Centerpull brakes
Gary Young
centerpull brakes, I have to admit that the latest Rivendell Reader
(#30) gave me reasons to pause.
First of all, in the letters section, a reader (Thomas Papetti) points
out that
dual-pivot sidepulls won't track an out-of-true rim the way all other
brake types will. I'm not sure how much that counts in favor of
centerpulls (Papetti doesn't discuss them at all). Even though most
riders would probably use long-reach dual pivots in lieu of
centerpulls, long-reach single-pivot sidepulls and cantilevers are
still available if tracking is a significant worry.
Then in an article, Jan Heine makes several claims for the superiority
of sidepulls.
He says, "The long lever on the cable side [above the pivot, if I
understand him correctly] and the short lever on the pad side [below
the pivot] gives centerpulls a huge mechanical advantage over
sidepulls. Just like a bolt-cutter, where long arms and short jaws
allow you to cut through thick steel bolts." Later on, he adds that
only with the advent of dual-pivot brakes did sidepulls catch up to
centerpulls in this respect.
That doesn't seem to jibe with Jobst's discussion in the FAQ, which
seems to suggest that single-pivot sidepulls and centerpulls had the
same mechanical advantage.
He argues that only the part of the arm below the pivot needs to be
beefy, because that's the only place where flex matters. "As a result,
the arms above the pivots can be incredibly skinny, as they don't need
to resist flex. That is where the weight savings of a centerpull
originate." He doesn't say what the weight savings is.
He writes, "And since the pivot on centerpull brakes is on the fork
leg, adding reach does not increase the flex or change the mechanical
advantage. So there is not incentive to go to short-reach brakes." I
think he means that since the distance between the pad and the pivot
point always remains the same, adding lever length above the pivot
doesn't effect the mechanical advantage. That sounds dubious to me --
doesn't changing the length of a cantilever brake's straddle cable
effect mechanical advantage even if all else remains the same?
Furthermore, from the photos of old centerpulls in the Reader, it
doesn't seem as if the distance from pivot to pad was always kept
constant (some long-reach brakes seem to achieve that reach in part by
increasing the lever below the pivot).
He notes that centerpulls don't stick out to the side like
centerpulls. It seems to me that that problem can be cured by using
v-brakes, though that introduces problems of its own (e.g., mating
them to road levers).
He says that even the standard-reach (what would be called long-reach
by most) dual-pivot brakes offered by Shimano don't leave much room
for fenders. Is that true? Just how big a tire would you have to run
before you would crowd out the dual pivots? (Elsewhere in the Reader,
Grant says that centerpulls will clear a 40mm tire or a 38mm tire with
fenders; what's the limit with the current long-reach dual pivots?)
Furthermore, why not long-reach single-pivots, which are still
available?
Probably his most controversial claim is that single-pivot sidepulls
"offered inferior performance" and became widespread mostly because of
Campagnolo's advertising and gruppo packaging. Contrast that with
Jobst's claim in the FAQ that, "The centerpull brake of the 1950's,
was popular for nearly a decade,
in spite of being entirely without merit, being worse in all respects
than the side pull brake with which it competed."
In the past, I've been pretty fed up with Grant's talk of reviving
centerpulls, because it so often appeared side-by-side with complaints
about Rivendell's financial straits and lack of popularity. I do
notice a more refreshing tone in this issue: he mentions a bike
planned for next year that will have braze-on pivots for centerpulls
and adds, "But we don't expect anybody to follow that lead., and we
fully expect to sell fewer bikes because of it. Centerpulls, for as
much sense as they make, will still scare off most customers."
Simon Brooke
> Though I've been critical of Grant Peterson's effort to revive
> centerpull brakes, I have to admit that the latest Rivendell Reader
> (#30) gave me reasons to pause.
Back in the eighties I was a great fan of centrepull brakes, partly
because I believed them to be greater in stopping power but mainly
because I found them much more easy to adjust. That is, in my opinion,
a big benefit!
As you point out they give considerable and equal leverage to both
blocks, acting symmetrically on both sides of the rim. This certainly
looks to me to be better leverage than the single pivot calipers that
were current at the time. However, cantilever brakes have at least
equal leverage, are lighter, are more securely mounted to the bike,
and are even easier to adjust - for a very small penalty in wind
resistance. Where ultimate speed is not the issue they seem to me to
be definitely preferable over the older style crossed lever
centrepulls. If ultimate low windage is a consideration you're
probably going to use dual pivot calipers these days anyway.
I know that V brakes have largely taken over from cantis, but
personally I'm not yet persuaded that they offer a real practical
benefit for most uses - I think they're more of a style statement, and
the special levers mean that they're not so easy to interchange with
other components. But I can't now see any reason to prefer old-style
crossed lever centrepulls to cantilevers.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
my other car is #<Subr-Car: #5d480>
;; This joke is not funny in emacs.
Tim McNamara
> I know that V brakes have largely taken over from cantis, but
> personally I'm not yet persuaded that they offer a real practical
> benefit for most uses - I think they're more of a style statement,
> and the special levers mean that they're not so easy to interchange
> with other components. But I can't now see any reason to prefer
> old-style crossed lever centrepulls to cantilevers.
I haven't used sidepulls since my mid-70s Schwinn Continental was
stolen in 1976. As I recall they were Dia-Compes. What I recall
about them is that they stopped the bike fine. I've never seen weight
comparisons, which by rights ought to include all the relevant hardware
such as hangers, straddle wires, etc. Also, it's never seemed that
there were cantilevers of the same quality as a Campy, Dura Ace or
Superbe sidepull.
From a design perspective, it seems to me that (1) centerpulls are
much more complicated than either single- or dual-pivot sidepulls; and
(2) centerpulls are more prone to flex under the force of the rim
acting on the brake pads, mainly due to flex in the hanger with the
center bolt and pivots. I've never tried centerpulls mounted on
braze-ons, which might reduce or eliminate the flex problem. A number
of people seem to claim this is the case, including Tony Oliver, Jan
Heine and Grant Petersen. They've used 'em and I haven't, so at this
point I have to take their word for it.
V-brakes were created to benefit the mountain bike industry. The
issue was cable routing and simplifying basic setup, which created an
economies-of-scale cost savings for manufacturers like Giant,
Cannondale, Trek, etc. The need for a cable hanger was problematic
for rear suspension and, to a lesser extent, front suspension. Plus
they were new and different, and a less-than-astute bike magazine
industry mistakenly took V-brakes as a consumer-side improvement
rather than a supply-side improvement.
There may be some benefits for consumers, of course. It's harder to
set up V-brakes wrongly than is the case with cantilevers. The lever
feel is different because there is less friction loss with the longer
cable pull. The mechanical advantage is slightly higher, trading off
modulation for reduced hand grip. There are downsides, including very
close tolerances between the rim and the brake, which is a problem if
the wheel gets bent or a spoke breaks. And the pads are much thinner,
wearing out faster and needing to be replaced more often (also, the
thinner pads are much less compressible, which adds to the "power
brake" feeling of V-brakes; this is mistakenly perceived as "more
stopping power").
Every decent brake- whether sidepull, centerpull, cantilever, V-brake,
disc brake, drum brake, what have you- provides enough stopping power
to make the wheel skid. In that regard, none of these brakes provide
more stopping power than the others. The question of choice really
rests on other factors (lever feel, cable routing, clearance, etc).
Gary Young
> Though I've been critical of Grant Peterson's effort to revive
> centerpull brakes, I have to admit that the latest Rivendell Reader
> (#30) gave me reasons to pause.
>
> First of all, in the letters section, a reader (Thomas Papetti) points
> out that
> dual-pivot sidepulls won't track an out-of-true rim the way all other
> brake types will. I'm not sure how much that counts in favor of
> centerpulls (Papetti doesn't discuss them at all). Even though most
> riders would probably use long-reach dual pivots in lieu of
> centerpulls, long-reach single-pivot sidepulls and cantilevers are
> still available if tracking is a significant worry.
>
> Then in an article, Jan Heine makes several claims for the superiority
> of sidepulls.
That should be "superiority of centerpulls."
Should be "centerpulls don't stick out to the side like cantilevers."
jobst....@stanfordalumni.org
> Though I've been critical of Grant Peterson's effort to revive
> centerpull brakes, I have to admit that the latest Rivendell Reader
> (#30) gave me reasons to pause.
I think two things should be noted about all brakes before the dual
pivot era, and that is they all had a 1:1 ratio in the "caliper" and a
4:1 ratio in the hand lever, all brakes being interchangeable under
any hand lever. This includes sidepull, centerpull and cantilever.
The second feature is that sidepull brakes have the pad pivot above
and only slightly (rim half width) offset from the braking surface so
that there is essentially no position change as the pad sweeps through
its wear life (cosine error). Centerpull and cantilever brakes
approach the rim at nearly a 45 degree angle and have large vertical
change throughout pad wear life, so much so that cantilever brakes
have dived under the rim leaving the bicycle with no brake at all.
The cantilever dives under but had the advantage of endless mud or
radial tire clearance, the centerpull goes into the tire as it wears
and offers no advantages whatsoever. I believe that is why it died so
quickly as it should have. It was sold on the premise that it had a
higher mechanical advantage, something that at first inspection it
appears to have through its long levers. They are twice as long as
the pad arms... but there are two of them, each receiving half the
force.
> First of all, in the letters section, a reader (Thomas Papetti)
> points out that dual-pivot sidepulls won't track an out-of-true rim
> the way all other brake types will. I'm not sure how much that
> counts in favor of centerpulls (Papetti doesn't discuss them at
> all). Even though most riders would probably use long-reach dual
> pivots in lieu of centerpulls, long-reach single-pivot sidepulls and
> cantilevers are still available if tracking is a significant worry.
> Then in an article, Jan Heine makes several claims for the
> superiority of sidepulls.
> He says, "The long lever on the cable side [above the pivot, if I
> understand him correctly] and the short lever on the pad side [below
> the pivot] gives centerpulls a huge mechanical advantage over
> sidepulls. Just like a bolt-cutter, where long arms and short jaws
> allow you to cut through thick steel bolts." Later on, he adds that
> only with the advent of dual-pivot brakes did sidepulls catch up to
> centerpulls in this respect.
> That doesn't seem to jibe with Jobst's discussion in the FAQ, which
> seems to suggest that single-pivot sidepulls and centerpulls had the
> same mechanical advantage.
They had to have the same ME or you couldn't operate them with the
same pad clearance. The purpose of the dual pivot is to allow half
the pad clearance of former brakes and this required accurate
centering. This is necessary to offer the higher mechanical
advantage today's avocational riders need to stop their bicycles.
Just recall the story bicycle shops had to come up with to explain why
riders could not stop their Campagnolo Record equipped bicycles...
"These are racing brakes. Racers only need to modulate speed, not
stop." and the like. If you believe that you deserve to be led around
by the nose. The faster you go the harder you must brake. Descending
a mountain pass with straights and hairpin turns requires standing the
bicycle on its front wheel into every turn. This is done with two
fingers by racers using 4:1 brakes.
> He argues that only the part of the arm below the pivot needs to be
> beefy, because that's the only place where flex matters. "As a
> result, the arms above the pivots can be incredibly skinny, as they
> don't need to resist flex. That is where the weight savings of a
> centerpull originate." He doesn't say what the weight savings is.
Flex in any part of the system eats up hand lever stroke. Who invents
this cock and bull stuff anyway? The lower arm must be stronger
because it is loaded in torsion from brake pad drag.
> He writes, "And since the pivot on centerpull brakes is on the fork
> leg, adding reach does not increase the flex or change the
> mechanical advantage. So there is not incentive to go to
> short-reach brakes." I think he means that since the distance
> between the pad and the pivot point always remains the same, adding
> lever length above the pivot doesn't effect the mechanical
> advantage. That sounds dubious to me -- doesn't changing the length
> of a cantilever brake's straddle cable effect mechanical advantage
> even if all else remains the same? Furthermore, from the photos of
> old centerpulls in the Reader, it doesn't seem as if the distance
> from pivot to pad was always kept constant (some long-reach brakes
> seem to achieve that reach in part by increasing the lever below the
> pivot).
These are not people to be believed. They have no idea what they are
talking about and do it profusely. It reminds me of the kooks I see at
InterBike every year with a new crank mechanism that will make you go
faster, not to mention how much mechanism and weight it adds to the
bicycle.
> He notes that centerpulls don't stick out to the side like
> sidepulls. It seems to me that that problem can be cured by using
> v-brakes, though that introduces problems of its own (e.g., mating
> them to road levers).
How far??? What is the issue here anyway. Is it perhaps streamlining
or just someone who suffers from the "loose ends" syndrome (things
that protrude, as in toilet paper rolls that pay off the front instead
of the back [hidden ends])?
> He says that even the standard-reach (what would be called
> long-reach by most) dual-pivot brakes offered by Shimano don't leave
> much room for fenders. Is that true?
NO.
> Just how big a tire would you have to run before you would crowd out
> the dual pivots? (Elsewhere in the Reader, Grant says that
> centerpulls will clear a 40mm tire or a 38mm tire with fenders;
> what's the limit with the current long-reach dual pivots?)
> Furthermore, why not long-reach single-pivots, which are still
> available?
> Probably his most controversial claim is that single-pivot sidepulls
> "offered inferior performance" and became widespread mostly because
> of Campagnolo's advertising and gruppo packaging. Contrast that
> with Jobst's claim in the FAQ that, "The centerpull brake of the
> 1950's, was popular for nearly a decade, in spite of being entirely
> without merit, being worse in all respects than the side pull brake
> with which it competed."
A conspiracy! The sidepull brake is the obvious mechanism for road
bicycles to all who understand mechanical design. All this other
stuff is amateur thinking guided by misunderstanding of the concept.
Even places like Campagnolo are not immune. After Tullio died the
place was run by incompetents who made the Delta brake, a non linear
response brake with huge cosine error. It was an Ide? fixe of someone
with "loose end" syndrome, externally clean but a mess inside.
http://draco.acs.uci.edu/rbfaq/FAQ/8f.15.html
> In the past, I've been pretty fed up with Grant's talk of reviving
> centerpulls, because it so often appeared side-by-side with complaints
> about Rivendell's financial straits and lack of popularity. I do
> notice a more refreshing tone in this issue: he mentions a bike
> planned for next year that will have braze-on pivots for centerpulls
> and adds, "But we don't expect anybody to follow that lead., and we
> fully expect to sell fewer bikes because of it. Centerpulls, for as
> much sense as they make, will still scare off most customers."
... and they should. Now let's hear it again concisely. What are the
advantages?
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> Every decent brake- whether sidepull, centerpull, cantilever,
> V-brake, disc brake, drum brake, what have you- provides enough
> stopping power to make the wheel skid. In that regard, none of
> these brakes provide more stopping power than the others. The
> question of choice really rests on other factors (lever feel, cable
> routing, clearance, etc).
That may be true today but for the older brakes, before dual pivot, it
was not. 4:1 leverage was more than a non athletic rider could
handle, especially with two fingers.
The different ratio hand levers caused problems for which people found
solutions. One of these was the Travel Agent, a clever and
appropriate name that we don't hear much about now that the dust has
settled.
Jobst Brandt
jobst....@stanfordalumni.org
Donald Gillies
>In the past, I've been pretty fed up with Grant's talk of reviving
>centerpulls, because it so often appeared side-by-side with complaints
>about Rivendell's financial straits and lack of popularity. I do
>notice a more refreshing tone in this issue: he mentions a bike
>planned for next year that will have braze-on pivots for centerpulls
>and adds, "But we don't expect anybody to follow that lead., and we
>fully expect to sell fewer bikes because of it.
I have owned 2 bikes with centerpulls (raleigh grand prix, dawes
low-end), and 3 bikes with sidepulls (schwinn paramount, trek 500,
alan), and 1 bike with dual-pivot sidepulls (trek 2300) and one bike
with U-brakes (schwinn moab). I currently live on a very steep hill
in san diego, present. In terms of stopping power, this is where I
think that things stack up.
sidepulls (campy) - worst
dual-pivots (shimano) - better
centerpulls - best
U-brakes - hard to gauge since these are on a totally different kind
of (mountain) bike.
It is worth pointing out that when i recently got the Alan bike with
campy sidepulls, I immediately removed the campy pads and put new
low-end pads on it, since the campy pads weren't working. I then took
off the low end pads and bought premium oversized shimano pads, since
the low-end pads weren't working. the premium (ultegra) pads just
barely work. I am still very unhappy with the campy gran sport
sidepull performance, and I feel jeopardized every time i go down the
hill.
Campy and Shimano marketing hype aside, i think you can easily
determine the most powerful brakes by looking historically at what got
installed on tandem bicycles in the past. In the late 1960's and
1970's and 1980's, the choices were :
cantilevers - best
centerpulls - second best
no sidepulls installed on tandems.
even today, nobody puts dual-pivots on tandems.
i like the higher braking precision in centerpulls. The lever travel
is farther on centerpulls and so you know there is more mechanical
advantage. you can see it just by placing a set of weinmann levers
next to some campy levers.
that's all i need to know.
- Don Gillies
San Diego, CA
Tim McNamara
> Tim McNamara writes:
>
> > Every decent brake- whether sidepull, centerpull, cantilever,
> > V-brake, disc brake, drum brake, what have you- provides enough
> > stopping power to make the wheel skid. In that regard, none of
> > these brakes provide more stopping power than the others. The
> > question of choice really rests on other factors (lever feel,
> > cable routing, clearance, etc).
>
> That may be true today but for the older brakes, before dual pivot,
> it was not. 4:1 leverage was more than a non athletic rider could
> handle, especially with two fingers.
I'll concede that and excuse myself by admitting a limited point of
viewq. Having always been an "athletic" rider, I never have had
trouble with being able to squeeze any brake lever hard enough to make
the brake work. Being 6'4" and having commensurately sized hands, I
have tended to find brake lever bodies too small and uncomfortable
(only the 1998 and later Campy Ergo lever bodies feel really
comfortable to me).
Certainly my sidepulls with non-aero levers take more effort to use
than my dual pivot Campy Ergo brakes/levers. I don't remember what
the centerpull lever feel was like. I will agree that all brakes are
not equal from the practical, ergonomic perspective.
Tim McNamara
> I have owned 2 bikes with centerpulls (raleigh grand prix, dawes
> low-end), and 3 bikes with sidepulls (schwinn paramount, trek 500,
> alan), and 1 bike with dual-pivot sidepulls (trek 2300) and one bike
> with U-brakes (schwinn moab). I currently live on a very steep hill
> in san diego, present. In terms of stopping power, this is where I
> think that things stack up.
>
> sidepulls (campy) - worst
> dual-pivots (shimano) - better
> centerpulls - best
>
> U-brakes - hard to gauge since these are on a totally different kind
> of (mountain) bike.
Actually, U-brakes were just a new name for an old design"
centerpulls. Take a close look, they are just centerpull brakes with
a slightly different arm shape.
> It is worth pointing out that when i recently got the Alan bike with
> campy sidepulls, I immediately removed the campy pads and put new
> low-end pads on it, since the campy pads weren't working. I then
> took off the low end pads and bought premium oversized shimano pads,
> since the low-end pads weren't working. the premium (ultegra) pads
> just barely work. I am still very unhappy with the campy gran sport
> sidepull performance, and I feel jeopardized every time i go down
> the hill.
Try Mathauser or KoolStop Continental slamon colored pads. They work
better than any other pad on the market IMHO.
Chalo
> From a design perspective, it seems to me that (1) centerpulls are
> much more complicated than either single- or dual-pivot sidepulls;
More so than single-pivot, less so than dual-pivot as the pivots are
symmetrical and there is no proportioning mechanism.
> and (2) centerpulls are more prone to flex under the force of the rim
> acting on the brake pads, mainly due to flex in the hanger with the
> center bolt and pivots.
If you have developed such an impression, it was probably due to the
reach length of any centerpull brakes you have tried being well in
excess of whichever sidepull you were using for comparison.
Centerpulls locate the mechanical pivots, and their accompanying play,
further down the lever arm, for less effect on overall pad deflection
at the rim. The "bridge" element containing the pivot studs is
typically stouter than the analogous portion of sidepull arm.
> I've never tried centerpulls mounted on
> braze-ons, which might reduce or eliminate the flex problem. A number
> of people seem to claim this is the case, including Tony Oliver, Jan
> Heine and Grant Petersen. They've used 'em and I haven't, so at this
> point I have to take their word for it.
Brazed-on pivots work. That is the definitive difference between the
road bike centerpull as used during the bike boom, and the U-brake as
used during the 80s MTB craze. The stopping power of a U-brake dwarfs
that of any road bike brake ever made, and U-brakes were no more
difficult to set up than a road caliper.
Brazing centerpull pivots to the frame usually reduces the overhung
length by more than half, and it usually anchors the brake to a
stiffer piece of the frame than a centerbolt does. What flex remains
can be attenuated by a booster plate, unlike flex that occurs at a
centerbolt.
> Every decent brake- whether sidepull, centerpull, cantilever, V-brake,
> disc brake, drum brake, what have you- provides enough stopping power
> to make the wheel skid.
--in the rear, if you are a single lightweight rider on a
short-wheelbase upright bike without a heavy load. The incapacity of
the road caliper brake as furnished to provide more stopping power
when appropriate is its most serious shortcoming.
The ability of cantilever brakes, U-brakes (and other stud-mounted
centerpulls), v-brakes, and hydraulic rim brakes to be set up to
deliver more stopping power than most riders require is what makes
them versatile and valuable, even if it is of no benefit to most sport
riders.
Chalo Colina
Simon Brooke
> Certainly my sidepulls with non-aero levers take more effort to use
> than my dual pivot Campy Ergo brakes/levers. I don't remember what
> the centerpull lever feel was like. I will agree that all brakes are
> not equal from the practical, ergonomic perspective.
If you mean the classic 1970s style centrepull - the things Weinnman
made in such huge numbers - the answer has to be 'worryingly spongy',
presumably because of flex in the system. Still, they worked well
enough when all the competition was single-pivot calipers, and those,
in their turn, were infinitely superior to the roller-lever brakes
they superceded.
When I was a kid bicycle brakes that we had access to did not match
the sort of performance we could get out of our bikes downhill. We
certainly could not have locked wheels at speed. Forty years of
development really have achieved something.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; gif ye hes forget our auld plane Scottis quhilk your mother lerit you,
;; in tymes cuming I sall wryte to you my mind in Latin, for I am nocht
;; acquyntit with your Southeron
;; Letter frae Ninian Winyet tae John Knox datit 27t October 1563
David L. Johnson
> Though I've been critical of Grant Peterson's effort to revive centerpull
> brakes, I have to admit that the latest Rivendell Reader (#30) gave me
> reasons to pause.
My memories of center-pull brakes were not all that pleasant. I remember
when most racing bikes had them, in the late '60s. The competition, then,
were usually poorly-designed sidepulls, which would tend to rotate so that
one pad would drag on the rim. Campy sidepulls changed all that, and
everyone went for them despite the outrageous cost. They could be
properly centered fairly easily, and stayed where you put them.
Centerpulls depended on the balance of their springs to center them. Use
and dirt would make them one-sided as easily as old sidepulls. They also
were mushy, so that it was easy to bottom out the lever in a hard stop,
especially in wet weather.
Modern dual-pivot sidepulls, and probably the Campy single-pivot rear
brake, are much easier to adjust, stay where they are adjusted, and do an
excellent job. I also think that V brakes work quite well, and have the
advantage of huge tire clearance. The angle problem mentioned by Jobst
has not been a difficulty for me, but would be if you were not attentive
to pad wear. I know that modern cantilever brakes also are easy to
adjust, but they still have the variable-pull characteristic of old
center-pulls.
> dual-pivot sidepulls won't track an out-of-true rim the way all other
> brake types will.
Why would that be the case? I don't see how the mechanism would be that
different. Of course, dual-pivot brakes have short reach and so small
possible "tracking" distance, but they would have some capability.
> He says, "The long lever on the cable side [above the pivot, if I
> understand him correctly] and the short lever on the pad side [below the
> pivot] gives centerpulls a huge mechanical advantage over sidepulls.
The problem with this is that any increased mechanical advantage means
more cable pull for an equivalent motion of the pad, so the lever has to
have less mechanical advantage as a result. Net advantage, 0. You have
to be able to exert maximum force on the system before the lever bottoms
out, and you need the same open pad clearance on any brake. There isn't
enough room to increase the mechanical advantage and still have a usable
lever. You can decrease, slightly, pad clearance when the brake is open,
but that means the wheels have to be kept true. A broken spoke makes the
bike impossible to ride, not the best for a tour.
The only other factor that comes into play is arm flex, which centerpulls
had in spades.
--
David L. Johnson
__o | Let's not escape into mathematics. Let's stay with reality. --
_`\(,_ | Michael Crichton
(_)/ (_) |
Simon Brooke
> gil...@cs.ubc.ca (Donald Gillies) writes:
>
> > I have owned 2 bikes with centerpulls (raleigh grand prix, dawes
> > low-end), and 3 bikes with sidepulls (schwinn paramount, trek 500,
> > alan), and 1 bike with dual-pivot sidepulls (trek 2300) and one bike
> > with U-brakes (schwinn moab). I currently live on a very steep hill
> > in san diego, present. In terms of stopping power, this is where I
> > think that things stack up.
> >
> > sidepulls (campy) - worst
> > dual-pivots (shimano) - better
> > centerpulls - best
> >
> > U-brakes - hard to gauge since these are on a totally different kind
> > of (mountain) bike.
>
> Actually, U-brakes were just a new name for an old design"
> centerpulls. Take a close look, they are just centerpull brakes with
> a slightly different arm shape.
To be fair, the U brakes mount to bosses on the forks rather than to a
saddle which mounts to a bolt in the classic 'brake bolt'
position. This must make them rather stronger and less flexible (and
also probably lighter) than old-design centrepulls.
Gary Young
<snip>
> I have owned 2 bikes with centerpulls (raleigh grand prix, dawes
> low-end), and 3 bikes with sidepulls (schwinn paramount, trek 500,
> alan), and 1 bike with dual-pivot sidepulls (trek 2300) and one bike
> with U-brakes (schwinn moab). I currently live on a very steep hill
> in san diego, present. In terms of stopping power, this is where I
> think that things stack up.
>
> sidepulls (campy) - worst
> dual-pivots (shimano) - better
> centerpulls - best
>
> U-brakes - hard to gauge since these are on a totally different kind
> of (mountain) bike.
>
> It is worth pointing out that when i recently got the Alan bike with
> campy sidepulls, I immediately removed the campy pads and put new
> low-end pads on it, since the campy pads weren't working. I then took
> off the low end pads and bought premium oversized shimano pads, since
> the low-end pads weren't working. the premium (ultegra) pads just
> barely work. I am still very unhappy with the campy gran sport
> sidepull performance, and I feel jeopardized every time i go down the
> hill.
Have you compared all three brakes using the same pad? Or at least the
same make of pad?
>
> Campy and Shimano marketing hype aside, i think you can easily
> determine the most powerful brakes by looking historically at what got
> installed on tandem bicycles in the past. In the late 1960's and
> 1970's and 1980's, the choices were :
>
> cantilevers - best
> centerpulls - second best
>
> no sidepulls installed on tandems.
> even today, nobody puts dual-pivots on tandems.
Sheldon has a different take on that:
"Few tandems come equipped with caliper brakes these days, because it
is widely believed that caliper brakes don't have sufficient stopping
power for tandem service. This belief is incorrect. Tandems set up for
racing can get perfectly adequate braking from good quality caliper
brakes....
In the 1970's, center-pull caliper brakes were common, which did
provide reasonable tire clearance, but these have gone out of fashion
and are not provided on new bikes."
bfd
"Gary Young" <garyy...@hotmail.com> wrote in message
news:bfbe6ed3.03101...@posting.google.com...
Agree, Calfee's 28.5 lb *racing* tandem also uses sidepull caliper brakes
too:
http://www.calfeedesign.com/tandem.shtml
Of course, a "standard" Calfee tandem frame starts at $5300 and if you want
the deluxe Dragonfly Custom tandem frame, 6 lb tandem frame, it will cost
you $7400.....
Chalo
> ...sidepull brakes have the pad pivot above
> and only slightly (rim half width) offset from the braking surface so
> that there is essentially no position change as the pad sweeps through
> its wear life (cosine error). Centerpull and cantilever brakes
> approach the rim at nearly a 45 degree angle and have large vertical
> change throughout pad wear life,
This trait of stud-mounted brakes can be accomodated by adusting the
pad height as it wears. The pad rub on tire sidewalls exhibited by
single-pivot sidepulls, however, is due to the extreme fore-to-aft
flex these brakes display and can not reliably be adjusted away.
This horrible characteristic of single-pivot sidepull brakes is IMO
one of the reasons for the annoying move to "short reach" road
calipers-- because the stubby arms of those brakes are somewhat
resistant to allowing sidewall rub for most average-sized riders.
> the centerpull goes into the tire as it wears
> and offers no advantages whatsoever.
When mounted on frame studs, it offers vastly superior maximum
stopping power to any caliper brake. I know this because I have bent
many forks under the braking forces generated by U-brakes. Before
applying stopping power like that, caliper brakes become so twisted
out of shape that applying more cable tension does not result in more
braking.
> Flex in any part of the system eats up hand lever stroke.
Insufficient stroke length can be addressed by using levers that pull
more cable, and pulling them harder. However, the swinging flex
endemic to all centerbolt-mounted brakes, and the torsional flex that
is particularly pronounced in single-pivot brakes, act
disproportionately to diminish the braking that can be applied
regardless of how hard or how far the cable is pulled.
The "ceiling" on stopping force resulting from flex-related distortion
of the brake mechanism is lower, and more abrupt, with single-pivot
calipers than with any other type of brake.
> > He notes that centerpulls don't stick out to the side like
> > sidepulls.
>
> How far??? What is the issue here anyway.
I have seen enough bikes damaged by the sidepull brake arm bashing
into the downtube to think of that design characteristic as a
liability.
> > He says that even the standard-reach (what would be called
> > long-reach by most) dual-pivot brakes offered by Shimano don't leave
> > much room for fenders. Is that true?
>
> NO.
It is true if you wish to run decent-sized tires and fenders at the
same time. Even the most careful brake placement will not allow
"standard reach" dual-pivot calipers to encompass 38mm tires with
fenders.
> The sidepull brake is the obvious mechanism for road
> bicycles to all who understand mechanical design. All this other
> stuff is amateur thinking guided by misunderstanding of the concept.
Sorry, but that's just not true. It might be "the obvious mechanism"
if one is unconcerned about generating the most stopping force from a
given amount of brake, and if one disregards the benefits of
voluminous tires, and if one happily tolerates pad rub due to a brake
design that can not be centered accurately. But most "who understand
mechanical design" demand (or at least desire) better performance than
that!
Getting the brake pivot as close as practiceable to the pads pays huge
dividends in turning lever force into stopping force. That very
translation is exactly where single-pivot calipers are so weak. They
only provide an approximately linear relationship between lever force
and braking force up to a point-- a point easily exceeded by many
riders in many circumstances.
Add to this the inherent characteristic of them being impossible to
center consistently, and it's not at all obvious that they are
superior to the worst of other brake designs, let alone the best of
them.
> Now let's hear it again concisely. What are the advantages?
Concisely? Stopping. Centering.
Chalo Colina
jobst....@stanfordalumni.org
> My memories of center-pull brakes were not all that pleasant. I
> remember when most racing bikes had them, in the late '60s. The
> competition, then, were usually poorly-designed sidepulls, which
> would tend to rotate so that one pad would drag on the rim. Campy
> sidepulls changed all that, and everyone went for them despite the
> outrageous cost. They could be properly centered fairly easily, and
> stayed where you put them.
I use those brakes today and find that they are as prone to going off
center as well as any sliding return spring brake. That is one thing
Campagnolo did not address but used the same return spring shape that
was the downfall of all other sidepull brakes. This is the dual
"ram's horn" shape, whose ends rotate about the center of the "ram's
horn" instead of the pivot bolt.
I was glad to see that the new Mavic side pull brake that I saw at
InterBike has solved this problem and has a no-slide return spring.
If you want to see how bad others are, note that Campagnolo and
Shimano have a special sleeve in which the spring slides like a
piston. This gets full of fine grit and changes the return force, the
problem with non-dual pivot brakes.
> Centerpulls depended on the balance of their springs to center them.
> Use and dirt would make them one-sided as easily as old sidepulls.
> They also were mushy, so that it was easy to bottom out the lever in
> a hard stop, especially in wet weather.
That is the reason for having dual pivots.
Their reasonably good centering may be the only sliver of benefit of
the centerpull configuration. It arises from its use of "torsion"
springs around the pivot bolts, and the short straddle cable that puts
a strong bias on returning to center almost as if it were made of a
rigid two bar linkage. To go off center the straddle cable would need
to slide in the cable yoke.
> Modern dual-pivot sidepulls, and probably the Campy single-pivot
> rear brake, are much easier to adjust, stay where they are adjusted,
> and do an excellent job. I also think that V brakes work quite
> well, and have the advantage of huge tire clearance. The angle
> problem mentioned by Jobst has not been a difficulty for me, but
> would be if you were not attentive to pad wear. I know that modern
> cantilever brakes also are easy to adjust, but they still have the
> variable-pull characteristic of old center-pulls.
No current single pivot brake centers well because they all use the
traditional "ram's horn" coil return spring.
>> dual-pivot sidepulls won't track an out-of-true rim the way all
>> other brake types will.
> Why would that be the case? I don't see how the mechanism would be
> that different. Of course, dual-pivot brakes have short reach and
> so small possible "tracking" distance, but they would have some
> capability.
It's not whether it should or not. The brake pads cannot move
independently of the other. That is the reason for these brakes...
to always remain centered. If you doubt it, try pushing the wheel
sideways with the brake applied. Open the QR so the wheel can move if
it wants to.
>> He says, "The long lever on the cable side [above the pivot, if I
>> understand him correctly] and the short lever on the pad side
>> [below the pivot] gives centerpulls a huge mechanical advantage
>> over sidepulls.
You'll notice that this ratio is 2:1 and that half the force goes to
each side resulting in a caliper ratio of 1:1. I wrote an article
about that in the 1970's for Bike World.
> The problem with this is that any increased mechanical advantage
> means more cable pull for an equivalent motion of the pad, so the
> lever has to have less mechanical advantage as a result. Net
> advantage, 0. You have to be able to exert maximum force on the
> system before the lever bottoms out, and you need the same open pad
> clearance on any brake. There isn't enough room to increase the
> mechanical advantage and still have a usable lever. You can
> decrease, slightly, pad clearance when the brake is open, but that
> means the wheels have to be kept true. A broken spoke makes the
> bike impossible to ride, not the best for a tour.
Today's road bicycles are dead in the water with a broken spoke, tire
clearance in the frame or fork being almost that of brake pad
clearance. This plays to the short bike, fast cornering aficionados.
Everything has got to be as tightly packed as possible.
> The only other factor that comes into play is arm flex, which
> centerpulls had in spades.
... to make up for all the positive features they didn't have.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> ...sidepull brakes have the pad pivot above and only slightly (rim
>> half width) offset from the braking surface so that there is
>> essentially no position change as the pad sweeps through its wear
>> life (cosine error). Centerpull and cantilever brakes approach the
>> rim at nearly a 45 degree angle and have large vertical change
>> throughout pad wear life,
> This trait of stud-mounted brakes can be accommodated by adjusting the
> pad height as it wears. The pad rub on tire sidewalls exhibited by
> single-pivot sidepulls, however, is due to the extreme fore-to-aft
> flex these brakes display and can not reliably be adjusted away.
> This horrible characteristic of single-pivot sidepull brakes is IMO
> one of the reasons for the annoying move to "short reach" road
> calipers-- because the stubby arms of those brakes are somewhat
> resistant to allowing sidewall rub for most average-sized riders.
Wait a minute, this is a geometric given, there is nothing you can do
to the motion of the pad because it sweeps around its pivot and that
pivot lies in the wrong place. Therefore when descending in bad
weather, pads wear and sweep upward if the pivot point is above and
outside of the tire. Cantilevers do the opposite and sweep downward,
the angle of attack of both being roughly 45 degrees instead of near
zero of a good sidepull.
>> the centerpull goes into the tire as it wears and offers no
>> advantages whatsoever.
> When mounted on frame studs, it offers vastly superior maximum
> stopping power to any caliper brake. I know this because I have
> bent many forks under the braking forces generated by U-brakes.
> Before applying stopping power like that, caliper brakes become so
> twisted out of shape that applying more cable tension does not
> result in more braking.
OK, if you say so but you'll have to do some measurements to convince
me. Regardless of where they are mounted, the mechanical advantage
cannot be higher than the average human reach allows. You seem to be
using hyperbole in that description. A brake that operates at the
yield point will break off in short order. I have never seen a
caliper that was bent from braking and I don't expect to see one.
>> Flex in any part of the system eats up hand lever stroke.
> Insufficient stroke length can be addressed by using levers that
> pull more cable, and pulling them harder. However, the swinging
> flex endemic to all center bolt-mounted brakes, and the torsional
> flex that is particularly pronounced in single-pivot brakes, act
> disproportionately to diminish the braking that can be applied
> regardless of how hard or how far the cable is pulled.
Levers that pull more cable are ones that have a lower mechanical
advantage. You can't have both or we wouldn't use power brakes on
cars. I don't know what torsional flex you are referring to but it
isn't large. The toe-in of brake pads arises from pad rotation due to
clearance and flex. That isn't much.
> The "ceiling" on stopping force resulting from flex-related
> distortion of the brake mechanism is lower, and more abrupt, with
> single-pivot calipers than with any other type of brake.
To what do you attribute this claim. I'm not sure what you mean by
the ceiling anyway. Could you expand on that.
>>> He notes that centerpulls don't stick out to the side like
>>> sidepulls.
>> How far??? What is the issue here anyway.
> I have seen enough bikes damaged by the sidepull brake arm bashing
> into the downtube to think of that design characteristic as a
> liability.
I guess we'll have to live with that as we do with drinking glasses
being brittle. I've been riding sidepull brakes a long time and have
not had one damaged. Neither mine or those of my riding companions.
>>> He says that even the standard-reach (what would be called
>>> long-reach by most) dual-pivot brakes offered by Shimano don't
>>> leave much room for fenders. Is that true?
>> NO.
> It is true if you wish to run decent-sized tires and fenders at the
> same time. Even the most careful brake placement will not allow
> "standard reach" dual-pivot calipers to encompass 38mm tires with
> fenders.
OK, I recall even back when brakes had far more clearance, split
fenders that went to the back of the fork and continued from the
brake bolt forward were the rave it you had to have racing brakes.
>> The sidepull brake is the obvious mechanism for road bicycles to
>> all who understand mechanical design. All this other stuff is
>> amateur thinking guided by misunderstanding of the concept.
> Sorry, but that's just not true. It might be "the obvious
> mechanism" if one is unconcerned about generating the most stopping
> force from a given amount of brake, and if one disregards the
> benefits of voluminous tires, and if one happily tolerates pad rub
> due to a brake design that can not be centered accurately. But most
> "who understand mechanical design" demand (or at least desire)
> better performance than that!
I qualified that with road bicycle, but I probably should have said
28mm tires or smaller. Even then, larger calipers are available from
people other than Campagnolo or Shimano. The point is that the side
pull, or more accurately, the center pivot-bolt brake offers the best
mechanism for bringing brake pads into contact with the rim.
> Getting the brake pivot as close as practiceable to the pads pays
> huge dividends in turning lever force into stopping force. That
> very translation is exactly where single-pivot calipers are so weak.
> They only provide an approximately linear relationship between lever
> force and braking force up to a point-- a point easily exceeded by
> many riders in many circumstances.
That is not the place where leverage needs to be gained. Besides tire
size demands that centerpull and cantilever (and their derivatives)
have their mounts far enough away so the wheel can be removed without
letting the air out. This puts the pivot point at an undesirable
location that makes the pad move at a steep angle across the braking
surface.
> Add to this the inherent characteristic of them being impossible to
> center consistently, and it's not at all obvious that they are
> superior to the worst of other brake designs, let alone the best of
> them.
Ah, but they can be centered as you can see on the new Mavic brake that
uses a spring that doesn't slide and suffer from friction variation,
the cause of off center brakes.
>> Now let's hear it again concisely. What are the advantages?
> Concisely? Stopping. Centering.
Somehow the stopping part is a mystery to me. I and the many riders
with whom I have ridden have taken a lot of steep and long descents
over many years and have not had a problem with that, yet you say they
stop better. Better than what? I can raise the rear wheel on
descents. I don't need more leverage.
Jobst Brandt
jobst....@stanfordalumni.org
Marcus Coles
>
> He says that even the standard-reach (what would be called long-reach
> by most) dual-pivot brakes offered by Shimano don't leave much room
> for fenders. Is that true? Just how big a tire would you have to run
> before you would crowd out the dual pivots? (Elsewhere in the Reader,
> Grant says that centerpulls will clear a 40mm tire or a 38mm tire with
> fenders; what's the limit with the current long-reach dual pivots?)
> Furthermore, why not long-reach single-pivots, which are still
> available?
>
While I have no doubt that mast centre-pulls will clear a 38mm or 40mm
tire and fender, one might have one heck of a time getting said tire
past the brake pads on some traditional centre-pulls. Unless the tire
was deflated or possibly V-brake pads were used.
Surely some of us can remember barely squeezing a fat 27 x 1 1/4" tire
past the pads in the good old days even with the QR or straddle released.
In my book the biggest selling points for centre-pull brakes when they
were popular were the aethetic symmetry and the fact that the village
idiot assembling bikes at the local hardware/sports/department store
could centre the brakes.
Prior to that point most people had only be exposed to coaster brakes or
poorly installed sidepull brakes that were forever rubbing one side of
the rim.
In my experience with the exception of rod brakes with leather pads.
Any bicycle brake I have tried can be set up to stop well in the dry for
at least a few stops. Including the stamped steel sidepulls that want
to rub the one side of the rim ;-)
IMHO the most important things become the ease of modulation and
repeatability.
Marcus
Donald Gillies
>You'll notice that this ratio is 2:1 and that half the force goes to
>each side resulting in a caliper ratio of 1:1. I wrote an article
>about that in the 1970's for Bike World.
This just shows that you can get anything published at all. Such
generalizations are clearly unwarranted, which is easily seen just by
looking at the variation in calipers within one brand such as
weinmann. The weinmann 750 had more mechanical advantage than the
weinmann 610. The earlier 610's had less mechanical advantage than
the later 610's, by virtue of the shorter upper arms in the calipers,
and a straddle wire and carrier that was designed to rest higher above
the caliper than the later straddle carriers.
The mechanical advantage varies _more_ over the stroke of the
centerpull brake, and the ideal brake has a high mechanical advantage
early in the stroke, and a low mechanical advantage late in the
stroke. This gets the pad to the rim quickly, then allows you to
easily modulate stopping force once you touch the rim. This is how
centerpulls and cantilevers work, and its why they are easier to
control and were the most popular brakes in the 1970's.
http://www.sheldonbrown.com/cantilever-geometry.html#vbrake
In my opinion, campy did everyone a disservice by popularizing the
lightweight short reach sidepull caliper, and it has taken almost a
generation to twist the centerpull caliper over to the side of the
brake (e.g. dual pivot) and produce a brake with almost the same
modulation in mechanical advantage and therefore to undo the damage
that campagnolo had wrought in the 1970's.
Tim McNamara
> Tim McNamara <tim...@bitstream.net> writes:
>
> > Actually, U-brakes were just a new name for an old design"
> > centerpulls. Take a close look, they are just centerpull brakes
> > with a slightly different arm shape.
>
> To be fair, the U brakes mount to bosses on the forks rather than to
> a saddle which mounts to a bolt in the classic 'brake bolt'
> position. This must make them rather stronger and less flexible (and
> also probably lighter) than old-design centrepulls.
Centerpulls mounted on brazed-on bosses were pretty much the standard
on randonee bikes and bikes custom built for touring and such for a
good few years. Those are basically identical to the U-brake,
although the latter was for some odd reason often mounted under the
chain stays. I think it was precisely the discussion of centerpulls
on brazed-on bosses in the Rivendell Reader that sparked this thread.
jobst....@stanfordalumni.org
>> You'll notice that this ratio is 2:1 and that half the force goes
>> to each side resulting in a caliper ratio of 1:1. I wrote an
>> article about that in the 1970's for Bike World.
> This just shows that you can get anything published at all. Such
> generalizations are clearly unwarranted, which is easily seen just
> by looking at the variation in calipers within one brand such as
> Weinmann. The Weinmann 750 had more mechanical advantage than the
> Weinmann 610. The earlier 610's had less mechanical advantage than
> the later 610's, by virtue of the shorter upper arms in the
> calipers, and a straddle wire and carrier that was designed to rest
> higher above the caliper than the later straddle carriers.
I think you'll find that they did not have different ratios because
their lever ratios were the same. You'll need to make some
measurements as I did to verify what the MA is. Often different pads
or pad clearance give the brake a different feel. Typically, when a
brake lever is close to the end of its travel, one suddenly notices
how much sponge there is in the remaining stroke.
> The mechanical advantage varies _more_ over the stroke of the
> centerpull brake, and the ideal brake has a high mechanical
> advantage early in the stroke, and a low mechanical advantage late
> in the stroke. This gets the pad to the rim quickly, then allows
> you to easily modulate stopping force once you touch the rim. This
> is how centerpulls and cantilevers work, and its why they are easier
> to control and were the most popular brakes in the 1970's.
> http://www.sheldonbrown.com/cantilever-geometry.html#vbrake
I think you'll find that the difference is insignificant unless you
run with excess pad clearance so that there is a large caliper motion,
an undesirable effect in any brake. This is why brake centering is
more important than some brake people seem to think. The dual pivot
is specifically aimed at that problem.
> In my opinion, Campy did everyone a disservice by popularizing the
> lightweight short reach sidepull caliper, and it has taken almost a
> generation to twist the centerpull caliper over to the side of the
> brake (e.g. dual pivot) and produce a brake with almost the same
> modulation in mechanical advantage and therefore to undo the damage
> that Campagnolo had wrought in the 1970's.
The whole short reach phenomenon was driven by frame builders and
their marketeers who played on the "close coupled", "tight", etc
spoiler on the family sedan gimmick. Campagnolo only made the
equipment to go on these bicycles. However, the short reach brake had
the same mechanical advantage of the standard reach brake. You can
verify that by simple measurements with a ruler.
Jobst Brandt
jobst....@stanfordalumni.org
Jeff Wills
Tim McNamara <tim...@bitstream.net> wrote in message news:<m265ipf...@localhost.bitstream.net>...
I'll offer my subjective impressions: in the past week I've ridden 3
different bikes over the same roads (although weather conditions have
been variable).
They've been:
1. Converted Raleigh (now single-speed) with centerpull calipers,
Kool-Stop salmon shoes, and Dia Compe SS-5 levers
2. K2 full-suspension mountain bike with Performance "Topo"
(presumably Tektro) "V"-brakes
3. Tour Easy recumbent with Shimano RX100 dual-pivot sidepull front,
Dia-Compe 986 cantilever rear, Kool-Stop salmon shoes, and Dia-Compe
SS-7 levers
Of those the best "feel" (by far) is with the V-brakes. There is very
little travel in the lever after the pads contact the rim and
modulation is excellent. I think this is primarily due to the minimal
brake pad that came with them. I also think that the large section
aluminum frame helps by keeping flex to a minimum.
The centerpull brakes on the Raleigh are quite good for braking power,
but there's lots of flex in the calipers. I can squeeze the levers
and watch the horizontal portion of the arms rise and fall. It's
disconcerting to squeeze the lever and have the bike's deceleration
improve only a bit.
The Tour Easy has a split personality (no surprise). The RX100 caliper
is stiff and modulates well, while the 986 cantilever mounted on the
chainstays modulates poorly. It's almost intolerably mushy- most of
which I attribute to the brake's mount: it's on the underside of the
chainstays, which lack any kind of bridge to keep them from spreading.
I regard the rear brake as a speed controller, reserving the front
brake for serious stopping.
In the interests of full disclosure: I'm 6-foot-4 (like Tim), hover
around 215 pounds, and I've been a bike mechanic for a couple decades.
The bikes in question are in good but not identical condition.
Jeff Wills
Donald Gillies
>The Tour Easy has a split personality (no surprise). The RX100 caliper
>is stiff and modulates well, while the 986 cantilever mounted on the
>chainstays modulates poorly. It's almost intolerably mushy- most of
>which I attribute to the brake's mount: it's on the underside of the
>chainstays, which lack any kind of bridge to keep them from spreading.
> I regard the rear brake as a speed controller, reserving the front
>brake for serious stopping.
I think this suggests that brake-lever action is a matter of feel and
taste more than anything else.
Once the pads touch the rim, i still want my lever travel to be LARGE
so that I have LOTS OF OPPORTUNITY to fine-tune the pressure on the
rims. Some people might attribute this as "mush" but with well-built
centerpull cable stops (weinmann front, raleigh circular brake bridge
in the rear), i do not feel that a weinmann centerpull is mushy. The
"mush" that some people deride is influenced by pad compression, rim
compression, and flex in the caliper arms and cables, and even in the
lever.
I do not like a brake where, once I get to the rim, a 1 mm movement in
the lever will lock the front wheel. Apparently, some people like
this but I do not like it. I especially do not like it on steep
downhill grades where braking precision is doubly important compared
to the flats of the midwest. On a steep downhill you are doubly in
jeopardy in terms of flying over the handlebars. In the midwest,
where i grew up, it's much harder to go over the handlebars with your
front brakes.
Tom Ace
> The mechanical advantage varies _more_ over the stroke of the
> centerpull brake, and the ideal brake has a high mechanical advantage
> early in the stroke, and a low mechanical advantage late in the
> stroke. This gets the pad to the rim quickly, then allows you to
> easily modulate stopping force once you touch the rim. This is how
> centerpulls and cantilevers work, and its why they are easier to
> control and were the most popular brakes in the 1970's.
I don't agree that varying mechanical advantage is desirable.
A brake with varying advantage will give different results depending
on rim width and pad thickness (the latter declining as the pad wears).
What I remember from the '70s was buyers looking at centerpulls and
thinking that symmetry had to be better. "They press evenly on both
sides of the rim" was a common remark.
Remember also that the competition at the time included some sidepulls
that weren't so great (for reasons that were not inherent to sidepulls,
but not everyone knew that). I had a Raleigh with a steel-caliper
sidepull brake where the only way to center it was to bend the springs.
I don't believe that varying advantage was responsible for the
popularity of centerpull brakes in the '70s.
Tom Ace
David L. Johnson
> I do not like a brake where, once I get to the rim, a 1 mm movement in the
> lever will lock the front wheel.
I don't think the be-all of "brake modulation" is lever movement. It's
response to changes in braking pressure. If you squeeze as hard as
you can, the brake should really grab, no matter how much or little the
lever moves, and if you pull lightly, it should brake lightly.
--
David L. Johnson
__o | "What am I on? I'm on my bike, six hours a day, busting my ass.
_`\(,_ | What are you on?" --Lance Armstrong
(_)/ (_) |
Tim McNamara
> Once the pads touch the rim, i still want my lever travel to be
> LARGE so that I have LOTS OF OPPORTUNITY to fine-tune the pressure
> on the rims. Some people might attribute this as "mush" but with
> well-built centerpull cable stops (weinmann front, raleigh circular
> brake bridge in the rear), i do not feel that a weinmann centerpull
> is mushy. The "mush" that some people deride is influenced by pad
> compression, rim compression, and flex in the caliper arms and
> cables, and even in the lever.
There's a number of places for perceptible flex in both centerpull and
sidepull brakes: cable housing compression, cable stretch, brake arm
flex and pad compression. I strongly suspect that rim compression is
negligible as is lever flex (although there are so many different
levers that YMMV).
Both sidepull and centerpull brakes are subject to flex induced by the
brake pads being dragged by the rim. Cenerpulls offer more sources of
flex, however: the straddle wire, the cable hangers, and the "bridge
plate" with the centerbolt and pivots; none of these exist in sidepull
brakes. Then there's the issue of centerbolt flexing and rocking
movements of the brake arms on their pivots (whether the centerbolt in
the case of sidepulls or the pivots in the case of centerpulls).
Basically, centerpull brakes offer more opportunities for loss of
efficiency through flex than is the case with sidepulls. Add to that
the truism that most centerpulls were of poor quality design and
construction in the first place, being sold on cheap bikes, and I
think that in part explains their fall from favor. I seriously doubt
that sidepulls would have replaced centerpulls if their performance
was as inferior as some of the centerpull supporters have claimed.
Bad designs have cropped up in bicycling and have tended to fall
by the wayside.
> I do not like a brake where, once I get to the rim, a 1 mm movement
> in the lever will lock the front wheel. Apparently, some people
> like this but I do not like it. I especially do not like it on
> steep downhill grades where braking precision is doubly important
> compared to the flats of the midwest.
Yes, I agree. This is the "power brake" feel that I mentioned several
posts back. People are used to this sort of sensation in car brakes,
and wrongly think that bike brakes ought to have a similar feel.
jobst....@stanfordalumni.org
>> I do not like a brake where, once I get to the rim, a 1 mm movement
>> in the lever will lock the front wheel.
> I don't think the be-all of "brake modulation" is lever movement.
> It's response to changes in braking pressure. If you squeeze as
> hard as you can, the brake should really grab, no matter how much or
> little the lever moves, and if you pull lightly, it should brake
> lightly.
Or to put it another way, brakes are force transducers not motion
transducers (as shift levers are). The ideal brake would have no
travel and a fixed mechanical advantage so that braking would be
proportional to hand lever pressure. Most automobile brakes approach
that concept once pad clearance is taken up. I sense that bicycle
brake manufacturers are not aware of this ideal and don't attempt to
reduce unnecessary hand lever travel any more than is needed to apply
the brake when pad clearance is ideal.
With the higher mechanical advantage of dual pivot brakes, some brakes
have insufficient pad adjustment to wear more than half the material
before they reach the stop.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> Once the pads touch the rim, i still want my lever travel to be
>> LARGE so that I have LOTS OF OPPORTUNITY to fine-tune the pressure
>> on the rims. Some people might attribute this as "mush" but with
>> well-built centerpull cable stops (Weinmann front, Raleigh circular
>> brake bridge in the rear), i do not feel that a Weinmann centerpull
>> is mushy. The "mush" that some people deride is influenced by pad
>> compression, rim compression, and flex in the caliper arms and
>> cables, and even in the lever.
> There's a number of places for perceptible flex in both centerpull
> and sidepull brakes: cable housing compression, cable stretch, brake
> arm flex and pad compression. I strongly suspect that rim
> compression is negligible as is lever flex (although there are so
> many different levers that YMMV).
I think it would be appropriate to dump "cable stretch" into the same
garbage can as "chain stretch" because cables do not measurably
stretch. The cable "sponge" comes from cable housing compression,
arising mostly from bends and stretches that straighten out under
cable tension. Cable bends that change radius also change effective
cable length because the metal coil on the inside of bends is solid
while the outside opens making the middle of the housing where the
cable runs change length.
> Both sidepull and centerpull brakes are subject to flex induced by
> the brake pads being dragged by the rim. Centerpulls offer more
> sources of flex, however: the straddle wire, the cable hangers, and
> the "bridge plate" with the center bolt and pivots; none of these
> exist in sidepull brakes. Then there's the issue of center bolt
> flexing and rocking movements of the brake arms on their pivots
> (whether the center bolt in the case of sidepulls or the pivots in
> the case of centerpulls).
The flex in centerpull brakes arises from bearing clearance at the
pivots and bending in the bridge. The straddle cable has no effect on
pad angle, the angle that causes toe-in of worn in pads.
> Basically, centerpull brakes offer more opportunities for loss of
> efficiency through flex than is the case with sidepulls. Add to
> that the truism that most centerpulls were of poor quality design
> and construction in the first place, being sold on cheap bikes, and
> I think that in part explains their fall from favor. I seriously
> doubt that sidepulls would have replaced centerpulls if their
> performance was as inferior as some of the centerpull supporters
> have claimed. Bad designs have cropped up in bicycling and have
> tended to fall by the wayside.
I think the Mafac, Universal and Weinmann centerpull brakes were
reasonably good for what they were but that didn't make up for the
inherent disadvantages that have been outlined here.
>> I do not like a brake where, once I get to the rim, a 1 mm movement
>> in the lever will lock the front wheel. Apparently, some people
>> like this but I do not like it. I especially do not like it on
>> steep downhill grades where braking precision is doubly important
>> compared to the flats of the Midwest.
> Yes, I agree. This is the "power brake" feel that I mentioned
> several posts back. People are used to this sort of sensation in
> car brakes, and wrongly think that bike brakes ought to have a
> similar feel.
I disagree. Brakes should have that response, but they must be
linear, not progressive. That is a subject we've visited often before
and is covered in the FAQ.
Jobst Brandt
jobst....@stanfordalumni.org
Helmut Springer
> one thing Campagnolo did not address but used the same return
> spring shape that was the downfall of all other sidepull brakes.
> This is the dual "ram's horn" shape, whose ends rotate about the
> center of the "ram's horn" instead of the pivot bolt.
Actually my SunTour GPX sidepulls have one central spiral spring
that doesn't slide. Stays centered pretty well. Out of production
for quite some time, ok.
> I was glad to see that the new Mavic side pull brake that I saw at
> InterBike has solved this problem and has a no-slide return
> spring.
How did they solve the problem?
--
MfG/Best regards
helmut springer
Benjamin Weiner
> The mechanical advantage varies _more_ over the stroke of the
> centerpull brake, and the ideal brake has a high mechanical advantage
> early in the stroke, and a low mechanical advantage late in the
> stroke. This gets the pad to the rim quickly, then allows you to
> easily modulate stopping force once you touch the rim. This is how
> centerpulls and cantilevers work, and its why they are easier to
> control and were the most popular brakes in the 1970's.
> http://www.sheldonbrown.com/cantilever-geometry.html#vbrake
Conventionally, mechanical advantage is the ratio
force out / force in, or equivalently lever movement in / out.
In that sense, a typical caliper or cantilever brake system
has an MA of about 4. It appears that your definitions are mixed.
In the conventional definition, the MA of a cantilever or centerpull
decreases somewhat through the stroke because the yoke angle increases
(as defined on Sheldon's webpage). Therefore the brake behaves
oppositely to what you consider desirable. In practice, they are
usable anyway.
AFAIK, brakes with varying mechanical advantage have never been a
great success; I have a Suntour Rollercam rear brake and it stops the
bike, but it's a nuisance in other ways.
> In my opinion, campy did everyone a disservice by popularizing the
> lightweight short reach sidepull caliper, and it has taken almost a
> generation to twist the centerpull caliper over to the side of the
> brake (e.g. dual pivot) and produce a brake with almost the same
> modulation in mechanical advantage and therefore to undo the damage
> that campagnolo had wrought in the 1970's.
Do dual pivots have any modulation in MA? It isn't clear to me
that they do. They have dual pivots like a centerpull, but no
straddle cable.
Simon Brooke
> I qualified that with road bicycle, but I probably should have said
> 28mm tires or smaller. Even then, larger calipers are available from
> people other than Campagnolo or Shimano. The point is that the side
> pull, or more accurately, the center pivot-bolt brake offers the best
> mechanism for bringing brake pads into contact with the rim.
Fundamentally because the distance between the pivot bolt and the pad
is greater, so the arc swept is of a greater diameter? Are you
ignoring for this discussion hydraulic-type rim brakes (e.g. Magura)
where the piston drives the pad linearly in a path normal to the rim?
Simon Brooke
> David L. Johnson writes:
>
> >> I do not like a brake where, once I get to the rim, a 1 mm movement
> >> in the lever will lock the front wheel.
>
> > I don't think the be-all of "brake modulation" is lever movement.
> > It's response to changes in braking pressure. If you squeeze as
> > hard as you can, the brake should really grab, no matter how much or
> > little the lever moves, and if you pull lightly, it should brake
> > lightly.
>
> Or to put it another way, brakes are force transducers not motion
> transducers (as shift levers are). The ideal brake would have no
> travel and a fixed mechanical advantage so that braking would be
> proportional to hand lever pressure. Most automobile brakes approach
> that concept once pad clearance is taken up. I sense that bicycle
> brake manufacturers are not aware of this ideal and don't attempt to
> reduce unnecessary hand lever travel any more than is needed to apply
> the brake when pad clearance is ideal.
Indeed. The Hayes hydraulic disks on my hill bike have quite limited
lever travel, but are exceedingly controlable and have plenty of
'feel'. Contrast the Weinnman centrepulls on my partner's old Raleigh,
where the lever continues to travel after the pads are fully engaged -
most of this travel being apparently due to flex in the crossed over
levers.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
... a mild, inoffensive sadist...
jobst....@stanfordalumni.org
>> one thing Campagnolo did not address but used the same return
>> spring shape that was the downfall of all other sidepull brakes.
>> This is the dual "ram's horn" shape, whose ends rotate about the
>> center of the "ram's horn" instead of the pivot bolt.
> Actually my SunTour GPX sidepulls have one central spiral spring
> that doesn't slide. Stays centered pretty well. Out of production
> for quite some time, OK.
They all have one spring. The problem is that he spring has a "ram's
horn" coil on either side of the pivot bolt that constitute the center
of rotation of the spring ends. If your brake does not have such a
spring, I would be interested to know what shape the spring is.
>> I was glad to see that the new Mavic side pull brake that I saw at
>> InterBike has solved this problem and has a no-slide return spring.
> How did they solve the problem?
The spring is a single smooth band that reaches from an anchor point
on the short arm to a "sliding point" at the long brake arm where it
doesn't slide due to its bending pint in the center over the anchor
bolt. It is elegantly positioned covering the split between the two
arms of the brake.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> I qualified that with road bicycle, but I probably should have said
>> 28mm tires or smaller. Even then, larger calipers are available
>> from people other than Campagnolo or Shimano. The point is that
>> the side pull, or more accurately, the center pivot-bolt brake
>> offers the best mechanism for bringing brake pads into contact with
>> the rim.
> Fundamentally because the distance between the pivot bolt and the
> pad is greater, so the arc swept is of a greater diameter? Are you
> ignoring for this discussion hydraulic-type rim brakes (e.g. Magura)
> where the piston drives the pad linearly in a path normal to the
> rim?
Yes, I take this thread to be concerned with mechanical brakes.
Hydraulic brakes are immune to most of the foibles of mechanical
brakes but have other problems that make them a separate discussion
that should not get mixed with this one.
Jobst Brandt
jobst....@stanfordalumni.org
Gary Young
<snip>
> Brazed-on pivots work. That is the definitive difference between the
> road bike centerpull as used during the bike boom, and the U-brake as
> used during the 80s MTB craze. The stopping power of a U-brake dwarfs
> that of any road bike brake ever made, and U-brakes were no more
> difficult to set up than a road caliper.
>
Aren't U-brakes still widely available in the BMX market? If so, is
there any advantage in reviving bike-boom centerpulls (as Grant
Petersen is proposing)? I suppose they would be lighter than U-brakes
if mounted on braze-on studs, but the tenor of this discussion seems
to be that they were often too light (i.e., too flexy).
Jeff Wills
<snip>
> Brazed-on pivots work. That is the definitive difference between the
> road bike centerpull as used during the bike boom, and the U-brake as
> used during the 80s MTB craze. The stopping power of a U-brake dwarfs
> that of any road bike brake ever made, and U-brakes were no more
> difficult to set up than a road caliper.
>
U-brakes are simply centerpull brakes with much beefier arms and
shorter straddle cables. I doubt the center "bridge" of an old-style
road centerpull flexes much. On mine, the crossed arms bend upwards
in response to brake lever pressure. On MTB-style U-brakes, the
crossed arms are at least 4 times larger.
Jeff
Marcus Coles
My mid 80's Bridgestone SC sidepulls also lack the ram's horn springs.
I believe these like the SunTour GPX were actually made by Dia-Compe.
They stay pretty well centered and appear to have a 3rd. arm, I imagine
for centering.
Rear brake pictured in place, sorry no movies ;-)
I didn't really want to pull it apart for pics or to figure out how it
works, until it stops working.
http://www.ody.ca/~marcoles/Brake.jpg
http://www.ody.ca/~marcoles/Brake%2001.jpg
http://www.ody.ca/~marcoles/Brake%2002.jpg
http://www.ody.ca/~marcoles/Brake%2003.jpg
Work well enough for me even with the pads near the bottom of the slots.
AFAIK also long out of production.
Marcus
Pete Biggs
> I was glad to see that the new Mavic side pull brake that I saw at
> InterBike has solved this problem and has a no-slide return spring.
> If you want to see how bad others are, note that Campagnolo and
> Shimano have a special sleeve in which the spring slides like a
> piston. This gets full of fine grit and changes the return force, the
> problem with non-dual pivot brakes.
I have a pair of 1997 Campagnolo Avanti single pivot calipers which have
those sleeves. I use one of the brakes but have never used the other one.
The sleeves move *with* the spring in the unused brake but within it in
the used one. I assume the sleeve is suppose to reduce friction against
the arm but eventually comes loose after some use - perhaps after too much
liberal lubrication/cleaning.
In any case, this model works and stays centered much better than the old
unbranded steel single pivot side pulls I used before on cheap bikes.
I like to use a dual pivot front brake for the light action and a single
pivot rear to help with pad clearance and modulation, and the weight
saving is a bonus.
~PB
Tim McNamara
> My mid 80's Bridgestone SC sidepulls also lack the ram's horn
> springs. I believe these like the SunTour GPX were actually made by
> Dia-Compe. They stay pretty well centered and appear to have a
> 3rd. arm, I imagine for centering.
>
> Rear brake pictured in place, sorry no movies ;-) I didn't really
> want to pull it apart for pics or to figure out how it works, until
> it stops working.
>
> http://www.ody.ca/~marcoles/Brake.jpg
> http://www.ody.ca/~marcoles/Brake%2001.jpg
> http://www.ody.ca/~marcoles/Brake%2002.jpg
> http://www.ody.ca/~marcoles/Brake%2003.jpg
Interesting. The spring is still curled like a ram's horn, but
with only one curl and it's wrapped around the pivot bolt. I've never
seen that configuration in a sidepull brake, although it's seen in
centerpull and cantilever brakes. I assume there's some sort of
spacer inside the spring's curl so that the brake arms aren't
compressing the spring.
Chalo
> U-brakes are simply centerpull brakes with much beefier arms and
> shorter straddle cables.
The straddle on a U-brake is user-adjustable. Some now offer linear
pull like a v-brake.
The size and cross-section of an MTB U-brake is in proportion to its
reach, which must clear a 2"+ tire with room to spare.
> I doubt the center "bridge" of an old-style road centerpull flexes much.
Oh yes it does. Not under cable tension, but under rim drag.
Chalo Colina
Chalo
> Chalo Colina writes:
>
> >> Centerpull and cantilever brakes approach the
> >> rim at nearly a 45 degree angle and have large vertical change
> >> throughout pad wear life,
>
> > This trait of stud-mounted brakes can be accommodated by adjusting the
> > pad height as it wears. The pad rub on tire sidewalls exhibited by
> > single-pivot sidepulls, however, is due to the extreme fore-to-aft
> > flex these brakes display and can not reliably be adjusted away.
>
> Wait a minute, this is a geometric given, there is nothing you can do
> to the motion of the pad because it sweeps around its pivot and that
> pivot lies in the wrong place.
The stud-mounted brake's pivot lies in the "wrong" place to yield pad
travel that is normal to the rim sidewall, but you can adjust the pad
in its slot as it wears. In this regard the single-pivot caliper's
pivot point is "right".
The single-pivot caliper's pivot lies in the "wrong" place because it
necessitates a long, flexible arm for most applications. The fore-aft
flex thus promoted can easily result in tire sidewall rub, and it can
not be remedied by periodic adjustment, because it is a result of
braking force. In this regard it is the frame-stud-mounted brake that
has its pivots in the "right" place: as close as practiceable to the
rim track for maximum arm stiffness.
If one were to make a frame-mounted centerpull or cantilever with the
pivots so tightly spaced that it allowed a maximum 25mm to 28mm tire
(like most short-reach calipers), then the pad sweep of such a brake
would be much closer to perpendicular to the rim sidewall.
As they are, stud-mounted brakes work well enough for skinny tire and
rim applications, while allowing really huge tires and rims to be used
as well.
> > I have bent many forks under the braking forces generated by U-brakes.
> > Before applying stopping power like that, caliper brakes become so
> > twisted out of shape that applying more cable tension does not
> > result in more braking.
>
> OK, if you say so but you'll have to do some measurements to convince
> me. Regardless of where they are mounted, the mechanical advantage
> cannot be higher than the average human reach allows. You seem to be
> using hyperbole in that description. A brake that operates at the
> yield point will break off in short order. I have never seen a
> caliper that was bent from braking and I don't expect to see one.
I have never bent (yielded) a brake, with the possible exception of a
flimsy centerbolt or two. That's not the problem I describe.
What I am talking about is the elastic distortion inherent in the
longer arms of a center-pivoted caliper. In many cases, I apply
enough cable tension that the forces exceed the "spring rate" of the
caliper within the available range of lever travel. The result is
that I can pull the brake harder until I run out of lever travel, but
the brake flexes enough so as not to provide additional braking force
past a point.
With long reach calipers, 70mm or more, the point at which this
happens is a pretty meager amount of braking force for me. Even with
normal road calipers, flex, and not nose wheelies, limits the braking
power I can get out of the system.
I have observed this phenomenon in particularly flexible brakes of
other types, like the nasty Dia Compe 986 cantilever and the Mafac
centerpull. Mostly, though, it's an ill reserved for single-pivot
calipers.
> > The "ceiling" on stopping force resulting from flex-related
> > distortion of the brake mechanism is lower, and more abrupt, with
> > single-pivot calipers than with any other type of brake.
>
> To what do you attribute this claim. I'm not sure what you mean by
> the ceiling anyway. Could you expand on that.
I hope that my above explanation clarifies what I meant by "ceiling".
That is, the point at which more squeeze at the lever does not provide
more braking.
> Somehow the stopping part is a mystery to me. I and the many riders
> with whom I have ridden have taken a lot of steep and long descents
> over many years and have not had a problem with that, yet you say they
> stop better. Better than what? I can raise the rear wheel on
> descents. I don't need more leverage.
But if your bike were longer, or lower, or more heavily loaded, or
tandem; or if you were heavier, you would easily discern the
shortcomings of caliper brakes compared to well-utilized cantilever or
U-brakes. It is the upright sport road bike-- alone among adult
bikes-- that has its available braking so limited by its usual weight
distribution as to be adequately served by caliper brakes.
Chalo Colina
Chalo
> Aren't U-brakes still widely available in the BMX market?
Yes, in straddle-cable, linear-pull, and twin-cable variations.
> If so, is there any advantage in reviving bike-boom centerpulls
> (as Grant Petersen is proposing)? I suppose they would be lighter than U-brakes
> if mounted on braze-on studs, but the tenor of this discussion seems
> to be that they were often too light (i.e., too flexy).
Lighter and smaller, road centerpulls are a more elegant fit to most
road wheels and tires than U-brakes are. Is this enough to warrant
using them over U-brakes? In my opinion, no.
U-brakes work well, fit lots of different bikes, are easy to install
and maintain, and still enjoy broad commercial support.
There are even swanky new versions available like this one, with two
sealed ball bearing cartridges per arm:
http://www.danscomp.com/cgi-bin/hazel.cgi?action=DETAIL&item=480020
Chalo Colina
jobst....@stanfordalumni.org
>>> one thing Campagnolo did not address but used the same return
>>> spring shape that was the downfall of all other sidepull brakes.
>>> This is the dual "ram's horn" shape, whose ends rotate about the
>>> center of the "ram's horn" instead of the pivot bolt.
>> Actually my SunTour GPX sidepulls have one central spiral spring
>> that doesn't slide. Stays centered pretty well. Out of production
>> for quite some time, OK.
>>> I was glad to see that the new Mavic side pull brake that I saw at
>>> InterBike has solved this problem and has a no-slide return
>>> spring.
>> How did they solve the problem?
> My mid 80's Bridgestone SC sidepulls also lack the ram's horn
> springs. I believe these like the SunTour GPX were actually made by
> Dia-Compe. They stay pretty well centered and appear to have a
> 3rd. arm, I imagine for centering.
> Rear brake pictured in place, sorry no movies ;-) I didn't really
> want to pull it apart for pics or to figure out how it works, until
> it stops working.
> http://www.ody.ca/~marcoles/Brake.jpg
> http://www.ody.ca/~marcoles/Brake%2001.jpg
> http://www.ody.ca/~marcoles/Brake%2002.jpg
> http://www.ody.ca/~marcoles/Brake%2003.jpg
> Work well enough for me even with the pads near the bottom of the
> slots. AFAIK also long out of production.
Since there is no picture of the brake off the bicycle with the arms
free to spread to their maximum, I can't see for sure what this brake
is but it looks like an early dual-pivot brake. The second pivot is
visible in the front view and the side view that also reveals an
intermediate plate.
If you could dismount the brake and photograph it from the front an
rear as well as into (parallel to the center plate) the parts, I could
make more of the picture. In any case the return spring cannot center
the brake because it is not anchored anywhere other than at its ends
on the two arms.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
The "rams-horn" spring has, as the animal, two coils, one on either
side of the anchor bolt. The spring in the pictures is called a
"torsion" spring that articulates about the center of the single,
centered coil. It has no centering effect, not being anchored
anywhere other than pushing at the two arms, as I explained in another
reply.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>>>> Centerpull and cantilever brakes approach the rim at nearly a 45
>>>> degree angle and have large vertical change throughout pad wear
>>>> life,
>>> This trait of stud-mounted brakes can be accommodated by adjusting
>>> the pad height as it wears. The pad rub on tire sidewalls
>>> exhibited by single-pivot sidepulls, however, is due to the
>>> extreme fore-to-aft flex these brakes display and can not reliably
>>> be adjusted away.
>> Wait a minute, this is a geometric given, there is nothing you can
>> do to the motion of the pad because it sweeps around its pivot and
>> that pivot lies in the wrong place.
> The stud-mounted brake's pivot lies in the "wrong" place to yield
> pad travel that is normal to the rim sidewall, but you can adjust
> the pad in its slot as it wears. In this regard the single-pivot
> caliper's pivot point is "right".
You can adjust vertical position with any brake that is reasonably
versatile since this adjustment is necessary for accommodating
different rims and frames.
> The single-pivot caliper's pivot lies in the "wrong" place because
> it necessitates a long, flexible arm for most applications. The
> fore-aft flex thus promoted can easily result in tire sidewall rub,
> and it can not be remedied by periodic adjustment, because it is a
> result of braking force. In this regard it is the
> frame-stud-mounted brake that has its pivots in the "right" place:
> as close as practicable to the rim track for maximum arm stiffness.
Mechanical function comes before light weight or we would all be riding
Modolo Chronos brakes, the smallest and lightest and most elegant
brake ever made. It was a forerunner of the Campagnolo Delta, a
complete misunderstanding of brake function. My normal reach
Campagnolo Record (single pivot) brakes of the 1960's does not flex
enough to interfere with its function and it requires no pad
adjustment from brand new pads until they are worn to the metal. That
is what counts in a brake that is to get you down something like the
Stelvio Pass in the rain, where pad and rim wear are large.
> If one were to make a frame-mounted centerpull or cantilever with
> the pivots so tightly spaced that it allowed a maximum 25mm to 28mm
> tire (like most short-reach calipers), then the pad sweep of such a
> brake would be much closer to perpendicular to the rim sidewall.
But still at a large angle from the pad contact zone, so you can't get
there from here. The answer is to make a single pivot brake with a
return spring without "cosine error" (relative motion to the brake
arm) and beef up the arms a bit. Since few riders experience any of
this, they don't understand why anyone should work on it and the
manufacturers see no need to work on an unmet but unknown need.
> As they are, stud-mounted brakes work well enough for skinny tire
> and rim applications, while allowing really huge tires and rims to
> be used as well.
So what's the difference between this and the cantilever or its
replacement, the V-brake?
>>> I have bent many forks under the braking forces generated by
>>> U-brakes. Before applying stopping power like that, caliper
>>> brakes become so twisted out of shape that applying more cable
>>> tension does not result in more braking.
>> OK, if you say so but you'll have to do some measurements to
>> convince me. Regardless of where they are mounted, the mechanical
>> advantage cannot be higher than the average human reach allows.
>> You seem to be using hyperbole in that description. A brake that
>> operates at the yield point will break off in short order. I have
>> never seen a caliper that was bent from braking and I don't expect
>> to see one.
> I have never bent (yielded) a brake, with the possible exception of
> a flimsy center bolt or two. That's not the problem I describe.
> What I am talking about is the elastic distortion inherent in the
> longer arms of a center-pivoted caliper. In many cases, I apply
> enough cable tension that the forces exceed the "spring rate" of the
> caliper within the available range of lever travel. The result is
> that I can pull the brake harder until I run out of lever travel,
> but the brake flexes enough so as not to provide additional braking
> force past a point.
You must both weigh much more than the average rider and have a more
forceful grip. There are limits to every mechanism, especially on a
bicycle where weight is thought to play such a great role.
> With long reach calipers, 70mm or more, the point at which this
> happens is a pretty meager amount of braking force for me. Even
> with normal road calipers, flex, and not nose wheelies, limits the
> braking power I can get out of the system.
I don't have much experience with brakes other than Universal and
Weinmann sidepulls of the 1960's and since then Campagnolo Record
brakes with which I have descended many tens of thousands of meters in
the Alps with the only complaint being wet braking. That comes with
rim brakes, a compromise well worth it.
> I have observed this phenomenon in particularly flexible brakes of
> other types, like the nasty Dia Compe 986 cantilever and the Mafac
> centerpull. Mostly, though, it's an ill reserved for single-pivot
> calipers.
I don't know which ones you mean, but as I said, I wouldn't know them
to compare. I steered clear of all that since the 1960's when I got
Campagnolo brakes and haven't seen good cause to abandon them.
>>> The "ceiling" on stopping force resulting from flex-related
>>> distortion of the brake mechanism is lower, and more abrupt, with
>>> single-pivot calipers than with any other type of brake.
>> To what do you attribute this claim. I'm not sure what you mean by
>> the ceiling anyway. Could you expand on that.
> I hope that my above explanation clarifies what I meant by "ceiling".
> That is, the point at which more squeeze at the lever does not provide
> more braking.
I haven't experienced that.
>> Somehow the stopping part is a mystery to me. I and the many
>> riders with whom I have ridden have taken a lot of steep and long
>> descents over many years and have not had a problem with that, yet
>> you say they stop better. Better than what? I can raise the rear
>> wheel on descents. I don't need more leverage.
> But if your bike were longer, or lower, or more heavily loaded, or
> tandem; or if you were heavier, you would easily discern the
> shortcomings of caliper brakes compared to well-utilized cantilever
> or U-brakes. It is the upright sport road bike-- alone among adult
> bikes-- that has its available braking so limited by its usual
> weight distribution as to be adequately served by caliper brakes.
Well, with all those conditions, I can see a market for brakes other
than the ones used on racing bicycles. That does not mean that the
single or dual pivot caliper brake is not a good brake. I for one,
would not attempt descending steep roads on a tandem without a disc on
the rear wheel.
Jobst Brandt
jobst....@stanfordalumni.org
Tim McNamara
> Tim McNamara <tim...@bitstream.net> writes:
>
> > Interesting. The spring is still curled like a ram's horn, but
> > with only one curl and it's wrapped around the pivot bolt. I've
> > never seen that configuration in a sidepull brake, although it's
> > seen in centerpull and cantilever brakes. I assume there's some
> > sort of spacer inside the spring's curl so that the brake arms
> > aren't compressing the spring.
>
> The "rams-horn" spring has, as the animal, two coils, one on either
> side of the anchor bolt. The spring in the pictures is called a
> "torsion" spring that articulates about the center of the single,
> centered coil. It has no centering effect, not being anchored
> anywhere other than pushing at the two arms, as I explained in
> another reply.
Ah, thanks. I was struggling over terminology in that post and didn't
have the term "torsion spring."
Jeff Wills
Allow me to backpedal- I went to the garage and squeezed the front
brake lever while looking at it from above. The pivots on the bridge
moved visibly.
Still, the U-brake's arms are much larger than older "road"
centerpulls, some of which featured a very long reach- the rear on my
Raleigh is a 750. (Old frame built for 27" wheels fitted with 700c's.)
Jeff
A Muzi
> <snip>
>
>>Brazed-on pivots work. That is the definitive difference between the
>>road bike centerpull as used during the bike boom, and the U-brake as
>>used during the 80s MTB craze. The stopping power of a U-brake dwarfs
>>that of any road bike brake ever made, and U-brakes were no more
>>difficult to set up than a road caliper.
Jeff Wills wrote:
> U-brakes are simply centerpull brakes with much beefier arms and
> shorter straddle cables. I doubt the center "bridge" of an old-style
> road centerpull flexes much. On mine, the crossed arms bend upwards
> in response to brake lever pressure. On MTB-style U-brakes, the
> crossed arms are at least 4 times larger.
You doubt it? Why? It flexes a lot.
Set up your brake as well as you can, pull the lever hard
and measure the distance change between the pivot bolts.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
A Muzi
I know that brake.
It's a sidepull with a single pivot. The return spring
does not pass through a slot in the center bolt but rather
wraps around the bolt.
Helmut Springer
> They all have one spring. The problem is that he spring has a
> "ram's horn" coil on either side of the pivot bolt that constitute
> the center of rotation of the spring ends. If your brake does not
> have such a spring, I would be interested to know what shape the
> spring is.
An internal spiral wrapped arround the center bolt, being fixed to
both arms of the brake. Very much like most cantilever.
Zog The Undeniable
> Though I've been critical of Grant Peterson's effort to revive
> centerpull brakes, I have to admit that the latest Rivendell Reader
> (#30) gave me reasons to pause.
>
> First of all, in the letters section, a reader (Thomas Papetti) points
> out that
> dual-pivot sidepulls won't track an out-of-true rim the way all other
> brake types will. I'm not sure how much that counts in favor of
> centerpulls (Papetti doesn't discuss them at all). Even though most
> riders would probably use long-reach dual pivots in lieu of
> centerpulls, long-reach single-pivot sidepulls and cantilevers are
> still available if tracking is a significant worry.
>
> Then in an article, Jan Heine makes several claims for the superiority
> of sidepulls.
>
> He says, "The long lever on the cable side [above the pivot, if I
> understand him correctly] and the short lever on the pad side [below
> the pivot] gives centerpulls a huge mechanical advantage over
> sidepulls. Just like a bolt-cutter, where long arms and short jaws
> allow you to cut through thick steel bolts." Later on, he adds that
> only with the advent of dual-pivot brakes did sidepulls catch up to
> centerpulls in this respect.
>
> That doesn't seem to jibe with Jobst's discussion in the FAQ, which
> seems to suggest that single-pivot sidepulls and centerpulls had the
> same mechanical advantage.
>
> He argues that only the part of the arm below the pivot needs to be
> beefy, because that's the only place where flex matters. "As a result,
> the arms above the pivots can be incredibly skinny, as they don't need
> to resist flex. That is where the weight savings of a centerpull
> originate." He doesn't say what the weight savings is.
>
> He writes, "And since the pivot on centerpull brakes is on the fork
> leg, adding reach does not increase the flex or change the mechanical
> advantage. So there is not incentive to go to short-reach brakes." I
> think he means that since the distance between the pad and the pivot
> point always remains the same, adding lever length above the pivot
> doesn't effect the mechanical advantage. That sounds dubious to me --
> doesn't changing the length of a cantilever brake's straddle cable
> effect mechanical advantage even if all else remains the same?
> Furthermore, from the photos of old centerpulls in the Reader, it
> doesn't seem as if the distance from pivot to pad was always kept
> constant (some long-reach brakes seem to achieve that reach in part by
> increasing the lever below the pivot).
>
> He notes that centerpulls don't stick out to the side like
> centerpulls. It seems to me that that problem can be cured by using
> v-brakes, though that introduces problems of its own (e.g., mating
> them to road levers).
>
> He says that even the standard-reach (what would be called long-reach
> by most) dual-pivot brakes offered by Shimano don't leave much room
> for fenders. Is that true? Just how big a tire would you have to run
> before you would crowd out the dual pivots? (Elsewhere in the Reader,
> Grant says that centerpulls will clear a 40mm tire or a 38mm tire with
> fenders; what's the limit with the current long-reach dual pivots?)
> Furthermore, why not long-reach single-pivots, which are still
> available?
>
> Probably his most controversial claim is that single-pivot sidepulls
> "offered inferior performance" and became widespread mostly because of
> Campagnolo's advertising and gruppo packaging. Contrast that with
> Jobst's claim in the FAQ that, "The centerpull brake of the 1950's,
> was popular for nearly a decade,
> in spite of being entirely without merit, being worse in all respects
> than the side pull brake with which it competed."
>
> In the past, I've been pretty fed up with Grant's talk of reviving
> centerpulls, because it so often appeared side-by-side with complaints
> about Rivendell's financial straits and lack of popularity. I do
> notice a more refreshing tone in this issue: he mentions a bike
> planned for next year that will have braze-on pivots for centerpulls
> and adds, "But we don't expect anybody to follow that lead., and we
> fully expect to sell fewer bikes because of it. Centerpulls, for as
> much sense as they make, will still scare off most customers."
There are also braze-on Mafac centerpulls - basically the predecessor of
Shimano's long-dead U-brake. These are supposed to be better than
normal centerpulls, but the braze-ons are not the same as for cantilever
brakes so you'd have to have a frame modified or built specially.
jobst....@stanfordalumni.org
>> If you could dismount the brake and photograph it from the front an
>> rear as well as into (parallel to the center plate) the parts, I
>> could make more of the picture. In any case the return spring
>> cannot center the brake because it is not anchored anywhere other
>> than at its ends on the two arms.
> I know that brake. It's a sidepull with a single pivot. The return
> spring does not pass through a slot in the center bolt but rather
> wraps around the bolt.
So what is the sub-frame doing in there and the bulge in the arm with
a screw in it? How does it center if the spring does not do it, as it
can't since it is not anchored anywhere, bearing only on the arms at
the brake pads?
Jobst Brandt
jobst....@stanfordalumni.org
Marcus Coles
It's almost off the bike
More pictures shortly.
Marcus
Marcus Coles
Picture files are large.
They will only be on the server until tomorrow.
http://www.ody.ca/~marcoles/PA180001.JPG
http://www.ody.ca/~marcoles/PA180002.JPG
http://www.ody.ca/~marcoles/PA180003.JPG
http://www.ody.ca/~marcoles/PA180004.JPG
http://www.ody.ca/~marcoles/PA180005.JPG
http://www.ody.ca/~marcoles/PA180006.JPG
http://www.ody.ca/~marcoles/PA180007.JPG
http://www.ody.ca/~marcoles/PA180008.JPG
http://www.ody.ca/~marcoles/PA180009.JPG
http://www.ody.ca/~marcoles/PA180010.JPG
http://www.ody.ca/~marcoles/PA180011.JPG
http://www.ody.ca/~marcoles/PA180012.JPG
http://www.ody.ca/~marcoles/PA180013.JPG
http://www.ody.ca/~marcoles/PA180014.JPG
Marcus
jobst....@stanfordalumni.org
> Kinda sorta both.
Thanks. That's what I needed to understand how these brakes centered
themselves.
The clue is the "dog bone" swivel pin that has a sphere at each end
and one in the middle. Geometrically the swivel pin is positioned by
its center sphere while its ends are engaged in the brake arms that
move in opposite directions, thereby tilting the pin and forcing each
arm to mirror the other's moves. As the pin tilts, its length is
foreshortened between the two brake arms for which it requires a
cylindrical bore in which to "pump" in and out as it tilts. Because
the arms rotate about the center-bolt and the intermediate plate does
not, the pin must be free to change its radial position, requiring a
slot in the intermediate plate.
The problem with this is that a cylindrical bore presents only a line
contact for a sphere while a slot (two parallel planes) present a
point contact. Machining a curved surface slot is probably
prohibitively cumbersome. With normal grit contamination and poor
lubrication, wear at these points is rapid and with such a short pin,
a small amount of wear will make centering poor. That is most likely
why we don't see this type of brake anymore.
...DEAD!
Jobst Brandt
jobst....@stanfordalumni.org
Marcus Coles
Thank you for inspiring me to dig further into the brake and for your
analysis of the design. The self centering function is no longer
"magic".
The "dog bone" is made from a hard nylon like plastic and judging from
the visible wear a sacrificial item in the design.
The brake design was used by Bridgestone on their mid-range 400, 500,
and 600 road bike models in 1984 and 1985 and then AFAIK disappeared.
This example has at least 10000km of mostly fair weather exposure, I
imagine the front brake, which has had most of the use in the three
years I've owned the bike, will exhibit more wear, although it does
continue to center well at this time.
I was hoping the brakes would last until the lugged steel frame became
too soft to ride ;^) Now I will have to consider earlier replacement.
Marcus
Carl Fogel
Dear Marcus,
Regrettably, some interested parties might not
read your post in time, so your pictures are
available for Jobst, Andrew, and anyone else at
the addresses below:
http://home.comcast.net/~carlfogel/download/PA180001.jpg
http://home.comcast.net/~carlfogel/download/PA180002.jpg
http://home.comcast.net/~carlfogel/download/PA180003.jpg
http://home.comcast.net/~carlfogel/download/PA180004.jpg
http://home.comcast.net/~carlfogel/download/PA180005.jpg
http://home.comcast.net/~carlfogel/download/PA180006.jpg
http://home.comcast.net/~carlfogel/download/PA180007.jpg
http://home.comcast.net/~carlfogel/download/PA180008.jpg
http://home.comcast.net/~carlfogel/download/PA180009.jpg
http://home.comcast.net/~carlfogel/download/PA180010.jpg
http://home.comcast.net/~carlfogel/download/PA180011.jpg
http://home.comcast.net/~carlfogel/download/PA180012.jpg
http://home.comcast.net/~carlfogel/download/PA180013.jpg
http://home.comcast.net/~carlfogel/download/PA180014.jpg
Naturally, I'll delete them if there are any objections.
Carl Fogel
Marcus Coles
Carl Fogel wrote:
>
> Dear Marcus,
>
> Regrettably, some interested parties might not
> read your post in time, so your pictures are
> available for Jobst, Andrew, and anyone else at
> the addresses below:
>
> http://home.comcast.net/~carlfogel/download/PA180001.jpg
> http://home.comcast.net/~carlfogel/download/PA180002.jpg
> http://home.comcast.net/~carlfogel/download/PA180003.jpg
> http://home.comcast.net/~carlfogel/download/PA180004.jpg
> http://home.comcast.net/~carlfogel/download/PA180005.jpg
> http://home.comcast.net/~carlfogel/download/PA180006.jpg
> http://home.comcast.net/~carlfogel/download/PA180007.jpg
> http://home.comcast.net/~carlfogel/download/PA180008.jpg
> http://home.comcast.net/~carlfogel/download/PA180009.jpg
> http://home.comcast.net/~carlfogel/download/PA180010.jpg
> http://home.comcast.net/~carlfogel/download/PA180011.jpg
> http://home.comcast.net/~carlfogel/download/PA180012.jpg
> http://home.comcast.net/~carlfogel/download/PA180013.jpg
> http://home.comcast.net/~carlfogel/download/PA180014.jpg
>
> Naturally, I'll delete them if there are any objections.
>
> Carl Fogel
Carl,
No objections.
Thanks for keeping them available for those interested.
Marcus
jobst....@stanfordalumni.org
> Thank you for inspiring me to dig further into the brake and for
> your analysis of the design. The self centering function is no
> longer "magic".
> The "dog bone" is made from a hard nylon like plastic and judging
> from the visible wear a sacrificial item in the design.
After considering it further, it seems to me that getting someone to
make a hardened steel "dog bone" might be a worthwhile cause. The
reason is that there are no significant forces on it, the brake having
no interest in staying centered or un-centered, its natural position
when opening being undefined and random. The only significant force
transmitted would be from an off center mounted brake or a laterally
untrue wheel.
> The brake design was used by Bridgestone on their mid-range 400,
> 500, and 600 road bike models in 1984 and 1985 and then AFAIK
> disappeared.
I find it a clever design, other than its wear susceptibility. It is
far better than a dual pivot for brake pad movement. It's mechanical
advantage is optional in the design because it remains centered and
doesn't need large pad clearance to prevent pad drag.
> This example has at least 10000km of mostly fair weather exposure, I
> imagine the front brake, which has had most of the use in the three
> years I've owned the bike, will exhibit more wear, although it does
> continue to center well at this time.
Unless it has large caliper flex, I would stay with it.
> I was hoping the brakes would last until the lugged steel frame
> became too soft to ride ;^) Now I will have to consider earlier
> replacement.
It's probably already softened up and doesn't climb hills well...
junk it!
Jobst Brandt
jobst....@stanfordalumni.org
Luns Tee
<jobst....@stanfordalumni.org> wrote:
>Helmut Springer writes:
>> Actually my SunTour GPX sidepulls have one central spiral spring
>> that doesn't slide. Stays centered pretty well. Out of production
>> for quite some time, OK.
>
>horn" coil on either side of the pivot bolt that constitute the center
>of rotation of the spring ends. If your brake does not have such a
>spring, I would be interested to know what shape the spring is.
I believe the SunTour GPX is designed the same as the Superbe
Pro caliper of the same era. The return spring is an internal coil
spring, contained at the pivot of the caliper. It's actually two
separate coil springs, one for each arm, that engage an washer that's
indexed to the pivot bolt.
There's an exploded picture of the Superbe Pro caliper at:
http://www.totalbike.com/cgi-bin/schematics.cgi?path=/reference/suntour/images/st-spbs
-Luns
jobst....@stanfordalumni.org
>>> Actually my SunTour GPX sidepulls have one central spiral spring
>>> that doesn't slide. Stays centered pretty well. Out of
>>> production for quite some time, OK.
>> They all have one spring. The problem is that he spring has a
>> "ram's horn" coil on either side of the pivot bolt that constitute
>> the center of rotation of the spring ends. If your brake does not
>> have such a spring, I would be interested to know what shape the
>> spring is.
> I believe the SunTour GPX is designed the same as the Superbe Pro
> caliper of the same era. The return spring is an internal coil
> spring, contained at the pivot of the caliper. It's actually two
> separate coil springs, one for each arm, that engage an washer
> that's indexed to the pivot bolt.
> There's an exploded picture of the Superbe Pro caliper at:
I see. This caliper is largely immune to return spring friction,
using a "torsion spring" concentric to the pivot shaft. The trouble
is there are two springs, both fighting for their share of the return
so that the retracted position lies in the dip between two
intersecting spring characteristics. That's better than sliding end
springs but putting them in reliefs in the middle of the arm presents
a strength problem.
It isn't easy.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> ...sidepull brakes have the pad pivot above and only slightly (rim
>> half width) offset from the braking surface so that there is
>> essentially no position change as the pad sweeps through its wear
>> life (cosine error). Centerpull and cantilever brakes approach the
>> rim at nearly a 45 degree angle and have large vertical change
>> throughout pad wear life,
> This trait of stud-mounted brakes can be accommodated by adjusting the
> pad height as it wears. The pad rub on tire sidewalls exhibited by
> single-pivot sidepulls, however, is due to the extreme fore-to-aft
> flex these brakes display and can not reliably be adjusted away.
You keep talking about cheap no use brake calipers. We've been riding
on Campagnolo and Shimano brakes for a long time and those who insist
on using flimsy brands out to switch and atop talking about ho bad
these brakes were. Just the same, you seem to recognize that pad wear
can cause cantilever brakes to pop under the rim in dirt and wet
conditions. It happens and it should be apparent that the arc
described by the pad attacks the rim at a 45 degree angle (large
cosine error) while a single pivot sidepull brake has a 5 degree
angle, one that allows me to wear a Kool-Stop Continental pad to the
metal without adjustment.
> This horrible characteristic of single-pivot sidepull brakes is IMO
> one of the reasons for the annoying move to "short reach" road
> calipers-- because the stubby arms of those brakes are somewhat
> resistant to allowing sidewall rub for most average-sized riders.
long (standard) reach Campagnolo Record brakes from the 1960's do not
flex enough to distort the wear pattern on the rim. They hold their
position even when braking hard enough to raise the rear wheel.
>> the centerpull goes into the tire as it wears and offers no
>> advantages whatsoever.
> When mounted on frame studs, it offers vastly superior maximum
> stopping power to any caliper brake. I know this because I have
> bent many forks under the braking forces generated by U-brakes.
> Before applying stopping power like that, caliper brakes become so
> twisted out of shape that applying more cable tension does not
> result in more braking.
So? Who uses centerpull brakes... and why? They are dogs!
>> Flex in any part of the system eats up hand lever stroke.
> Insufficient stroke length can be addressed by using levers that pull
> more cable, and pulling them harder. However, the swinging flex
> endemic to all centerbolt-mounted brakes, and the torsional flex that
> is particularly pronounced in single-pivot brakes, act
> disproportionately to diminish the braking that can be applied
> regardless of how hard or how far the cable is pulled.
> The "ceiling" on stopping force resulting from flex-related distortion
> of the brake mechanism is lower, and more abrupt, with single-pivot
> calipers than with any other type of brake.
Not on high quality calipers. You haul out discarded brake brands and
types that have had no business on bicycles in the last ten years.
>>> He notes that centerpulls don't stick out to the side like
>>> sidepulls.
>> How far??? What is the issue here anyway.
> I have seen enough bikes damaged by the sidepull brake arm bashing
> into the downtube to think of that design characteristic as a
> liability.
I've seen bicycle damaged by letting them fall over onto a curb. So
what if there are oafs around who can damage a bicycle. As I recall
in a crash, both center and side pull brakes have gotten dinged by or
dinged the down tube.
>>> He says that even the standard-reach (what would be called
>>> long-reach by most) dual-pivot brakes offered by Shimano don't
>>> leave much room for fenders. Is that true?
>> NO.
> It is true if you wish to run decent-sized tires and fenders at the
> same time. Even the most careful brake placement will not allow
> "standard reach" dual-pivot calipers to encompass 38mm tires with
> fenders.
Long ago, split fenders were mad to not compromise the brake for
fenders. The front half begins ahead of the fork, the rear behind.
I don't see this if it is racing bicycles we are talking about.
>> The sidepull brake is the obvious mechanism for road bicycles to
>> all who understand mechanical design. All this other stuff is
>> amateur thinking guided by misunderstanding of the concept.
> Sorry, but that's just not true. It might be "the obvious
> mechanism" if one is unconcerned about generating the most stopping
> force from a given amount of brake, and if one disregards the
> benefits of voluminous tires, and if one happily tolerates pad rub
> due to a brake design that can not be centered accurately. But most
> "who understand mechanical design" demand (or at least desire)
> better performance than that!
How much do you need? I often think of that as I overtake riders
descending steep roads. Riders who are using all sorts of
demonstrative cornering techniques as they pour on the brakes early
into turns. I suppose for these folks more brake force is necessary.
> Getting the brake pivot as close as practicable to the pads pays huge
> dividends in turning lever force into stopping force.
I'm sure you meant that differently than it came out. The shorter the
brake arms the greater the angular sweep in its stroke and the greater
the cosine error involved in pad wear gets. The amount of flex in the
levers is the measure of performance at any given mechanical
advantage. Of course we've been at mechanical advantage before. It
can be only so large that hand lever travel is not used up by the time
the pads make contact, that is pad clearance dictates mechanical
advantage upper limits.
> That very translation is exactly where single-pivot calipers are so
> weak. They only provide an approximately linear relationship
> between lever force and braking force up to a point-- a point easily
> exceeded by many riders in many circumstances.
Not so. Many riders have such weak hands that they could not
adequately brake with 4:1 brakes that were standard before dual pivot
calipers came along. You may recall the old saw of "Campagnolo
Brakes are for racing and racers only need to modulate speed, not stop!"
I heard it often enough to gag. It's tough when you can't tell the
customer he is a wimp and should develop more grip. So there we have
it. Dual pivot! The brake that absolutely centers and can operate
with minimal pad clearance. Up the ME! By the way, the ME is so high
that you cannot wear the pads to the metal, there being insufficient
adjustment at that level.
> Add to this the inherent characteristic of them being impossible to
> center consistently, and it's not at all obvious that they are
> superior to the worst of other brake designs, let alone the best of
> them.
That is true, but how accurately do you need it. I've been using them
for many years and add a bit of oil when they go off center in the
rain.
>> Now let's hear it again concisely. What are the advantages?
> Concisely? Stopping. Centering.
Well that is what single pivot Campagnolo brakes do for me.
Jobst Brandt
jobst....@stanfordalumni.org
Tom Nakashima
Contiental pad down.
I first thought something was wrong with the calipers when I was actually
braking metal to metal.
I also have the Campagnolo long reach single pull brakes. Is it necessary
for Kool Stop to use all
the metal and less pad. Seems like their other design brake shoes don't have
that much metal in them.
-tom
<jobst....@stanfordalumni.org> wrote in message
news:dcGqb.4574$Wy2....@typhoon.sonic.net...
Tim McNamara
> This was surprise to me all that metal in the shoe when I wore the
> Kool Stop Contiental pad down. I first thought something was wrong
> with the calipers when I was actually braking metal to metal. I
> also have the Campagnolo long reach single pull brakes. Is it
> necessary for Kool Stop to use all the metal and less pad. Seems
> like their other design brake shoes don't have that much metal in
> them.
Try the Scott/Mathauser version- just a big chunk o' brake pad in an
old-style holder. Mine last for ages and ages. Road and canti:
http://www.rivendellbicycles.com/webalog/brakes/15093.html
http://www.rivendellbicycles.com/webalog/brakes/15095.html
Sheldon might have these too, IIRC.
jobst....@stanfordalumni.org
>> A single pivot sidepull brake has a 5 degree angle, one that allows
>> me to wear a Kool-Stop Continental pad to the metal without
>> adjustment.
> This was surprise to me all that metal in the shoe when I wore the
> Kool Stop Continental pad down. I first thought something was wrong
> with the calipers when I was actually braking metal to metal. I
> also have the Campagnolo long reach single pull brakes. Is it
> necessary for Kool Stop to use all the metal and less pad. Seems
> like their other design brake shoes don't have that much metal in
> them.
That's a lot of brake pad to wear down. The wear limit should be
obvious because that is where the usable pad blends into the backing
that is 50% wider than the pad. See picture at:
http://www.koolstop.com/brakes/#continental
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> This was surprise to me all that metal in the shoe when I wore the
>> Kool Stop Continental pad down. I first thought something was
>> wrong with the calipers when I was actually braking metal to metal.
>> I also have the Campagnolo long reach single pull brakes. Is it
>> necessary for Kool Stop to use all the metal and less pad. Seems
>> like their other design brake shoes don't have that much metal in
>> them.
> Try the Scott/Matthauser version- just a big chunk o' brake pad in an
> old-style holder. Mine last for ages and ages. Road and cantilever:
> http://www.rivendellbicycles.com/webalog/brakes/15093.html
> http://www.rivendellbicycles.com/webalog/brakes/15095.html
That pad has no greater wear depth than the Continental. Besides, the
Continental cannot slip out or be dislodged by a tire change, the
reason for those triangular guides on brake pad insert holders. The
continental may not appeal to the equipment purists but it is a better
choice.
Jobst Brandt
jobst....@stanfordalumni.org
g.daniels
how much better
Tim McNamara
> ok. are the rivendales better than the dia-compe center pulls circa
> 1990-1985? how much better
Well, Rivendell is currently selling DiaCompe 610s, so I'd hazard a
guess that the answer to your question is "no." ;-)
Dale Stanbrough
> So? Who uses centerpull brakes... and why? They are dogs!
I have a bike with 700C tyres, drop handle bars and ceterpull
brakes (it was converted from a mountain bike). I've never
been able to find brakes that could replace them. Are there
any other brakes suitable for this set up?
Dale
A Muzi
> jobst....@stanfordalumni.org wrote:
>
>
>
>>So? Who uses centerpull brakes... and why? They are dogs!
>
>
> I have a bike with 700C tyres, drop handle bars and ceterpull
> brakes (it was converted from a mountain bike). I've never
> been able to find brakes that could replace them. Are there
> any other brakes suitable for this set up?
>
> Dale
>
To define terms ( a popular motif here today!) are your
brakes mounted on studs attached to the frame and to the
fork? Or do they attach with a single center bolt through
the brake's bridge? If the latter, what size are they?
[short=610, long=750 for Weinmanns, other brands vary]
There are _always_ alternates.
Dale Stanbrough
A Muzi <a...@yellowjersey.org> wrote:
> Dale Stanbrough wrote:
>
> > jobst....@stanfordalumni.org wrote:
> >
> >
> >
> >>So? Who uses centerpull brakes... and why? They are dogs!
> >
> >
> > I have a bike with 700C tyres, drop handle bars and ceterpull
> > brakes (it was converted from a mountain bike). I've never
> > been able to find brakes that could replace them. Are there
> > any other brakes suitable for this set up?
> >
> > Dale
> >
> To define terms ( a popular motif here today!) are your
> brakes mounted on studs attached to the frame and to the
> fork? Or do they attach with a single center bolt through
> the brake's bridge? If the latter, what size are they?
> [short=610, long=750 for Weinmanns, other brands vary]
The brake arms are attached to studs brazed? onto the front
of the forks. The pads sit 1/2 way along the length of the
brake arm, and the top is connected traingularly to the center
pull mechanism.
-----
| ^ |
|/ \|
/ \ <- center pull cables.
/| |\
\\| | |//
\\*|*// <- brake arms and pads
| | |
| | | <- forks
| | |
+-+-+
|
|
|
|
| <- wheel
(whew!)
Most bike shop staff say you can't combine brakes which act off
pivots on the forks with drop handle bars and large profile
rims/tyres.
Dale
Tim McNamara
> In article <vr618a6...@corp.supernews.com>,
> A Muzi <a...@yellowjersey.org> wrote:
> > To define terms ( a popular motif here today!) are your brakes
> > mounted on studs attached to the frame and to the fork? Or do
> > they attach with a single center bolt through the brake's bridge?
> > If the latter, what size are they? [short=610, long=750 for
> > Weinmanns, other brands vary]
>
> The brake arms are attached to studs brazed? onto the front of the
> forks. The pads sit 1/2 way along the length of the brake arm, and
> the top is connected traingularly to the center pull mechanism.
<ASCII art snipped>
Sounds like cantilever brakes. Snoop around the brakes section at
www.sheldonbrown.com and you'll see photos and examples of each type of
brake. ISTR Mr. Muzi's shop as having some photos on their Web site
as well.
> Most bike shop staff say you can't combine brakes which act off
> pivots on the forks with drop handle bars and large profile
> rims/tyres.
They'd be wrong. With a pair of DiaCompe 287 brake levers, you can
use drop bars with cantilevers very easily. With a pair of 287V
levers, you can use them with V-brakes.
Jeff Wills
Tim McNamara <tim...@bitstream.net> wrote in message news:<m2r80cm...@localhost.bitstream.net>...
However, Mr. Stanbrough's bike has 700C wheels on a mountain bike
frame, which means the cantilever studs are not correctly positioned.
I'd guess they sit about 31mm too low for cantilever brakes to work.
There are brakes that have a large range of vertical adjustment-
Paul's Motolite is one:
http://www.mtbreview.com/reviews/Brake_System/product_20515.shtml
These are expensive and rare, though. Drilling some mounting holes in
the frame and fork and bolting on caliper (centerpull or sidepull)
brakes might be possible- but only by someone who's an experienced
mongrelizer.
Jeff
A Muzi
>>>>So? Who uses centerpull brakes... and why? They are dogs!
>>Dale Stanbrough wrote:
>>>I have a bike with 700C tyres, drop handle bars and ceterpull
>>>brakes (it was converted from a mountain bike). I've never
>>>been able to find brakes that could replace them. Are there
>>>any other brakes suitable for this set up?
> In article <vr618a6...@corp.supernews.com>,
> A Muzi <a...@yellowjersey.org> wrote:
>>To define terms ( a popular motif here today!) are your
>>brakes mounted on studs attached to the frame and to the
>>fork? Or do they attach with a single center bolt through
>>the brake's bridge? If the latter, what size are they?
>>[short=610, long=750 for Weinmanns, other brands vary]
Dale Stanbrough wrote:
> The brake arms are attached to studs brazed? onto the front
> of the forks.
-snip a drawing of great effort-
> Most bike shop staff say you can't combine brakes which act off
> pivots on the forks with drop handle bars and large profile
> rims/tyres.
They're cantilevers and those are exceptionally verstaile.
You can get excellent response from them with road levers.
Sheldon Brown has a nice overview (which youshould read) but
basically you can change the position of the pad in relation
to the arm and also the angle/length of the transverse
cable. The latter can change the brake from a low-gear
device to high-gear action or the inverse as you require.
g.daniels
is it an economimc decision?
Jasper Janssen
>However, Mr. Stanbrough's bike has 700C wheels on a mountain bike
>frame, which means the cantilever studs are not correctly positioned.
> I'd guess they sit about 31mm too low for cantilever brakes to work.
I doubt this. 700C wheels don't usually fit on a mountain bike frame, but
they do fit on certain hybrid frames, many of which are in essence
mountain bike frames designed to take 700C wheels. I think it's much more
likely that that's what he has.
Jasper
Dale Stanbrough
yep, it's a Cannondale bike that originally had flat handlebars (i.e.
it looked like a mountain bike, but with 700C wheels and eyelets for
touring).
Dale