home-made tires

"Gary Young" <[email hidden]> a écrit:

Quoted message said:

I thought I'd share something I just happened across -- an account
of how Germans made their own bicycle tires during the post-WWII
shortages:

The description reminds me of an older picture I chanced across some time
ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

The picture shows an interesting transition between the solid rubber tyres
of Fräulein Sorg and the ultra-fat pneumatics of Louise Albl. Mitzi has what
looks like a string of squash balls attached to her rims.

It's also interesting to note that the older young ladies have foot pegs,
and are therefore presumably riding fixed, while the young Albls have none.

James Thomson

All you need to make your own bike, is you start with the essential
materials, steel and rubber. Form them, cut them, and then simply assemble
them.

Quoted message said:

James Thomson said:

"Gary Young" <[email hidden]> a écrit:

Quoted message said:

I thought I'd share something I just happened across -- an account
of how Germans made their own bicycle tires during the post-WWII
shortages:

The description reminds me of an older picture I chanced across some time
ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

The picture shows an interesting transition between the solid rubber tyres
of Fräulein Sorg and the ultra-fat pneumatics of Louise Albl. Mitzi has what
looks like a string of squash balls attached to her rims.

It's also interesting to note that the older young ladies have foot pegs,
and are therefore presumably riding fixed, while the young Albls have none.

James Thomson

Dear James,

My ignorance never ceases to amaze me . . .

Do you know what those huge levers (or whatever) near the riders'
right hands are?

I'm guessing that they're handles for adjusting the tension of some
kind of suspension, judging by faintly similar things in side-view
diagrams in Sharpe's "Bicycles & Tricycles" (figures 272 and 276), but
Sharpe doesn't seem to think that the huge lever on one side of the
handlebars needs any explanation.

I assumed they were brake levers.

Greg
--
The ticketbastard Tax Tracker:
http://www.ticketmastersucks.org/tracker.html

Carl Fogel said:

Quoted message said:

Quoted message said:

I thought I'd share something I just happened across -- an account
of how Germans made their own bicycle tires during the post-WWII
shortages:

Quoted message said:

Quoted message said:

The description reminds me of an older picture I chanced across
some time ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Quoted message said:

Quoted message said:

The picture shows an interesting transition between the solid
rubber tyres of Fräulein Sorg and the ultra-fat pneumatics of
Louise Albl. Mitzi has what looks like a string of squash balls
attached to her rims.

Quoted message said:

Quoted message said:

It's also interesting to note that the older young ladies have foot
pegs, and are therefore presumably riding fixed, while the young
Albls have none.

Quoted message said:

My ignorance never ceases to amaze me...

Quoted message said:

Do you know what those huge levers (or whatever) near the riders'
right hands are?

Quoted message said:

I'm guessing that they're handles for adjusting the tension of some
kind of suspension, judging by faintly similar things in side-view
diagrams in Sharpe's "Bicycles & Tricycles" (figures 272 and 276),
but Sharpe doesn't seem to think that the huge lever on one side of
the handlebars needs any explanation.

They operate the front brake that presses a pad against the top of the
tire.

Jobst Brandt

James Thomson said:

"Gary Young" <[email hidden]> a écrit:

Quoted message said:

I thought I'd share something I just happened across -- an account
of how Germans made their own bicycle tires during the post-WWII
shortages:

The description reminds me of an older picture I chanced across some time
ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

The picture shows an interesting transition between the solid rubber tyres
of Fräulein Sorg and the ultra-fat pneumatics of Louise Albl. Mitzi has what
looks like a string of squash balls attached to her rims.

It's also interesting to note that the older young ladies have foot pegs,
and are therefore presumably riding fixed, while the young Albls have none.

James Thomson

Dear James,

My ignorance never ceases to amaze me . . .

Do you know what those huge levers (or whatever) near the riders'
right hands are?

I'm guessing that they're handles for adjusting the tension of some
kind of suspension, judging by faintly similar things in side-view
diagrams in Sharpe's "Bicycles & Tricycles" (figures 272 and 276), but
Sharpe doesn't seem to think that the huge lever on one side of the
handlebars needs any explanation.

Cheers,

Carl Fogel

Carl Fogel said:

Quoted message said:

Quoted message said:

>> I thought I'd share something I just happened across -- an
>> account of how Germans made their own bicycle tires during the
>> post-WWII shortages:

Quoted message said:

Quoted message said:

Quoted message said:

> The description reminds me of an older picture I chanced across
> some time ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Quoted message said:

Quoted message said:

Quoted message said:

> The picture shows an interesting transition between the solid
> rubber tyres of Fräulein Sorg and the ultra-fat pneumatics of
> Louise Albl. Mitzi has what looks like a string of squash balls
> attached to her rims.

Quoted message said:

Quoted message said:

Quoted message said:

> It's also interesting to note that the older young ladies have
> foot pegs, and are therefore presumably riding fixed, while the
> young Albls have none.

Quoted message said:

Quoted message said:

Quoted message said:

My ignorance never ceases to amaze me...

Quoted message said:

Quoted message said:

Quoted message said:

Do you know what those huge levers (or whatever) near the riders'
right hands are?

Quoted message said:

Quoted message said:

Quoted message said:

I'm guessing that they're handles for adjusting the tension of
some kind of suspension, judging by faintly similar things in
side-view diagrams in Sharpe's "Bicycles & Tricycles" (figures 272
and 276), but Sharpe doesn't seem to think that the huge lever on
one side of the handlebars needs any explanation.

Quoted message said:

Quoted message said:

I assumed they were brake levers.

Quoted message said:

Here's a diagram from Sharp with a similar right-hand monster lever:

Quoted message said:

http://i14.tinypic.com/3zs1od1.jpg

Quoted message said:

And here's James's picture again:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Quoted message said:

Whatever they are, those damn levers are almost big enough to serve
as the handle for a car jack.

Quoted message said:

Maybe they push a spoon brake down directly onto the front tire,
like a plunger?

Quoted message said:

I skimmed Sharp's text again, but he seems to think that the purpose
of the odd levers must be obvious to the meanest intelligence and
not worth mentioning.

I've seen these things and find that they are not for descending
hills, there being no place to dissipate heat in the skid pad that is
pressed against the tire. The tire rubber melts and leaves a skid
mark on the pad and if the brake is used for descending, the pad, if
metal, gets red hot.

As you see, bicycle tech has not been subjected to much engineering
even then.

Jobst Brandt

On Fri, 30 Mar 2007 11:44:49 -0700, "G.T." <[email hidden]>

Quoted message said:

Quoted message said:

James Thomson said:

"Gary Young" <[email hidden]> a écrit:

> I thought I'd share something I just happened across -- an account
> of how Germans made their own bicycle tires during the post-WWII
> shortages:
The description reminds me of an older picture I chanced across some time
ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

The picture shows an interesting transition between the solid rubber tyres
of Fräulein Sorg and the ultra-fat pneumatics of Louise Albl. Mitzi has what
looks like a string of squash balls attached to her rims.

It's also interesting to note that the older young ladies have foot pegs,
and are therefore presumably riding fixed, while the young Albls have none.

James Thomson

Dear James,

My ignorance never ceases to amaze me . . .

Do you know what those huge levers (or whatever) near the riders'
right hands are?

I'm guessing that they're handles for adjusting the tension of some
kind of suspension, judging by faintly similar things in side-view
diagrams in Sharpe's "Bicycles & Tricycles" (figures 272 and 276), but
Sharpe doesn't seem to think that the huge lever on one side of the
handlebars needs any explanation.

I assumed they were brake levers.

Greg

Dear Greg,

Here's a diagram from Sharp with a similar right-hand monster lever:

http://i14.tinypic.com/3zs1od1.jpg

And here's James's picture again:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Whatever they are, those damn levers are almost big enough to serve as
the handle for a car jack.

Maybe they push a spoon brake down directly onto the front tire, like
a plunger?

I skimmed Sharp's text again, but he seems to think that the purpose
of the odd levers must be obvious to the meanest intelligence and not
worth mentioning.

Cheers,

Carl Fogel

Quoted message said:

Aha! Here's a patent diagram for a front-suspension bike with spoon
brake:

http://patentpending.blogs.com/photos/uncategorized/capture8102005854...

There still are replicas being made with that sort of brake
mechanism.
In case you care for a fresh picture, just let me know and I shall
provide it in a few days.

Sergio
Pisa

Quoted message said:

Carl Fogel said:

Quoted message said:

> I thought I'd share something I just happened across -- an account
> of how Germans made their own bicycle tires during the post-WWII
> shortages:

Quoted message said:

Quoted message said:

The description reminds me of an older picture I chanced across
some time ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Quoted message said:

Quoted message said:

The picture shows an interesting transition between the solid
rubber tyres of Fräulein Sorg and the ultra-fat pneumatics of
Louise Albl. Mitzi has what looks like a string of squash balls
attached to her rims.

Quoted message said:

Quoted message said:

It's also interesting to note that the older young ladies have foot
pegs, and are therefore presumably riding fixed, while the young
Albls have none.

Quoted message said:

My ignorance never ceases to amaze me...

Quoted message said:

Do you know what those huge levers (or whatever) near the riders'
right hands are?

Quoted message said:

I'm guessing that they're handles for adjusting the tension of some
kind of suspension, judging by faintly similar things in side-view
diagrams in Sharpe's "Bicycles & Tricycles" (figures 272 and 276),
but Sharpe doesn't seem to think that the huge lever on one side of
the handlebars needs any explanation.

They operate the front brake that presses a pad against the top of the
tire.

Jobst Brandt

Dear Jobst,

Thanks! I just scanned a diagram from Sharp that shows the big lever
and (prodded by Greg) wondered if that was the explanation.

Looking for "spoon brake," I fetched up at Wikipedia, which has a
section on it in bicycle brake systems, but only a picture of a
retro-fitted monster on a Chinese cargo bike:

http://en.wikipedia.org/wiki/Bicycle_brake_systems#Spoon_brakes

Sheldon mentions spoon brakes, too, but no picture:

http://www.sheldonbrown.com/gloss_sp-ss.html

Aha! Here's a patent diagram for a front-suspension bike with spoon
brake:

http://patentpending.blogs.com/photos/uncategorized/capture810200585422_pm.jpg

I'm guessing that the huge lever is needed to provide enough force for
the direct plunger. I'd heard of spoon brakes, but never thought about
what would be needed to push the spoon against the tire.

Cheers,

Carl Fogel

Quoted message said:

On Fri, 30 Mar 2007 11:44:49 -0700, "G.T." <[email hidden]>

Quoted message said:

Quoted message said:

On Fri, 30 Mar 2007 09:51:40 +0200, "James Thomson"
<[email hidden]> wrote:

> "Gary Young" <[email hidden]> a écrit:
>
>> I thought I'd share something I just happened across -- an account
>> of how Germans made their own bicycle tires during the post-WWII
>> shortages:
> The description reminds me of an older picture I chanced across some time
> ago:
>
> http://woment.mur.at/images/GrazerDamenBicycleClub.jpg
>
> The picture shows an interesting transition between the solid rubber tyres
> of Fräulein Sorg and the ultra-fat pneumatics of Louise Albl. Mitzi has what
> looks like a string of squash balls attached to her rims.
>
> It's also interesting to note that the older young ladies have foot pegs,
> and are therefore presumably riding fixed, while the young Albls have none.
>
> James Thomson

Dear James,

My ignorance never ceases to amaze me . . .

Do you know what those huge levers (or whatever) near the riders'
right hands are?

I'm guessing that they're handles for adjusting the tension of some
kind of suspension, judging by faintly similar things in side-view
diagrams in Sharpe's "Bicycles & Tricycles" (figures 272 and 276), but
Sharpe doesn't seem to think that the huge lever on one side of the
handlebars needs any explanation.

I assumed they were brake levers.

Greg

Dear Greg,

Here's a diagram from Sharp with a similar right-hand monster lever:

http://i14.tinypic.com/3zs1od1.jpg

And here's James's picture again:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Whatever they are, those damn levers are almost big enough to serve as
the handle for a car jack.

Maybe they push a spoon brake down directly onto the front tire, like
a plunger?

I skimmed Sharp's text again, but he seems to think that the purpose
of the odd levers must be obvious to the meanest intelligence and not
worth mentioning.

Cheers,

Carl Fogel

Aha! Jobst explained that they are indeed levers for spoon brakes.

The diagram from Sharp is a little hard to follow because the spoon
that presses down on the front tire looks almost like part of an oddly
abbreviated front fender.

CF

Quoted message said:

Dear Sergio,
Yes, please!

O.k., will do.
There is such a replica that I convinced a shopkeeper friend of mine
to purchase, some three years ago.
If I ride my bike over there you'll get the pictures tomorow.

Sergio
Pisa

Quoted message said:

Carl Fogel said:

Quoted message said:

>>> I thought I'd share something I just happened across -- an
>>> account of how Germans made their own bicycle tires during the
>>> post-WWII shortages:

Quoted message said:

Quoted message said:

>> The description reminds me of an older picture I chanced across
>> some time ago:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Quoted message said:

Quoted message said:

>> The picture shows an interesting transition between the solid
>> rubber tyres of Fräulein Sorg and the ultra-fat pneumatics of
>> Louise Albl. Mitzi has what looks like a string of squash balls
>> attached to her rims.

Quoted message said:

Quoted message said:

>> It's also interesting to note that the older young ladies have
>> foot pegs, and are therefore presumably riding fixed, while the
>> young Albls have none.

Quoted message said:

Quoted message said:

> My ignorance never ceases to amaze me...

Quoted message said:

Quoted message said:

> Do you know what those huge levers (or whatever) near the riders'
> right hands are?

Quoted message said:

Quoted message said:

> I'm guessing that they're handles for adjusting the tension of
> some kind of suspension, judging by faintly similar things in
> side-view diagrams in Sharpe's "Bicycles & Tricycles" (figures 272
> and 276), but Sharpe doesn't seem to think that the huge lever on
> one side of the handlebars needs any explanation.

Quoted message said:

Quoted message said:

I assumed they were brake levers.

Quoted message said:

Here's a diagram from Sharp with a similar right-hand monster lever:

Quoted message said:

http://i14.tinypic.com/3zs1od1.jpg

Quoted message said:

And here's James's picture again:

http://woment.mur.at/images/GrazerDamenBicycleClub.jpg

Quoted message said:

Whatever they are, those damn levers are almost big enough to serve
as the handle for a car jack.

Quoted message said:

Maybe they push a spoon brake down directly onto the front tire,
like a plunger?

Quoted message said:

I skimmed Sharp's text again, but he seems to think that the purpose
of the odd levers must be obvious to the meanest intelligence and
not worth mentioning.

I've seen these things and find that they are not for descending
hills, there being no place to dissipate heat in the skid pad that is
pressed against the tire. The tire rubber melts and leaves a skid
mark on the pad and if the brake is used for descending, the pad, if
metal, gets red hot.

As you see, bicycle tech has not been subjected to much engineering
even then.

Jobst Brandt

Dear Jobst,

Hunting around in Sharp, I see even more support for your views about
the inadequacy of very old brakes.

After considerable calculations (probably limited by the design and
materials of 1896), Sharp arrived at this conclusion:

"That is, no brake, however powerful, can stop the machine on a
gradient of 121 in 1,000, about 1 in 8."

--Chapter XXXII

Even if Sharp's calculations are mistaken, it sounds as if back in the
spoon-brake era it was assumed that a sustained 12% grade was simply
suicidal.

Sharp mentions pneumatic (!) spoon brakes:

"In the pneumatic brake the movment of the brake block on the tire is
produced by means of compressed air, pumped by a rubber collapsible
ball placed on the handle-bar, and led through a small india-rubber
tube to an air chamber, which can be fastened to any convenient part
of the frame. With this simple apparatus the brake can be as easily
applied to the rear as to the front wheel."

Sharp was also dubious about the new-fangled band-brakes, which were
applied to not only the hubs, but to the crank axle (presumably on a
fixie). After more calculations, he concluded that the crank-axle
brake was a bad idea:

"This example shows the ineffectiveness of a crank-axle band brake,
since the elasticity of the gear is such that the brake lever would be
close up against the handle-bar long before the required pull was
exerted by the band."

"If oil gets in between the band and the drum, the coefficient of
friction will be much less, and a much greater pull will be required,
than in the above examples."

Cheers,

Carl Fogel

Carl Fogel said:

Quoted message said:

I've seen these things and find that they are not for descending
hills, there being no place to dissipate heat in the skid pad that is
pressed against the tire. The tire rubber melts and leaves a skid
mark on the pad and if the brake is used for descending, the pad, if
metal, gets red hot.

Quoted message said:

Quoted message said:

As you see, bicycle tech has not been subjected to much engineering
even then.

Quoted message said:

Hunting around in Sharp, I see even more support for your views about
the inadequacy of very old brakes.

Quoted message said:

After considerable calculations (probably limited by the design and
materials of 1896), Sharp arrived at this conclusion:

Quoted message said:

"That is, no brake, however powerful, can stop the machine on a
gradient of 121 in 1,000, about 1 in 8."

Quoted message said:

--Chapter XXXII

Quoted message said:

Even if Sharp's calculations are mistaken, it sounds as if back in the
spoon-brake era it was assumed that a sustained 12% grade was simply
suicidal.

Quoted message said:

Sharp mentions pneumatic (!) spoon brakes:

Quoted message said:

"In the pneumatic brake the movement of the brake block on the tire is
produced by means of compressed air, pumped by a rubber collapsible
ball placed on the handle-bar, and led through a small india-rubber
tube to an air chamber, which can be fastened to any convenient part
of the frame. With this simple apparatus the brake can be as easily
applied to the rear as to the front wheel."

Quoted message said:

Sharp was also dubious about the new-fangled band-brakes, which were
applied to not only the hubs, but to the crank axle (presumably on a
fixie). After more calculations, he concluded that the crank-axle
brake was a bad idea:

Quoted message said:

"This example shows the ineffectiveness of a crank-axle band brake,
since the elasticity of the gear is such that the brake lever would be
close up against the handle-bar long before the required pull was
exerted by the band."

Quoted message said:

"If oil gets in between the band and the drum, the coefficient of
friction will be much less, and a much greater pull will be required,
than in the above examples."

It's conversion of kinetic energy to heat, not pull or coefficient of
friction that lies at the root of this. Aluminum rims dissipate brake
heat while soft brake pads generate it.

When I read this stuff, I get an indication of how poor engineering
was in those days. Sharp was apparently not a mechanical engineer and
not skilled in the art of thermodynamics or he would have known what
steady state heat rejection was required to descend the 12% grade.

It reminds me of the SF Cable Cars that have an even worse emergency
brake that doesn't work. As a last resort the third (Red) lever in
front of the gripman is used to drive a steel wedge into the cable
slot in the belief that because it can be jammed in there tightly, it
will dissipate heat and slow the car. Nothing of the kind occurred
the few times it was used, but no one noticed because when the cable
car crashed into a truck at the bottom of the hill, the lubricating
molten steel froze, welding the car to the street. It was reported
that the holding power was so great the car had to be freed with
cutting torches, thereby proving that it is a good brake. That belief
lives on in SF today. Where is Sharp and his spoon brake when we need
him?

Jobst Brandt

sergio said:

Quoted message said:

Aha! Here's a patent diagram for a front-suspension bike with spoon
brake:

http://patentpending.blogs.com/photos/uncategorized/capture8102005854...

There still are replicas being made with that sort of brake
mechanism.
In case you care for a fresh picture, just let me know and I shall
provide it in a few days.

Sergio
Pisa

Dear Sergio,

Yes, please!

Cheers,

Carl Fogel

Quoted message said:

Carl Fogel said:

Quoted message said:

I've seen these things and find that they are not for descending
hills, there being no place to dissipate heat in the skid pad that is
pressed against the tire. The tire rubber melts and leaves a skid
mark on the pad and if the brake is used for descending, the pad, if
metal, gets red hot.

Quoted message said:

Quoted message said:

As you see, bicycle tech has not been subjected to much engineering
even then.

Quoted message said:

Hunting around in Sharp, I see even more support for your views about
the inadequacy of very old brakes.

Quoted message said:

After considerable calculations (probably limited by the design and
materials of 1896), Sharp arrived at this conclusion:

Quoted message said:

"That is, no brake, however powerful, can stop the machine on a
gradient of 121 in 1,000, about 1 in 8."

Quoted message said:

--Chapter XXXII

Quoted message said:

Even if Sharp's calculations are mistaken, it sounds as if back in the
spoon-brake era it was assumed that a sustained 12% grade was simply
suicidal.

Quoted message said:

Sharp mentions pneumatic (!) spoon brakes:

Quoted message said:

"In the pneumatic brake the movement of the brake block on the tire is
produced by means of compressed air, pumped by a rubber collapsible
ball placed on the handle-bar, and led through a small india-rubber
tube to an air chamber, which can be fastened to any convenient part
of the frame. With this simple apparatus the brake can be as easily
applied to the rear as to the front wheel."

Quoted message said:

Sharp was also dubious about the new-fangled band-brakes, which were
applied to not only the hubs, but to the crank axle (presumably on a
fixie). After more calculations, he concluded that the crank-axle
brake was a bad idea:

Quoted message said:

"This example shows the ineffectiveness of a crank-axle band brake,
since the elasticity of the gear is such that the brake lever would be
close up against the handle-bar long before the required pull was
exerted by the band."

Quoted message said:

"If oil gets in between the band and the drum, the coefficient of
friction will be much less, and a much greater pull will be required,
than in the above examples."

It's conversion of kinetic energy to heat, not pull or coefficient of
friction that lies at the root of this. Aluminum rims dissipate brake
heat while soft brake pads generate it.

When I read this stuff, I get an indication of how poor engineering
was in those days. Sharp was apparently not a mechanical engineer and
not skilled in the art of thermodynamics or he would have known what
steady state heat rejection was required to descend the 12% grade.

I see a date of 1896 for Sharp, but when were those spoon brakes
invented? Joule only started publishing discoveries about thermodynamics
around 1850.

Quoted message said:

Yes, please!

By the way, that one is a replica of a Pedersen bike.

Sergio
Pisa

While we're at it, Avocet smooth tread tires are still among the
lowest RR tires on the market. It was the introduction of these tires
that initiated the RR tests shown at:

http://www.sheldonbrown.com/brandt/rolling-resistance-tubular.html

It's nice to see that other manufacturers have cesased putting
miniature automobile tread on their tires and motorcycle road tires
are all slicks today. Progress is slow.

http://www.avocet.com/tirepages/tires.html
http://www.paloaltobicycles.com/alps_photos/f70.html

That's me riding up the Col d'Iseran on Avocet slicks.

Jobst Brandt

Andrew Muzi said:

Quoted message said:

Quoted message said:

Even if Sharp's calculations are mistaken, it sounds as if back in the
spoon-brake era it was assumed that a sustained 12% grade was simply
suicidal.

-more snip-

Quoted message said:

Quoted message said:

It's conversion of kinetic energy to heat, not pull or coefficient of
friction that lies at the root of this. Aluminum rims dissipate brake
heat while soft brake pads generate it.

Quoted message said:

Quoted message said:

When I read this stuff, I get an indication of how poor engineering
was in those days. Sharp was apparently not a mechanical engineer and
not skilled in the art of thermodynamics or he would have known what
steady state heat rejection was required to descend the 12% grade.

Quoted message said:

Quoted message said:

It reminds me of the SF Cable Cars that have an even worse emergency
brake that doesn't work. As a last resort the third (Red) lever in
front of the gripman is used to drive a steel wedge into the cable
slot in the belief that because it can be jammed in there tightly, it
will dissipate heat and slow the car. Nothing of the kind occurred
the few times it was used, but no one noticed because when the cable
car crashed into a truck at the bottom of the hill, the lubricating
molten steel froze, welding the car to the street. It was reported
that the holding power was so great the car had to be freed with
cutting torches, thereby proving that it is a good brake. That belief
lives on in SF today. Where is Sharp and his spoon brake when we need
him?

Quoted message said:

You mentioned that once before and it's an interesting problem. I know
this wanders far afield but what would you suggest?

Quoted message said:

[er, for cable car emergency, not bicycle rims at steep grade]

I'd connect the big red lever to a 18" square plate with bus tire
tread on its underside and press it against the road to create a huge
skid mark. These cable cars are not as heavy as buses that substitute
when the cable is out of service.

Beyond that, the run-aways occur mainly on the Hyde street hill and
occur because losing the cable from the grip is not clearly
understood. I have written to them about this a few times and finally
gave up.

In order to spare riders that sinking feeling as the car dives over
the crest of the hill, some gripmen try to ease over the crest, gently
as they leave the stop before the hill at which the cable is held but
allowed to slip while the car is braked to a stop (on level ground).
The only way a cable car can travel slower than the cable (9.5mph) is
to let it slip in the grip. Cresting a hill when not synchronous with
the cable can separate it from the grip that opens downward. Lifting
the cable off the "crown wheel" that supports it as it crests the
hill, takes a large force, the force that causes losing the cable and
a runaway.

It's all so simple but has escaped understanding for more than 100
years.

Jobst Brandt

Ben C said:

Quoted message said:

Carl Fogel said:

> I've seen these things and find that they are not for descending
> hills, there being no place to dissipate heat in the skid pad that is
> pressed against the tire. The tire rubber melts and leaves a skid
> mark on the pad and if the brake is used for descending, the pad, if
> metal, gets red hot.

Quoted message said:

> As you see, bicycle tech has not been subjected to much engineering
> even then.

Quoted message said:

Hunting around in Sharp, I see even more support for your views about
the inadequacy of very old brakes.

Quoted message said:

After considerable calculations (probably limited by the design and
materials of 1896), Sharp arrived at this conclusion:

Quoted message said:

"That is, no brake, however powerful, can stop the machine on a
gradient of 121 in 1,000, about 1 in 8."

Quoted message said:

--Chapter XXXII

Quoted message said:

Even if Sharp's calculations are mistaken, it sounds as if back in the
spoon-brake era it was assumed that a sustained 12% grade was simply
suicidal.

Quoted message said:

Sharp mentions pneumatic (!) spoon brakes:

Quoted message said:

"In the pneumatic brake the movement of the brake block on the tire is
produced by means of compressed air, pumped by a rubber collapsible
ball placed on the handle-bar, and led through a small india-rubber
tube to an air chamber, which can be fastened to any convenient part
of the frame. With this simple apparatus the brake can be as easily
applied to the rear as to the front wheel."

Quoted message said:

Sharp was also dubious about the new-fangled band-brakes, which were
applied to not only the hubs, but to the crank axle (presumably on a
fixie). After more calculations, he concluded that the crank-axle
brake was a bad idea:

Quoted message said:

"This example shows the ineffectiveness of a crank-axle band brake,
since the elasticity of the gear is such that the brake lever would be
close up against the handle-bar long before the required pull was
exerted by the band."

Quoted message said:

"If oil gets in between the band and the drum, the coefficient of
friction will be much less, and a much greater pull will be required,
than in the above examples."

It's conversion of kinetic energy to heat, not pull or coefficient of
friction that lies at the root of this. Aluminum rims dissipate brake
heat while soft brake pads generate it.

When I read this stuff, I get an indication of how poor engineering
was in those days. Sharp was apparently not a mechanical engineer and
not skilled in the art of thermodynamics or he would have known what
steady state heat rejection was required to descend the 12% grade.

I see a date of 1896 for Sharp, but when were those spoon brakes
invented? Joule only started publishing discoveries about thermodynamics
around 1850.

Dear Ben,

For what it's worth . . .

"Archibald Sharp was an instructor in engineering design at the
Central Technical College in South Kensington (now Imperial College)."

http://www3.imperial.ac.uk/portal/pls/portallive/docs/1/6963908.PDF

And for the technically minded, here are the brake calculations:

http://i3.tinypic.com/43h8nwy.jpg

Left-click on the lower right for the full-size detailed scan that
shows the tiny subscripts in the equations.

The next page indicates that the final calculation in the scan is for
a front brake only:

"If the brake be applied to the back wheel, the corresponding gradient
is:

x = (0.4 x 125.7) / 180 = .279

i.e. about 1 in 4."

Again, I have no idea if the calculations are correct, but there is
the suggestion that someone interested enough in bicycle physics
around 1896 to write a 500+ page book littered with similar equations
considered a 12% grade suicidal for such primitive brakes.

Never having used a spoon brake, I don't know how well they work, but
similar leather pads pressed down onto the rims of wagon wheels (as
opposed to side caliper-style brakes) are notoriously feeble.

As an aside, I look forward to a lively discussion of the ejection
forces that led to the demise of the front spoon brake.

🙂

Cheers,

Carl Fogel