Cantilever style booster for centerpulls?

I understand that cantilevers try to spread the frame so a booster helps stiffen things up. How
about centerpulls? Would Mafac or Weinmann centerpulls benefit from having pivots connected at
front? If used as is maybe not worthwhile, but if brazed on pivots were used wouldn't this be same
as cantilevers trying to spread stays apart?

Pete Geurds Douglassville, PA

 

On 19 Apr 2003 19:08:03 GMT, [email protected] (Pete Geurds) wrote:

>I understand that cantilevers try to spread the frame so a booster helps stiffen things up.

All fork-leg mounted brakes do. Put an axial force into the rim, and there has to be a reaction
somewhere.

It's more noticeable with V brakes. Owing to the long lever arm, the force that the cable provides
is helpful (for direction), but small. On cantis, the angle of the straddle cable isn't helpful, but
the force in the cable is higher. For a well-tuned setup, it's probably similar, but typical "slack
straddles" will produce less force on the bosses.

>How about centerpulls?

Only if your centrpulls (or even U brakes !) are well enough set up to be able to produce real force
on the rim. Many aren't, simply because roadies can live without the butt-saving deceleration that
the average lemming on an MTB needs from time to time.

 

Andy Dingley wrote:

"Many aren't, simply because roadies can live without the butt-saving deceleration that the average
lemming on an MTB needs from time to time."

THAT'S something I've wondered about a long time, just why does an MTB need such powerfull brakes? I
can see why a tandem or a packed touring bike might, they have a lot more weight to stop.

But they're stopping on asphault, which offers a lot more traction than dirt or sand, which is what
an MTB is designed to be ridden on. Whether it really get's ridden on dirt is not the point here, so
don't distract me with statistics!

And let's face it people, once a tire starts to slide, which on dirt, even a department store set of
sidepuls can do, you aren't going to get any more stopping power out of your brakes. I don't care
how powerful they are!

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

Chris Zacho The Wheelman wrote:

> THAT'S something I've wondered about a long time, just why does an MTB need such powerfull brakes?

It doesn't, and they don't have them!

a good, well maintained front brake is powerful enough to cause the rear wheel to lift off. Any
decent road or mountain bike can do this, if you dare.

There is no use for a more powerful brake than that, 'cause once the rear wheel is on the point of
liftoff, you're at the maximum usable braking.

The reason mountain bikes use cantilever brakes is not for the sake of more "power" but it has to do
with tire clearance.

Sheldon "Everybody Needs Good Brakes" Brown
+---------------------------------------------------------------------+
| There are two times in a man's life when he should not speculate: | when he can't afford it, and
| when he can. --Mark Twain |
+---------------------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

Andy Dingley wrote:
> On 19 Apr 2003 19:08:03 GMT, [email protected] (Pete Geurds) wrote:
>>How about centerpulls?
>
>
> Only if your centrpulls (or even U brakes !) are well enough set up to be able to produce real
> force on the rim. Many aren't, simply because roadies can live without the butt-saving
> deceleration that the average lemming on an MTB needs from time to time.

Road brakes are no weaker than MTB brakes, and in many cases can provide more stopping power than
MTB brakes, a fact which is easily demonstrated.

The limit of braking on a road bike is the point at which the rear wheel lifts off the ground, and
the bike pitches end over end. Even one solitary single pivot road brake caliper (which has about
40% less caliper force than a double pivot caliper) can produce enough braking power on a front
wheel to pitch a bike over. (By the way, this is a brake force of roughly 1/2 g.)

In contrast, on many loose off-road surfaces, the front tire of an MTB will skid before the pitch
over limit is reached, and therefore have a lower braking limit than a road brake.

Mark McMaster [email protected]

 

On Sun, 20 Apr 2003 22:31:42 -0400, Mark McMaster <[email protected]> wrote:

>Road brakes are no weaker than MTB brakes,

Your argument demonstrates why MTB brakes are no more "effective", but we're talking here about the
simple mechanics of the caliper / fork / wheel setup.

Brakes adjusted to give high reaction forces are more common on MTBs. Maybe it's because they're
riding different kit, maybe it's because roadies prefer a less aggressive adjustment and (as you
point out) know that a huge rim force still doesn't slow you down any better.

 

In article <[email protected]>, Sheldon Brown <[email protected]> wrote:

> Chris Zacho The Wheelman wrote:
>
> > THAT'S something I've wondered about a long time, just why does an MTB need such powerfull
> > brakes?
>
> It doesn't, and they don't have them!
>
> a good, well maintained front brake is powerful enough to cause the rear wheel to lift off. Any
> decent road or mountain bike can do this, if you dare.
>
> There is no use for a more powerful brake than that, 'cause once the rear wheel is on the point of
> liftoff, you're at the maximum usable braking.
>
> The reason mountain bikes use cantilever brakes is not for the sake of more "power" but it has to
> do with tire clearance.
>
> Sheldon "Everybody Needs Good Brakes" Brown
> +---------------------------------------------------------------------+
> | There are two times in a man's life when he should not speculate: | when he can't afford it,
> | and when he can. --Mark Twain |
> +---------------------------------------------------------------------+ Harris Cyclery, West
> Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find
> parts shipped Worldwide http://captainbike.com http://sheldonbrown.com

I've got one for ya, Sheldon: the more slacked-out geometry and further-back weight distribution of
an MTB means that there is greater potential braking force because the rear wheel lifts later.

But it doesn't stop there: MTBers also use things like 8" hydraulic rotors front and rear, a braking
system that would look like too much on a scooter that can do 80 km/h and weighs more. Why?

My guess is that what these riders are looking for are easily-modulated brakes. In limited traction
situations, the most important thing is that you use what traction there is.

--
Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club

 

Pete Geurds writes:

> I understand that cantilevers try to spread the frame so a booster helps stiffen things up. How
> about centerpulls?

> Would Mafac or Weinmann centerpulls benefit from having pivots connected at front? If used as is
> maybe not worthwhile, but if brazed on pivots were used wouldn't this be same as cantilevers
> trying to spread stays apart?

They would be a little less flexible but not much, the forces on the bridge being primarily tension
rather than bending. However, the centerpull brake has the same (but inverse) problem as the
cantilever in that its pad motion is at 45 degrees to the plane of the rim. As pads wear, the
centerpull climbs up into the tire while the cantilever goes the other way and dives under the rim.
In both cases (blown tire or pup under pads)cause a complete loss of control.

Brakes of that era all had the same mechanical advantage of 1:1 in the caliper or cantilever, while
the hand lever had a 4:1 ratio. With the advent of the dual pivot caliper, that allowed reducing pad
clearance, with its forced pad centering, hand levers have changed to a higher mechanical advantage
of about 5.6:1.

Historically the centerpull was one of those ideas that came about through a misunderstanding of the
advantage of the single pivot "side pull" of the day. That side pull, the Campagnolo Record,
required no adjustment for the life of the pad down to the metal. In geometry, that is called
"cosine error". Sweeping a lever through small angles around zero causes essentially no change in
the line of action. In contrast, the dual pivot has large "sine error" on the short arm extending
from the offset pivot (the dual pivot). The solution to this is to offer brake pads with so little
rubber that they cannot be worn down much before replacement and therefore need not be adjusted...
just replaced.

Jobst Brandt [email protected] Palo Alto CA

 

RE/
>THAT'S something I've wondered about a long time, just why does an MTB need such powerfull brakes?
>I can see why a tandem or a packed touring bike might, they have a lot more weight to stop.
>
>But they're stopping on asphault,

Seems to me like the braking power of any bike is limited more by the adhesion of the front tire
than anything in the brakes.

Having said that, the reasons I moved to hydraulic disc brakes on my MTB and cable discs on the bike
I use mainly for sort-of road riding are:

1) Modulation

2) Tolerance of wobbly wheels

3) Tolerance of off-center wheels

4) Rain reliability

5) Mud-friendliness.

6) No chance of a mis-aligned pad taking out the sidewall after riding away from a crash (been
there....)

7) Wheel interchangability between bikes (given that the MTB is going to have discs for sure, but
the "sort-of-road" bike started out with v-brakes and probably could have stayed that way...

8) I like the sound the front brake makes when it's doing all the heavy lifting on a long
descent...(go figure....)

-----------------------
PeteCresswell

 

Pete Cresswell writes:

>> THAT'S something I've wondered about a long time, just why does an MTB need such powerfull
>> brakes? I can see why a tandem or a packed touring bike might, they have a lot more weight
>> to stop.

>> But they're stopping on asphault,

There are two problems here. One is that the terms power and force are not synonymous and one is
often confused with the other, as in this thread. You can have a brake that grabs and will stop the
front wheel with little hand lever force. You can also have a brake that will help you descend steep
terrain and dissipate power continuously. The first one might be better for many trail applications,
while the second is a necessity for descending steep paved mountain passes with many curves that
require braking.

> Seems to me like the braking power of any bike is limited more by the adhesion of the front tire
> than anything in the brakes.

That would be braking force. Yes, road bicycles don't skid front wheels because they have better
traction on pavement than on a dirt road or trail, regardless of tread pattern.

> Having said that, the reasons I moved to hydraulic disc brakes on my MTB and cable discs on the
> bike I use mainly for sort-of road riding are:

> 1) Modulation

> 2) Tolerance of wobbly wheels

> 3) Tolerance of off-center wheels

> 4) Rain reliability

> 5) Mud-friendliness.

> 6) No chance of a mis-aligned pad taking out the sidewall after
riding away from > a crash (been there....)

> 7) Wheel interchangability between bikes (given that the MTB is going to have discs for sure, but
> the "sort-of-road" bike started out with v-brakes and probably could have stayed that way...

> 8) I like the sound the front brake makes when it's doing all the heavy lifting on a long
> descent...(go figure....)

I don't see where any of the above reasons rule out rim brakes except for the rain. Disc brakes have
too little surface to dissipate power at the rate that rim brakes do, but that will change as more
people go to insulators for rims (aka carbon fiber). Modulation, wobbly wheels, compatibility with
hand-up wheels in a race, and "heavy lifting"? are no better with discs than with rim brakes.

The big negative for disc brakes is the failure mode and reliability when descending something like
passes in the Alps where missing a hairpin turn is DEATH. It's a long way down. When you lose fluid
or get even a tiny leak, it is serious trouble. Besides, hydraulic and cable operated calipers both
have a linear characteristic. Therefore, modulation should be mainly a problems of adjustment, not
whether it is a hydraulic or mechanical transducer.

Jobst Brandt [email protected] Palo Alto CA

 

<[email protected]> wrote in message news:aN%[email protected]...

> The big negative for disc brakes is the failure mode and
reliability
> when descending something like passes in the Alps where
missing a
> hairpin turn is DEATH. It's a long way down. When you
lose fluid or
> get even a tiny leak, it is serious trouble.

You don't even need a leak to have major brake failure with disks. The main problem, safety-wise, is
that they can overheat and "go away" very suddenly. Rim brakes' fade is much more gradual, and when
it does happen you still have some braking power left.

Rim brakes also cool off a lot faster -- usually in seconds. Disks get hotter and hotter, and may
take several minutes to cool down. And it's not just the rotors and pads that get hot, but the
calipers, oil, etc.

Matt O.

 

Ryan Cousineau at [email protected] wrote on 4/21/03 6:31 PM:
>
> Well, I know, and that explains the 6" rotors, but why the 8" rotors? I've given my thesis:
> modulation.

Y'know, I've seen "modulation" bandied about since the push-n-rush to linear-pull (V) brakes. I must
ask, "exactly what you mean here by that term?"

It would seem you have more relative braking force using a larger brake pad surface against a larger
rotor which can dissipate heat more efficiently.

So, you have the ability to generate greater amounts of braking force against the momentum of
the wheel.

You can arguably modulate your speed by applying this higher braking force.

But, the disk systems I've messed with seem to have (like V-brakes) a narrower range of modulation
of the actual braking force - simply put, they are either on or off. For most applications, it would
seem that you jump quickly from too little braking force to too much. That, by definition is less
modulation.

The "modulation" of speed is actually achieved by using a device which gives you less modulation of
the braking force - the practical application being that a rider gives little shots of maximum
braking force, rather than increasing braking force through modulation at the levers.

What is sounds like is that you are discussing braking force, and that more braking force is better.
Is that what you are saying?

-- Jim

 

Jobst,

Whats your opinion on hydraulic rim brakes like the Maguras?

I have not ridden them but hear they are strong and resposnive. I assume that is due to the
hydraulic activation reducing things like cavle stretch induced percieved loss of braking "power"

Tom

 

I have gone hydro and will never go back. I see the principal advantages as:

1) One finger braking. On a tricky decent, I can keep my middle finger on the brake and the
rest of my hand planted firmly on the grip. I do not have to choose between applying the
brakes and holding on for dear life.

2) Mud clearance and the fact that they actually work in the mud. Muddy rim brakes grind the
rims but are still slippery.

3) Heat dissipation. The rotors are smaller and heat up faster than rim brakes, but they have a
higher surface to volume ratio, especially with the cutouts that are now standard. The
rim/tire combo is a torous and the disc is, well a disc. Also, I will never again blow out a
tire because I overheated the rims. If you do a lot of serious downhills, 8" rotors are
better than six inch because of heat dissipation.

4) They sound cool: sort of a deep "whawhhh…" Even better; when breaking in new pads,
they wail like a banshee.

5) Knocked you rim out of true? No problem. The disc is fastened directly to the hub. Keeping
your wheelset true is still a good thing, but you will not get that annoying intermittent
brake rum because of it.

-dave

 

In article <[email protected]>, "Matt O'Toole"
<[email protected]> wrote:

> <[email protected]> wrote in message news:aN%[email protected]...
>
> > The big negative for disc brakes is the failure mode and
> reliability
> > when descending something like passes in the Alps where
> missing a
> > hairpin turn is DEATH. It's a long way down. When you
> lose fluid or
> > get even a tiny leak, it is serious trouble.
>
> You don't even need a leak to have major brake failure with disks. The main problem, safety-wise,
> is that they can overheat and "go away" very suddenly. Rim brakes' fade is much more gradual, and
> when it does happen you still have some braking power left.
>
> Rim brakes also cool off a lot faster -- usually in seconds. Disks get hotter and hotter, and may
> take several minutes to cool down. And it's not just the rotors and pads that get hot, but the
> calipers, oil, etc.
>
> Matt O.

Goodness, all these dangerous discs! I'm glad nothing important like my car or motorcycle uses these
deadly brake types.

PS: was I away when most bicycles stopped having two completely independent braking systems? Has
anyone here ever experienced complete brake failure, except maybe "I was riding a track bike
with no front brake, and..."?

--
Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club

 

Tom who? writes shyly:

> What's your opinion on hydraulic rim brakes like the Maguras?

> I have not ridden them but hear they are strong and resposnive. I assume that is due to the
> hydraulic activation reducing things like cavle stretch induced percieved loss of braking "power"

The "cable stretch" bugaboo is untrue. Cables do not perceptibly stretch and most reasonable pads do
not fade. What is seen as cable stretch is primarily caliper flex and pad compression. Meanwhile,
hydraulic brakes are not immune to these problems, especially if they are mounted like cantilevers
without "brake boosters" to prevent fork spreading. Plastic hydraulic line have their own version of
"cable stretch" in that they expand.

You can't make them any more forceful than any other brake given the constraints. Pad clearance must
be taken up and hand levers (human hands) haven't changed in a few thousand years. Therefore, the
mechanical advantage of the hand to brake pad is fairly well fixed. The self centering dual pivot
brake has run up against this limit with its pads dragging on rims when climbing out of the saddle.

With a mechanical advantage currently in use, descending mountain roads in wet weather wears brake
pads enough to require brake adjustment as the hand lever runs out of travel. Taking up pad
clearance and pad wear are the limitation of brakes without power assist as is used in cars. With
hand operation, hand lever stroke is limited to what the hand can readily span at a given force.

The Magura web site sidesteps these issues.

Jobst Brandt [email protected] Palo Alto CA

 

Ryan Cousineau writes:

>>> The big negative for disc brakes is the failure mode and reliability when descending something
>>> like passes in the Alps where missing a hairpin turn is DEATH. It's a long way down. When you
>>> lose fluid or get even a tiny leak, it is serious trouble.

>> You don't even need a leak to have major brake failure with disks. The main problem, safety-wise,
>> is that they can overheat and "go away" very suddenly. Rim brakes' fade is much more gradual, and
>> when it does happen you still have some braking power left.

>> Rim brakes also cool off a lot faster -- usually in seconds. Disks get hotter and hotter, and may
>> take several minutes to cool down. And it's not just the rotors and pads that get hot, but the
>> calipers, oil, etc.

> Goodness, all these dangerous discs! I'm glad nothing important like my car or motorcycle uses
> these deadly brake types.

Stop wringing your hands. Bicycle disc brakes are not motor vehicle brakes and must compete in
weight and size to trivially simple caliper rim brakes. If you want to cite motorcycle brakes in
this context, I suggest you get some from a motorcycle shop and install them on your bicycle.

> PS: was I away when most bicycles stopped having two completely independent braking systems? Has
> anyone here ever experienced complete brake failure, except maybe "I was riding a track bike
> with no front brake, and..."?

I see, you haven't tried this but next time you are descending a mountain road, entering a sharp
turn, try using just the rear brake instead of the front one, in the last moment. I think you'll see
the light... maybe.

Jobst Brandt [email protected] Palo Alto CA

 

"Jim Edgar" <[email protected]> wrote in message news:BACA1A3D.3EBFE%[email protected]...

> Y'know, I've seen "modulation" bandied about since the
push-n-rush to
> linear-pull (V) brakes. I must ask, "exactly what you
mean here by that
> term?"

"Modulation" refers to the ability to precisely control the amount of braking, in a way that
feels comfortable to the user. Brakes without good modulation have an on/off nature, with little
in between.

Matt O.

 

Ryan Cousineau at [email protected] wrote on 4/22/03 7:32 AM:
> PS: was I away when most bicycles stopped having two completely independent braking systems? Has
> anyone here ever experienced complete brake failure, except maybe "I was riding a track bike
> with no front brake, and..."?

Well, then you'd have to have the chain break as well, or be running a cog with no lockring...

;^)

 

Matt O'Toole at [email protected] wrote on 4/22/03 11:20 AM:
> "Jim Edgar" <[email protected]> wrote in message
> news:BACA1A3D.3EBFE%[email protected]...
>
>> Y'know, I've seen "modulation" bandied about since the push-n-rush to linear-pull (V) brakes. I
>> must ask, "exactly what you mean here by that term?"
>
> "Modulation" refers to the ability to precisely control the amount of braking, in a way that feels
> comfortable to the user. Brakes without good modulation have an on/off nature, with little in
> between.

Yep, that's what it _should_ mean.

It just seems that the original poster was speaking about braking force rather than actual braking
modulation - that's what I wasn't sure about.

Seems to me that V/Linear brakes have generally less modulation to braking force, and that disc
systems seem similar to V/linears in that respect.

-- Jim