Progressive brakes?
Frank Krygowski
about how nicely "progressive" the brakes are.
I have trouble with this concept. To me, that means the more force I
apply to the levers, the more torque the brakes apply to the wheel,
with the relationship between force and brake torque being not greatly
different from direct proportion. It seems to me that would be very
normal. And while I don't have much of the connoisseur in me, I'd
think that most deviations from that ideal would be small and hard to
detect.
(Of course, I also want sufficient stopping force, I don't want brakes
to drag when released, I don't want to lose all braking when wet, etc
- but those have nothing to do with that "progressive" adjective.)
So, absent real oddities like parallelogram linkages (ala Campy Delta
brakes), coaster brakes or band brakes, what would make bike brakes
_not_ be progressive? Seems to me friction in the cable would be the
main thing, followed by friction in the pivots. But cables are not
part of a brake set, and I'd think pivot friction wouldn't vary
much.
So besides those sources of friction... what matters?
BTW, almost all my bikes have cantilever brakes of one type or
another. They all seem "progressive" to me.
- Frank Krygowski
Jobst Brandt
> I frequently read road tests or component tests that talk
> approvingly about how nicely "progressive" the brakes are.
> I have trouble with this concept. To me, that means the more force
> I apply to the levers, the more torque the brakes apply to the
> wheel, with the relationship between force and brake torque being
> not greatly different from direct proportion. It seems to me that
> would be very normal. And while I don't have much of the
> connoisseur in me, I'd think that most deviations from that ideal
> would be small and hard to detect.
They would, so much so, that it killed the Campagnolo Delta brake and
its forerunner the Modolo Kronos:
> (Of course, I also want sufficient stopping force, I don't want
> brakes to drag when released, I don't want to lose all braking when
> wet, etc - but those have nothing to do with that "progressive"
> adjective.)
Non-linear brakes are a sure way to crash!
> So, absent real oddities like parallelogram linkages (ala Campy
> Delta brakes), coaster brakes or band brakes, what would make bike
> brakes _not_ be progressive? Seems to me friction in the cable
> would be the main thing, followed by friction in the pivots. But
> cables are not part of a brake set, and I'd think pivot friction
> wouldn't vary much.
These aren't "real oddities" but non-linear brakes that various
manufacturers believed were the way to better braking. In fact that
is why we have disk brakes on cars, because drum brakes are self-servo
mechanisms that at times even cause complete brake "lock-up" or the
converse, total brake fade.
> So besides those sources of friction... what matters?
Change in mechanical advantage and self servo, both are serious
intruders in braking.
> BTW, almost all my bikes have cantilever brakes of one type or
> another. They all seem "progressive" to me.
The progression is self defeating because it is not normal to the
braking surface and has other drawbacks that are killers. Cantilever
brakes have such serious cosine error that they pop under the braking
surface into the spokes, never to return, while Dual pivot have cosine
error that sweeps the pads into the tire for a blowout.
Stick with the centrally pivoted caliper brake and the side pull lever
mechanism that have close to zero cosine error.
Jobst Brandt
AMuzi
Add that to the "carve through corners" phrasebook.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
Tom Sherman °_°
> Frank Krygowski wrote:
>> [...]
>> BTW, almost all my bikes have cantilever brakes of one type or
>> another. They all seem "progressive" to me.
>>
>> - Frank Krygowski
>
>
> Add that to the "carve through corners" phrasebook.
>
I watched a guy carve through a corner today on a CAT D-4 with an
articulated blade.
--
Tom Sherman - 42.435731,-83.985007
I am a vehicular cyclist.
Tosspot
<thread highjack>
> The progression is self defeating because it is not normal to the
> braking surface and has other drawbacks that are killers. Cantilever
> brakes have such serious cosine error that they pop under the braking
> surface into the spokes, never to return, while Dual pivot have cosine
> error that sweeps the pads into the tire for a blowout.
>
> Stick with the centrally pivoted caliper brake and the side pull lever
> mechanism that have close to zero cosine error.
>
> Jobst Brandt
I saw a set of Weinmanns yesterday. Normal boss mount, but looked like
hydraulic pipe going to them. Brake actuation caused some parts of the
brake to rotate as the pads moved in. Couldn't get the number, they
might have been PBS3000's, but they looked very new. Any ideas?
Oh, it was the cosine error that reminded me btw.
Frank Krygowski
> Frank Krygowski wrote:
> >
>
> > So besides those sources of friction... what matters?
>
> Change in mechanical advantage and self servo, both are serious
> intruders in braking.
I understand. Self servo, especially, would make braking much
different from straight "progressive" - that is, it would make brake
torque far from proportional to applied lever force. And it would
make braking action inconsistent, dependent on brake shoe friction
coefficient. But self-servo is very rare in bike brakes.
Yet in comparisons or road tests in Buycycling and other enthusiast
magazines, I find statements implying that (perhaps) Paul cantilevers
are more progressive and controllable than (say) Shimano cantilevers.
Or than Shimano dual pivot brakes. They're not talking about any self-
servo action in either brake type.
I'm left to assume that only pivot friction really matters - that
absent rolling element bearings at various pivots, a small amount of
stick-slip friction is possible, and that this might effect response.
Consequently, I assume that brakes with similar pivots will have
similar "progressiveness" or controllability.
So is it entirely, or almost entirely, marketing hype?
- Frank Krygowski
Lou Holtman
What do you think of stiffness?
>
> So is it entirely, or almost entirely, marketing hype?
I use on several bikes, lets see,
- dual pivot brakes,
- single pivot brakes,
- mechanical diskbrakes,
- hydraulic dis brakes,
- V-brakes,
- Magura hydraulic rim brakes,
and they all have a different feeling and 'progressiveness' so no it is
entirely marketing hype IMO.
Single pivot brakes on my ATB's? No thanks Jobs.
Lou
pm
Brake forces produce a torque that tilts the the brake pads out of
alignment to the rim, a contributor to less-than-linear brake
performance, shudder, etc. For cantilever brakes, the stiffness of the
bosses, fork and seatstays, and the particular geometry of the brake
(which, independently of mechanical advantage, affects the amount of
levering-out which you can feel if you wrap your hand around your seat
stays then apply the brake). Misalignment reduces the contact area
between brake shoe and rim, reducing performance.
I already hear the objection brewing from somewhere, isn't frictional
force just the product of a coefficient of friction and the normal
force, and not a function of contact area? This is the first model of
friction that many people are introduced to -- but it's a model that
tends not to be true for compliant materials, such as bicycle brake
shoes are made of. For compliant materials, the _real_ (i.e.
microscopic) area of contact saturates at a relatively low pressure,
so that the amount of available friction at a given normal force
becomes dependent on (macroscopic) area of contact.
http://depts.washington.edu/nanolab/ChemE554/Summaries%20ChemE%20554/Introduction%20Tribology.htm
-pm
Jobst Brandt
>>> So besides those sources of friction... what matters?
>> Change in mechanical advantage and self servo, both are serious
>> intruders in braking.
> I understand. Self servo, especially, would make braking much
> different from straight "progressive" - that is, it would make brake
> torque far from proportional to applied lever force. And it would
> make braking action inconsistent, dependent on brake shoe friction
> coefficient. But self-servo is very rare in bike brakes.
> Yet in comparisons or road tests in Buycycling and other enthusiast
> magazines, I find statements implying that (perhaps) Paul cantilevers
> are more progressive and controllable than (say) Shimano cantilevers.
> Or than Shimano dual pivot brakes. They're not talking about any self-
> servo action in either brake type.
> I'm left to assume that only pivot friction really matters - that
> absent rolling element bearings at various pivots, a small amount of
> stick-slip friction is possible, and that this might effect response.
> Consequently, I assume that brakes with similar pivots will have
> similar "progressiveness" or controllability.
Pivot friction is insignificant to transmission of hand applied
braking, the pivot being even slightly lubricated. The rotational
load is the only one you might feel but once applied has little
consequence.
> So is it entirely, or almost entirely, marketing hype?
It must be, because any substantial change in brake force transmission
would cause crashes as the Campagnolo Delta did. It's gone! That
brake changed my appreciation of R&D at Campagnolo. They are now
classic, unskilled product designers. Tullio and team are history.
Jobst Brandt
JG
a cantilever is more or less the same as a center pivot side-pull.
There is, however, an r-multiplier...
(PeteCresswell)
>I have trouble with this concept. To me, that means the more force I
>apply to the levers, the more torque the brakes apply to the wheel,
>with the relationship between force and brake torque being not greatly
>different from direct proportion. It seems to me that would be very
>normal. And while I don't have much of the connoisseur in me, I'd
>think that most deviations from that ideal would be small and hard to
>detect.
Maybe they're talking about granularity or "modulation".
Going down a steep hill on loose gravel, I can play my disc front
brake without locking it up and losing control. I think I would
have trouble doing that with at least some rim brakes.
--
PeteCresswell
Andre Jute
> Stick with the centrally pivoted caliper brake and the side pull lever
> mechanism that have close to zero cosine error.
>
> Jobst Brandt
Or buy hydraulic rim brakes to shortcut all these problems and gain
perfect predictability.
I must confess, when I first saw Krygowski's post I wondered what sort
of newbie or cheapskate or incompetent he might be. Surely the problem
with bicycle brakes is to avoid being thrown headfirst over the
handlebars, except for those too cheap to buy brakes that work, and
those too cackhanded to change brake blocks and make simple
adjustments.
Andre Jute
Feed a tree today, produce more CO2!
Andre Jute
A few years ago an old sporting buddy of mine stopped by and we went
cycling, him on my Gazelle Toulouse which has a disc front brake.
"Gee," he said, "this brake reminds me of the orange on the floor of
that Citroen you loved so. You glanced at it and it locked up all four
wheels!" Of course, that's a slander; with time and practice you could
learn to use, if not to love, that pressbulb that operated the
Citroen's very poweful brakes. But he's right, discbrakes on a bike
takes some getting used to, and some learned skill to operate
smoothly. -- AJ
Dan O
> On Oct 3, 12:50 am, "(PeteCresswell)" <x...@y.Invalid> wrote:
>
>
>
> > Per Frank Krygowski:
>
> > >I have trouble with this concept. To me, that means the more force I
> > >apply to the levers, the more torque the brakes apply to the wheel,
> > >with the relationship between force and brake torque being not greatly
> > >different from direct proportion. It seems to me that would be very
> > >normal. And while I don't have much of the connoisseur in me, I'd
> > >think that most deviations from that ideal would be small and hard to
> > >detect.
>
> > Maybe they're talking about granularity or "modulation".
>
> > Going down a steep hill on loose gravel, I can play my disc front
> > brake without locking it up and losing control. I think I would
> > have trouble doing that with at least some rim brakes.
>
> A few years ago an old sporting buddy of mine stopped by and we went
> cycling, him on my Gazelle Toulouse which has a disc front brake.
> "Gee," he said, "this brake reminds me of the orange on the floor of
> that Citroen you loved so. You glanced at it and it locked up all four
> wheels!" Of course, that's a slander; with time and practice you could
> learn to use, if not to love, that pressbulb that operated the
> Citroen's very poweful brakes. But he's right, discbrakes on a bike
> takes some getting used to, and some learned skill to operate
> smoothly.
Did I mention that I braked on the descent to a blind rail crossing
the other day?
(There was no train there, BTW.)
More than half of my brief professional motorcycle racing career was
with no rear brake (disc w/ leaky hydraulic), and much of it was with
no front brake, either (front brakes were not useful and maybe even
not allowed on some oval courses).
(PeteCresswell)
>discbrakes on a bike
>takes some getting used to, and some learned skill to operate
>smoothly.
My experience is that it depends on the brakes.
Some are grabby - especially in high humidity - some are very,
very smooth.
My Hope hydros are super-smooth right out of the box.
I've got one set of Avid mechs (silver colored calipers) that are
smooth except in high humidity.
I've got an Avid mech (black, different model from the silver) on
the front of my siglespeed that's always a little grabby - but I
don't know if that's a setup issue, something with the pads/disc,
or inherent in the caliper.
--
PeteCresswell
thirty-six
The rim and its cleanliness. Get the rim squeaky (grease-free) clean
and just about any block will work well. Get some WD on it and there
is no progression, there are no brakes.
Frank Krygowski
> Frank Krygowski <frkry...@gmail.com> considered Sat, 2 Oct 2010
> which bind badly as tension increases. The result is that it's easy
> enough to start the brakes working, but the amount of pressure you
> need to increase braking level is excessive.
> It's something I would be particularly keen to check when cables have
> complex routing.
I've come across that too; but it seems to be a problem in the cable,
rather than in the brake itself.
I believe that one reason Shimano went to high mechanical advantage
brakes (dual pivot or direct cantilever) is that the lesser cable
tension causes significantly less cable friction. Because of the
bends in the cables, the benefit is more than proportional.
My concern, though, was the brake set itself. Are there design
features - beyond, say, better bearings - that make a brake set more
"progressive"? Does anyone really think a boutique cantilever brake
set is more "progressive" than a standard one?
- Frank Krygowski
landotter
Have you ever seen the little tension modulators that come on some
entry level vee brake bkes? They make the vees feel squishy like a
brake which compresses the housing more. For some modulation is in the
squishy feel.
>
> My concern, though, was the brake set itself. Are there design
> features - beyond, say, better bearings - that make a brake set more
> "progressive"? Does anyone really think a boutique cantilever brake
> set is more "progressive" than a standard one?
Seems like a load of nonsense to me. Different canti designs will fall
from the rim closer or further, which may be of consequence, and some
designs are prone to squealing, but the feel is mostly cable routing,
yoke angle, and choice of pad.
kolldata
yoke angle, and choice of pad.
and rider reflex !
forgiving !
the touch of a Krupp shore gun mount !
sensitive !
durabble !
well made !
unbreakable (and foolproof)
even an idiot can ride it
POWERFUL
slight oversteer
slight understeer
understeers
over....
grips the road like ( field oxen ?)
instruments are readable
shifter detents are crisp and accurate (once found)
frankly, progressive' falls into' the road test humor category.
smoothly applicable brakes are progressive. maybe the meaning is
designer accomadated a high percentage of blind all thumbs 'mechanics'
with a easily adjusted mechanism. side pulls.
look carefully and find progressive means sloppy.
BTWOC: spray braking surfaces with CRC Brake Prep uh I mean CRC
Rubber Dressing.
a good rain tire
eh ?
A GOOD RAIN TIRE
eh ?
futrino
They are Weinmann PBS 300, There is actually a cable that turns the
round plastic knob looking thing, and it sort of cork screws the brake
pad closer, they feel different, like they get stronger with more lever
pull, but not with more lever force, not linear.
on the non cable side of the brakes, there is another dial with a +/-
and you can turn it to increase brake power.
Also strange that you can't move the brake pads toward the rim with your
hands. there is something in the brake bridge that moves the left pad
in when the right pad screws in.
futrino
>>
>> I saw a set of Weinmanns yesterday. Normal boss mount, but looked like
>> hydraulic pipe going to them. Brake actuation caused some parts of the
>> brake to rotate as the pads moved in. Couldn't get the number, they
>> might have been PBS3000's, but they looked very new. Any ideas?
>>
>> Oh, it was the cosine error that reminded me btw.
> I too have these brakes on a women's Zenith 531 Reynolds tubed bike.
> They are Weinmann PBS 300, There is actually a cable that turns the
> round plastic knob looking thing, and it sort of cork screws the brake
> pad closer, they feel different, like they get stronger with more lever
> pull, but not with more lever force, not linear.
>
> on the non cable side of the brakes, there is another dial with a +/-
> and you can turn it to increase brake power.
>
> Also strange that you can't move the brake pads toward the rim with your
> hands. there is something in the brake bridge that moves the left pad
> in when the right pad screws in.
I found some pics, can't read the language
futrino
Jobst Brandt
>>>> I saw a set of Weinmanns yesterday. Normal boss mount, but looked like
>>>> hydraulic pipe going to them. Brake actuation caused some parts of the
>>>> brake to rotate as the pads moved in. Couldn't get the number, they
>>>> might have been PBS3000's, but they looked very new. Any ideas?
>>>> Oh, it was the cosine error that reminded me btw.
>>> I too have these brakes on a women's Zenith 531 Reynolds tubed bike.
>>> They are Weinmann PBS 300, There is actually a cable that turns the
>>> round plastic knob looking thing, and it sort of cork screws the brake
>>> pad closer, they feel different, like they get stronger with more
>>> lever pull, but not with more lever force, not linear.
>>> On the non cable side of the brakes, there is another dial with a +/-
>>> and you can turn it to increase brake power.
Make that brake clearance adjustment, rather than power.
>>> Also strange that you can't move the brake pads toward the rim
>>> with your hands. There is something in the brake bridge that
>>> moves the left pad in when the right pad screws in.
>> I found some pics. Can't read German:
http://www.rennrad-news.de/forum/showthread.php?t=60575
> here's one in English:
These geeks are proving that the bicycle industry can't afford good
engineers, as they come up with one weird brake design after anothr as
some similarly clumsy manufacurer after another will bring to market.
Jobst Brandt
Tosspot
Them's the badgers, many thanks. Can't see how they be better than a
reasonable V-brake setup though. Still, was interesting.
thirty-six
We could be sayin the same thing bout your wonky pedals if anyone
experienced in the industry would believe your rant.
kolldata
cleaned with Iso. EWhen fouled and removable, cleaned with thinner
then CHOH then reapplied. make you forget soft rain Eagles.
Progressive. This is a word used by writer's maybe engineers on
layoffs. The word is addressed to the writer's readership. Readerships
vary eg Motor Trend vs Autoweek vs R&T...
The action sending me over the bars is modulated by Schumacher/ Alonso
and I guess Lance A