brake failure

Marian

On May 19, 2:37*am, A Muzi <a...@yellowjersey.org> wrote:
> > "M-gineering" <ikmotgeens...@m-gineering.nl> wrote in message
> >news:g0p7uf$afe$1@localhost.localdomain...
> >> Are the brakes setup so that the noodle bottoms out against the
> >> clampbolt on the V-s? Check that there is sufficient space, if not
> >> change the washers on the brakeblock holder around
> Tom Kunich wrote:
> > I'm certainly glad that I'm not practicing engineering in the
> > Netherlands where they apparently speak some sort of foreign
> > language...... :-)
>
> huh.
> That seemed quite clear (and sorta good advice BTW) to me. It's both a
> real and a common problem.
>
> I already suggested cantilevers rather than liner brakes to her weeks
> ago but those weren't readily available to her. Linear ("V") brakes are
> more prone to crud embedding and have rapid pad and rim wear. That goes
> double in dirt and rain.

If it's any consolation, my mechanic agrees with you. But he couldn't
get cantilevers in before I was due to leave.

I'm taking a very pragmatic approach to choosing roads on this bike
tour.

1) Ask everyone around me the best route from here to there.
2) Take the road everyone tells me to avoid using.

Even if I was walking most of the time I wasn't going that much slower
than the four wheel drive power bus with the tires only slightly
shorter than me. And the mud rarely came up above my calves. It was
however the sucking kind where I sometimes had to wiggle my toes to
keep my shoes on when I pulled out for the next step.

-M

Marian

On May 20, 7:05*pm, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> <jobst.bra...@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.

> (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)..

Hmm... since the rear brake cable does run along the top of the bike
perhaps this would explain why my bodge of coming down off the saddle
and going astride the top tube while pulling on the brake cable with
one hand helped some. (That being before I gave up braking completely
and decided to walk down hills.)

-M

travis.harry@gmail.com

On May 18, 9:16 pm, jobst.bra...@stanfordalumni.org wrote:
> Andrew Muzi wrote:
> >>> I already suggested cantilevers rather than liner brakes to her
> >>> weeks ago but those weren't readily available to her. Linear
> >>> ("V") brakes are more prone to crud embedding and have rapid pad
> >>> and rim wear. That goes double in dirt and rain.
> >> Are you blaming the pads or the mechanics of the linear brake?
> >> My current touring/commuting bike has cantilever brakes that use
> >> "V" type pad (lots of surface area but thin.) For what it's worth,
> >> I do find the pads wear quickly. Given that I ride in rain, snow,
> >> salt, etc, that's to be expected, and at $4 a pair, I'm not too
> >> broken up about it. What I really love is that I can change them
> >> out without having to reset the brakes, something I never liked
> >> about traditional cantilever brakes with smooth stud shoes.
> > Although Kool Stop pads are better than OEM (also not readily
> > available to Marian), linear systems promote rapid rim wear and seem
> > to be more prone to crud in the pads - whether it jams in faster or
> > just scrapes rim chunks into the pad faster I can't say.
>
> Having had many years to research brakes, starting with Universal,
> pre-Campagnolo brakes, Weinmann, and various centerpull calipers, I
> searched for several effects: 1) Embedded grit in pads, 2) Hand lever
> braking force required and 3) brake pad wear rate. In that pursuit I
> also measured mechanical advantage of various brakes and discovered
> that contrary to he bicycling press, all calipers had a 1:1 ratio and
> hand levers had 4:1. That is, the mechanical advantage was the same
> for all brakes (Including Campagnolo when they took over the high
> quality end of the business and having an excellent QR.
>
> What I found was that Kool-Stop Salmon pads were the best, Campagnolo
> a distant second, and Mafac, horrible in that they always chewed up
> rims. Universal didn't come off well either. The most striking
> feature of Kool-Stop pads was that even when riding through wet dirt
> and picking up road mud and grit, the pads would clear themselves once
> back on pavement by merely pumping the brake hard.
>
> Not being one to worry about fashion and having a line of
> practicality, I chose the Continental model because, unlike inserts
> (typically in Campagnolo and Universal brakes) these pads could not be
> accidentally knocked out of the pad holder when inserting a wheel,
> something I observed happening a few times to the surprise of a rider
> after a wheel change.
>
> High pitch squeal is mainly caused by contamination on the braking
> surface, mainly humidity, but also from soft drink splash or even
> urine from roadside relief while standing astride the bicycle. Squeal
> can be cleared up by heavy braking on a steep descent that gets rims
> hot. It is not a matter of pad toe-in as is often claimed.
>
> Just the same, toe-in occurs naturally because when braking hard
> caliper arms bend forward in a way that makes the rear of the pad wear
> faster than the forward end. I suppose someone noticed that well worn
> pads seldom squealed AND that they had toe-in, which led to brutal
> deformation of brake calipers. If this were a manually added feature,
> then it should be added by running a rasp lengthwise across the brake
> pad, not by bending brake calipers.
>
> http://www.koolstop.com/brakes/index.php
> --
> Jobst Brandt

One can find online--trust me--a more recent review of perhaps 8
different replacement brake pads done by a British bicycling mag. I
cannot recall the testing methodology. But the design included testing
wet and dry separately and reporting braking distance as well as
remarks on aluminum extracted from the rims by the different pads.. I
found troubling the substantial negative rank order correlation
between wet and dry performance. Not perfectly negative, but high
enough that you would not pick out one pad as a reasonable compromise,
sacrificing just a little performance in one condition to achieve high
performance in the other.

Tim McNamara

In article
<a90e4292-e84e-47b0-a0c3-8aa5c0c944a1@y38g2000hsy.googlegroups.com>,
"travis.harry@gmail.com" <travis.harry@gmail.com> wrote:

> One can find online--trust me--a more recent review of perhaps 8
> different replacement brake pads done by a British bicycling mag. I
> cannot recall the testing methodology. But the design included
> testing wet and dry separately and reporting braking distance as well
> as remarks on aluminum extracted from the rims by the different
> pads.. I found troubling the substantial negative rank order
> correlation between wet and dry performance. Not perfectly negative,
> but high enough that you would not pick out one pad as a reasonable
> compromise, sacrificing just a little performance in one condition to
> achieve high performance in the other.

Years ago, VeloNews compared a variety of brake pads using the old
Schwinn brake testing rig (basically a flywheel with a rim attached,
mounted in a fork). Wet and dry performance was tested. The Kool Stop
salmon material came out the best in both categories, as I recall.
VeloNews used to have this report posted on their Web site. Maybe
someone can ferret it out again.

A Muzi

-snip brakes-
Marian wrote:
> Even if I was walking most of the time I wasn't going that much slower
> than the four wheel drive power bus with the tires only slightly
> shorter than me. And the mud rarely came up above my calves. It was
> however the sucking kind where I sometimes had to wiggle my toes to
> keep my shoes on when I pulled out for the next step.

It's not just sticky. As the plumbers say, "It's alive!"
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

Peter Cole

travis.harry@gmail.com wrote:

> One can find online--trust me--a more recent review of perhaps 8
> different replacement brake pads done by a British bicycling mag. I
> cannot recall the testing methodology. But the design included testing
> wet and dry separately and reporting braking distance as well as
> remarks on aluminum extracted from the rims by the different pads.. I
> found troubling the substantial negative rank order correlation
> between wet and dry performance. Not perfectly negative, but high
> enough that you would not pick out one pad as a reasonable compromise,
> sacrificing just a little performance in one condition to achieve high
> performance in the other.

There's this:

http://www.bicyclesource.com/testing_brake_pads

Not really very much difference, except for some in the wet test. I'm
suspicious that those use a more abrasive compound.

and this:

http://www.mtbr.com/reviews/brake_p...umreviews.shtml

I've never found stopping power to be a concern. The only thing that is
an issue is rim wear.

A Muzi

> "travis.harry@gmail.com" <travis.harry@gmail.com> wrote:
>> One can find online--trust me--a more recent review of perhaps 8
>> different replacement brake pads done by a British bicycling mag. I
>> cannot recall the testing methodology. But the design included
>> testing wet and dry separately and reporting braking distance as well
>> as remarks on aluminum extracted from the rims by the different
>> pads.. I found troubling the substantial negative rank order
>> correlation between wet and dry performance. Not perfectly negative,
>> but high enough that you would not pick out one pad as a reasonable
>> compromise, sacrificing just a little performance in one condition to
>> achieve high performance in the other.

Tim McNamara wrote:
> Years ago, VeloNews compared a variety of brake pads using the old
> Schwinn brake testing rig (basically a flywheel with a rim attached,
> mounted in a fork). Wet and dry performance was tested. The Kool Stop
> salmon material came out the best in both categories, as I recall.
> VeloNews used to have this report posted on their Web site. Maybe
> someone can ferret it out again.

There may be a difference in aluminum flaking on real rims as opposed to
a steel disc but it likely has value anyway.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

jobst.brandt@stanfordalumni.org

Travis Harry wrote:

>>>>> I already suggested cantilevers rather than liner brakes to her
>>>>> weeks ago but those weren't readily available to her. Linear
>>>>> ("V") brakes are more prone to crud embedding and have rapid pad
>>>>> and rim wear. That goes double in dirt and rain.

>>>> Are you blaming the pads or the mechanics of the linear brake?
>>>> My current touring/commuting bike has cantilever brakes that use
>>>> "V" type pad (lots of surface area but thin.) For what it's
>>>> worth, I do find the pads wear quickly. Given that I ride in
>>>> rain, snow, salt, etc, that's to be expected, and at $4 a pair,
>>>> I'm not too broken up about it. What I really love is that I can
>>>> change them out without having to reset the brakes, something I
>>>> never liked about traditional cantilever brakes with smooth stud
>>>> shoes.

>>> Although Kool Stop pads are better than OEM (also not readily
>>> available to Marian), linear systems promote rapid rim wear and
>>> seem to be more prone to crud in the pads - whether it jams in
>>> faster or just scrapes rim chunks into the pad faster I can't say.

>> Having had many years to research brakes, starting with Universal,
>> pre-Campagnolo brakes, Weinmann, and various centerpull calipers, I
>> searched for several effects: 1) Embedded grit in pads, 2) Hand
>> lever braking force required and 3) brake pad wear rate. In that
>> pursuit I also measured mechanical advantage of various brakes and
>> discovered that contrary to he bicycling press, all calipers had a
>> 1:1 ratio and hand levers had 4:1. That is, the mechanical
>> advantage was the same for all brakes (Including Campagnolo when
>> they took over the high quality end of the business and having an
>> excellent QR.

>> What I found was that Kool-Stop Salmon pads were the best,
>> Campagnolo a distant second, and Mafac, horrible in that they
>> always chewed up rims. Universal didn't come off well either. The
>> most striking feature of Kool-Stop pads was that even when riding
>> through wet dirt and picking up road mud and grit, the pads would
>> clear themselves once back on pavement by merely pumping the brake
>> hard.

>> Not being one to worry about fashion and having a line of
>> practicality, I chose the Continental model because, unlike inserts
>> (typically in Campagnolo and Universal brakes) these pads could not
>> be accidentally knocked out of the pad holder when inserting a
>> wheel, something I observed happening a few times to the surprise
>> of a rider after a wheel change.

>> High pitch squeal is mainly caused by contamination on the braking
>> surface, mainly humidity, but also from soft drink splash or even
>> urine from roadside relief while standing astride the bicycle.
>> Squeal can be cleared up by heavy braking on a steep descent that
>> gets rims hot. It is not a matter of pad toe-in as is often
>> claimed.

>> Just the same, toe-in occurs naturally because when braking hard
>> caliper arms bend forward in a way that makes the rear of the pad
>> wear faster than the forward end. I suppose someone noticed that
>> well worn pads seldom squealed AND that they had toe-in, which led
>> to brutal deformation of brake calipers. If this were a manually
>> added feature, then it should be added by running a rasp lengthwise
>> across the brake pad, not by bending brake calipers.

http://www.koolstop.com/brakes/index.php

> One can find online --trust me-- a more recent review of perhaps 8
> different replacement brake pads done by a British bicycling mag. I
> cannot recall the testing methodology.

How about "testing method"? Methodology is the study of methods, just
as zoology is the study of animals.

> But the design included testing wet and dry separately and reporting
> braking distance as well as remarks on aluminum extracted from the
> rims by the different pads... I found troubling the substantial
> negative rank order correlation between wet and dry performance.
> Not perfectly negative, but high enough that you would not pick out
> one pad as a reasonable compromise, sacrificing just a little
> performance in one condition to achieve high performance in the
> other.

The most important criterion is grit accumulation IN the pad material,
something that cannot be washed off or even picked out with a sharp
tool. I explained the wet and dry performance here often in the past.
Pads that work when the rim is wet are also grit generators, because
it is the grit that is chewing up the rim that have traction on wet
rims.

As a test of this, try using rim brakes after riding through snow so
that the inner rim surface has a layer of snow. Practically no
braking will occur until all snow is melted and the rim friction
surface dries. This is a striking experiment about the effect of
water on braking. In contrast, when riding in moderate rain, rim
sidewalls are mostly dry once braking has warmed the rim. That is,
the rim does not have a contiguous coat of water.

Therefore, the testers, as often, don't understand the problem nor
tribology (study of friction and wear). In that vein, railroad
locomotives lose traction on wet rails because the critical last
monolayer of water molecules are not displaced by pressure (as with
brake pads) but require grit (locomotives have a large sand supply for
this). On double track railways in mountains, uphill tracks are white
with crushed sand debris while the downhill track is dark and rusty
from freight train iron brake shoes.

Jobst Brandt

Tom Kunich

<jobst.brandt@stanfordalumni.org> wrote in message
news:483651a0$0$34494$742ec2ed@news.sonic.net...
>
> A problem with single pivot brakes is that the caliper return spring
> has significant cosine error causing spring sliding at contact points
> on its brake arms. The spring rotation centers are in the two ram's
> horn coils on either side of the brake anchor. With a return spring
> having a single coil wrapped around the anchor about which brake arms
> rotate has no cosine error. This makes a reliable self centering
> caliper that does not need "dual pivot" remain centered and prevent
> one sided brake drag.
>
> On conventional single pivot brake calipers, drag can only be avoided
> keeping spring contact points clean and lubricated. I am amazed that
> brake designers missed that point. This is apparent on the dual pivot
> brake because it has greater cosine error than prior single pivot
> brakes and uses a special plastic slider bearing to accommodate that
> greater spring-to-brake-arm motion.
>
> Are we making any progress yet?

Duhhhhh, I wish you'd post stuff like that more often. It's plain after
you've mentioned it but I don't bother looking that closely at that stuff in
the first place assuming that the designers know what they're doing.

Tom Kunich

"dabac" <dabac.39vf3z@no-mx.forums.cyclingforums.com> wrote in message
news:dabac.39vf3z@no-mx.forums.cyclingforums.com...
>
> I also considered using the shifter cable from an old Positron RD to
> see if that would reduce the slack enough to get decent performance out
> of the rear brake, as according to the yachting world a solid wire is
> less springy than a multi strand wire(for a given diameter).

The problem isn't the inner wire but the outer casing I believe.

Tom Kunich

"jim beam" <spamvortex@bad.example.net> wrote in message
news:rd6dnYoPP5mIs6vVnZ2dnUVZ_gednZ2d@speakeasy.net...
>
> higher maintenance???

You have to keep your rims perfectly straight and the brakes in good
adjustment all the time.

jobst.brandt@stanfordalumni.org

Tom Kunich wrote:

>> I also considered using the shifter cable from an old Positron RD
>> to see if that would reduce the slack enough to get decent
>> performance out of the rear brake, as according to the yachting
>> world a solid wire is less springy than a multi strand wire(for a
>> given diameter).

No matter how closely you pack circular cross section strands,
they will have less cross sectional area than an equivalent diameter
solid wire, however, for the forces in brake cables, the stranded
cables do not stretch.

> The problem isn't the inner wire but the outer casing I believe.

Brake cable housing is, in essence, a stack of rings that when formed
into a curve as brake cables require, the central axis of the housing
elongates because the inner length is incompressible and the outer
length is free to open gaps between coils. If the housing has any
kinks, these will straighten and cause a spongy feeling when braking.
That my be where the "cable stretch

Because this well understood characteristic of "Bowden" cables makes
no difference to a force transmitting function, brake cables use it,
however, STI shifting relies on constant derailleur position and for
this reason Shimano made an STI shift cable housing that is not a
stack of rings (or even a close packed coil) and made a cable housing
that has long helix embedded wires. This housing is not designed to
transmit force, especially braking force, because it will burst and
collapse axially if used for brakes.

http://en.wikipedia.org/wiki/Bowden_cable

Jobst Brandt

dabac

Well, every little helps if you're trying to get a borderline setup to perform adequately...

dabac

I fear that this may bog down in another quagmire of semantics, but cables do become longer. It may well be that each individual strand doesn't elongate, but a cable as a whole can certainly become longer - presumably by the voids in the cross section compressing when the cable is under tension. Smaller voids, smaller diameter. And as the diameter decreases the virtual center that the strands are wound around gets smaller, thus allowing the cable to become longer even if the strands themselves aren't stretching.
I once tried running some nice and thick cables originally intended for scooters as brake cables on my bike and they gave a hopelessly mushy feel that just didn't go away until I replaced them with some thinner but more densely laid bicycle-specific cables.