing cantilevers,
> any and all V-brakes, Magura rim brakes, and every disc brake I have
> ever had occasion to try.  8" Hayes hydraulic discs do not approach
> the braking torque this brake provides.

The only thing you missed was getting some red Kool-Stop pads.
However, what you have there is a brute force V-brake.  Not having a
head-on view, I can't estimate its mechanical advantage but while you
were at it, you could have dropped the brake arm pivot point another
centimeter or two to reduce cosine error.  What you have conclusively
proven, is that sponge is the enemy of good braking.  I assume the
other dimensions are fairly standard.

> I made the brake to replace a set of Avid Tri-Align brakes that I
> had broken.  The fork was a pair of Bontrager legs stuck in a
> deep-arch magnesium crown I made in order to accept the 700c wheel
> because the legs were for 26".  When I decided to invest the effort
> of making my own brakes, I sought out some suspension fork legs.
> The ones I got were Specialized Future Shock Carbon legs, because
> they were available cheap, legs only, at a local shop.  They've
> since been heavily reworked to shorten and stiffen the travel and to
> reinforce the bushings.

The problem is that the forks shown have an extra weak crown with
respect to spreading from cantilevers.  This crown should contain most
of the metal that is in the brake bridge, going straight across to th
other side.  The whole design looks like a machinists make work, hewn
from solid blocks of aluminum.

> I made a new fork brace, both to clear the 700c tire and to provide a
> new location for the brake pivots.  Those pivots are 12.7mm (1/2") in
> diameter rather than the usual 8mm, and they fit more closely than the
> studs do in most cantilever or V brakes.  They are brass for its
> improved bearing qualities against aluminum.

You should have dropped them down and extended the brake arms
proportionally up.

> I made a booster arch that holds the fork arch at three points. The
> former brake pivots were used to anchor the booster to the fork legs
> for more extra additional bonus redundancy.

Well the fork isn't contributing much, as bad as the crown is.

> The brake arms are longer overall than regular V-brakes, but have
> lower mechanical advantage due to the relocated pivot points.  The
> pads are Kool-Stop Thinline.  When I used the brake levers shown in
> these pictures (Snafu Ultimate Levers), I was able to switch from
> linear-pull leverage to cantilever leverage, and either one worked
> just fine.  The feel was different, but either ratio gave plenty of
> braking without running out of travel.

Where are the pivots?  What it the length ratio to regular V-brakes?

> I had not seen Shimano V-brakes at the time I made these.  I used
> Marinovative Cheap Trick brakes as a design guide, but the box brace
> was my own invention.  I had already observed that booster arches
> helped me get strong braking, and I had seen that boosters tended to
> flex forward visibly during hard stops.  I chose to bolt the booster
> to the fork brace at top, and I provided a more mechanically rigid
> interface at the pivots.

> I am convinced that all the improvement in power over an ordinary
> brake (and it is quite a bit) is attributable to the lack of flex in
> the system.  Neither cable force nor pad frictional force can twist
> the brake into a less effective configuration.  It takes a
> relatively small force at the lever to get lots of braking, which I
> believe supports my impression that flex is the primary source of
> most brakes' inability to directly proportion lever force to braking
> force.  There is nothing else so different about these brakes as to
> account for the improvement in braking force over commercially
> available brakes.

Well, that's one discovery I think many manufacturers never made. That
"sponge" is the enemy of good braking is evident from adjusting
sidepull brakes so they have little pad clearance.  They seem to have
more power suddenly, when in fact it is the better handful the grip
makes when it isn't nearly closed.  Add to that a brake that doesn't
flex and you have a large handful (two fingers) of brake available.

> After making this brake, I soon had to make a new fork crown,
> because the enhanced braking bent the steerer and caused the fork
> stanchions to crawl up in their clamps.  I made a stem and fork
> crown to match each other, so that they could be joined with a rod
> to resist bending loads on the steerer.  At one point I attempted to
> swap this front end onto a lugged steel frame, but the braking
> forces bent the frame (!)  and I was obliged to switch back.

You should have done all this as a grade school bikie and saved yourself
a lot of work by starting out with a better design on paper rather
than in hardware.  This takes too long.  Each iteration being
expensive and slow.  Doing this on a CAD screen with the experience
you have gained is rewarding... but don't let that stop you.  We may
yet benefit from some of these things.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: 6 or 8 inches front disc?
Newsgroups: rec.bicycles.tech
Message-ID: <RjTqb.4799$Wy2.55124@typhoon.sonic.net>
Date: Fri, 07 Nov 2003 20:32:49 GMT

Jose Rizal writes:

>> The only thing you missed was getting some red Kool-Stop pads.
>> However, what you have there is a brute force V-brake.  Not having
>> a head-on view, I can't estimate its mechanical advantage but while
>> you were at it, you could have dropped the brake arm pivot point
>> another centimeter or two to reduce cosine error.  What you have
>> conclusively proven, is that sponge is the enemy of good braking.
>> I assume the other dimensions are fairly standard.

> But dropping the pivot point means a longer arm, which increases
> bending moment and potentially flex.  There needs to be a happy
> medium between pivot/pad length and mechanical advantage.

Only if you insist on staying with the flimsy levers conventional
brakes have.  This is an experiment in brake design and getting rid of
a large cosine error is part of the problem.  When riding in rapid pad
wear conditions, repositioning pads is not acceptable.  Therefore,
deducing pad dive is important.  Parallelogram links help greatly but
add complexity and clearances that could introduce chatter.

>>> I made a new fork brace, both to clear the 700c tire and to
>>> provide a new location for the brake pivots.  Those pivots are
>>> 12.7mm (1/2") in diameter rather than the usual 8mm, and they fit
>>> more closely than the studs do in most cantilever or V brakes.
>>> They are brass for its improved bearing qualities against
>>> aluminum.

>> You should have dropped them down and extended the brake arms
>> proportionally up.

> Which might mean beefing up the arms to counteract the increased
> bending moment trying to flex the arm or pivot.

Yes, so what's wrong with that?  It doesn't change the force at the
pivot unless the ME is changes.  I didn't suggest that.  In fact, with
a more rigid brake the ME could probably go back to 4:1 as in the days
of yore.

>> Well, that's one discovery I think many manufacturers never
>> made. That "sponge" is the enemy of good braking is evident from
>> adjusting sidepull brakes so they have little pad clearance.  They
>> seem to have more power suddenly, when in fact it is the better
>> handful the grip makes when it isn't nearly closed.  Add to that a
>> brake that doesn't flex and you have a large handful (two fingers)
>> of brake available.

> I've always assumed that the cyclists' interpretation of the term
> "sponge" involves flex of the brake arms and/or the pads themselves
> (evident when there is a noticeable toe-in, depending on how thin
> the pads); that is, once at least part of the pads are in contact
> with the rim and some braking starts, and the brake levers are
> squeezed further, corresponding further movement of the pads due to
> flexing of some part of the system gives the "spongy" feeling.  Pad
> clearance results merely in changing brake lever travel before
> braking starts.

Yes, that's my take on that as well.  However, it all eats up hand
lever travel and gets into the region of ones grip that isn't as
strong as when the lever is nearer its free position.  One of the
features of dual pivot brake levers is that part of the return spring
is in the hand lever so that the caliper does not have to pull as
hard.  This reduces cable tension in the pad-clearance take up stroke,
and therefore, reduces friction that makes the transition from free
travel to braking more distinct and also makes brakes lock up more
easily on application.

I was made more aware of this while walking a bicycle with these
brakes down a steep trail.  The transition between rolling and wheel
lock-up was hard to control in comparison to my 4:1 Campagnolo Record
brakes as I reported in my tour report 2003.

http://www-math.science.unitn.it/Bike/Countries/Europe/Tour_Reports/Tour_of_the_Al

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: chumpychump@hotmail.com (Chalo)
Newsgroups: rec.bicycles.tech
Subject: Re: 6 or 8 inches front disc?
Date: 7 Nov 2003 15:41:53 -0800
Message-ID: <8b4b7de4.0311071541.1853f87e@posting.google.com>

jobst.brandt@stanfordalumni.org wrote:

> Chalo Colina writes:
>
> >> I had to make my own brakes for the other bike!  They give me all
> >> the stopping power I can use.
>
> > 

> > 

>
> The only thing you missed was getting some red Kool-Stop pads.
> However, what you have there is a brute force V-brake.

Yes, that's how it applies force to the rim.  How it applies a LOT of
force to the rim has more to do with the integrated brace than with
the arms, though.

Later, I was able to apply my design principles to a normal V-brake
(Marinovative Cheap Trick) for a friend's trials bike.  I made two
arches from 1/8" plate, bolted one behind the brake studs and the
other in front, with a screw and a standoff joining them together at
the top.  The resulting system was much more powerful than the same
brake with a conventional booster.

> The problem is that the forks shown have an extra weak crown with
> respect to spreading from cantilevers.  This crown should contain most
> of the metal that is in the brake bridge, going straight across to th
> other side.  The whole design looks like a machinists make work, hewn
> from solid blocks of aluminum.

Your critique of the proportion of the fork crown to the fork brace
ignores the fact that this fork is telescopic; that if the legs are
not braced they will not only move up and down independently, but they
will also freely rotate about their axes.  Furthermore, there is
necessary clearance between the fork stanchions and the fork bushings.
 The structure in which the brake pivots are rooted is the fork brace
and not the fixed portion of the fork legs.  The crown is actually
unable to contribute any of its rigidity to the brake pivots.

Therefore, the cross section of the fork crown "arms" is oriented to
match the applicable loads: large fore-to-aft and smaller laterally.
The crown was not more sophisticated due to the limitations at that
time of my CNC mill (2 axis, 1.5HP, no coolant) and my CAD/CAM system
(graph paper and a trig calculator).

> > I made a new fork brace, both to clear the 700c tire and to provide a
> > new location for the brake pivots.
>
> You should have dropped them down and extended the brake arms
> proportionally up.

I limited the total length of the arms so that they would not
intersect the downtube even if suspension pressure were lost.  There's
a lot of inertia in the rotating assembly of my bikes, and I did not
want to bungle a non-replaceable frame I had just made dedicated parts
for.

I could have lowered the pivots more without lengthening the arms
above the pads.  As it is, I can use up the limited pad thickness
without having to reposition the pads, so a flatter pad trajectory
would not help in that regard.

> > I made a booster arch that holds the fork arch at three points. The
> > former brake pivots were used to anchor the booster to the fork legs
> > for more extra additional bonus redundancy.
>
> Well the fork isn't contributing much, as bad as the crown is.

My chief motivation for bolting to the legs at the studs was that it
gave me another adhesive-bonded part to hold mechanically.  I reckoned
if the thing were glued in four places and one broke loose, that would
be better than if it were glued in only two places.  The fact that the
booster arch thus attached at 5 points instead of 3 was a bonus.

> Where are the pivots?  What it the length ratio to regular V-brakes?

The pivots are brass sleeves over the 3/8" stainless socket head cap
screws whose heads protrude from the front.  They are in the
neighborhood of 40mm below the rim sidewall, compared to about 25mm
for V-brakes.  The upper arms are longer than those of V-brakes, but
not by much.  I don't have the drawings handy, but the ratio of cable
travel to pad throw is about 3:1, which is about the lower end of the
possible leverage range for V-brakes.

> You should have done all this as a grade school bikie and saved yourself
> a lot of work by starting out with a better design on paper rather
> than in hardware.

The pictured system _is_ the better design, inasmuch as everything
else bent or broke or flexed too much or offered inadequate braking.
In the years since I built the system you see, I have changed only the
handlebars in order to get a different bend, and the fork internals.
It is the only front end in my big pile of bikes that doesn't want for
anything.  Its only significant shortcoming is higher weight than most
other sytems, and I'll happily accept that to enjoy the benefits.

Chalo Colina

From: jobst.brandt@stanfordalumni.org
Subject: Re: 6 or 8 inches front disc?
Newsgroups: rec.bicycles.tech
Message-ID: <VSWqb.4895$Wy2.56299@typhoon.sonic.net>
Date: Sat, 08 Nov 2003 00:35:01 GMT

Chalo Colina writes:

>>>> I had to make my own brakes for the other bike!  They give me all
>>>> the stopping power I can use.

>> The only thing you missed was getting some red Kool-Stop pads.
>> However, what you have there is a brute force V-brake.

> Yes, that's how it applies force to the rim.  How it applies a LOT
> of force to the rim has more to do with the integrated brace than
> with the arms, though.

I agree, rigidity is most of the battle and it seems to get ignored
most of the time.

> Later, I was able to apply my design principles to a normal V-brake
> (Marinovative Cheap Trick) for a friend's trials bike.  I made two
> arches from 1/8" plate, bolted one behind the brake studs and the
> other in front, with a screw and a standoff joining them together at
> the top.  The resulting system was much more powerful than the same
> brake with a conventional booster.

I don't know who invented the term "booster" but I guess we're stuck
with it.  It's really a brake bridge that closes the force loop of pad
pressure rather than dump it into the fork blades that wold bind in
their compression without it.  Even solid forks have suffered from
this with cantilevers spreading with brake force.  Suspension brought
that to a head and it has been marginally addressed since.

>> The problem is that the forks shown have an extra weak crown with
>> respect to spreading from cantilevers.  This crown should contain
>> most of the metal that is in the brake bridge, going straight
>> across to th other side.  The whole design looks like a machinists
>> make work, hewn from solid blocks of aluminum.

> Your critique of the proportion of the fork crown to the fork brace
> ignores the fact that this fork is telescopic; that if the legs are
> not braced they will not only move up and down independently, but
> they will also freely rotate about their axes.  Furthermore, there
> is necessary clearance between the fork stanchions and the fork
> bushings.  The structure in which the brake pivots are rooted is the
> fork brace and not the fixed portion of the fork legs.  The crown is
> actually unable to contribute any of its rigidity to the brake
> pivots.

Just the same the fore and aft forces tend to spread this crown, it
being a triangle with the front side missing.  Bending loads on a
straight across crown would not be a problem at the cross section
used.

> Therefore, the cross section of the fork crown "arms" is oriented to
> match the applicable loads: large fore-to-aft and smaller laterally.
> The crown was not more sophisticated due to the limitations at that
> time of my CNC mill (2 axis, 1.5HP, no coolant) and my CAD/CAM
> system (graph paper and a trig calculator).

It looks that way, but I'm sure a straight across crown with a strut
back to the steering axis would be better in weight and rigidity.  A
bit more reduction of the I-bean cross sections wouldn't hurt.

>>> I made a new fork brace, both to clear the 700c tire and to
>>> provide a new location for the brake pivots.

>> You should have dropped them down and extended the brake arms
>> proportionally up.

> I limited the total length of the arms so that they would not
> intersect the downtube even if suspension pressure were lost.
> There's a lot of inertia in the rotating assembly of my bikes, and I
> did not want to bungle a non-replaceable frame I had just made
> dedicated parts for.

As you mentioned below, you changed the pad operating radius.  I
couldn't tell from the views shown.

> I could have lowered the pivots more without lengthening the arms
> above the pads.  As it is, I can use up the limited pad thickness
> without having to reposition the pads, so a flatter pad trajectory
> would not help in that regard.

That's what I was getting at.

>>> I made a booster arch that holds the fork arch at three
>>> points. The former brake pivots were used to anchor the booster to
>>> the fork legs for more extra additional bonus redundancy.

>> Well the fork isn't contributing much, as bad as the crown is.

> My chief motivation for bolting to the legs at the studs was that it
> gave me another adhesive-bonded part to hold mechanically.  I reckoned
> if the thing were glued in four places and one broke loose, that would
> be better than if it were glued in only two places.  The fact that the
> booster arch thus attached at 5 points instead of 3 was a bonus.

>> Where are the pivots?  What it the length ratio to regular V-brakes?

> The pivots are brass sleeves over the 3/8" stainless socket head cap
> screws whose heads protrude from the front.  They are in the
> neighborhood of 40mm below the rim sidewall, compared to about 25mm
> for V-brakes.  The upper arms are longer than those of V-brakes, but
> not by much.  I don't have the drawings handy, but the ratio of
> cable travel to pad throw is about 3:1, which is about the lower end
> of the possible leverage range for V-brakes.

Sounds good.  Now the package needs to get smaller without losing the
gains made.  I think that can be done.

>> You should have done all this as a grade school bikie and saved
>> yourself a lot of work by starting out with a better design on
>> paper rather than in hardware.

> The pictured system _is_ the better design, inasmuch as everything
> else bent or broke or flexed too much or offered inadequate braking.
> In the years since I built the system you see, I have changed only the
> handlebars in order to get a different bend, and the fork internals.
> It is the only front end in my big pile of bikes that doesn't want for
> anything.  Its only significant shortcoming is higher weight than most
> other systems, and I'll happily accept that to enjoy the benefits.

This project seems to support my thoughts on brakes in that a rigid
system is more important than a high ME one and without power brakes
we have only a limited stroke at the rim given by the reach of the
human hand.  That's what makes this a difficult problem but one that
is just about within reach, so to speak.

Just think how much was wasted in the Campagnolo Delta brake that was
ultimately rigid but had a variable ratio ME, and terrible cosine
error to boot.  When I see things like that, I wonder where all the
engineers went.  This stuff is known outside the bicycle world but it
cant get in.

Jobst Brandt
jobst.brandt@stanfordalumni.org