Centerpull brakes

Simon Brooke said:

Tim McNamara said:

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.

Donald Gillies said:

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

sheldonbrown.comcantilever geometry.htmlOpen ↗

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.

Quoted message said:

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 [email hidden]

My comments at the bottom-

Tim McNamara <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Quoted message said:

Tim McNamara said:

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.

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 said:

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

(Jeff Wills) said:

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.

- Don Gillies San Diego, CA

Donald Gillies said:

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 (_)/ (_) |

(Donald Gillies) said:

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.

Quoted message said:

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.

David L. Johnson said:

Quoted message said:

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.

Quoted message said:

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 [email hidden]

Tim McNamara said:

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

Quoted message said:

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.

Quoted message said:

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 [email hidden]

Quoted message said:

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.

Quoted message said:

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

Donald Gillies said:

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.

Quoted message said:

sheldonbrown.comcantilever geometry.htmlOpen ↗

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.

Quoted message said:

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.

Quoted message said:

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?

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗ ;; 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

Quoted message said:

David L. Johnson said:

Quoted message said:

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.

Quoted message said:

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.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

... a mild, inoffensive sadist...

Helmut Springer said:

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

Quoted message said:

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.

Quoted message said:

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 [email hidden]

Simon Brooke said:

Quoted message said:

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.

Quoted message said:

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 [email hidden]

[email hidden] (Chalo) wrote in message
news:<[email hidden]>... <snip>

Quoted message said:

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).

[email hidden] (Chalo) wrote in message
news:<[email hidden]>... <snip>

Quoted message said:

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

Helmut Springer said:

Quoted message said:

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.

Quoted message said:

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.

ody.caBrake.jpgOpen ↗ ody.caBrake%2001.jpgOpen ↗
ody.caBrake%2002.jpgOpen ↗ ody.caBrake%2003.jpgOpen ↗

Work well enough for me even with the pads near the bottom of the slots. AFAIK also long out of
production.

Marcus

Quoted message said:

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

Marcus Coles said:

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.

ody.caBrake.jpgOpen ↗ ody.caBrake%2001.jpgOpen ↗
ody.caBrake%2002.jpgOpen ↗ ody.caBrake%2003.jpgOpen ↗

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.