brake failure

jim beam

Tom Kunich wrote:
> <jobst.brandt@stanfordalumni.org> wrote in message
> news:483210c5$0$34531$742ec2ed@news.sonic.net...
>>
>> 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.
>
> Visually the V-Brake appears to have a MA of about 2.5:1. From the feel
> of it I also think that it has a significantly higher MA than a standard
> sidepull brake. Is there some question about this?
>
>

jobst isn't very good at math. and he's not shy of manufacturing
erroneous presumption to argue against something he just plain doesn't like.

Tom Kunich

"jim beam" <spamvortex@bad.example.net> wrote in message
news:loudnT3VoP8goK_VnZ2dnUVZ_tLinZ2d@speakeasy.net...
> Tom Kunich wrote:
>> Visually the V-Brake appears to have a MA of about 2.5:1. From the feel
>> of it I also think that it has a significantly higher MA than a standard
>> sidepull brake. Is there some question about this?
>
> jobst isn't very good at math. and he's not shy of manufacturing
> erroneous presumption to argue against something he just plain doesn't
> like.

Let's try to keep this on a technical level. Jobst has his opinions on the
usefulness of such things but he is an expert mechanical engineer.

jim beam

Tom Kunich wrote:
> "jim beam" <spamvortex@bad.example.net> wrote in message
> news:loudnT3VoP8goK_VnZ2dnUVZ_tLinZ2d@speakeasy.net...
>> Tom Kunich wrote:
>>> Visually the V-Brake appears to have a MA of about 2.5:1. From the
>>> feel of it I also think that it has a significantly higher MA than a
>>> standard sidepull brake. Is there some question about this?
>>
>> jobst isn't very good at math. and he's not shy of manufacturing
>> erroneous presumption to argue against something he just plain doesn't
>> like.
>
> Let's try to keep this on a technical level. Jobst has his opinions on
> the usefulness of such things but he is an expert mechanical engineer.

well, jobst, as an "expert mechanical engineer" [bizarrely] presents a
spoke load calculation as a wheel strength calculation, so it's hard to
be very receptive to that argument. now he seemingly can't figure out
simple mechanical advantage ratios.

[sorry, was that technical enough to be useful?]

Ryan Cousineau

In article <2f-dnc88sbgsj6_VnZ2dnUVZ8uadnZ2d@posted.plusnet>,
"Clive George" <clive@xxxx-x.fsnet.co.uk> wrote:

> <jobst.brandt@stanfordalumni.org> wrote in message
> news:483210c5$0$34531$742ec2ed@news.sonic.net...
>
> > 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. It sounds like the
> > explanations of the centerpull days where Mafac Racer brakes were said
> > to have twice the MA of, for instance, a Universal side pull.
> > Although commonly believed, it was not fact. From the wording of
> > Sheldon's text, it seems to be left over from those days.
>
> Um, the MA of linear brakes _is_ different to calipers and conventionally
> set up cantis. That's why they have different levers and why getting them to
> work on a bike with drop bars is a PITA. See also tektro mini-Vs. Or are you
> being deliberately obtuse, coz I thought this was ancient knowledge?

Apropos to this matter, it has been mentioned before, but there's a new
drop-bar lever for use with V-brakes, the Tektro RL520A:

http://www.tektro.com/02products/11rl.php

> > I am unsure whether readers here are familiar with the term "bell
> > crank", an important mechanical device that escaped the understanding
> > of most high school physics students in my day, and apparently is no
> > longer used as an example of a simple mechanisms with special use.
> >
> > http://www.flying-pig.co.uk/mechani.../bellcrank.html
>
> BPB sidewinder?

I'm familiar with this mechanism thanks to my father's hobby of
control-line aircraft. Bell cranks are used to connect the control
cables to the rod for moving the tailplane. In that design, the
mechanical advantage (more about control precision than needing
leverage, I think) can be adjusted with either the bell crank geometry
or the length of the arm that attaches the control rod to the tailplane.

Here's a discussion of setting up a control-line plane for novice flyers
using changes in bell-crank geometry to slow the control response:

http://www.hbci.com/~bkuhl/control.htm#fly

--
Ryan Cousineau rcousine@gmail.com http://www.wiredcola.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."

jobst.brandt@stanfordalumni.org

Clive George wrote:

>> 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. It sounds like the
>> explanations of the centerpull days where Mafac Racer brakes were said
>> to have twice the MA of, for instance, a Universal side pull.
>> Although commonly believed, it was not fact. From the wording of
>> Sheldon's text, it seems to be left over from those days.

> Um, the MA of linear brakes _is_ different to calipers and
> conventionally set up cantis. That's why they have different levers
> and why getting them to work on a bike with drop bars is a PITA.
> See also tektro mini-Vs. Or are you being deliberately obtuse, coz
> I thought this was ancient knowledge?

"MA of linear brakes _is_ different" yes, how different and what is
"linear" about it in contrast to other brakes that should also be
linear?

>> I am unsure whether readers here are familiar with the term "bell
>> crank", an important mechanical device that escaped the understanding
>> of most high school physics students in my day, and apparently is no
>> longer used as an example of a simple mechanisms with special use.

http://www.flying-pig.co.uk/mechani.../bellcrank.html

> BPB sidewinder?

Please explain your cryptic question.

Jobst Brandt

jobst.brandt@stanfordalumni.org

Tom Kunich wrote:

>> 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.

> Visually the V-Brake appears to have a MA of about 2.5:1. From the
> feel of it I also think that it has a significantly higher MA than a
> standard sidepull brake. Is there some question about this?

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.
--
Jobst Brandt

Clive George

<jobst.brandt@stanfordalumni.org> wrote in message
news:48326aa1$0$34542$742ec2ed@news.sonic.net...
> Clive George wrote:
>
>>> 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. It sounds like the
>>> explanations of the centerpull days where Mafac Racer brakes were said
>>> to have twice the MA of, for instance, a Universal side pull.
>>> Although commonly believed, it was not fact. From the wording of
>>> Sheldon's text, it seems to be left over from those days.
>
>> Um, the MA of linear brakes _is_ different to calipers and
>> conventionally set up cantis. That's why they have different levers
>> and why getting them to work on a bike with drop bars is a PITA.
>> See also tektro mini-Vs. Or are you being deliberately obtuse, coz
>> I thought this was ancient knowledge?
>
> "MA of linear brakes _is_ different" yes, how different and what is
> "linear" about it in contrast to other brakes that should also be
> linear?

I'm not concerned about the "linear" bit, though I do know that conventional
cantis are definitely non-linear in their MA through the brake travel - I'd
guess Vs/linear wouldn't suffer that. Also the basic form of the brake arm
is a straight line, so maybe linear refers to that.

The MA is twice (or is it half?) that of other brakes - ie takes twice the
cable pull to move the pads a certain amount.

>>> I am unsure whether readers here are familiar with the term "bell
>>> crank", an important mechanical device that escaped the understanding
>>> of most high school physics students in my day, and apparently is no
>>> longer used as an example of a simple mechanisms with special use.
>
> http://www.flying-pig.co.uk/mechani.../bellcrank.html
>
>> BPB sidewinder?
>
> Please explain your cryptic question.

Bother, Sidetrak BPB. Misremembered the name.

To fit Vs to a drop bar bike, there are various solutions to the problem of
the brake levers not pulling enough cable for the brakes. The most popular
one appears to be a device called a Travel Agent, which has two pulley
faces - cable comes from lever onto little pulley, round, through hole, and
out via big (2x diamater) pulley. This means you get twice the cable pull.
The Sidetrak BPB does the same sort of thing with levers, hence me
mentioning it after your bell crank link.

(as an aside, Thorn use a bellcrank to drive their cantis fitted behind the
front forks on their drop bar tandems - they swear by the suntour
self-energising cantis, which were only available in rear fitting, hence the
bodge).

(I'm still a little concerned that I'm explaining this to you BTW - this is
ancient knowledge for anybody in the touring, cyclocross and tandem world).

cheers,
clive

jim beam

jobst.brandt@stanfordalumni.org wrote:
> Tom Kunich wrote:
>
>>> 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.
>
>> Visually the V-Brake appears to have a MA of about 2.5:1. From the
>> feel of it I also think that it has a significantly higher MA than a
>> standard sidepull brake. Is there some question about this?
>
> 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.

observe: the KING of conjecture, speculation and presumption tries to
defend his territory.

jobst, you are laboring under a serious misconception here. as someone
that has never bothered to check the facts [hardly an unique phenomenon
with you], this is perhaps understandable, but it's NOT a basis for your
continued criticism. do your homework.

jim beam

Clive George wrote:
> <jobst.brandt@stanfordalumni.org> wrote in message
> news:48326aa1$0$34542$742ec2ed@news.sonic.net...
>> Clive George wrote:
>>
>>>> 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. It sounds like the
>>>> explanations of the centerpull days where Mafac Racer brakes were said
>>>> to have twice the MA of, for instance, a Universal side pull.
>>>> Although commonly believed, it was not fact. From the wording of
>>>> Sheldon's text, it seems to be left over from those days.
>>
>>> Um, the MA of linear brakes _is_ different to calipers and
>>> conventionally set up cantis. That's why they have different levers
>>> and why getting them to work on a bike with drop bars is a PITA.
>>> See also tektro mini-Vs. Or are you being deliberately obtuse, coz
>>> I thought this was ancient knowledge?
>>
>> "MA of linear brakes _is_ different" yes, how different and what is
>> "linear" about it in contrast to other brakes that should also be
>> linear?
>
> I'm not concerned about the "linear" bit, though I do know that
> conventional cantis are definitely non-linear in their MA through the
> brake travel - I'd guess Vs/linear wouldn't suffer that. Also the basic
> form of the brake arm is a straight line, so maybe linear refers to that.
>
> The MA is twice (or is it half?) that of other brakes - ie takes twice
> the cable pull to move the pads a certain amount.
>
>>>> I am unsure whether readers here are familiar with the term "bell
>>>> crank", an important mechanical device that escaped the understanding
>>>> of most high school physics students in my day, and apparently is no
>>>> longer used as an example of a simple mechanisms with special use.
>>
>> http://www.flying-pig.co.uk/mechani.../bellcrank.html
>>
>>> BPB sidewinder?
>>
>> Please explain your cryptic question.
>
> Bother, Sidetrak BPB. Misremembered the name.
>
> To fit Vs to a drop bar bike, there are various solutions to the problem
> of the brake levers not pulling enough cable for the brakes. The most
> popular one appears to be a device called a Travel Agent, which has two
> pulley faces - cable comes from lever onto little pulley, round, through
> hole, and out via big (2x diamater) pulley. This means you get twice the
> cable pull. The Sidetrak BPB does the same sort of thing with levers,
> hence me mentioning it after your bell crank link.
>
> (as an aside, Thorn use a bellcrank to drive their cantis fitted behind
> the front forks on their drop bar tandems - they swear by the suntour
> self-energising cantis, which were only available in rear fitting, hence
> the bodge).
>
> (I'm still a little concerned that I'm explaining this to you BTW - this
> is ancient knowledge for anybody in the touring, cyclocross and tandem
> world).

why let facts get in the way? just throw in stubbornness, lack of
information, some red herrings and a few straw men, then have yourself a
jobstian argument!


>
> cheers,
> clive
>

Tom Kunich

<jobst.brandt@stanfordalumni.org> wrote in message
news:48326b75$0$34542$742ec2ed@news.sonic.net...
> Tom Kunich wrote:
>
>>> 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.
>
>> Visually the V-Brake appears to have a MA of about 2.5:1. From the
>> feel of it I also think that it has a significantly higher MA than a
>> standard sidepull brake. Is there some question about this?
>
> 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.

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 can't quite understand what you're arguing - that V-brakes don't have the
mechanical advantage claimed or that there's something wrong with that idea.

jobst.brandt@stanfordalumni.org

Tom Kunich wrote:

>>>> 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.

>>> Visually the V-Brake appears to have a MA of about 2.5:1. From the
>>> feel of it I also think that it has a significantly higher MA than
>>> a standard sidepull brake. Is there some question about this?

>> 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.

> 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.

> I can't quite understand what you're arguing - that V-brakes don't
> have the mechanical advantage claimed or that there's something
> wrong with that idea.

I feel the word "arguing" is inappropriate. I asked what the
effective MA of the brake is from hand lever to brake pad amd what
made it "linear". This problem is made clear by the dual pivot that
reduced pad clearance to accommodate the higher overall MA, human hand
stroke remaining constant.

--
Jobst Brandt

jobst.brandt@stanfordalumni.org

Tom Kunich wrote:

>>>> 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.

>>> Visually the V-Brake appears to have a MA of about 2.5:1. From the
>>> feel of it I also think that it has a significantly higher MA than
>>> a standard sidepull brake. Is there some question about this?

>> 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.

> 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 mentioned dimensions in this thread or
that measurements were made and how. I just find the language used
for brakes is misleading and asked what is "linear" and what the MA of
the brake mentioned is. Just because the cable moves farther doesn't
prove that this difference isn't canceled by the caliper leverage.

> I can't quite understand what you're arguing - that V-brakes don't
> have the mechanical advantage claimed or that there's something
> wrong with that idea.

I feel the word "arguing" is inappropriate. I asked what the
effective MA of the brake is from hand lever to brake pad amd what
made it "linear". This problem is made clear by the dual pivot that
reduced pad clearance to accommodate the higher overall MA, human hand
stroke remaining constant.

--
Jobst Brandt

Tom Kunich

<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.

> 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".

OK, we know that since they are rotating that they cannot be "linear" if
you're using the pure definition. But this world is full of misnamed things.

> This problem is made clear by the dual pivot that
> reduced pad clearance to accommodate the higher overall MA, human hand
> stroke remaining constant.

The other problems are that the the pads wear to the unusable point a great
deal faster since they move a lot less. It is far too possible to lock the
front wheel with all that MA.

In the dirt that's not much of a problem but at the moment I'm recovering
from a rather nasty fall because one of these modern clipless pedals
released my foot in a high speed turn and it stuck in the front wheel spokes
breaking the carbon fork off and laying me into the emergency hospital. I'm
recovering rapidly and thank heavens that I didn't get any serious injuries,
but plainly there is a possibility of putting too much braking force on a
wheel.

A Muzi

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!
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
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