brake failure

Clive George

<jobst.brandt@stanfordalumni.org> wrote in message
news:48343b9f$0$34567$742ec2ed@news.sonic.net...
> 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.

Ah, that's a different problem :-)

AIUI one reason they're better than conventional cantis because the MA is
closer to linear - doesn't the geometry of conventional cantis work against
them in that regard? OTOH they also had thinner pads, which gives an
improvement at the expense of durability.
But I mustn't forget the pads - I hate conventional canti pads, cos they're
too darn hard to set up :-)

On a tandem, Vs should be better for the back, because the cable stretch
would be less of an issue with the travel being doubled and hence the force
halved.

cheers,
clive

A Muzi

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

>> Clive George wrote:
>>> 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.

> <jobst.brandt@stanfordalumni.org> wrote
>> 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.

>> Clive George wrote:
>>> 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> wrote
>> 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.

Clive George wrote:
> Ah, that's a different problem :-)
>
> AIUI one reason they're better than conventional cantis because the MA
> is closer to linear - doesn't the geometry of conventional cantis work
> against them in that regard? OTOH they also had thinner pads, which
> gives an improvement at the expense of durability.
> But I mustn't forget the pads - I hate conventional canti pads, cos
> they're too darn hard to set up :-)
>
> On a tandem, Vs should be better for the back, because the cable stretch
> would be less of an issue with the travel being doubled and hence the
> force halved.

"cable stretch"
?
Oh, now you've done it. Long thread coming...
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

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.

> Ah, that's a different problem :-)

> AIUI one reason they're better than conventional cantis because the
> MA is closer to linear - doesn't the geometry of conventional cantis
> work against them in that regard? OTOH they also had thinner pads,
> which gives an improvement at the expense of durability. But I
> mustn't forget the pads - I hate conventional canti pads, cos
> they're too darn hard to set up :-)

> On a tandem, Vs should be better for the back, because the cable
> stretch would be less of an issue with the travel being doubled and
> hence the force halved.

Consider the design problem. The V-brake got rid of the straddle
cable and brake lever elbows that stuck out making a simpler and
slimmer mechanism. To achieve good tire clearance, brake levers
extended far above the pads making an undesirable mechanical advantage
that had to be corrected with appropriate hand levers.

The first thing that followed in response to user complaints was the
"travel agent" to give compatibility for folks who didn't want to
throw out their accustomed hand levers. In any event, the MA is not
significantly different and pad sweep still leads to drop under as
cantilevers did.

I asked what the MA and linearity was because I don't believe either
of these is different from cantilevers they replace. It is a simpler
design and does not have the hazard of dropping a straddle cable onto
a knobby tire, an effect that causes an immediate endo. To make up
for that, their long thin pads wear out faster and have no benefit
other than being different from other brakes.

Jobst Brandt

clare at snyder dot ontario dot canada

On 21 May 2008 03:05:07 GMT, 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.
>
>> 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.

You are the scientist, and you want the proof, YOU make the 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

Because you ain't listening??

** Posted from http://www.teranews.com **

clare at snyder dot ontario dot canada

On 21 May 2008 15:11:27 GMT, jobst.brandt@stanfordalumni.org wrote:

>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


The maximum MA is not likely any better with the "V" brake, but it is
consistent -linear - and therefore gives a better brake feel and in my
experience slightly better brake "action".
** Posted from http://www.teranews.com **

velodancer

There are several reasons why "linear" brakes now own the market.
Considerably easier setup, slightly better overall leverage ratios
leading to a lighter feel, useful for mountain bikes. (Lighter feel is
also the primary reason for increasing disc sizes on mountain bikes.)
And the leverage ratio is almost completely unchanged throughout the
lever stroke, which is something maddening about cantilever brakes as
can easily be ascertained with Sheldon's discussion of straddle cable
setup. As a downside to the higher overall leverage ratio, pads do
have to be set closer to the rim. This does have one beneficial effect
of reducing pad dive under the rim.

Large amounts of braking force are lost in the cable and housing
system. Thus doubling of cable travel halves this lost force, also
increasing braking efficiency and contributing to the rapid conversion
to "linear" pull brakes over cantilevers. This is the same effect used
by SRAM in their "1:1" rear derailleur shifting system to halve the
effect of friction on shifting precision. Lost force reduction also
accounts for the popularity of hydraulic disc brakes versus cable
activated disc brakes despite their complexity.

jobst.brandt@stanfordalumni.org

someone wrote:

> There are several reasons why "linear" brakes now own the market.
> Considerably easier setup, slightly better overall leverage ratios
> leading to a lighter feel, useful for mountain bikes. (Lighter feel
> is also the primary reason for increasing disc sizes on mountain
> bikes.) And the leverage ratio is almost completely unchanged
> throughout the lever stroke, which is something maddening about
> cantilever brakes as can easily be ascertained with Sheldon's
> discussion of straddle cable setup. As a downside to the higher
> overall leverage ratio, pads do have to be set closer to the rim.
> This does have one beneficial effect of reducing pad dive under the
> rim.

I don't see any evidence for these claims that echo promotional copy.
As was mentioned, these do not have a significantly different MA.
Sheldon's article has no measurements or meaningful force diagrams to
support "common knowledge".

> Large amounts of braking force are lost in the cable and housing
> system. Thus doubling of cable travel halves this lost force, also
> increasing braking efficiency and contributing to the rapid
> conversion to "linear" pull brakes over cantilevers. This is the
> same effect used by SRAM in their "1:1" rear derailleur shifting
> system to halve the effect of friction on shifting precision. Lost
> force reduction also accounts for the popularity of hydraulic disc
> brakes versus cable activated disc brakes despite their complexity.

Hold the phone... we've been here before. Empty claims and religion!
This is so much deja-vu from the days of the centerpull heyday where
all these claims were also made... or better yet, alluded to and the
faithful followed the leader and solidified the beliefs.

Jobst Brandt

JG

I'm having trouble figuring out what is being argued, er discussed, in
this thread...

1. 'Linear' is a perfectly obvious concept and one I've seen Jobst
embrace in previous posts. The horizontal displacement of the brakes
pads of a V brake move in fixed proportion (MA of the calipers) to the
horizontal displacement of the cable anchor points.

2. All brakes are probably close to linear in the distance between pad
contact and pad deforming, caliper bending, fork twisting full
application. However, figuring out what that is, is complicated by
yoke configuration.

3. High profile cantilevers, set near horizontal (i.e. MAFAC's) are
not only linear in the above sense, but of fixed MA as they are
indifferent to changes in yoke length.

4. Cantilevers don't dive down much more than center pivoted brakes in
their immediate ranges. This is easily determined by running a string
from the fork center to a cantilever mount and observing it passes
pretty close to the rim. (Dual pivots have some advantage here.)

5. All brake systems (okay not hydraulics) change their geometry with
pad wear. There is no need for V brakes to have thin pads. The
correct solution is to maintain the pad surface in the same plane -
hence the shaft mount of traditional cantilevers.

JG

jobst.brandt@stanfordalumni.org

someone wrote:

> I'm having trouble figuring out what is being argued, er discussed,
> in this thread...

> 1. 'Linear' is a perfectly obvious concept and one I've seen Jobst
> embrace in previous posts. The horizontal displacement of the
> brakes pads of a V brake move in fixed proportion (MA of the
> calipers) to the horizontal displacement of the cable anchor points.

> 2. All brakes are probably close to linear in the distance between
> pad contact and pad deforming, caliper bending, fork twisting full
> application. However, figuring out what that is, is complicated by
> yoke configuration.

> 3. High profile cantilevers, set near horizontal (i.e. MAFAC's) are
> not only linear in the above sense, but of fixed MA as they are
> indifferent to changes in yoke length.

> 4. Cantilevers don't dive down much more than center pivoted brakes
> in their immediate ranges. This is easily determined by running a
> string from the fork center to a cantilever mount and observing it
> passes pretty close to the rim. (Dual pivots have some advantage
> here.)

Dive is given by the position of the pivot around which the brake arm
rotates. In the sidepull single pivot, the pivot is centered over the
rim and has essentially zero cosine error (foreshortening as it
articulates). The cantilever has large cosine error, arcing at close
to 45 degrees from the contact area. V-brakes, using the same pivot
points do likewise.

> 5. All brake systems (okay not hydraulics) change their geometry
> with pad wear. There is no need for V brakes to have thin pads.
> The correct solution is to maintain the pad surface in the same
> plane - hence the shaft mount of traditional cantilevers.

Not true. With classic sidepull brakes, pads can be worn to the metal
(pad holder) without changing enough to require adjustment. I do it
all the time with my brakes.

I take it trigonometry is no longer taught in schools.

Jobst Brandt

clare at snyder dot ontario dot canada

On 22 May 2008 04:03:18 GMT, jobst.brandt@stanfordalumni.org wrote:

>someone wrote:
>
>> There are several reasons why "linear" brakes now own the market.
>> Considerably easier setup, slightly better overall leverage ratios
>> leading to a lighter feel, useful for mountain bikes. (Lighter feel
>> is also the primary reason for increasing disc sizes on mountain
>> bikes.) And the leverage ratio is almost completely unchanged
>> throughout the lever stroke, which is something maddening about
>> cantilever brakes as can easily be ascertained with Sheldon's
>> discussion of straddle cable setup. As a downside to the higher
>> overall leverage ratio, pads do have to be set closer to the rim.
>> This does have one beneficial effect of reducing pad dive under the
>> rim.
>
>I don't see any evidence for these claims that echo promotional copy.
>As was mentioned, these do not have a significantly different MA.
>Sheldon's article has no measurements or meaningful force diagrams to
>support "common knowledge".
>
>> Large amounts of braking force are lost in the cable and housing
>> system. Thus doubling of cable travel halves this lost force, also
>> increasing braking efficiency and contributing to the rapid
>> conversion to "linear" pull brakes over cantilevers. This is the
>> same effect used by SRAM in their "1:1" rear derailleur shifting
>> system to halve the effect of friction on shifting precision. Lost
>> force reduction also accounts for the popularity of hydraulic disc
>> brakes versus cable activated disc brakes despite their complexity.
>
>Hold the phone... we've been here before. Empty claims and religion!
>This is so much deja-vu from the days of the centerpull heyday where
>all these claims were also made... or better yet, alluded to and the
>faithful followed the leader and solidified the beliefs.
>
>Jobst Brandt


Lets stop feeding the (deaf) troll.
** Posted from http://www.teranews.com **

Tim McNamara

In article <4835c236$0$34549$742ec2ed@news.sonic.net>,
jobst.brandt@stanfordalumni.org wrote:

> I take it trigonometry is no longer taught in schools.

Depends. Is it on the tests required by NCLB? If it ain't on the
tests, it ain't in the classroom.

jobst.brandt@stanfordalumni.org

Tim McNamara <timmcn@bitstream.net> wrote:

>> I take it trigonometry is no longer taught in schools.

> Depends. Is it on the tests required by NCLB? If it ain't on the
> tests, it ain't in the classroom.

I should have said that it isn't shown where angle functions enter
into our daily lives. I have yet to meet a recent engineer who knows
what cosine error is. They have a hard enough time keeping sine and
cosine apart. These same folks ride bike and claim to understand
things like rim and disk brakes and don't see the difference between
arguing and discussing the merits of one design over another.

Jobst Brandt

jim beam

jobst.brandt@stanfordalumni.org wrote:
> Tim McNamara <timmcn@bitstream.net> wrote:
>
>>> I take it trigonometry is no longer taught in schools.
>
>> Depends. Is it on the tests required by NCLB? If it ain't on the
>> tests, it ain't in the classroom.
>
> I should have said that it isn't shown where angle functions enter
> into our daily lives. I have yet to meet a recent engineer who knows
> what cosine error is. They have a hard enough time keeping sine and
> cosine apart.

quoth the "engineer" that can't recognize how straddle cable angle
affects mechanical advantage.


> These same folks ride bike and claim to understand
> things like rim and disk brakes and don't see the difference between
> arguing and discussing the merits of one design over another.

quoth the "engineer" that can't recognize how straddle cable angle
affects mechanical advantage.

you're quite amazing jobst. your inability to read or learn is somehow
completely juxtaposed to your phenomenal ability to attribute your own
faults to others. it really is absolutely incredible.

jim beam

Tom Kunich wrote:
> "jim beam" <spamvortex@bad.example.net> wrote in message
> news:r-udnWFZwNTkDq7VnZ2dnUVZ_q7inZ2d@speakeasy.net...
>> jobst.brandt@stanfordalumni.org wrote:
>>> 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.
>
> Jim, because of your dislike of Jobst's style you're failing to
> understand what he's saying. In truth he is correct that in order to get
> the same BRAKE PAD TRAVEL you need to have the same overall ratios.
> There is a small problem in that idea though - in order to make the
> brake lever forces smaller, they set the system up to use SHORTER
> TRAVEL. The results of this is that linear brakes have to have very
> straight wheels and the pads are set much closer to the rims.

there's two things - the leverage ratios you refer to for "v" and
caliper brakes, and the leverage ratios for cantilevers. the latter is
variable, as a function of straddle cable angle.


>
> So in truth the linear braking system does use a higher MA but at the
> cost of higher maintenance.
>

higher maintenance???