brake failure

carlfogel@comcast.net

On Tue, 20 May 2008 11:43:20 -0500, A Muzi <am@yellowjersey.org>
wrote:

> jobst.brandt@stanfordalumni.org wrote:
>> This is getting more wishy-washy with each response and is similar to
>> the claims to which I referred about center pull and cantilever brakes
>> in times gone by. No measurements were made, just conjecture.
>
>Measurements, part one:
>On the bike I rode in today with a Weinmann type 500 sidepull*, the
>cable stop to centerbolt center is 61mm. Centerbolt to center of pad is
>55mm.
>
>On a new V equipped bike near me now, cable stop to brake pivot is
>111mm. Brake pivot to center of pad is 36mm.
>
>SP- 61:55 or 90.1%
>V- 111:36 or 32.4%
>
>they differ overall by 35+%
>
>Measurements, part two:
>On a dual mode lever the pivot to cable mount is
>Standard mode 28mm
>'Linear' mode 37mm
>or a difference of 25% in cable movement.
>
>My conclusion is that you measured in a different era (when virtually
>all bicycle brakes were nicely standardized within a narrow band) and
>that you don't get out much to see modern low-end bikes with today's
>linear brakes. Measuring carefully but ignoring another group is still
>not complete comprehensive data of the whole!
>
>Is there no one in your neighborhood with a $199 'hybrid' bicycle? There
>are probably more new bikes sold in 2008 with "V" brakes than with dual
>pivot calipers, at least in the USA.
>
>*Fashionably equipped with Kool Stop "Vans Shoe" shoes!

Dear Andrew,

Thanks for the measurements--I was beginning to wonder if Sheldon and
the rest of the world had missed something.

Cheers,

Carl Fogel

Michael Press

In article <FICdnSkWHuRvYK_VnZ2dnUVZ_gudnZ2d@earthlink.com>,
"Tom Kunich" <cyclintom@yahoo. com> wrote:

> <jobst.brandt@stanfordalumni.org> wrote in message
> news:4832d837$0$34541$742ec2ed@news.sonic.net...
> > Tom Kunich wrote:
> >> No Jobst, I actually MEASURED the distances from the fulcrum and it
> >> was about 2.5:1. I say about because of the adjustments for the shoe
> >> placement.
> >
> > I didn't notice that anyone mentions dimensions in this thread or that
> > measurements were made and how. I just fine the language used for
> > brakes is misleading and asked what is linear and what the MA is in
> > the brake mentioned. Just because the cable moves farther doesn't
> > prove that this difference is canceled by the caliper leverage.
>
> After all these years you should be more than prepared for the inaccurate
> language used by most people when talking about mechanical things.
>
> I used a metric tape measure to measure the distance to the brake shoe
> center and to the cable attachment point. The leverage of the (Shimano XT)
> unit was approximately 2.5:1. We don't need precision here.

We do need accuracy of language, and accuracy is what you
are talking about here where you misuse the word `precision.'
They are not synonyms. Precision measures the repeatability
of a measuring technique.

Accuracy in a clock is how closely it reads to the `real' time.
Precision of a clock is the variability of the intervals between ticks.

--
Michael Press

carlfogel@comcast.net

On May 19, 5:44*pm, jobst.bra...@stanfordalumni.org wrote:
> Andrew Muzi wrote:
> >>> That's all generally helpful but the specific bike here has linear
> >>> ("V") brakes, which not only have a ratio with greater cable
> >>> travel and greater pressure at the rim for a given effort at the
> >>> lever, but are notorious for chewing rims and pads.
> >> Maybe you can tell me what is "linear" about these brakes and what
> >> the MA (mechanical advantage) is. *Appearances can deceive. *It was
> >> once believed that centerpull brakes had twice the MA of sidepull
> >> calipers based on the length of caliper input levers on which the
> >> straddle cable acts. *This ignored that there are two of these,
> >> which divides that apparent MA in two.
> >> Other than these considerations, more pad force does not affect
> >> whether they develop grit or not.
> > "Linear" a.k.a. "Direct Pull" a.k.a. "V" type brakes really are
> > different from all other cable actuated bicycle brakes. *Here are
> > the lurid details, provided by Sheldon from beyond the grave:
>
> *http://www.sheldonbrown.com/canti-direct.html
>
> Sheldon isn't able to explain that maze of words today, in the absence
> of picture or reasonable proof that the mechanical advantage is
> significantly higher or lower between one brake and another, nor how
> these differences were measured or verified. *

[snip]

> Jobst Brandt

Dear Jobst,

This may be what you're looking for:

http://sheldonbrown.com/cantilever-geometry.html

Cheers,

Carl Fogel

clare at snyder dot ontario dot canada

On Tue, 20 May 2008 09:35:59 -0700, "Tom Kunich" <cyclintom@yahoo.
com> wrote:

><jobst.brandt@stanfordalumni.org> wrote in message
>news:4832d837$0$34541$742ec2ed@news.sonic.net...

>> I asked what the effective MA of the brake is from hand lever to brake pad
>> amd what
>> brake pad amd what made it "linear".
>
What makes it linear?
The mechanical advantage does not change with either the position of
the brake handle, or the position of the pad. Moving the handle the
first 1/16" moves the pads the same distance as the last 1/16" (within
a VERY small variance - so small as to be inconsequential)
This is NOT true of a center-pull or a cantilever because the angle of
the pull changes in an "arc" both at the handle end and at the
"caliper" end. Worse yet, the non-linearity ADDS instead of
cancelling.
The dual pivot "linear pull" handles pull straight - as does the "V"
brake "caliper".

Really quite a simple concept.
** Posted from http://www.teranews.com **

Tom Kunich

<clare at snyder dot ontario dot canada> wrote in message
news:bqu6349olpm1j1c9g748ptceh69eqe70gj@4ax.com...
>
> The mechanical advantage does not change with either the position of
> the brake handle, or the position of the pad. Moving the handle the
> first 1/16" moves the pads the same distance as the last 1/16" (within
> a VERY small variance - so small as to be inconsequential)

We agree, but I'm dotting the "i" for Jobst who could argue the stripes off
of a zebra. Technically the distance between the fulcrum and the cable
attachment points changes by a tiny amount as you squeeze the brake lever.

jobst.brandt@stanfordalumni.org

Carl Fogel wrote:

>>>>> That's all generally helpful but the specific bike here has
>>>>> linear ("V") brakes, which not only have a ratio with greater
>>>>> cable travel and greater pressure at the rim for a given effort
>>>>> at the lever, but are notorious for chewing rims and pads.

>>>> Maybe you can tell me what is "linear" about these brakes and
>>>> what the MA (mechanical advantage) is. Â*Appearances can
>>>> deceive. Â*It was once believed that centerpull brakes had twice
>>>> the MA of sidepull calipers based on the length of caliper input
>>>> levers on which the straddle cable acts. Â*This ignored that there
>>>> are two of these, which divides that apparent MA in two. Other
>>>> than these considerations, more pad force does not affect whether
>>>> they develop grit or not.

>>> "Linear" a.k.a. "Direct Pull" a.k.a. "V" type brakes really are
>>> different from all other cable actuated bicycle brakes. Â*Here are
>>> the lurid details, provided by Sheldon from beyond the grave:

Â*http://www.sheldonbrown.com/canti-direct.html

>> Sheldon isn't able to explain that maze of words today, in the
>> absence of picture or reasonable proof that the mechanical
>> advantage is significantly higher or lower between one brake and
>> another, nor how these differences were measured or verified. Â*

> This may be what you're looking for:

http://sheldonbrown.com/cantilever-geometry.html

It is NOT. The combination of cable yoke angles and brake lever
angles is highly confusing to most people. For that reason, measuring
hand lever stroke and combined pad(s) stroke is the only unambiguous
measure of MA. The article by Sheldon is as vague as claims by brake
manufacturers.
--
Jobst Brandt

jobst.brandt@stanfordalumni.org

clare who? wrote:

>>> I asked what the effective MA of the brake is from hand lever to
>>> brake pad and what brake pad and what made it "linear".

OK, how much more linear and how about a graph of had lever motion vs
pad motion comparing the most common brakes.

> What makes it linear?

> The mechanical advantage does not change with either the position of
> the brake handle, or the position of the pad. Moving the handle the
> first 1/16" moves the pads the same distance as the last 1/16"
> (within a VERY small variance - so small as to be inconsequential)
> This is NOT true of a center-pull or a cantilever because the angle
> of the pull changes in an "arc" both at the handle end and at the
> "caliper" end. Worse yet, the non-linearity ADDS instead of
> canceling. The dual pivot "linear pull" handles pull straight - as
> does the "V" brake "caliper".

Show how much this is on a graph.

> Really quite a simple concept.

Not simple at all. Just recall how long it took the concept of the
Dual Pivot brake to be even partly understood and why two pivots.

We aren't getting any closer to the answer of MA or linearity.

Jobst Brandt

jim beam

jobst.brandt@stanfordalumni.org wrote:
> clare who? wrote:
>
>>>> I asked what the effective MA of the brake is from hand lever to
>>>> brake pad and what brake pad and what made it "linear".
>
> OK, how much more linear and how about a graph of had lever motion vs
> pad motion comparing the most common brakes.

ok, how about NOT having 1/sin theta affecting the mechanical advantage
of the straddle cable?????



>
>> What makes it linear?
>
>> The mechanical advantage does not change with either the position of
>> the brake handle, or the position of the pad. Moving the handle the
>> first 1/16" moves the pads the same distance as the last 1/16"
>> (within a VERY small variance - so small as to be inconsequential)
>> This is NOT true of a center-pull or a cantilever because the angle
>> of the pull changes in an "arc" both at the handle end and at the
>> "caliper" end. Worse yet, the non-linearity ADDS instead of
>> canceling. The dual pivot "linear pull" handles pull straight - as
>> does the "V" brake "caliper".
>
> Show how much this is on a graph.
>
>> Really quite a simple concept.
>
> Not simple at all. Just recall how long it took the concept of the
> Dual Pivot brake to be even partly understood and why two pivots.
>
> We aren't getting any closer to the answer of MA or linearity.
>

and you aren't getting any closer to you ever being able to pay any
freakin' attention to anything you didn't read before age 30. and
precious little of /that/ seems to have sunk in properly.

from: http://sheldonbrown.com/cantilever-geometry.html [thanks carl]

Yoke Angle Mechanical
(Degrees) Advantage
90° 1
80° 1.015
70° 1.063
60° 1.15
50° 1.31
40° 1.55
30° 2
20° 2.92
10° 5.76
5° 11.47
0° Infinity!

jim beam

jobst.brandt@stanfordalumni.org wrote:
> Carl Fogel wrote:
>
>>>>>> That's all generally helpful but the specific bike here has
>>>>>> linear ("V") brakes, which not only have a ratio with greater
>>>>>> cable travel and greater pressure at the rim for a given effort
>>>>>> at the lever, but are notorious for chewing rims and pads.
>
>>>>> Maybe you can tell me what is "linear" about these brakes and
>>>>> what the MA (mechanical advantage) is. Appearances can
>>>>> deceive. It was once believed that centerpull brakes had twice
>>>>> the MA of sidepull calipers based on the length of caliper input
>>>>> levers on which the straddle cable acts. This ignored that there
>>>>> are two of these, which divides that apparent MA in two. Other
>>>>> than these considerations, more pad force does not affect whether
>>>>> they develop grit or not.
>
>>>> "Linear" a.k.a. "Direct Pull" a.k.a. "V" type brakes really are
>>>> different from all other cable actuated bicycle brakes. Here are
>>>> the lurid details, provided by Sheldon from beyond the grave:
>
> http://www.sheldonbrown.com/canti-direct.html
>
>>> Sheldon isn't able to explain that maze of words today, in the
>>> absence of picture or reasonable proof that the mechanical
>>> advantage is significantly higher or lower between one brake and
>>> another, nor how these differences were measured or verified.
>
>> This may be what you're looking for:
>
> http://sheldonbrown.com/cantilever-geometry.html
>
> It is NOT. The combination of cable yoke angles and brake lever
> angles is highly confusing to most people.

"some people" = you.


> For that reason, measuring
> hand lever stroke and combined pad(s) stroke is the only unambiguous
> measure of MA. The article by Sheldon is as vague as claims by brake
> manufacturers.

rubbish jobst. the math is clear and unambiguous.

Clive George

<jobst.brandt@stanfordalumni.org> wrote in message
news:48339163$0$34489$742ec2ed@news.sonic.net...

> We aren't getting any closer to the answer of MA or linearity.

Not helped by you deliberately ignoring what's going on. The cable pull for
a V/linear brake system is more than for others, thus the MA of the brake
end is different. However this is compensated for in the lever, thus the MA
for the total system returns to being the same.

There are _two_ different MAs to consider - the one you're going on about,
for the whole system, is useful for some things, and the one everybody else
is going on about, that of cable travel to pad travel, is useful for people
who wish to know how to make components work together.

jobst.brandt@stanfordalumni.org

Clive George wrote:

>> We aren't getting any closer to the answer of MA or linearity.

> Not helped by you deliberately ignoring what's going on. The cable
> pull for a V/linear brake system is more than for others, thus the
> MA of the brake end is different. However this is compensated for
> in the lever, thus the MA for the total system returns to being the
> same.

That is what I was trying to resolve. The way it was first stated,
one would believe that the overall mechanical advantage was greater
than with other brakes, therefore greater stopping force, something
that is not reasonably possible, so thanks for "the same" statement.

> There are _two_ different MAs to consider - the one you're going on
> about, for the whole system, is useful for some things, and the one
> everybody else is going on about, that of cable travel to pad
> travel, is useful for people who wish to know how to make components
> work together.

To me it was a method by which the V-brake caliper could be made to
work without running out of hand reach. Meanwhile much hay has been
made of its supposed greater MA and linearity for better performance.

Jobst Brandt

Tom Kunich

"Clive George" <clive@xxxx-x.fsnet.co.uk> wrote in message
news:wvCdnSiKBsOEm6nVnZ2dnUVZ8qjinZ2d@posted.plusnet...
> <jobst.brandt@stanfordalumni.org> wrote in message
> news:48339163$0$34489$742ec2ed@news.sonic.net...
>
>> We aren't getting any closer to the answer of MA or linearity.
>
> Not helped by you deliberately ignoring what's going on. The cable pull
> for a V/linear brake system is more than for others, thus the MA of the
> brake end is different. However this is compensated for in the lever, thus
> the MA for the total system returns to being the same.

A lot of people simply install the linear brake onto a normal touring bike
and retain the original levers. You need to set the brakes very close to the
rims and you need to have very straight rims but they work fine.

> There are _two_ different MAs to consider - the one you're going on about,
> for the whole system, is useful for some things, and the one everybody
> else is going on about, that of cable travel to pad travel, is useful for
> people who wish to know how to make components work together.

I think that you have the correct idea of reality Clive, but that, perhaps,
isn't the subject here.

Tom Kunich

<jobst.brandt@stanfordalumni.org> wrote in message
news:48343b9f$0$34567$742ec2ed@news.sonic.net...
>
> To me it was a method by which the V-brake caliper could be made to
> work without running out of hand reach. Meanwhile much hay has been
> made of its supposed greater MA and linearity for better performance.

Ahh, now I understand what you were getting at. I wish you'd just come out
and say that in the first place.

But as I pointed out to Clive, some people simply install the linear brakes
onto their original street bike retaining the levers (whether they are
shifters or old-style brake levers) and just keep them in adjustment.

Clive George

"Tom Kunich" <cyclintom@yahoo. com> wrote in message
news:s5idncCIfJm826nVnZ2dnUVZ_gSdnZ2d@earthlink.com...
> "Clive George" <clive@xxxx-x.fsnet.co.uk> wrote in message
> news:wvCdnSiKBsOEm6nVnZ2dnUVZ8qjinZ2d@posted.plusnet...
>> <jobst.brandt@stanfordalumni.org> wrote in message
>> news:48339163$0$34489$742ec2ed@news.sonic.net...
>>
>>> We aren't getting any closer to the answer of MA or linearity.
>>
>> Not helped by you deliberately ignoring what's going on. The cable pull
>> for a V/linear brake system is more than for others, thus the MA of the
>> brake end is different. However this is compensated for in the lever,
>> thus the MA for the total system returns to being the same.
>
> A lot of people simply install the linear brake onto a normal touring bike
> and retain the original levers. You need to set the brakes very close to
> the rims and you need to have very straight rims but they work fine.

I suspect in that instance they actually work very well :-) But you'd need
to keep them in adjustment and everything straight etc.

cheers,
clive