How to quiet V brakes?
Tyler Rutherford
I've heard there is a way to quiet V-brakes. Anyone know what it is?
(Besides taking them off). I've Shimano XT's.
Chuck Fry
In article <6cv65o$l...@bgtnsc01.worldnet.att.net>,
Tyler Rutherford <lo...@worldnet.att.net> wrote:
>I've heard there is a way to quiet V-brakes. Anyone know what it is?
>(Besides taking them off). I've Shimano XT's.
First, check brake toe-in. The trailing edges of the pads should
contact the rim first. Do what you have to do to make this happen.
Next, make sure the rim is *really* clean, as in soap and water washed
at a bare minimum. Try to get all the old buildup off, use a scouring
pad if necessary. I've had good results using automotive brake cleaner
(which is toxic and may damage rubber, so use it carefully and
preferably on a bare rim).
Be sure the pads are also clean. As with automotive brake linings, if
they've ever been seriously contaminated with oil or grease, THROW THEM
OUT and get a new set!
The last time I cleaned my rims this thoroughly, I had some initial
screeching, which went away as the brake pad material was deposited on
the rim again. Now my V-brakes (STX/LX) are nice and quiet.
-- Chuck
--
Chuck Fry -- Jack of all trades, master of none
chu...@chucko.com (text only please), chuc...@home.com (MIME enabled),
chu...@gateway.idiom.com (SPAM ONLY)
charles beristain
"Tyler Rutherford" <lo...@worldnet.att.net> wrote:
>I've heard there is a way to quiet V-brakes. Anyone know what it is?
>(Besides taking them off). I've Shimano XT's
I solved the problem with a carbon fiber booster ( it
stiffens/damps).. not a squeak since... and i tried everything prior
to that .. nothing worked for long.. but the booster.
charlie
stolen bike and accident databases at http://pages.prodigy.com/CharlieB/
Arthur D. Mitchell
Headphones..just kidding. Newer pads often quite them. Make sure you DO
NOT have any toe in the brake pad. Older pads (from the XT debut) simply
make noise. You may also have play in the calipers if they have some
mileage on them. Shimano sells a shim kit to fix this. If the brakes
move a lot front to rear when you grab them, get the shim kit from a bike
shop.
--
A Post from:
Art's Bike Shop-Check it out!
http://mustang.apollonian.com/~bike_guy/
Tyler Rutherford wrote:
> I've heard there is a way to quiet V-brakes. Anyone know what it is?
> (Besides taking them off). I've Shimano XT's.
Sheldon Brown
Tyler Rutherford wrote:
>
> > I've heard there is a way to quiet V-brakes. Anyone know what it
> > is? (Besides taking them off). I've Shimano XT's.
Jobst Brandt suggested:
> If you can use plain cantilevers, do so. The V-brake is a compromise
> solution for rear suspension. Other than that, it has the same basic
> geometry as a cantilever because its pivot points are the same. The
> additional levers and appropriately lower hand lever ratio combine to
> make a clumsy brake that chatters, especially the one with the
> parallelogram linkage. The V-brake is a dud brought on by suspension.
I think there are two variables being confounded here:
1. The "direct-pull" design, also known by Shimano's trademark "V-Brake" vs.
conventional cantilevers.
B. Simple direct-pull brakes, such as the Shimano LX and various other brands
vs. parallelogram-linkage type V-Brakes, specifically the Shimano XT and XTR.
As to issue 1., I've come to conclude that, when used with suitable levers,
they are often superior to conventional center-pull cantilevers. The problem
with center-pull cantilevers is that the mechanical advantage (commonly, but
inaccurately called "power") varies as the brake is applied. As the shoes
wear, the brake travels farther before the shoes contact the rim. This
increases the angle of the transverse cable, so the mechanical advantage
decreases with shoe wear.
This can be corrected if the shoes are re-adjusted in their attachment to the
arm. It's a pain to readjust the shoes, especially after they have worn to
fit the rim profile, so most people compensate for the wear by turning the
cable adjuster. Unfortunately, adjusting the cable raises the yoke and
reduces the mechanical advantage.
The details of this are explained in my article on Cantilever Geometry:
http://www.sheldonbrown.com/cantilever_geometry.html
Direct pull cantilevers don't suffer from this problem. The mechanical
advantage is basically fixed by the design of the cantis, and the placement of
the bosses with respect to the rim. Mechanical advantage remains essentially
constant regardless of the pad wear. Advising someone to switch to
center-pull cantilevers entails replacing the entire brake system, since the
levers are incompatible.
As to issue B., the parallelogram linkage is the source of the squealing
problem, not the fact that direct-pull cantilevers are used. The vast
majority of direct-pull brakes don't have this linkage, and don't have this problem.
The parallelogram linkage is not valueless, but for most cyclists it isn't
necessary either. The problem it addresses arises when very plump tires are
used on very skinny rims, which is currently fashionable on many mountain
bikes.
With such rims and tires, any simple cantilever, whether direct-pull or
center-pull, has a problem with the brake shoes needing to be adjusted very,
very carefully. The adjustment must find the safe area between the Scylla of
the shoe rubbing on the tire sidewall when the brake is not engaged, and the
Charybdis of the shoes diving under the rim, into the spokes, as the shoes
wear down.
Sheldon "Progress Is Good" Brown
Newtonville, Massachusetts
+--------------------------------------------+
| All great truths begin as blasphemies. |
| --G. B. Shaw |
+--------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-1040 FAX 617-244-1041
http://www.sheldonbrown.com/harris
Jobst Brandt
Tyler Rutherford writes:
> I've heard there is a way to quiet V-brakes. Anyone know what it
> is? (Besides taking them off). I've Shimano XT's.
If you can use plain cantilevers, do so. The V-brake is a compromise
solution for rear suspension. Other than that, it has the same basic
geometry as a cantilever because its pivot points are the same. The
additional levers and appropriately lower hand lever ratio combine to
make a clumsy brake that chatters, especially the one with the
parallelogram linkage. The V-brake is a dud brought on by suspension.
Are we making progress?
Jobst Brandt <jbr...@hpl.hp.com>
Mark Chandler
In article <6cva5k$n1t$1...@shell5.ba.best.com>, chu...@shell5.ba.best.com (Chuck Fry) wrote:
> In article <6cv65o$l...@bgtnsc01.worldnet.att.net>,
> Tyler Rutherford <lo...@worldnet.att.net> wrote:
> >(Besides taking them off). I've Shimano XT's.
>
> contact the rim first. Do what you have to do to make this happen.
*IF* you must toe the pads, the leading edge of the pad should contact
the rim first. By "leading," I mean the end facing the front of the
bike.
> Next, make sure the rim is *really* clean, as in soap and water washed
> at a bare minimum. Try to get all the old buildup off, use a scouring
> pad if necessary. I've had good results using automotive brake cleaner
> (which is toxic and may damage rubber, so use it carefully and
> preferably on a bare rim).
I've used "synthetic" steel wool sanding pads with great success. No
little bits of metal to imbed in the rim (and rust), and your hands are
spared from said shards, too.
> Be sure the pads are also clean. As with automotive brake linings, if
> they've ever been seriously contaminated with oil or grease, THROW THEM
> OUT and get a new set!
Some fine sandpaper will work wonders here.
> The last time I cleaned my rims this thoroughly, I had some initial
> screeching, which went away as the brake pad material was deposited on
> the rim again. Now my V-brakes (STX/LX) are nice and quiet.
Another thing to consider are different pads. One bikes and wheels that
would NOT shut up, I fixed the problem with WTB RazorBlades. The
abrasive compound took the rim down to bare metal in 2-3 rides, and the
dual-compound worked great from then on.
--mc
Mark Chandler m...@hooked.net Concord, CA
Matt O'Toole
Jobst Brandt wrote in message <6cvrn0$n...@hplntx.hpl.hp.com>...
>If you can use plain cantilevers, do so. The V-brake is a compromise
>solution for rear suspension. Other than that, it has the same basic
>geometry as a cantilever because its pivot points are the same. The
>additional levers and appropriately lower hand lever ratio combine to
>make a clumsy brake that chatters, especially the one with the
>parallelogram linkage.
The length of the lever arm has nothing to do with the brake's chattering.
Chattering is caused by sloppy pivots and linkages. Although XT and XTR
V-brakes have parallel push linkages which are often sloppy and prone to
chatter, other models of long arm brakes do not. The main brake pivot is
also a problem, but it always was with some models. It'st not a question of
design, but of manufacturing tolerances. Many older cantilevers were
sloppily made, while newer brakes, V-type or no, are usually much better.
>The V-brake is a dud brought on by suspension.
Traditional cantilevers were usually duds when purchased with a new bike,
because they were never set up properly. If the monkeys can't be trained,
it's better to remove them from the show.
>Are we making progress?
If it means better braking for the masses, sure. The only penalty is a few
extra grams over the best traditional cantis, which are too expensive
anyway. While some Shimano V-brakes chatter and squeal, so did some of the
older models, with their sloppy pivots and crappy pads. There are other
alternatives now, just as there were then.
Matt O.
Matt O'Toole
Mark Chandler wrote:
>Another thing to consider are different pads. One bikes and wheels that
>would NOT shut up, I fixed the problem with WTB RazorBlades. The
>abrasive compound took the rim down to bare metal in 2-3 rides, and the
>dual-compound worked great from then on.
Not if you have to pay for those WTB pads. A new rim might be cheaper than
that little ritual!
Matt O.
Propeloton
After reading ALL these posts-please-once again-how are V barkes 'better'???
pietro
Chuck Fry
In article <6d05nh$hen$1...@was.hooked.net>, Mark Chandler <m...@hooked.net> wrote:
>In article <6cva5k$n1t$1...@shell5.ba.best.com>, chu...@shell5.ba.best.com (Chuck Fry) wrote:
>> First, check brake toe-in. The trailing edges of the pads should
>> contact the rim first. Do what you have to do to make this happen.
>
>*IF* you must toe the pads, the leading edge of the pad should contact
>the rim first. By "leading," I mean the end facing the front of the
>bike.
Sorry about the confusion. I mean the same thing, but my terminology is
backwards relative to yours.
"Leading" to me means the end facing against the direction of rotation.
A given spot on the wheel in normal rotation goes past the "leading"
edge of the pad first, then the "trailing" edge. Hope this makes my
meaning clear.
>> Be sure the pads are also clean. As with automotive brake linings, if
>> they've ever been seriously contaminated with oil or grease, THROW THEM
>> OUT and get a new set!
>
>Some fine sandpaper will work wonders here.
If only the surface of the pad is glazed or contaminated, sure. But if
they've been soaked in lubricant, they're useless.
This is one of the reasons I recommend against spray lubes -- they go
everywhere but where you want them. Anyone lubing their chain from a
spray can is likely spritzing oil all over the rim. This cannot help
braking.
Garry Lee
The V-brake is a dud brought on by suspension.
Can't agree.
Theoretically you're right but adjusting cantilevers by moving in the
blocks is fiddly and error-prone whereas the V is difficult to set up
badly. That's its advantage. I don't use the one with the fiddly bits.
The best brakes of all of course are Magura.
Sheldon Brown
Peter Propeloton asked:
>
> After reading ALL these posts-please-once again-how are V barkes 'better'???
Sorry you missed my post on this topic, where I expained:
> ...when used with suitable levers,
> they are often superior to conventional center-pull cantilevers. The problem
> with center-pull cantilevers is that the mechanical advantage (commonly, but
> inaccurately called "power") varies as the brake is applied. As the shoes
> wear, the brake travels farther before the shoes contact the rim. This
> increases the angle of the transverse cable, so the mechanical advantage
> decreases with shoe wear.
>
> This can be corrected if the shoes are re-adjusted in their attachment to the
> arm. It's a pain to readjust the shoes, especially after they have worn to
> fit the rim profile, so most people compensate for the wear by turning the
> cable adjuster. Unfortunately, adjusting the cable raises the yoke and
> reduces the mechanical advantage.
>
> The details of this are explained in my article on Cantilever Geometry:
> http://www.sheldonbrown.com/cantilever_geometry.html
>
> Direct pull cantilevers don't suffer from this problem. The mechanical
> advantage is basically fixed by the design of the cantis, and the placement of
> the bosses with respect to the rim. Mechanical advantage remains essentially
> constant regardless of the pad wear. Advising someone to switch to
> center-pull cantilevers entails replacing the entire brake system, since the
> levers are incompatible.
Sheldon "Ditto" Brown
Newtonville, Massachusetts
+-------------------------------------------------------------+
| I often quote myself. It adds spice to my conversation. |
| --George Benard Shaw |
+-------------------------------------------------------------+
ADM
There is NO toe required on XT or above V-brakes!!!!! Using toe will
decrease braking power and the life of the brake pad! Don't do it!
> --
> A Post from:
> Art's Bike Shop-Check it out!
> http://mustang.apollonian.com/~bike_guy/
>
>
> First, check brake toe-in. The trailing edges of the pads should
ADM
Please take no offense Jobst, but are you crazy? I can stop on a dime
with Vs and canti's cannot compare. On the east coast of the US, the
trails are STEEP, ROCKY, and technical while MUDDY at the same time.
NOTHING compares to V brakes for cost vs. stopping power! They are to
MTBs what STI is to road bikes. Everyone has to realize that Bike stuff
is an open market like everything else. No matter who puts a product on
the market, it will not last unless it works!!!! Demand will die unless
the product works. Stop Shimano bashing. If they build a good thing
people buy it, it works. If they build a bad thing, people stop buying it
and it goes away. Anyone remember that automatic toe deice on cantis a
couple years ago? No, cause it sucked and no one wanted to use it.
Art
ADM
I agree as far as you go until the necessity of the Parallel brakes. Fat tires are not
the main concern, since canti brakes can be adjusted if you know what you are doing.
With a canti, as force is applied to close the brake, the pads move in an arc, which if
continued, will force the brakes BELOW the rim! I have seen it happen with properly
adjusted brakes. Teh nut holing the pad is often not able to withstand repeated HARD
braking. I agree XT style Vs are not for everyone, but is the riding style (fast with
hard braking) that makes them needed, not fat tires.
ADM
Now I stop, before I didn't! Controlled speed, not all on or all off!
Propeloton wrote:
> After reading ALL these posts-please-once again-how are V barkes 'better'???
> pietro
Sheldon Brown
I wrote:
> The parallelogram linkage is not valueless, but for most cyclists it isn't
> necessary either. The problem it addresses arises when very plump tires are
> used on very skinny rims, which is currently fashionable on many mountain
> bikes.
>
> With such rims and tires, any simple cantilever, whether direct-pull or
> center-pull, has a problem with the brake shoes needing to be adjusted very,
> very carefully. The adjustment must find the safe area between the Scylla of
> the shoe rubbing on the tire sidewall when the brake is not engaged, and the
> Charybdis of the shoes diving under the rim, into the spokes, as the shoes
> wear down.
Art responded:
>
> I agree as far as you go until the necessity of the Parallel brakes.
You believe parallel brakes _are_ a necessity? Billions of cyclists have not
found this to be the case.
> Fat tires are not the main concern, since canti brakes can be adjusted
> if you know what you are doing.
Yes, but unfortunately there are a great many people who _don't_ know what
they're doing in this regard. Even if the brakes are adjusted properly, the
adjustment changes as the pads wear. For riders who don't check the condition
of their pads, this can cause a problem.
> With a canti, as force is applied to close the brake, the pads move in an arc, which if
> continued, will force the brakes BELOW the rim! I have seen it happen with properly
> adjusted brakes. Teh nut holing the pad is often not able to withstand repeated HARD
> braking. I agree XT style Vs are not for everyone, but is the riding style (fast with
> hard braking) that makes them needed, not fat tires.
If you don't have fat tires on skinny rims, you can set the shoe so that it
hits higher up on the rim, reducing the risk of diving. Unfortunately, with
fat tires/skinny rims, you can't have the shoe of a simple cantilever hit at
the top edge of the rim without having it also scrub on the sidewall of the tire.
The tallness/angle of the rim's braking surfaces also come into this. There
was a year, a few years back, when Trek was supplying skinny aero rims on some
of their mountain bikes, which were a particular problem.
Puleeeeeeeeeeeze, if you're going to ask a question on one of the Newsgroups
or email lists that I frequent, don't ask me by private email at the same
time. It's really a bummer to go to the trouble of composing a private
answer, then to have the question re-asked in public and either have to ignore
it or rephrase it to make it more general in application.
Sheldon "Each Type Has Its Applications" Brown
Newtonville, Massachusetts
+-----------------------------------------------------------------+
| Remember that engineering is about trade-offs. None of |
| these systems are ideal, each of them has advantages and |
| disadvantages. Which issues are most important is a matter |
| of judgment and personal choice. Don't expect that you |
| will have the same priorities that I (or anyone else for |
| that matter) has. |
| --David Wittenberg |
+-----------------------------------------------------------------+
Stephen David Gravrock
I realize I'm too young to be a proper retro-grouch, but I have to agree
with Jobst here, at least to some extent.
I would disagree with the statement that V-brakes are a dud. I do
think that they have advantages, specifically simplicity and ease of
adjustment. Simply put, standard cantis are a pain in the butt to set up
properly, and almost always come out of the bike shop with a suboptimal
setup.
I wouldn't take the v-brakes off of a bike that came with them and
replace them with centerpulls. However, if one is willing to tinker,
there's no point in making the upgrade on a bike that -didn't- come with
V-brakes. It's worth remembering that v-brakes were designed as a solution
to the cable routing problems inherent in suspension (an elegant solution,
IMO) not a replacement for standard cantis.
> As to issue 1., I've come to conclude that, when used with suitable
> levers, they are often superior to conventional center-pull cantilevers.
> The problem with center-pull cantilevers is that the mechanical
> advantage (commonly, but inaccurately called "power") varies as the
> brake is applied. As the shoes wear, the brake travels farther before
> the shoes contact the rim. This increases the angle of the transverse
> cable, so the mechanical advantage decreases with shoe wear.
> This can be corrected if the shoes are re-adjusted in their attachment
> to the arm. It's a pain to readjust the shoes, especially after they
> have worn to fit the rim profile, so most people compensate for the wear
> by turning the cable adjuster. Unfortunately, adjusting the cable
> raises the yoke and reduces the mechanical advantage.
Brake pad attachment should be adjusted regularly, even with v-brakes.
(Not speaking of the paralell-push type here.) If you don't do this, and
simply turn the barrel adjuster, the geometry of the system will change,
as you pointed out. The change is small with V-brakes, but it's still
there. I'll grant that it's a pain, but brake pad placement is perhaps the
most important step in brake adjustment. The barrel adjuster should be
used for fine-tuning only.
The decline in the mechanical advantage as the pads compress, which you
pointed out, is the most distintive characterisic of centerpull cantis.
While it's really a matter of preference, I find the modulation more to my
liking than the constant m.a. of v-brakes. (I suspect that a more constant
m.a. could be achieved with Servo-Wave levers or similar, but I digress.)
On the other hand, this is also the main flaw of cantis: the m.a. is
highest before the pads contact the rim. This is undesirable because the
higher m.a. means more cable must be pulled, therefore with standard
levers too much lever travel will already be used when the pads make
contact.
This can be corrected by using v-brake levers. That does reduce the m.a.
of the entire system, for reasons I won't go into here. Read
http://www.sheldonbrown.com/cantilever_geometry.html.
> Advising someone to switch to center-pull cantilevers entails replacing
> the entire brake system, since the levers are incompatible.
Only if you're using standard levers with v-brakes. My limited trials
using XT v-brake levers with cantis shows that the levers are not only
compatible, but improve overall brake function and ease of setup. In fact,
I would recommend making the lever upgrade first, if one wants v-brakes
but doesn't have the cash to do it all at once.
Bottom line, it comes down to two questions: How much are you willing to
mess with the brakes, and what sort of modulation do you prefer?
They both work.
John Stevenson
In article <6cvrn0$n...@hplntx.hpl.hp.com>,
jbr...@hpl.hp.com (Jobst Brandt) wrote:
>If you can use plain cantilevers, do so. The V-brake is a compromise
>solution for rear suspension. Other than that, it has the same basic
>geometry as a cantilever because its pivot points are the same. The
>additional levers and appropriately lower hand lever ratio combine to
>make a clumsy brake that chatters, especially the one with the
>parallelogram linkage. The V-brake is a dud brought on by suspension.
>
Jobst, many riders use the XT and XTR V-brakes without problems. Many
old-style cantilevers have problems with brake squeal. Whatever the cause
of squeal is, I don't think you can assign it to something as simple as the
long arm and parallelogram pivot of these brakes.
>Are we making progress?
Yes. I used to wander round MTB races squeezing brake levers and examining
other people's brakes. In well over 50 per cent of cases they were set up
to deliver a low total mechanical advantage, a hard lever feel and lousy
braking. The problem was that when riders replaced their brake blocks, they
would shove the studs all the way into the carriers, then set the straddle
wire up so that it pointed upwards in a sharp inverted-v. The result was
brakes that might as well not be there.
The original formulation of Murphy's Law states that if there are two ways
to do something, and one of them is wrong, people will choose the wrong
one. Cantilever brakes used to illustrate this perfectly.
V-brakes, on the other hand, cannot be assembled incorrectly. If you set a
V-brake up so the pads hit the rim you will get much, much better braking
than most people ever achieved with cantilevers. This is progress, IMNAAHO.
>
>Jobst Brandt <jbr...@hpl.hp.com>
>
Cheers
john
john stevenson (email: john...@magna.com.au)
List manager, mtb-oz - the mailing list for mountain bikers down under
"If they made a drug that made you feel like a dog with its head out of a car window, I'd take it!" -- Mike Robbins
Jobst Brandt
Sheldon Brown writes:
> Puleeeeeeeeeeeze, if you're going to ask a question on one of the
> Newsgroups or email lists that I frequent, don't ask me by private
> email at the same time. It's really a bummer to go to the trouble
> of composing a private answer, then to have the question re-asked in
> public and either have to ignore it or rephrase it to make it more
> general in application.
I've been promoting this concept for awhile now and the lame excuses I
get for sending e-mail are so tenuous they are transparent BS. I hope
you make more progress in this direction. These dual mailings/postings
are worse than spam... or even an empty spam can.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
Art's Bike Shop writes:
> Please take no offense Jobst, but are you crazy?
So why do I have to receive this in e-mail to which I respond only to
find it here on the net? As you know, I replied to you on this but
judging from the polite opening, I also assumed you don't know how to
respond to newsgroups and saved a copy of my reply which I will amend
here.
Mybe you don't understand the rudiments of communication. To offer
insults and ask that no offense is taken, is the height of rudeness.
Can you think of a better opening for a discussion?
> I can stop on a dime with Vs and canti's cannot compare.
And to what do you attribute this substantial difference? The
mechanical advantage is the same and the pads and rims are the same.
The radius of sweep is also the same. Where does this perceived
difference come from? The parallelogram linkage does not change the
arc of the pad sweep, it only keeps the pad facing inward as it traces
th4e same path that a cantilever does. To make up for that, it has
more parts that can chatter.
> On the east coast of the US, the trails are STEEP, ROCKY, and
> technical while MUDDY at the same time. NOTHING compares to V
> brakes for cost vs. stopping power! They are to MTBs what STI is to
> road bikes.
What makes you think that your trails are different from all the rest
of the challenging trails in the world. I suspect you have not
bicycled elsewhere. Let me assure you that the same difficult trails
are to be found in most of the world, including the USA.
> Everyone has to realize that Bike stuff is an open market like
> everything else. No matter who puts a product on the market, it
> will not last unless it works!!!! Demand will die unless the
> product works.
I think you misunderstood. The V-brake was made to address rear
suspension that makes cantilevers impractical. It's hard to hang a
straddle cable over a moving rear suspension on most bikes. The
V-brake was not intended to be an improvement over cantilevers. That
gullible MTB riders took it to be an "upgrade" is only a windfall for
the manufacturer.
> Stop Shimano bashing.
I didn't see the word Shimano in anything I wrote about this. I think
you jump to conclusions. Are you perhaps over-stocked on V-brakes?
> If they build a good thing people buy it, it works. If they build a
> bad thing, people stop buying it and it goes away. Anyone remember
> that automatic toe deice on cantis a couple years ago? No, cause it
> sucked and no one wanted to use it.
Don't tell me what remains on the market. I have seen many rave
devices vanish without a trace, such as the Campagnolo Delta brake and
many goofy cranks, chainwheels, and wheels. They all sound as good as
gold until someone points out that the new emperor has no clothes, or
the novelty wears off and there is no points gained for having the
stuff. Helium wheels come to mind along with Rolf. How about
FiberFlite? I got rejoinders like yours when I found these spokes to
be anything but useful.
Jobst Brandt <jbr...@hpl.hp.com>
Matt O'Toole
Thanks for the picture!
When I first saw XT V-brakes, I thought they were the coolest thing going.
No more fiddly brake adjstments, no pads hitting tires, no pot-metal pad
holders, etc! Then, I wiggled the thing, hmm. Linkages shouldn't wiggle!
Sheldon Brown wrote in message <34F4C2CC...@sheldonbrown.com>...
>Despite the difficulties introduced by the extra linkage, it really is a
>rather clever idea, and I'd expect that when they get the bugs out of the
>engineering, it is likely to be a success.
The bugs aren't in the engineering, they're in the sloppy manufacture. If
Craig Metalcraft can produce Superlinks to the fine tolerances necessary,
for $5 retail, then a huge company like Shimano could make brake linkages
that are tight to begin with, and that would remain that way for a
reasonable period of time. If they cared, that is. For years, Shimano made
cantilevers that wiggled badly on the brake posts. Of course, the real
problem was no industry standard for brake posts, but Dia Compe sold nice
brakes with neat bushings that were glued over the posts with Loctite,
solving the problem. Despite the extra, close tolerance part, Dia Compe
brakes were half the price of similar Shimanos.
Matt O.
Jobst Brandt
Sheldon Brown writes:
>> The parallelogram linkage does not change the arc of the pad sweep,
>> it only keeps the pad facing inward as it traces the same path that
>> a cantilever does.
> Actually, that's not correct. In a typical simple cantilever setup,
> the shoe is moving downward at about a 45 degree angle, in the
> section of its arc that brings it into contact with the rim.
If you look more carefully, you'll find that the pivot point for the
brake is the same, the distance from the pivot to the contact point is
the same and only the parallelogram version keeps the pad from
rotating. The motion of the pad is identical to the cantilever. The
reason this is so is that the width of tire that must pass between the
pivot pints prescribes the location, not the type of actuation.
> Shimano's parallelogram linkage causes the pivoting arms to be
> basically vertical in the useful range of their motion, so the
> direction of pad movement is basically horizontal.
The pivot point is not changed by the parallelogram and that is what
counts for the braking motion.
> Readers with modern newsreaders can see this from the linked .gif;
> for readers with older newsreaders, my apologies for the bandwidth.
> Despite the difficulties introduced by the extra linkage, it really
> is a rather clever idea, and I'd expect that when they get the bugs
> out of the engineering, it is likely to be a success.
It is already a success for what it does, and that is to enable rear
suspension bikes to have a pseudo-cantilever brake.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
Matt O'Toole writes:
> The bugs aren't in the engineering, they're in the sloppy manufacture. If
> Craig Metalcraft can produce Superlinks to the fine tolerances necessary,
> for $5 retail, then a huge company like Shimano could make brake linkages
> that are tight to begin with, and that would remain that way for a
> reasonable period of time.
I think the clearance is necessary to prevent the brake from jamming
when it is exposed to fine road grit. I am sure that the performance
you see is related to the reliability of the brake and that this has
been thoroughly tested. The problem lies in the fundamental design,
and this is demanded by the application. The V-brake is not an
improvement over cantilevers, it is a compromise for large clearance
brake on a rear suspension bike.
Jobst Brandt <jbr...@hpl.hp.com>
Garry Lee
The V-brake is not an
>improvement over cantilevers, it is a compromise for large clearance
>brake on a rear suspension bike.
In maximum power it is not an improvement but in easy of adjustment it is
light years ahead of Cantis.
Matt O'Toole
Jobst Brandt wrote in message <6d4jj1$6...@hplntx.hpl.hp.com>...
>If you look more carefully, you'll find that the pivot point for the
>brake is the same, the distance from the pivot to the contact point is
>the same and only the parallelogram version keeps the pad from
>rotating. The motion of the pad is identical to the cantilever. The
>reason this is so is that the width of tire that must pass between the
>pivot pints prescribes the location, not the type of actuation.
This is true. Its value is that the pad wears flat, instead of at an ever
increasing angle. The angle makes it difficult or impossible to readjust
the pads to restore brake geometry and also clear the tire, unless the pads
are sanded square again, which takes even more time. With the pads wearing
square, they can be made thinner, and simply replaced instead of fiddled
with.
Yes, bike mechanics should be able to adjust brakes quickly and efficiently.
The reality is, they usually can't, and the customer winds up with brakes
that don't work, or the shop owner watches his mechanic piss away a $40 hour
fiddling with someone's old cantilevers. It is better for both to forget
the whole process, and just slip in a new $12 set of pads.
>It is already a success for what it does, and that is to enable rear
>suspension bikes to have a pseudo-cantilever brake.
Yes, but the practical result has been that most people get better brakes.
It doesn't matter that it's not due to the type of brake, but improved
quality control in the setup process.
Matt O.
Dave Blake
jbr...@hpl.hp.com carefully typed:
>Matt O'Toole writes:
>> The bugs aren't in the engineering, they're in the sloppy manufacture. If
>> Craig Metalcraft can produce Superlinks to the fine tolerances necessary,
>> for $5 retail, then a huge company like Shimano could make brake linkages
>> that are tight to begin with, and that would remain that way for a
>> reasonable period of time.
>I think the clearance is necessary to prevent the brake from jamming
>when it is exposed to fine road grit. I am sure that the performance
>you see is related to the reliability of the brake and that this has
>been thoroughly tested. The problem lies in the fundamental design,
>and this is demanded by the application. The V-brake is not an
>improvement over cantilevers, it is a compromise for large clearance
>brake on a rear suspension bike.
The clearance that you speak of for preventing jamming from road grit
is largely radial clearance around the bushing on the pivot of the
brake boss. The squeal comes from fore and aft movement of the
brake. A close examination of the Shimano brake arms shows that there
is inconsistency between the length of the cylinder in the brake arm
and the length of the bushing. There is no need for a high
variability in these two lengths, as any inconsistency leads to a
poorly functioning brake. Put bluntly, they are not made well. There
was a similar fate for some of the older Dia Compe cantilevers which
would not shut up. Further, the parallogram design is completely
underdesigned for maintaining stiffness along the vector of the rim
motion. Once it softens up, there is no stopping the squealing.
However, if you look at a V brake design from someone like
Avid, you find no such inconsistencies, and no such squealing.
The brake is relatively easy to set up, and requires much
less maintenance that cantilever brakes. There is no
parallelogram on the 2.0 brakes, and the bushing length is
a tight match to that of the brake arm cylinder. They don't
squeal.
Also, the direct pull design has the advantage of keeping the
mechanical lever at the brake end of the brake cable nearly
constant throughout the wear of the brake pad, making
readjustments of the brake arm much less frequent to
maintain braking power. A decent V brake works as well as a
perfectly set up cantilever brake, does not squeal, and
requires much less maintenance. Are we making progress ?
Yes.
--
Dave Blake
dbl...@phy.ucsf.edu
Sheldon Brown
Jobst wrote:
> >> The parallelogram linkage does not change the arc of the pad sweep,
> >> it only keeps the pad facing inward as it traces the same path that
> >> a cantilever does.
I demurred:
> > Actually, that's not correct. In a typical simple cantilever setup,
> > the shoe is moving downward at about a 45 degree angle, in the
> > section of its arc that brings it into contact with the rim.
Jobst insisted:
> If you look more carefully, you'll find that the pivot point for the
> brake is the same, the distance from the pivot to the contact point is
> the same and only the parallelogram version keeps the pad from
> rotating. The motion of the pad is identical to the cantilever.
I thought this too, the first time I saw the design, but further examination
revealed this not to be the case. If you don't believe me from looking at the
drawing, check out one of these brakes on a bike. It is true that the _one_
of the four pivot axes, the one that does not move, is the same as that of a
one-piece cantilever.
E___(Brake shoe)
| | \________________
Rim | | ____ C o+++++++o D
| |__/ + +
______/ + +
+ +
+ +
+ +
+ +
+ +
+ +
B o+++++++o A (Fixed frame boss)
As the brake is applied, link A-D pivots counterclockwise in a circular arc
around the boss pivot A.
The linear direction of motion of point D (and of all of link C-D, to which
the shoe hardware E is attached) is tangential to this circle at point D.
This tangent is perpendicular to radius A-D. Since line A-D is essentially
vertical in the working range of the brake, the motion is essentially in a
horizontal direction. The motion is actually still part of a circular arc,
but it is the near-horizontal arc of that circle.
In the case of a rigid, simple cantilever (whichever type of cable connection
isused) The motion involved is the tangent of the circle at the radius A-E,
and is, indeed, on the order of 45 degrees.
> > Shimano's parallelogram linkage causes the pivoting arms to be
> > basically vertical in the useful range of their motion, so the
> > direction of pad movement is basically horizontal.
Jobst:
> The pivot point is not changed by the parallelogram and that is what
> counts for the braking motion.
Me:
The entire Earth revolves around a common axis, but the direction of linear
motion of a Californian is not the same as that of an Azerbaijani, and, in
fact they are moving toward stars on the opposite sides of the universe.
> > Despite the difficulties introduced by the extra linkage, it really
> > is a rather clever idea, and I'd expect that when they get the bugs
> > out of the engineering, it is likely to be a success.
Jobst:
> It is already a success for what it does, and that is to enable rear
> suspension bikes to have a pseudo-cantilever brake.
Once again, you're confounding the issue of cable connection, which indeed is
related to the problems of suspension bikes, with the issue of parallelogram
vs simple cantilevers.
The parallelogram linkage could be applied just as easily to a conventional
center-pull cantilever as to a direct-pull (side-pull) cantilever. It is just
coincidence that both features appeared in the Shimano line at the same model change.
Sheldon "Prefers .GIFs To ASCII Art" Brown
Newtonville, Massachusetts
+-----------------------------------+
| Habit is the nursery of errors. |
| --Victor Hugo |
+-----------------------------------+
Michael Prybell
You couldn't get a cantilever brake to stop you and you own a bike
shop?!?!?!? God help your poor customers. I must be living on borrowed
time, all I use and have ever used on MTBs are cantilevers.
For some strange reason they work pretty darn good on my bikes.
--
=============================================
= Life is like good singletrack. It has it's painfull =
= moments, but for the most part it's a great time !!! =
= Hammer On, Mike. mikepry...@worldnet.att.net =
=============================================
ADM wrote in message <34F49060...@mustang.apollonian.com>...
Mark McMaster
Jobst Brandt wrote:
>
> Sheldon Brown writes:
>
> >>>> The parallelogram linkage does not change the arc of the pad
> >>>> sweep, it only keeps the pad facing inward as it traces the same
> >>>> path that a cantilever does.
>
> >>> setup, the shoe is moving downward at about a 45 degree angle, in
> >>> the section of its arc that brings it into contact with the rim.
>
> you'll find it travels in an arc of radius A-D which is a smaller arc
> than a rigid cantilever follows. The difference is that the face of
> the V-brake pad remains parallel to the initial position while the
> cantilever rotates. Rotation is not the problem because the face
> wears off to match the rim. It is the cosine error that, unlike
> single pivot brakes in the small angle region, is about 45 degrees
> where sine is cosine and both are too much. This is unchanged by the
> parallelogram.
But if the pad moves on the an arc of radius A-D, but offset from D by
the distance D-E, than we need only keep arm A-D in an angular region
near the vertical to keep the pad from diving. Further, if we were to
put more spacers on the brake pad bolts, to push arm A-D outward so that
it angles away from the plane of the wheel, than the pad would actually
rise when the brake is actuated.
> > In the case of a rigid, simple cantilever (whichever type of cable
> > connection is used) The motion involved is the tangent of the circle
> > at the radius A-E, and is, indeed, on the order of 45 degrees.
>
> No the radius is A-(pad contact), a larger radius than the parallel
> V-brake.
As long as the arc length of the travel is reasonably smaller than the
radius, we can keep the angular travel small, and keep arm A-D near the
vertical.
> >> The pivot point is not changed by the parallelogram and that is
> >> what counts for the braking motion.
Due to the parallelogram (pantagraph), the pad does not travel on an arc
around the actual pivot point, but around a virtual pivot point that is
offset from A the same distance and direction as the pad is offset from
D.
Mark McMaster
MMc...@ix.netcom.com
David M Anthony
In article <6d4n53$7...@hplntx.hpl.hp.com>,
Jobst Brandt <jbr...@hpl.hp.com> wrote:
>Matt O'Toole writes:
>
>> The bugs aren't in the engineering, they're in the sloppy manufacture. If
>> Craig Metalcraft can produce Superlinks to the fine tolerances necessary,
>> for $5 retail, then a huge company like Shimano could make brake linkages
>> that are tight to begin with, and that would remain that way for a
>> reasonable period of time.
>
>I think the clearance is necessary to prevent the brake from jamming
>when it is exposed to fine road grit. I am sure that the performance
>you see is related to the reliability of the brake and that this has
>been thoroughly tested. The problem lies in the fundamental design,
>and this is demanded by the application. The V-brake is not an
>improvement over cantilevers, it is a compromise for large clearance
>brake on a rear suspension bike.
>
So is there no advantage to the near linear mechanical advantage aspect
of the sidepull/V-brake?
Now, the changing ratio of centre pull cantilever is not as bad as,
say for example, the Campy delta brake, but why is it better than
the straight-pulls?
Dave
--
Dave Anthony
Stephen David Gravrock
> Now, the changing ratio of centre pull cantilever is not as bad as,
> say for example, the Campy delta brake, but why is it better than
> the straight-pulls?
It's not inherently better. In fact, it makes setup more complicated. OTOH
it provides a variety of possible setups. Centerpull cantilevers give a
greater variety of possible setups than any other brake system. Granted,
this is not a good thing for the person who doesn't like to tinker.
Once the brakes are set up, the two systems will provide very different
modulation. While properly set-up cantis have about the same average
mechanical advantage as v-brakes, the feel is very different. Which is
better? It's really a matter of personal preference.
They both work well.
Mark Hickey
"Matt O'Toole" <ma...@deltanet.com> wrote:
>Jobst Brandt wrote in message <6d4jj1$6...@hplntx.hpl.hp.com>...
>>If you look more carefully, you'll find that the pivot point for the
>>brake is the same, the distance from the pivot to the contact point is
>>the same and only the parallelogram version keeps the pad from
>>rotating. The motion of the pad is identical to the cantilever. The
>>reason this is so is that the width of tire that must pass between the
>>pivot pints prescribes the location, not the type of actuation.
To put it a different light, it really doesn't matter much what the
pad does on the way to the rim - if it did a double flip with a
half-gainer and ended up parallel just as it touched the pad, it would
work just the same as a humble cantilever adjusted properly. The fact
that the high end V-brakes hold the pad parallel when not braking is a
performance non-issue.
>Its value is that the pad wears flat, instead of at an ever
>increasing angle. The angle makes it difficult or impossible to readjust
>the pads to restore brake geometry and also clear the tire, unless the pads
>are sanded square again, which takes even more time. With the pads wearing
>square, they can be made thinner, and simply replaced instead of fiddled
>with.
This is the one "advantage" to a parallelogram linkage (even wear of
the pad), but you could also have the same effect by simply throwing
away your canti brake pads when they're only half worn out (which will
still take a lot longer than cooking off a set of V-pads).
>Yes, but the practical result has been that most people get better brakes.
>It doesn't matter that it's not due to the type of brake, but improved
>quality control in the setup process.
Kinda sad, but true (that V's caught on largely because it was harder
to mess up the set-up). Personally, I find canti brakes easier to set
up, but then again, I'm just a hopeless retrogrouch. OTOH, I am now
riding some intensely steep and intermittently slippery downhills
(steps, actually) on which my canti's work MUCH better than a V, since
I can control the modulation at the hairy edge of control, instead of
"just over it". And it's *still* my legs that get tired instead of my
arms.... ;-)
Mark Hickey
Habanero Cycles
http://www.cynetfl.com/habanero/
Home of the $675 ti frame
Sheldon Brown
I wrote:
> > E___(Brake shoe)
> > | | \________________
> > Rim | | ____ C o+++++++o D
> > | |__/ + +
> > ______/ + +
> > + +
> > + +
> > + +
> > + +
> > + +
> > + +
> > B o+++++++o A (Fixed frame boss)
>
> > As the brake is applied, link A-D pivots counterclockwise in a circular arc
> > around the boss pivot A.
>
> > The linear direction of motion of point D (and of all of link C-D,
> > to which the shoe hardware E is attached) is tangential to this
> > circle at point D. This tangent is perpendicular to radius A-D.
> > Since line A-D is essentially vertical in the working range of the
> > brake, the motion is essentially in a horizontal direction. The
> > motion is actually still part of a circular arc, but it is the
> > near-horizontal arc of that circle.
Jobst disagreed:
> I think if you take your compass and trace the path of the brake pad,
> you'll find it travels in an arc of radius A-D which is a smaller arc
> than a rigid cantilever follows.
The size of the circle is relevant to issues of mechanical advantage, but
that's not what I'm discussing.
This is also the arc of radius B-D, for what that's worth. I never said nor
implied that it wasn't moving in an arc, but the issue is which part of the
circle that arc is taken from.
> The difference is that the face of
> the V-brake pad remains parallel to the initial position while the
> cantilever rotates. Rotation is not the problem because the face
> wears off to match the rim.
It is true that the rotation is not a serious problem with pad wear. I never
said it was. The real problem addressed by the linkage is the
dive/sidewall-rubbing issue with overhanging balloon tires.
> It is the cosine error that, unlike
> single pivot brakes in the small angle region, is about 45 degrees
> where sine is cosine and both are too much. This is unchanged by the
> parallelogram.
Au contraire, the angle _is_ changed by the parallelogram; that's what the
parallelogram is about. The tops of the vertical links (and the entire upper
horizontal link) are traveling in an arc at the top of the circle. The angle
is close to 90 degrees (or 0, depending on how you choose to measure it.)
Cosine error is negligible at this angle.
> > In the case of a rigid, simple cantilever (whichever type of cable
> > connection is used) The motion involved is the tangent of the circle
> > at the radius A-E, and is, indeed, on the order of 45 degrees.
>
> No the radius is A-(pad contact), a larger radius than the parallel
> V-brake.
The letter "E" in my ASCII sketch was intended to represent the pad contact.
Sorry if this wasn't clear.
> >> The pivot point is not changed by the parallelogram and that is
> >> what counts for the braking motion.
>
> > The entire Earth revolves around a common axis, but the direction of
> > linear motion of a Californian is not the same as that of an
> > Azerbaijani, and, in fact they are moving toward stars on the
> > opposite sides of the universe.
>
> I think that this nonsequitur could be resolved with a bit of
> mechanical drawing.
Unfortunately, some people dislike it when even on-topic images are posted, so
I'll have to make do with ASCII art and the mind's eye. Let us imagine a less
astronomical example: a bicycle wheel, spinning in the normal direction, with
the bike held in a stand. We will look at it from the right side.
Every part of the tire tread is turning at the same speed, and moving in an
arc of the same circle...but the tread at the bottom of the wheel is moving
toward the rear, while the tread at the 9:00 o'clock position is moving
straight up, and the tread at the 1:30 o'clock position is moving forward and
down at...a 45 degree angle, just like a simple cantilever!
The tread at the top of the wheel is moving _horizontally_ toward the front.
The upper horizontal link of the parallelogram (C-D) is at the top of its
circle, moving horizontally. Since the shoe is moving in a near-horizontal
direction, it can't rub on the bulging tire, and is not at risk for diving
under the rim, Q.E.D.
Sheldon "Virtually Horizontal" Brown
Newtonville, Massachusetts
+----------------------------------------------------+
| A little inaccuracy sometimes saves tons of |
| explanation. --H.H.Munro ("Saki")(1870-1916) |
+----------------------------------------------------+
Jobst Brandt
Sheldon Brown writes:
> E___(Brake shoe)
> | | \________________
> Rim | | ____ C o+++++++o D
> | |__/ + +
> ______/ + +
> + +
> + +
> + +
> + +
> + +
> + +
> B o+++++++o A (Fixed frame boss)
> As the brake is applied, link A-D pivots counterclockwise in a
> circular arc around the boss pivot A.
And yes, Sheldon is correct, as I learned when inspecting the linkage
on the bicycle more carefully. The motion of the pad is at the top of
the arc and therefore moves horizontally on the parallelogram.
Although the path takes a smaller radius than that of a cantilever
pad, it is in the ideal arc of the stroke where vertical motion is
minimum.
I don't use the brake so I can't speak from experience but opinions on
the brakes merit seem to vary from "chattering monster" to "excellent".
I must admit. I think the parallelogram version is an advance over its
predecessors. The extra linkage and cable mechanism will have to
demonstrate its durability. Assuming it is reliable, I believe it
should replace the cantilever. Not using fat tires, I don't think
I'll get one just the same.
Jobst Brandt <jbr...@hpl.hp.com>
Dave Blake
jbr...@hpl.hp.com carefully typed:
>I don't use the brake so I can't speak from experience but opinions on
>the brakes merit seem to vary from "chattering monster" to "excellent".
>I must admit. I think the parallelogram version is an advance over its
>predecessors. The extra linkage and cable mechanism will have to
>demonstrate its durability. Assuming it is reliable, I believe it
>should replace the cantilever. Not using fat tires, I don't think
>I'll get one just the same.
There are a number of considerations with the V brake that
are different, and in some cases worse, than cantilevers.
1) It puts an increased reactive force on the brake boss, so most
frames require a brake booster. The reactive force increases
monotonically with brake arm length. It is maximal for
infinitely long brake arms, or brakes with no straddle
cable like Maguras. Is it an improvement when you need a
brake booster where you didn't with cantilevers ?
2) The linkage is underdesigned. On a good pair of V brakes
from Shimano it doesn't last one hard season. The largest
effect of the poor linkage is the squealing of the brakes.
As the linkage wears, the brake becomes less stiff in
the direction of rim movement. Then the brake pad will
grab the rim, and release at the end of its flex in the
direction of rim travel. A reactive force brings the pad
forward from where it grabs the brake again, and the
result is a SQUEAL similar to that of an inexperienced
machinist turning stainless steel. The way to get rid of
brake squeal is to make the brake stiffer in the direction
of rim movement. With V brakes, that means first getting a
brake booster, then using the shim kit, then throwing the
brakes away every half season.
V brakes ought to be designed with NO linkage and keeping the
brake arms as short as possible while still allowing tire
clearance with the direct pull. That way you can avoid brake
boosters and flexy linkages while maintaining the primary
V brake advantage - nearly perfect leverage with little
maintenance.
--
Dave Blake
dbl...@phy.ucsf.edu
Chuck Fry
In article <6d6pc6$p...@hplntx.hpl.hp.com>,
Jobst Brandt <jbr...@hpl.hp.com> wrote:
>And yes, Sheldon is correct, as I learned when inspecting the linkage
>on the bicycle more carefully.
Good! I'm glad to see the two most knowledgeable posters in r.b.t
finally resolving their differences over this. :-)
Seriously, thanks to both of you for the reasoned and well thought out
discussion.
-- Chuck
--
Chuck Fry -- Jack of all trades, master of none
chu...@chucko.com (text only please), chuc...@home.com (MIME enabled),
chu...@gateway.idiom.com (SPAM ONLY)
Matt O'Toole
Mark Hickey wrote in message <34f6b4b...@news.nuri.net>...
>This is the one "advantage" to a parallelogram linkage (even wear of
>the pad), but you could also have the same effect by simply throwing
>away your canti brake pads when they're only half worn out (which will
>still take a lot longer than cooking off a set of V-pads).
Shimano finally (almost) figured it out just before V-brakes came out. A
good solution to the brake adjustment issue is pad holders with inexpensive,
thin, slip-in pads. That way, you can replace your pads before brake
geometry changes. Also, thin pads are a lot less flexy and squishy. The
feel at the lever is much improved with very thin pads. Shimano started on
this tack, but never got it right. The LX brakes had pads that were way too
thick and squishy, and too bulky and hard to adjust. The XT pads were
thinner, but still too large and clunky. Neither pad was ever available as
a separate, slip-in replacement. This is no surprise, as most bike shops
would rather sell you a $30 set of Ritcheys. I remember that Mathauser pads
were designed this way, but those slip-ins were never available separately,
either.
Matt O.
alex wetmore
Matt O'Toole wrote in message <6d79g2$9ni$1...@news01.deltanet.com>...
>Shimano finally (almost) figured it out just before V-brakes came out. A
>good solution to the brake adjustment issue is pad holders with
inexpensive,
>thin, slip-in pads. That way, you can replace your pads before brake
>geometry changes. Also, thin pads are a lot less flexy and squishy. The
>feel at the lever is much improved with very thin pads. Shimano started on
>this tack, but never got it right. The LX brakes had pads that were way
too
>thick and squishy, and too bulky and hard to adjust. The XT pads were
>thinner, but still too large and clunky. Neither pad was ever available as
>a separate, slip-in replacement. This is no surprise, as most bike shops
>would rather sell you a $30 set of Ritcheys. I remember that Mathauser
pads
>were designed this way, but those slip-ins were never available separately,
>either.
I think that you are mistaken about slipins not being available. My bike
originally came with STX-RC cantilever brakes (basically silver versions of
the LX cantis) that also had slipin pads. The replacement pads were
available at my LBS, which I know because I went through a few pairs of them
before wising up and switching to another type of brake pad.
Also, another LBS had the replacement Mathauser pads for their system that
took slip in pads.
Speaking of Mathauser, does anyone know if they have a pad that works with
V-brakes?
thanks,
alex
--
http://www.phred.org/~alex
Capt...@sheldonbrown.com
Dave Blake wrote:
>
> [a V-Brake] puts an increased reactive force on the brake boss,
This is not correct. For a given pad/rim material, and the same boss
positioning relative to the rim, the reactive force on the boss is related to
the braking force, and nothing else.
> so most frames require a brake booster.
This is also incorrect. The vast majority of bikes with these brakes do not
have nor need boosters. It is true that boosters can improve the "feel" of
any cantilever, and the more mechanical advantage the brake system has, the
more it benefits from a booster.
> The reactive force increases monotonically with brake arm length.
A interesting adverb...it's not in any of the dictionaries I consulted; what's
it mean?
The effective brake arm length, where boss loading is concerned, is the
distance from the boss to the part of the rim the brake shoe presses on.
Sheldon "Always Ready To Learn A New Word" Brown
Newtonville, Massachusetts
+-------------------------------------------+
| I millihelen = the amount of |
| beauty required to launch one ship. |
| --Peter Shickele |
+-------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-1040 FAX 617-244-1041
http://www.sheldonbrown.com/harris
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Joseph Bauder
I remember that Mathauser pads
> were designed this way, but those slip-ins were never available separately,
> either.
>
Matt,
We have them at Rivendell. (http://www.rivendellbicycles.com,
510-933-7304) We have them currently in stock. (the slip-ins, that is)
Joe
Dave Blake
Capt...@sheldonbrown.com carefully wrote:
>Dave Blake wrote:
>>
>> [a V-Brake] puts an increased reactive force on the brake boss,
>
>This is not correct. For a given pad/rim material, and the same boss
>positioning relative to the rim, the reactive force on the boss is related to
>the braking force, and nothing else.
>
There is a force normal to the rim surface at the brake
pad that is balanced by the opposing forces at both
ends of the cantilever arm. If the brake pad is roughly
centered on the cantilever arm, the forces are equal
at either end. The further you move the cable attachment
end away from the brake pad, the lower the force at that
end of the brake, and the higher the force on the boss.
"normal" canti V-brake
Cable------> Cable--->
| |
| |
| |
| |
------pad<------------ |
| |
| |
| |
| |
boss------> -------pad<------------
|
|
|
|
boss--------->
It is a prerequisite of any motionless system that all forces
acting on it sum to zero. That the force on the end of the V
brake is about half that of cantilevers is well described and
used in advertising. The necessary side effect is a doubling of
the force on the brake boss.
>> so most frames require a brake booster.
>
>This is also incorrect. The vast majority of bikes with these brakes do not
>have nor need boosters. It is true that boosters can improve the "feel" of
>any cantilever, and the more mechanical advantage the brake system has, the
>more it benefits from a booster.
There is more to it than this. Maguras have no straddle cable
to provide a horizontal force, and they are almost useless
without a brake booster. V brakes have a direct pull cable that
bears about one third of the braking force. Cantis have
a cable that bears about one half, if they are well set up.
That a brake booster is often needed can be inferred by
the number of V brake users that stop brake squealing by
using a brake booster. If their brake bosses were not flexing
with the V brakes, a booster would not have this effect. Brake
boosters have much less of a silencing effect with cantis.
>> The reactive force increases monotonically with brake arm length.
>
>A interesting adverb...it's not in any of the dictionaries I consulted; what's
>it mean?
Webster's ninth collegiate has it. In reference to a function,
monotonic means that the first derivative is either always
positive or always negative. In this case, an increase in
brake arm length always leads to an increase in the force
on the brake boss during braking.
--
Dave Blake
dbl...@phy.ucsf.edu
Stephen David Gravrock
The XT pads were, and still are, available as a slip-in replacement. They
cost about $35 for the set of four. The replacement pads are about half as
much.
I agree, they should be thinner. XT cartridge pads are still among the
best dry pads on the market, IMO. My biggest complaint is that they're
only available as a set of four, you can't buy just the front or rear set.
Since I only use them in front, this means I've got an extra set of
holders sitting around.
Bogdan Miliu
Whaaat? First of all v-brakes are better because they have more leverage.
Longer arms give you more leverage, physics 101. Second the parrallel push
action is better, because it requires no toe-in and more even wear and
tear.
The XT is a bad design because it has bushings in the link which wear out.
The XTR has a better system. Bearings I think.
There is a upgrade kit for the XT vees which goes for a couple of bucks
which would solve the squaking.
Bogdan
U of Manitoba
Jobst Brandt wrote:
> Tyler Rutherford writes:
>
> > I've heard there is a way to quiet V-brakes. Anyone know what it
> > is? (Besides taking them off). I've Shimano XT's.
>
> If you can use plain cantilevers, do so. The V-brake is a compromise
> solution for rear suspension. Other than that, it has the same basic
> geometry as a cantilever because its pivot points are the same. The
> additional levers and appropriately lower hand lever ratio combine to
> make a clumsy brake that chatters, especially the one with the
> parallelogram linkage. The V-brake is a dud brought on by suspension.
>
> Are we making progress?
>
> Jobst Brandt <jbr...@hpl.hp.com>
Hajaj
On 27 Feb 1998 09:40:32 -0800, chu...@shell5.ba.best.com (Chuck Fry)
wrote:
>In article <6d6pc6$p...@hplntx.hpl.hp.com>,
>Jobst Brandt <jbr...@hpl.hp.com> wrote:
>>And yes, Sheldon is correct, as I learned when inspecting the linkage
>>on the bicycle more carefully.
>
>Good! I'm glad to see the two most knowledgeable posters in r.b.t
>finally resolving their differences over this. :-)
>
>Seriously, thanks to both of you for the reasoned and well thought out
>discussion.
> -- Chuck
I'll second that. But, Jobst, did you really end up agreeing that
V-brakes are better than traditional cantilever brakes?
Hajaj
Den Blaa Kurér Copenhagen
chrell...@post3.tele.dk
remove '06660' to reply
Do What Thou Wilt Shall be the Whole of the Law
And for you automated email spammers out there,
here's the email addresses of the current board of
the Federal Communications Commission:
Chairman Reed Hundt: rhu...@fcc.gov
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Commissioner Susan Ness: sn...@fcc.gov
Sheldon Brown
Dave Blake wrote:
> >>
> >> [a V-Brake] puts an increased reactive force on the brake boss,
I replied:
> >This is not correct. For a given pad/rim material, and the same boss
> >positioning relative to the rim, the reactive force on the boss is related to
> >the braking force, and nothing else.
Dave came back with:
> There is a force normal to the rim surface at the brake
> pad that is balanced by the opposing forces at both
> ends of the cantilever arm. If the brake pad is roughly
> centered on the cantilever arm, the forces are equal
> at either end. The further you move the cable attachment
> end away from the brake pad, the lower the force at that
> end of the brake, and the higher the force on the boss.
> It is a prerequisite of any motionless system that all forces
> acting on it sum to zero. That the force on the end of the V
> brake is about half that of cantilevers is well described and
> used in advertising. The necessary side effect is a doubling of
> the force on the brake boss.
Well, yes, this is basically true, though it doesn't double, just increases by
50%.
This only applies to the static forces perpendicular to the rim. The actual
braking forces parallel to the rim, which tend to twist the front bosses
outward and the rears inward are unaffected by the cable geometry.
Sheldon "All Generalizations Are False" Brown
Newtonville, Massachusetts
+----------------------------------------+
| The race is not always to the swift, |
| nor the battle to the strong |
| -but thats the way to bet. |
| --Damon Runyon |
+----------------------------------------+
Valued Customer
So does anyone know if cable life is any longer on V-brakes because you use
less force to stop? Also, if people weigh less than 160 then the modulation
on a V-brake isn't that great and you don't need that much power. However,
if a rider weighs over 160 then they can put that modulation to greater use.
As a satisfied customer of both Magura and V-brakes I must say they do shine
in emergency situations.
The above is the opinion of a 200+ lb. rider
Lyle Beidler
> >> [a V-Brake] puts an increased reactive force on the brake boss,
>The further you move the cable attachment
> end away from the brake pad, the lower the force at that
> end of the brake, and the higher the force on the boss.
The above statements are correct, as any mechanical engineering
undergrad (such as myself) can tell you.
However, your assertions that brake boosters MUST be used for V-brakes
and Maguras is crap. I have both on my bike (magura front, v rear) and
run brake boosters on neither. I get excellent results from both this
way. Your assertion that "maguras are useless without a brake booster"
is just plain off.
--
Lyle Beidler Pennsylvanian by birth, Nittany Lion by the grace of God
lkb...@psu.edu http://www.personal.psu.edu/lkb128/
Don't blame me, I voted for Bill and Opus
"How can one equation replace six pages of work?" - engineering student
Dave Blake
lkb...@psu.edu carefully wrote:
>However, your assertions that brake boosters MUST be used for V-brakes
>and Maguras is crap. I have both on my bike (magura front, v rear) and
>run brake boosters on neither. I get excellent results from both this
>way. Your assertion that "maguras are useless without a brake booster"
>is just plain off.
You are correct, and it certainly matters how the bosses
are mounted, and what type of frame it is. I run Avid
2.0s on my front fork, and the fork is a rigid CroMo fork
with 1 inch OD tubes. It don't need no stinkin booster.
But put the same brakes on the Bridgestone with the Ritchey
Logic fork, and a booster helps a LOT.
When both Maguras and Vs became popular, a lot of my
friends who raced found a new need for a brake booster
where none was previously necessary with cantis.
--
Dave Blake
dbl...@phy.ucsf.edu
tku...@diabloresearch.com
In article <6d6pc6$p...@hplntx.hpl.hp.com>,
jbr...@hpl.hp.com (Jobst Brandt) wrote:
>
> I don't use the brake so I can't speak from experience but opinions on
> the brakes merit seem to vary from "chattering monster" to "excellent".
> I must admit. I think the parallelogram version is an advance over its
> predecessors. The extra linkage and cable mechanism will have to
> demonstrate its durability. Assuming it is reliable, I believe it
> should replace the cantilever. Not using fat tires, I don't think
> I'll get one just the same.
Just as a matter of my opinion:
V-brakes with the complicated parallelogram mechanism are accidents
waiting to happen. I've heard of the mechanism failing in several
cases and you just don't get enough out of it to worry about it.
As Jobst points out, the brake (properly adjusted) is near it's
peak and so the vertical motion is mininal. My Avid V-type brakes
work fine.
As to the efficacy of V-brakes. I LIKE being able to hook one
finger over the lever and stop the bike almost in it's length.
My type of off-road riding tends to be fairly difficult stuff and
I don't want to use my strength up applying brakes. I have a hard
enough time holding on for dear life. :-)
Like the dual-pivot brakes that Jobst doesn't like, the V-brake may
not ADD any additional braking (and it may have some weaknesses)
but I prefer the 'power brakes' feeling of them both to my older
brakes.
I think that the controvery is really more one of opinion than
concrete fact.
alex wetmore
Bogdan Miliu wrote in message <34F9BF2D...@cc.umanitoba.ca>...
>Whaaat? First of all v-brakes are better because they have more leverage.
>Longer arms give you more leverage, physics 101. Second the parrallel push
>action is better, because it requires no toe-in and more even wear and
>tear.
There are two pieces to the mechanical advantage in a braking system... the
brake lever and the brakes themselves. While V-brakes and other direct pull
cantilevers have a greater mechanical advantage then normal low profile
cantilevers they much be used with a brake lever which has a lower
mechanical advantage (and thus less leverage). Now this is a desirable
thing (because it minimizes the effects of cable stretch), but it doesn't
improve the overall mechanical advantage of the brake system.
You can prove to yourself that this is the case by considering how a brake
lever is built and why direct pull cantilevers require new brake levers
which have a lower mechanical advantage.
Too much mechanical advantage is a bad thing. I could build and design you
a brake system with a mechanical advantage of twenty to one (so if you
pulled the lever 1cm the shoe would move .5mm), but this would be useless on
a bicycle because you'd pull the brake levers all the way to the handlebars
before the brake shoes touched the rim. If you want to see a system that
isn't this severe check out any current bike which has cantilevers, the
stock Shimano yoke, and STI, Ergo, or other aero brake levers (besides the
Dia Compe 287 levers). With a bike using these components you have to set
the brake shoes very close to the rim or you can easily pull the levers all
the way to the handlebars.
I'd strongly recommend reading
http://www.sheldonbrown.com/cantilever_geometry.html
Jobst Brandt
Hajaj writes:
> I'll second that. But, Jobst, did you really end up agreeing that
> V-brakes are better than traditional cantilever brakes?
Except for the added linkage that seems to cause more brake chatter,
the parallelogram V-brake solves the problem of brake pads popping
under the rim. I have not used them so I can't say whether this
advantage overrides the disadvantages. The other point is that they
are essential for most rear suspension bikes.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
Bogdan Miliu writes:
> Whaaat? First of all v-brakes are better because they have more
> leverage. Longer arms give you more leverage, physics 101. Second
> the parrallel push action is better, because it requires no toe-in
> and more even wear and tear.
Maybe you ought to first review that subject yourself. The human hand
has a limited and roughly uniform grasp for which hand levers are
designed. This travel must encompass bringing the pads into contact,
the elasticity of the system and pad wear before the lever exhausts
its stroke. As we have seen, high mechanical advantage brakes require
adjustment during one competitive event if much wet grit is
encountered. A higher mechanical advantage is not practically possible
as we have seen with the dual pivot brakes for the road.
I think you should measure the mechanical advantage before you assume
it is greater. It is not.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
Sheldon Brown writes:
>> That the force on the end of the V brake is about half that of
>> cantilevers is well described and used in advertising. The
>> necessary side effect is a doubling of the force on the brake boss.
> Well, yes, this is basically true, though it doesn't double, just
> increases by 50%.
If the lever were infinitely long the load on the boss would be equal
and opposite the pad force. That's as low as you can get so it
couldn't be double.
> This only applies to the static forces perpendicular to the rim.
> The actual braking forces parallel to the rim, which tend to twist
> the front bosses outward and the rears inward are unaffected by the
> cable geometry.
I found the traveler V-brake interesting for its clever pulley drive
that allows regular 4:1 (road) levers to be used. It has a 2:1 step
up ratio in the pulley at the right angle drive curve that runs the
brake cable across to the other lever. The cable enters a small
pulley for a half wrap and exits a large pulley by having a crossover
drilling to use the same cable. This means that STI-like levers with
conventional 4:1 ratio can be used with the V-brake.
Jobst Brandt <jbr...@hpl.hp.com>
Matt O'Toole
Valued Customer wrote in message ...
>So does anyone know if cable life is any longer on V-brakes because you use
>less force to stop? Also, if people weigh less than 160 then the modulation
>on a V-brake isn't that great and you don't need that much power. However,
>if a rider weighs over 160 then they can put that modulation to greater
use.
>As a satisfied customer of both Magura and V-brakes I must say they do
shine
>in emergency situations.
Brake cables are plenty strong to withstand any load a cyclist could put on
them. The only reason a brake cable would break would be damage by
corrosion or chafing. I've never even seen a brake cable die from fatigue,
which is a common problem with some derailer cables.
Matt O.
Lyle Beidler
> V-brakes with the complicated parallelogram mechanism are accidents
> waiting to happen. I've heard of the mechanism failing in several
> cases and you just don't get enough out of it to worry about it.
While the parallelogram is mostly unneccessary, and one more thing to go
wrong, I guess they do help a little. as to their reliability, I bought
a used pair (cheap; the only reason I bought the XTR, rather than the
simpler LX or XT), and haven't had any problems, but then, I rely mostly
on my front brakes, which are not V's.
> As to the efficacy of V-brakes. I LIKE being able to hook one
> finger over the lever and stop the bike almost in it's length.
> My type of off-road riding tends to be fairly difficult stuff and
> I don't want to use my strength up applying brakes. I have a hard
> enough time holding on for dear life. :-)
AMEN! AMEN! AMEN!
Bill Broadley
Jobst Brandt <jbr...@hpl.hp.com> wrote:
: And to what do you attribute this substantial difference? The
: mechanical advantage is the same and the pads and rims are the same.
: The radius of sweep is also the same. Where does this perceived
: difference come from? The parallelogram linkage does not change the
: arc of the pad sweep, it only keeps the pad facing inward as it traces
: th4e same path that a cantilever does. To make up for that, it has
: more parts that can chatter.
I believe v-brakes do have an advantage over traditional canti's.
V-brakes use 100% of their force (ignoring friction) applying tension
between the two v-brake arms. Canti's are setup with non-straight straddle
cables. So the cosine of the angle is applied as tension between
the brake arms (good), but the sine of the angle just pulls upward on the
brake mounts without doing any useful braking. Whats worse is this
usually gets worse as you brake harder because the angle increases.
So v-brakes have a linear (100%) relationship between cable tension
and pressure on the brake pads, while canti's have a non-linear and
decreasing amount of pressure on the brake pads in relationship
to the cable tension.
What am I missing?
Hmmm upon further thought I guess as long as the straddle cable
is perpendicular to the arm of the canti that it doesn't make a difference.
Well at least with v-brakes you don't have to worry about losing efficiency
to improper straddle cable length.
--
Bill Broadley Bi...@math.ucdavis.edu UCD Math Sys-Admin
Linux is great. http://math.ucdavis.edu/~bill PGP-ok
Mark Hickey
"Valued Customer" <Chee...@msn.com> wrote:
>So does anyone know if cable life is any longer on V-brakes because you use
>less force to stop? Also, if people weigh less than 160 then the modulation
>on a V-brake isn't that great and you don't need that much power. However,
>if a rider weighs over 160 then they can put that modulation to greater use.
>As a satisfied customer of both Magura and V-brakes I must say they do shine
>in emergency situations.
>
>The above is the opinion of a 200+ lb. rider
Good questions.
A couple thoughts (with no concrete conclusions, so don't anyone get
too excited).
The brake cable itself is much stronger than it needs to be in any
case. I've never seen one break from anything other than wearing out
due to overuse, or from being damaged by rust or a crimp. Which means
that the longer-pull V-brake levers should actually wear out the cable
sooner, since it's pulling more of it back and forth through the brake
cable housing - though this is probably balanced by the fact that it's
under lower tension.
Also, cable stretch isn't *all* bad - it's part of what gives cantis
better "modulation" (editors note: better = what I like).
YMMV,
Mark Hickey
Bill Broadley <bi...@math.ucdavis.edu> wrote:
>I believe v-brakes do have an advantage over traditional canti's.
>
>V-brakes use 100% of their force (ignoring friction) applying tension
>between the two v-brake arms. Canti's are setup with non-straight straddle
>cables. So the cosine of the angle is applied as tension between
>the brake arms (good), but the sine of the angle just pulls upward on the
>brake mounts without doing any useful braking. Whats worse is this
>usually gets worse as you brake harder because the angle increases.
>What am I missing?
I've never thought about it in these terms, but your post made me stop
and think about it for a moment.
On one hand, you're right, more of the "force" goes into squeezing the
pads into the rims (though not a LOT more). This in itself is a good
thing.
OTOH, it just hit me (*ouch*) - the "upward pull" component of the
cantilever brakes is going to be one of the reasons they don't squeal
like pigs, by providing an off-axis "bias" which should tend to damp
many of the oscillations that would otherwise develop. I'll wager
that if you could reach back and give a strong upward pull to a
V-brake singing its one known song, it would be as silent as a mouse
at a cat show.
Of course, this would more likely result in a nasty and humilitating
accident, so I'd take it as a personal favor if you didn't actually do
it... ;-)
Hey, but wait a minute. What if you hooked a small bungie cord from
your seat rails to the top of your V brake arms? You should be able
to accomplish the same thing.
Gee, I'd try it out myownself, but I don't have a bike with V-brakes -
=-)
Anyone feeling adventurous out there?
Paul Spencer
> > V-brakes with the complicated parallelogram mechanism are accidents
> > waiting to happen. I've heard of the mechanism failing in several
> > cases and you just don't get enough out of it to worry about it.
I switched a while back from LX V's (no linkage) to XT V's (linkage).
Given the comments here, I wasn't expecting much; but after using
them for a while, the XT brakes are *WAY* better. Better braking,
better modulation, and best of all, once they're set up, the XT
brakes require zero adjustments (unlike the constant readjustment of
the LX pads as they wear).
The linkage is pretty well built; the only way I can see it breaking
is if you damage it in a crash.
....paul
--
Paul Spencer Silicon Graphics Advanced Systems Division
spe...@sgi.com Mountain View, California
Jobst Brandt
Mark Hickey writes:
>> V-brakes use 100% of their force (ignoring friction) applying
>> tension between the two v-brake arms. Canti's are setup with
>> non-straight straddle cables. So the cosine of the angle is
>> applied as tension between the brake arms (good), but the sine of
>> the angle just pulls upward on the brake mounts without doing any
>> useful braking. What's worse is this usually gets worse as you
>> brake harder because the angle increases.
> I've never thought about it in these terms, but your post made me
> stop and think about it for a moment.
> On one hand, you're right, more of the "force" goes into squeezing
> the pads into the rims (though not a LOT more). This in itself is a
> good thing.
I think the linkages, cable angles and rotations confuse the issue.
All the force (friction losses being about constant) goes to pressing
the pads against the rim, regardless of approach angle. The force is
not leaking out somewhere. Because the mechanical advantage remains
close to constant during any single brake application and its recent
predecessors. all the sines and cosines have no affect. The lever to
pad ratio is given.
> OTOH, it just hit me (*ouch*) - the "upward pull" component of the
> cantilever brakes is going to be one of the reasons they don't squeal
> like pigs, by providing an off-axis "bias" which should tend to damp
> many of the oscillations that would otherwise develop. I'll wager
> that if you could reach back and give a strong upward pull to a
> V-brake singing its one known song, it would be as silent as a mouse
> at a cat show.
Involving your hand would constitute a damper, so I don't think this
would prove the point. High pitched squeals are a function of the
pads. That's why the most rigid caliper brakes can squeal. Lower
frequency noise is a combination of pars and elasticities in the brake
and its mounting. The V-brake doesn't look good in that department.
Jobst Brandt <jbr...@hpl.hp.com>
m...@hooked.net
In article <6dhjk9$5c...@fido.asd.sgi.com>,
spe...@hailwood.engr.sgi.com (Paul Spencer) wrote:
>
> > > V-brakes with the complicated parallelogram mechanism are accidents
> > > waiting to happen. I've heard of the mechanism failing in several
> > > cases and you just don't get enough out of it to worry about it.
>
> I switched a while back from LX V's (no linkage) to XT V's (linkage).
> Given the comments here, I wasn't expecting much; but after using
> them for a while, the XT brakes are *WAY* better. Better braking,
> better modulation, and best of all, once they're set up, the XT
> brakes require zero adjustments (unlike the constant readjustment of
> the LX pads as they wear).
Just curious, when you were swapping things back and forth, did you pair
the LXs with the same levers, cables, and pads as the XTs?
Once I upgraded the poor, stock LX pads to something like a WTB, I found
no reason to deal with the hassles of XT V's.
I've got onZa HOLAs, Avid 2.0s, LX, and XT V's on my bikes. The only
ones that squeal are the XTs.
> The linkage is pretty well built; the only way I can see it breaking
> is if you damage it in a crash.
Shimano supposedly has a tune-up kit that includes a new linkage ass'y.
It's not for folks who break 'em, but for those that have already
shimmed noisy brakes and got no relief.
> ....paul
>
> --
> Paul Spencer Silicon Graphics Advanced Systems Division
> spe...@sgi.com Mountain View, California
--mc
Garry Lee
The force is
>not leaking out somewhere.
If it's not going somewhere why is it very very difficult to brake when
your straddle wire makes a very disadvantageous angle with the
cantilevers? I'm not contraditing the above statement. I'm just ignorant
of engineering and wish to understand it.
Good straddle angle=soft powerful brakes.
Bad straddle angle=hard weak brakes.
I understand that it's got to do with leverage but without moving your
hand, with brakes on, there's a huge difference.
Bard Brors
Bill Broadley wrote:
> >> V-brakes use 100% of their force (ignoring friction) applying
> >> tension between the two v-brake arms. Canti's are setup with
> >> non-straight straddle cables. So the cosine of the angle is
> >> applied as tension between the brake arms (good), but the sine of
> >> the angle just pulls upward on the brake mounts without doing any
> >> useful braking. What's worse is this usually gets worse as you
> >> brake harder because the angle increases.
Mark Hickey wrote :
> > I've never thought about it in these terms, but your post made me
> > stop and think about it for a moment.
>
> > On one hand, you're right, more of the "force" goes into squeezing
> > the pads into the rims (though not a LOT more). This in itself is a
> > good thing.
Jobst Brandt writes :
>
> I think the linkages, cable angles and rotations confuse the issue.
> All the force (friction losses being about constant) goes to pressing
> the pads against the rim, regardless of approach angle. The force is
> not leaking out somewhere. Because the mechanical advantage remains
> close to constant during any single brake application and its recent
> predecessors. all the sines and cosines have no affect. The lever to
> pad ratio is given.
>
The point of the two previous posters is that with V-brakes, 100% of the
force (ignoring friction loss in the cable housing) is horizontal and
used for braking. With ordinary cantilevers, there is useless *vertical*
force applied to the cable hanger and brake bosses.
Bard Brors
Matt McCluskey
I have found out that by putting a brake booster on my rear XT-V brakes
has made them quieter. Could this help reduce the harmonics on the rim
by making the forces a little bit "stiffer" on the rim? My brakes
squealed when they were new (with no booster) but after a while when the
pads wear down, they hardly make any noise at all. All of the brakes
I've had before, CODA, STX, and those with red and black Richey pads
have all made noise when new.
--
"Cool as a cucumber in a bowl of hot sauce" -Beastie Boys
Matt McCluskey
REPLY TO: mmcc...@ef0023.efhd.ford.com
Visteon "See the Possibilities..."
Tullio
Bard Brors wrote:
> The point of the two previous posters is that with V-brakes, 100% of the
> force (ignoring friction loss in the cable housing) is horizontal and
> used for braking. With ordinary cantilevers, there is useless *vertical*
> force applied to the cable hanger and brake bosses.
That's like saying that the pistons in a car's engine are useless
because they move vertically while the car needs to move horizontally.
Todd
Tullio's Big Dog Cyclery
LaSalle, IL
e-mail: tul...@TheRamp.net
Raleigh-Specialized-Bianchi
Waterford-Torelli-GT/Dyno
Burley-Co-Motion
Jobst Brandt
Bard Brors writes:
>> I think the linkages, cable angles and rotations confuse the issue.
>> All the force (friction losses being about constant) goes to
>> pressing the pads against the rim, regardless of approach angle.
>> The force is not leaking out somewhere. Because the mechanical
>> advantage remains close to constant during any single brake
>> application and its recent predecessors. all the sines and cosines
>> have no affect. The lever to pad ratio is given.
> The point of the two previous posters is that with V-brakes, 100% of
> the force (ignoring friction loss in the cable housing) is
> horizontal and used for braking. With ordinary cantilevers, there is
> useless *vertical* force applied to the cable hanger and brake bosses.
I can only repeat what I wrote above. You cannot make the force
vanish regardless of the linkage. The linkage has a mechanical
advantage and transmits the force to the rim. If you don't like that
ratio, that's a different matter, but it is not "useless force". This
sounds much like the pedal cranks that have a 90 degree forward elbow
to help you get over top dead center. It doesn't happen.
Jobst Brandt <jbr...@hpl.hp.com>
Tom Ace
Jobst Brandt wrote:
> I can only repeat what I wrote above. You cannot make the force
> vanish regardless of the linkage. The linkage has a mechanical
> advantage and transmits the force to the rim. If you don't like that
> ratio, that's a different matter, but it is not "useless force".
It's not a question of the force disappearing, it's whether it's
applied to the rim (useful) or to the cantilever boss (not).
This can be a problem if a low-profile cantilever brake is set
up with too long a straddle cable. As others have pointed out,
V-brakes don't offer this particular opportunity to screw up the
installation.
This is covered in Sutherland's; if the straddle cable is not the
right length, "...part of the force gets wasted in pulling on the
brake post, which has no effect on braking." I know Sutherland's
handbook is not error-free, but they're not all wet in this case.
Tom Ace
cr...@best.com
Dave Blake
cr...@best.comX carefully typed:
>This is covered in Sutherland's; if the straddle cable is not the
>right length, "...part of the force gets wasted in pulling on the
>brake post, which has no effect on braking." I know Sutherland's
>handbook is not error-free, but they're not all wet in this case.
What happens to the ratio of pad movement to lever movement
when the straddle cable is too long ?
It seems to me that the leverage is simply decreasing further,
and that small tugs on the brake levers lead to comparatively
large movements of the cantilevers. This is the weak but
idiot proof way to set up cantis. You don't get much
force out, but that is because you have changed the lever
ratio - not because more vertical force is applied to the
cantilever boss.
--
Dave Blake
dbl...@phy.ucsf.edu
NOSPAM Lee Porter
Then compare a "properly installed and adjusted canti" to a V-brake!
In article <34FDCD1F...@best.comX>, Tom Ace <cr...@best.comX> wrote:
> This is covered in Sutherland's; if the straddle cable is not the
> right length, "...part of the force gets wasted in pulling on the
> brake post, which has no effect on braking." I know Sutherland's
> handbook is not error-free, but they're not all wet in this case.
>
> Tom Ace
> cr...@best.com
--
,__o
_-\_<,
(*)/'(*) Lee Porter
>>>Remove (NOSPAM) to reply<<<
Tom Ace
Dave Blake wrote:
> What happens to the ratio of pad movement to lever movement
> when the straddle cable is too long ?
>
> It seems to me that the leverage is simply decreasing further,
> and that small tugs on the brake levers lead to comparatively
> large movements of the cantilevers. This is the weak but
> idiot proof way to set up cantis. You don't get much
> force out, but that is because you have changed the lever
> ratio - not because more vertical force is applied to the
> cantilever boss.
I disagree. The leverage does change as you describe, but I
think there's also more waste.
On his page at http://www.sheldonbrown.com/cantilever_geometry.html
Sheldon defines a term "anchor angle" as "the angle between the end
of the transverse cable and the anchor arm" and illustrates it with
a diagram. Long transverse cables used with low-profile arms can
exhibit an anchor angle of >90 degrees.
If the anchor angle were 180 degrees, no force would be applied at
the pad; the cantilever boss would see all the force. A 180 degree
angle doesn't happen in practice (with a wheel installed), but it
illustrates the limiting case where braking action is nil no matter
how hard you pull the cable.
It's not like the waste begins abruptly when the anchor angle hits
180 degrees; some is present at smaller angles as well.
Tom Ace
cr...@best.com
Sheldon Brown
Dave Blake wrote:
>
> > What happens to the ratio of pad movement to lever movement
> > when the straddle cable is too long ?
> >
> > It seems to me that the leverage is simply decreasing further,
> > and that small tugs on the brake levers lead to comparatively
> > large movements of the cantilevers. This is the weak but
> > idiot proof way to set up cantis. You don't get much
> > force out, but that is because you have changed the lever
> > ratio - not because more vertical force is applied to the
> > cantilever boss.
Tom Ace demurred:
> I disagree. The leverage does change as you describe, but I
> think there's also more waste.
>
The confusion results from this concept of "waste." Aside from friction and
flex, there is no waste in a leverage system.
Leverage (mechanical advantage) in this application is the ratio between the
distance the brake shoes move/the distance the hand lever moves; or, to look
at it another way, how much force is applied to the hand lever/how much force
the shoes apply to the rim.
This is a single ratio, inescapably the same whether you look at as distance
or as force.
"Work" is defined as force X distance. You put work into the lever and get it
out at the shoes. No work is done on the studs, since they are basically
immobile. This concept of "waste" due to particular lever/cable angles is a chimera.
> On his page at http://www.sheldonbrown.com/cantilever_geometry.html
> Sheldon defines a term "anchor angle" as "the angle between the end
> of the transverse cable and the anchor arm" and illustrates it with
> a diagram. Long transverse cables used with low-profile arms can
> exhibit an anchor angle of >90 degrees.
>
> If the anchor angle were 180 degrees, no force would be applied at
> the pad; the cantilever boss would see all the force. A 180 degree
> angle doesn't happen in practice (with a wheel installed), but it
> illustrates the limiting case where braking action is nil no matter
> how hard you pull the cable.
This is true. When the angle is 180 degrees there is no longer a leverage
system, so this represents an asymptote.
> It's not like the waste begins abruptly when the anchor angle hits
> 180 degrees; some is present at smaller angles as well.
When this angle is 179 degrees+, the mechanical advantage is approaching
infinity. You get less and less pad movement for your lever movement. If
that pad movement were in a useful range of positions, it would be applying
nearly irresistible force against the rim, but as a practical matter, it is
not useful.
To understand braking geometry, you must keep your eye on the ball of
mechanical advantage. There's only a fairly narrow range of mechanical
advantages that are useful:
Too little and you need the hands of a gorilla to stop.
Too much, and you run out of lever travel and wind up squeezing the lever
against the handlebar.
Center-pull brakes are particularly confusing because they have two different
leverage systems, which vary as they travel, and each of these may vary in
either direction, depending on design and setup.
Sheldon "Waste Not, Want Not" Brown
Newtonville, Massachusetts
+---------------------------------------------------------+
| The Law, in its majestic equality, forbids the rich, |
| as well as the poor, to sleep under the bridges, |
| to beg in the streets, and to steal bread. |
| --Anatole France |
+---------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-1040 FAX 617-244-1041
http://www.sheldonbrown.com/harris
Jobst Brandt
Garry Lee writes:
>> The force is not leaking out somewhere.
> If it's not going somewhere why is it very very difficult to brake
> when your straddle wire makes a very disadvantageous angle with the
> cantilevers? I'm not contradicting the above statement. I'm just
> ignorant of engineering and wish to understand it.
As you also say, it has something to do with leverage, and in that
vein, you will note that force times distance (work) is a constant in
any lever system, ignoring friction. Therefore, as the straddle cable
assumes a less perpendicular angle with the lever motion, its
mechanical advantage changes. The geometry of straddle cable and
lever angles is deceptive because several angles are changing at the
same time.
Jobst Brandt <jbr...@hpl.hp.com>
cr...@best.com
In article <34FEC986...@sheldonbrown.com>,
Capt...@sheldonbrown.com wrote:
>The confusion results from this concept of "waste." Aside from friction and
>flex, there is no waste in a leverage system.
But we use real-world cables that have stretch to them.
Consider for a moment a V-brake and a conventional cantilever set up to have
the same mechanical advantage. The V-brake's performance will be compromised
less by cable stretch. V-brakes pull more cable under less tension.
>"Work" is defined as force X distance. You put work into the lever and get
>it out at the shoes. No work is done on the studs, since they are basically
>immobile. This concept of "waste" due to particular lever/cable angles is a
>chimera.
No work is done on the studs, but work is expended to stretch cables,
calculated by the same formula of force * distance (where distance
is the amount of cable stretch). This is where waste comes in.
>When this angle is 179 degrees+, the mechanical advantage is approaching
>infinity. You get less and less pad movement for your lever movement. If
>that pad movement were in a useful range of positions, it would be applying
>nearly irresistible force against the rim, but as a practical matter, it is
>not useful.
False. At 179 degrees the mechanical advantage is near zero. (Minimal
lever travel causes lots of pad movement.)
>To understand braking geometry, you must keep your eye on the ball of
>mechanical advantage. There's only a fairly narrow range of mechanical
>advantages that are useful:
>
>Too little and you need the hands of a gorilla to stop.
>
>Too much, and you run out of lever travel and wind up squeezing the lever
>against the handlebar.
Agreed.
But in addition, it's my contention that configurations that pull hard on
the boss are more prone to waste energy in cable stretch.
Tom Ace
cr...@best.com
Tom Ace
Jobst Brandt wrote:
>> But we use real-world cables that have stretch to them.
>
>I don't believe a word of it. Have you measured the stretch? I think
>you'll find the compliance is in the caliper linkage and brake
>hangers. Unless you damaged the cable housing by streching is, there
>is no practical length change. Watch carefully what cable motion you
>can see going into the housing and that coming out of the far end.
>You'll be amazed.
If cables don't stretch, why are the rear brakes on all my bikes
spongier than the front ones (especially noticeable on my tandem)?
I'm not talking about poor control due to greater friction inside
a long cable housing, I mean more sponginess.
Also, watch a few cantilever transverse cables. In some cases, the
bend at the yoke gets sharper under tension and relaxes afterwards.
>> Consider for a moment a V-brake and a conventional cantilever set up
>> to have the same mechanical advantage. The V-brake's performance
>> will be compromised less by cable stretch. V-brakes pull more cable
>> under less tension.
>
>Wait a minute! That's called different mechanical advantage and
>V-brake hand levers have half the mechanical advantage of cantilevers.
I was referring to two setups with the same overall mechanical
advantage, from input (force on the lever) to output (force at
the brake pad). This is consistent with the sense that Sheldon
was using the term 'mechanical advantage' in the article I was
replying to.
>> No work is done on the studs, but work is expended to stretch cables,
>> calculated by the same formula of force * distance (where distance
>> is the amount of cable stretch). This is where waste comes in.
>
>It does not!
I'll ask the same question you asked me. Have you measured cable
stretch? And did you measure the effects of the sharpening of
bends in cantilever transverse cables?
Tom Ace
cr...@best.com
Mark Hickey
Tom Ace <cr...@best.comX> wrote:
>If the anchor angle were 180 degrees, no force would be applied at
>the pad; the cantilever boss would see all the force. A 180 degree
>angle doesn't happen in practice (with a wheel installed), but it
>illustrates the limiting case where braking action is nil no matter
>how hard you pull the cable.
>
>It's not like the waste begins abruptly when the anchor angle hits
>180 degrees; some is present at smaller angles as well.
Ah, but therein lies the rub. Er, maybe lack of it...
First, let's assume your straddle is at 180 degrees (that is, flat).
Now, when you pull on the brake lever, it's going to pull in the pads.
Not much, but it will pull them in as the center of the straddle
rises. If you figure a 150mm staddle length and a 20mm pull, the pads
will move in 2.5mm or so (that is, on each side).
In fact, these revolutionary new brakes will be more "V" than the "V"
brakes. They will require microscopic clearances between the pad and
rim, but MAN will they have some POWER. The mechanical advantage will
be ENORMOUS.
Oops, they will have so little travel we'll have to use a brake lever
with a longer pull.
Hmmm. They still have so little travel we'll need a harder brake pad
to keep from using all the travel just to compress a reasonably
pliable brake pad. Better make the pads a LOT thinner while we're at
it - that way, you won't notice the braking would go away altogether
long before you'd ever wear out a "real" brake pad.
In other words, we'd have to make all the same types of changes that
the V-brakes use to make it work right.
So in the end, there is no waste of energy, just a matter of deciding
how much mechanical advantage you have to work with. In fact, if you
concentrate on the first 5mm of pull (with the 180 degree straddle),
your mechanical advantage would be over 30 to 1! You'd have to keep
the wheels REAL true, though.... ;-)
Jobst Brandt
Tom Ace writes:
>> The confusion results from this concept of "waste." Aside from
>> friction and flex, there is no waste in a leverage system.
> But we use real-world cables that have stretch to them.
I don't believe a word of it. Have you measured the stretch? I think
you'll find the compliance is in the caliper linkage and brake
hangers. Unless you damaged the cable housing by streching is, there
is no practical length change. Watch carefully what cable motion you
can see going into the housing and that coming out of the far end.
You'll be amazed.
> Consider for a moment a V-brake and a conventional cantilever set up
> to have the same mechanical advantage. The V-brake's performance
> will be compromised less by cable stretch. V-brakes pull more cable
> under less tension.
Wait a minute! That's called different mechanical advantage and
V-brake hand levers have half the mechanical advantage of cantilevers.
To make up for that they have twice as much in the caliper linkage.
When there is little cable travel, a small elasticity in the caliper
looks like a lot of sponge at the hand lever. This is not cable
stretch.
> No work is done on the studs, but work is expended to stretch cables,
> calculated by the same formula of force * distance (where distance
> is the amount of cable stretch). This is where waste comes in.
It does not!
Jobst Brandt <jbr...@hpl.hp.com>
Mark Hickey
Tom Ace <cr...@best.comX> wrote:
>Jobst Brandt wrote:
>Also, watch a few cantilever transverse cables. In some cases, the
>bend at the yoke gets sharper under tension and relaxes afterwards.
>>> No work is done on the studs, but work is expended to stretch cables,
>>> calculated by the same formula of force * distance (where distance
>>> is the amount of cable stretch). This is where waste comes in.
>>
>>It does not!
>
>I'll ask the same question you asked me. Have you measured cable
>stretch? And did you measure the effects of the sharpening of
>bends in cantilever transverse cables?
I've been thinking about finding an example to illustrate why there is
no "power" lost in the brake cables or transverse cables.
You have two fishing rods. One is a deep sea rod, extremely stiff and
built for winching tunas out of the deep with nary a wiggle.
The second is a classic freshwater rod, calibrated to give lots of
flex to keep that feisty trout securely hooked.
They both happen to be exactly the same length (though it wouldn't
matter) and by some miracle of technology, happen to weigh exactly the
same - both weigh exactly two ounces.
You tie a 5 pound weight to each end of each pole (yep, 20 pounds
total). If you're reading this in Yurrup, you use 2.2soumething kg
weights, OK?
Now you lift that stiff rod by the middle (more or less, you'll have
to balance it) using a fishing scale calibrated by the NBS, that is
hanging from a 1/4" steel cable, and accurate down to 0.0001 grams.
It reads 10 pounds, 2 ounces exactly.
Now you do the same thing with the fly rod. Only this time, you
substitute a bungee cord (or a very hefty rubber band if you don't
have a bungee cord laying about). Yep, you'll have to raise your hand
a bit further to get those weights off the ground. You read the
scale. Hmmmm. 10 pounds, 2 ounces exactly.
No energy is being wasted at all, even though the thin rod is bent
dramatically by the force, and the bungee cord has lengthened. 10
pounds, 2 ounces of force up, 10 pounds, 2 ounces of force down.
The same applies in bicycle brakes - although obviously in an almost
microscopic sense in terms of cable stretch and straddle cable
deformation.
Hope this helps put this in "real world" terms....
Tom Ace
Mark Hickey wrote:
> Now you do the same thing with the fly rod. Only this time, you
> substitute a bungee cord (or a very hefty rubber band if you don't
> have a bungee cord laying about). Yep, you'll have to raise your hand
> a bit further to get those weights off the ground. You read the
> scale. Hmmmm. 10 pounds, 2 ounces exactly.
>
> No energy is being wasted at all, even though the thin rod is bent
> dramatically by the force, and the bungee cord has lengthened. 10
> pounds, 2 ounces of force up, 10 pounds, 2 ounces of force down.
> The same applies in bicycle brakes - although obviously in an almost
> microscopic sense in terms of cable stretch and straddle cable
> deformation.
"You'll have to raise your hand a bit further to get those weights
off the ground." The analogous situation with a hand brake is having
to squeeze it farther. If there's too much sponginess, you can pull
the lever to the handlebar before getting the braking action you want.
Also, the words "energy" and "force" have specific meanings. Although
the force ends up the same in your example, it's not accurate to say
"No energy is being wasted at all"; it took energy to stretch the
bungee cord.
Tom Ace
cr...@best.com
Mark Nockleby
Capt...@sheldonbrown.com writes:
>> The reactive force increases monotonically with brake arm length.
>A interesting adverb...it's not in any of the dictionaries I consulted; what's
>it mean?
checking a calculus text would be good. To increse monotonically means that
the function (I guess the reactive force in this case, what ever that is)
only increaces and never decreases (even momentarily) over a range. Or the
slope is always nonzero.
-mark.
--
For PGP key, http://physics.ucsc.edu/users/noc/plan
My mail address is disguised to avoid automated
advertisments. Please remove no-spam from the address in order to reply.
Tom Ace
Jobst Brandt wrote:
> Yes and the sponge is in the calipers. The straddler cable is part of
> the brake mechanism, not the cable pull itself. My point is that
> pushing sponge off on transmission loss is an old saw without teeth.
You ignored my question about why rear brakes are spongier
than front ones. I have seen this on several bikes, with
identical levers and calipers front and back (calipers with
the same reach front and back).
If it's not the longer cable that makes them spongier (noticeable
after the pads are pushing against the rim), what is it?
Tom Ace
cr...@best.com
Matt O'Toole
Tom Ace wrote in message <35021A11...@best.comX>...
>You ignored my question about why rear brakes are spongier
>than front ones. I have seen this on several bikes, with
>identical levers and calipers front and back (calipers with
>the same reach front and back).
>If it's not the longer cable that makes them spongier (noticeable
>after the pads are pushing against the rim), what is it?
Could it be that the cable isn't really taut to begin with, and needs a
slight load on it to make it so? Anyone who's played with sailboats knows
what I'm talking about. Even 3/16" rigging cables often can't be pulled
taut with body weight, so a lever/latch mechanism is employed to do this.
Then, tension is applied and adjusted with a turnbuckle. I think if you
measured cable stretch, you'd find that there is an initial creep due to the
individual wires' settling, but after that, stretch is close to zero.
There might be a similar initial creep or settling in the cable housing.
Matt O.
Jobst Brandt
Tom Ace writes:
>> I don't believe a word of it. Have you measured the stretch? I
>> think you'll find the compliance is in the caliper linkage and
>> brake hangers. Unless you damaged the cable housing by stretching
>> is, there is no practical length change. Watch carefully what
>> cable motion you can see going into the housing and that coming out
>> of the far end. You'll be amazed.
> If cables don't stretch, why are the rear brakes on all my bikes
> spongier than the front ones (especially noticeable on my tandem)?
> I'm not talking about poor control due to greater friction inside
> a long cable housing, I mean more sponginess.
> Also, watch a few cantilever transverse cables. In some cases, the
> bend at the yoke gets sharper under tension and relaxes afterwards.
>>> Consider for a moment a V-brake and a conventional cantilever set
>>> up to have the same mechanical advantage. The V-brake's
>>> performance will be compromised less by cable stretch. V-brakes
>>> pull more cable under less tension.
>> Wait a minute! That's called different mechanical advantage and
>> V-brake hand levers have half the mechanical advantage of
>> cantilevers.
> I was referring to two setups with the same overall mechanical
> advantage, from input (force on the lever) to output (force at the
> brake pad). This is consistent with the sense that Sheldon was
> using the term 'mechanical advantage' in the article I was replying
> to.
The overall mechanical advantage can be the same but the internal ones
of the hand levers and calipers are 2:1 or more different. That makes
their comparison in cable motion and linkages largely different. Thus
the comparison, the way it was made is shifting sponge from one
component to another.
>>> No work is done on the studs, but work is expended to stretch cables,
>>> calculated by the same formula of force * distance (where distance
>>> is the amount of cable stretch). This is where waste comes in.
>> It does not!
> I'll ask the same question you asked me. Have you measured cable
> stretch? And did you measure the effects of the sharpening of
> bends in cantilever transverse cables?
The above implies that work is done. Brake activation is a control
function and does no work. In fact the perfect brake (and many
automobile brakes approach this today) would have no lever motion,
with braking becoming stronger the harder you squeeze. The motion is
only a mechanical compromise.
Yes and the sponge is in the calipers. The straddler cable is part of
the brake mechanism, not the cable pull itself. My point is that
pushing sponge off on transmission loss is an old saw without teeth.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
Tom Ace writes:
> You ignored my question about why rear brakes are spongier than
> front ones. I have seen this on several bikes, with identical
> levers and calipers front and back (calipers with the same reach
> front and back).
> If it's not the longer cable that makes them spongier (noticeable
> after the pads are pushing against the rim), what is it?
I must be the cable and its housing. My experience is that any such
elasticities arise from shape changes in the housing and plastic
liners and other routing problems, the least of it being the cable
itself. The reason I am so sure of this is that in a straight line
tension test, the cable shows insignificant elongation for a 40 lb
load. With a 4:1 lever ratio that is about what most brake
applications put in there.
However, cutting the brake cable force in half may be a benefit of the
V-brake. I thought the "traveler" adapter on the V-brake that routes
the cable around the 90 degree bend on a two sized pulley was pretty
smart. The cable comes from normal drop bar 4:1 brake levers, enters
the smaller of the two siamesed pulleys and exits across to the other
side off tits twice as large twin. Presto, we have an interchangeable
brake without the ungainly brake levers.
Jobst Brandt <jbr...@hpl.hp.com>
Frank Krygowski
In a previous article, cr...@best.comX (Tom Ace) says:
>If cables don't stretch, why are the rear brakes on all my bikes
>spongier than the front ones (especially noticeable on my tandem)?
>I'm not talking about poor control due to greater friction inside
>a long cable housing, I mean more sponginess.
>
>Also, watch a few cantilever transverse cables. In some cases, the
>bend at the yoke gets sharper under tension and relaxes afterwards.
Steel brake cables are not stretchable to any measureable degree - at
least, not at the loads bicycle brakes put on them. Take a close look at
your brakes and you can see several sources of sponginess.
One obvious one is the straightening of bends in the cables when under
tension. The easiest place to see this is on the straddle cable of
cantilevers. If you put a brand new, "straight" out-of-the-box straddle
cable on without pre-bending it, it will form an arc. When you apply
tension to the brakes main cable, it must straighten that arc into two more
or less straight lines. This eats up some lever travel.
You get a similar effect every time the brake cables bend. Watch the shape
of the housing any place the brake cable bends in open air (that is, not
contained under the handlebar tape). You'll see the housing move when
tension is applied to the cable. In general, the equilibrium shape of the
untensioned cable is different than the shape under tension. The motion
from one shape to the other eats up lever travel.
You can reduce this source of sponginess by pre-bending your straddle cables
so they run in a straight line from the yoke to the brake arms even when
the brake is released. Similarly, be sure that every run of the cable is
pre-shaped as much as possible to it's loaded shape.
My tandem came with a pretty flimsy front cable stop for the cantilever,
made of thin stamped aluminum. That was a source of sponginess too, when
it flexed under load. And on some brakes there's some clearance at the
pivots that eats up a bit of travel.
As to your tandem's rear brake: I know on mine (with old-style "non-aero"
levers) the front cable makes just one near-180 degree arc before reaching
the cantilever's yoke. The rear one does that 180 degrees in one plane,
then another 90 degrees in another plane to point it toward the rear of the
bike. Then at the rear seat tube, it does a three dimensional S curve to
snake around to the back of the seatpost and into the rear cable housing
stop. Each one of these extra curves adds a bit of motion as the cable and
housing take a different shape under tension.
I'm betting these effects contribute far more to the sponginess than actual
stretching of the cables.
--
Frank Krygowski ae...@yfn.ysu.edu
Tom Ace
Frank Krygowski wrote:
> Steel brake cables are not stretchable to any measureable
> degree - at least, not at the loads bicycle brakes put on
> them. Take a close look at your brakes and you can see
> several sources of sponginess.
[additional useful information snipped]
I stand corrected about the mechanism of sponginess in cables.
As Frank and Jobst have pointed out, what I was noticing had
more to do with housing and straightening of bends than with
any elongation of the cable inside.
But no matter whether the housing or the cable is the culprit,
a brake whose mechanical advantage requires high tension in
the cable will suffer more from any give in the cable/housing.
Tom Ace
cr...@best.com
Mark Hickey
>"You'll have to raise your hand a bit further to get those weights
>off the ground." The analogous situation with a hand brake is having
>to squeeze it farther. If there's too much sponginess, you can pull
>the lever to the handlebar before getting the braking action you want.
Ah, but that stretch is *reducing* the pressure you are applying.
Net/net, it's a wash. X force in equals X braking force out. The
beaurty of canti brakes is that the longer travel allows for more
cable stretch without running out of useful brake pad travel.
Actually, in terms of real-world braking, it would be accurate to say
that no force is being wasted, since exactly the same force being
applied at the levers is being appied at the braking surface. If you
want to consider the stretch of the bungee cord, you would be very
accurate in saying that the stretch *decreased* the tension on the
cable - but again, in such a small degree as to be negligable.
Mark McMaster
Jobst Brandt wrote:
>
> Tom Ace writes:
>
> > You ignored my question about why rear brakes are spongier than
> > front ones. I have seen this on several bikes, with identical
> > levers and calipers front and back (calipers with the same reach
> > front and back).
>
> > If it's not the longer cable that makes them spongier (noticeable
> > after the pads are pushing against the rim), what is it?
>
> I must be the cable and its housing. My experience is that any such
> elasticities arise from shape changes in the housing and plastic
> liners and other routing problems, the least of it being the cable
> itself. The reason I am so sure of this is that in a straight line
> tension test, the cable shows insignificant elongation for a 40 lb
> load. With a 4:1 lever ratio that is about what most brake
> applications put in there.
I'm also quite certain that the housing adds elasticity. The spiral
wound housing would be quite stiff indeed if it didn't have to make any
bends, but as soon as its routing is curved, gaps form between the
spiral loops at the outer radius of the housing curvature. Tensioning
the cable attempts to close these gaps, leading to the "spongy"
feeling. The rear brake having a longer housing with more bends has
more of this sponginess.
In bike shops, they frequently recommend that the new bikes be brought
back within 30 days for derailleur cable adjustments due to "cable
stretch". Of course cables are too stiff and strong to actually
stretch, and their is little force on the derailleur cables anyway.
What really happens is that the housings and their ferrules get seated
better or the housings settle into a different curvature, resulting in
an offset in the index cable, which is mistaken for stretching of the
cables themselves.
Mark McMaster
MMc...@ix.netcom.com
Todd West
Mark McMaster <MMc...@ix.netcom.com> wrote:
>I'm also quite certain that the housing adds elasticity. The spiral
>wound housing would be quite stiff indeed if it didn't have to make any
>bends, but as soon as its routing is curved, gaps form between the
>spiral loops at the outer radius of the housing curvature. Tensioning
>the cable attempts to close these gaps, leading to the "spongy"
>feeling. The rear brake having a longer housing with more bends has
>more of this sponginess.
Umm, not quite. Just about every housing that's sold these days (at
least that I know of) molds a bunch of straight wires into the middle of
the plastic housing. Putting tension on the cable does change housing's
curvature because the cable can't support anything but tensile loads,
and thus the effective distance between the lever and the brakes or
derailleur.
You're also neglecting the effects of any flex in the frame or fork (of
which there's usually quite a bit---go play with a pre-1997 Trek Y rear
triangle if you want to see a really impressive case) and in the brake
arms themselves.
>stretch". Of course cables are too stiff and strong to actually
>stretch, and their is little force on the derailleur cables anyway.
>What really happens is that the housings and their ferrules get seated
>better or the housings settle into a different curvature, resulting in
>an offset in the index cable, which is mistaken for stretching of the
>cables themselves.
I'd be surprised if there's much change in the seating of the housings.
The individual wires in the cable don't undergo any plastic deformation,
but the cable as a whole can and does. The only reason cables stay
together is because the wires are wound around each other, and when
they're tensioned the angle of winding increases, lengthening the cable.
Over time, the wires will seat into each other, producing a sight,
permanent increase in the cable's length (hence the standard 30 day
tune-up) and there will still be some stretch every time pull on the
cable. This effect is very much like what happens to the casings of
bike tires when they're inflated, if that helps to conceptualize what's
going on. It's been a long time since I spent my summers working in a
wire factory, and I've forgotten what typical stretch-outs are, but a
few millimeters should be in the ballpark---I usually get about a gear
of stretch out of my rear deraillure over the cable's lifetime.
Todd
--
Anti-spam boggling in effect. Edit reply-to address before sending mail.
Chuck Fry
In article <3503f60b...@news.nuri.net>,
Mark Hickey <mhi...@cynetfl.com> wrote:
>>"You'll have to raise your hand a bit further to get those weights
>>off the ground." The analogous situation with a hand brake is having
>>to squeeze it farther. If there's too much sponginess, you can pull
>>the lever to the handlebar before getting the braking action you want.
>
>Ah, but that stretch is *reducing* the pressure you are applying.
BZZZT! Sorry Mark, but you're wrong. The force is the same whether the
cable stretches or not. You should know better than to argue with
engineers on an engineering topic. :-)
Work (in the engineering sense) is essentially wasted in stretching the
cable. And the stretch may prevent you from applying the desired
braking force, if the lever runs out of travel before the desired force
can be applied, as the previous poster said.
But tension is not reduced or lost by this effect.
-- Chuck, armchair Mech.E
--
Chuck Fry -- Jack of all trades, master of none
chu...@chucko.com (text only please), chuc...@home.com (MIME enabled),
chu...@gateway.idiom.com (SPAM ONLY)
Jobst Brandt
Todd West writes:
> The individual wires in the cable don't undergo any plastic
> deformation, but the cable as a whole can and does.
There was no claim of plastic elongation but rather elastic length
change, also known as sponge when squeezing the brake lever.
> The only reason cables stay together is because the wires are wound
> around each other, and when they're tensioned the angle of winding
> increases, lengthening the cable. Over time, the wires will seat
> into each other, producing a sight, permanent increase in the
> cable's length (hence the standard 30 day tune-up) and there will
> still be some stretch every time pull on the cable.
I think you should inspect a brake cable more carefully, noting that
the cable is tightly wrapped without voids. The angle of the cable
strands cannot change unless there is space between them. Cable
manufacturers have perfected the art of tightly wrapping strands.
After all, there isn't much market for springy cable.
> This effect is very much like what happens to the casings of bike
> tires when they're inflated, if that helps to conceptualize what's
> going on.
It doesn't. A bicycle tire is made to be compliant and is full of air.
The constriction of bias ply tires is a separate subject that is
brought up often by contributors who do not recognize the mechanism.
> It's been a long time since I spent my summers working in a wire
> factory, and I've forgotten what typical stretch-outs are, but a few
> millimeters should be in the ballpark---I usually get about a gear
> of stretch out of my rear derailleur over the cable's lifetime.
I don't know what the allusion to wire factory is supposed to mean but
it didn't include anything about engineering involvement. What are
"stretch-outs" and what are they there for? What means "a few
millimeters"? A few per meter or per arbitrary cable length? The way
you say "over the cable's lifetime" it sounds like a long term creep.
Jobst Brandt <jbr...@hpl.hp.com>
Jobst Brandt
Mark McMaster writes:
> I'm also quite certain that the housing adds elasticity. The spiral
> wound housing would be quite stiff indeed if it didn't have to make
> any bends, but as soon as its routing is curved, gaps form between
> the spiral loops at the outer radius of the housing curvature.
> Tensioning the cable attempts to close these gaps, leading to the
> "spongy" feeling. The rear brake having a longer housing with more
> bends has more of this sponginess.
The cable housing in a straight line is a helical stack of no-space
wires, that if they are square cross section, are essentially
incompressible for the loads in question. When curved, the only
contact of these wires is around the inside of the curve. High load
cables use square cross section wire because that gives a larger
Hertzian (elastic) contact patch where the wires are in hard contact.
Most bicycle "spaghetti" is made of round cross section wire and
leaves only a theoretical point contact on the inside of bends.
Cable housings are wound in such a way that they are a spring with
tension pre-load. That is, the coils are preloaded against each other.
That is why the housing tends to snap back into a straight line if
curved by hand. exceeding the elastic limit leaves space between coils
and makes the housing useless because it then behaves the way one
imagines cable housing might compress.
> In bike shops, they frequently recommend that the new bikes be
> brought back within 30 days for derailleur cable adjustments due to
> "cable stretch". Of course cables are too stiff and strong to
> actually stretch, and their is little force on the derailleur cables
> anyway. What really happens is that the housings and their ferrules
> get seated better or the housings settle into a different curvature,
> resulting in an offset in the index cable, which is mistaken for
> stretching of the cables themselves.
And some high pressure contact points are worn off.
Jobst Brandt <jbr...@hpl.hp.com>
alex wetmore
Todd West wrote in message <6e13vj$1bh$1...@hermes.rdrop.com>...
>Umm, not quite. Just about every housing that's sold these days (at
>least that I know of) molds a bunch of straight wires into the middle of
>the plastic housing. Putting tension on the cable does change housing's
>curvature because the cable can't support anything but tensile loads,
>and thus the effective distance between the lever and the brakes or
>derailleur.
This is true of shifter cable housing, but not brake cable housing. All of
the brake cable housing that I've seen is still spiral wound. I don't
believe that shifter housing (which is made out of straight wires) is strong
enough to handle the loads of braking.
Tom
On Sat, 7 Mar 1998, Matt O'Toole wrote:
>
> Tom Ace wrote in message <35021A11...@best.comX>...
>
> >You ignored my question about why rear brakes are spongier
> >than front ones. I have seen this on several bikes, with
> >identical levers and calipers front and back (calipers with
> >the same reach front and back).
>
> >If it's not the longer cable that makes them spongier (noticeable
> >after the pads are pushing against the rim), what is it?
>
My guess is the rear chainstays aren't as rigid as the front forks are in
a twisting moment. Thus, the fronts feel more rigid because the brake
pivots move less when the brakes are applied. A brake booster can help
aliviate this, but will not remidy this completely, since the stays are
still weaker in the rear than the front.
___
TTTTT OO M M The sixth sick shiek's sixth sheep's sick. |~~~|
T O O MM MM @o o@
T O O M M M So if it is in or if it is on it is as it is, *
T OO M M be it in or on. `-'
Matt O'Toole
Tom wrote ...
>My guess is the rear chainstays aren't as rigid as the front forks are in
>a twisting moment. Thus, the fronts feel more rigid because the brake
>pivots move less when the brakes are applied. A brake booster can help
>aliviate this, but will not remidy this completely, since the stays are
>still weaker in the rear than the front.
This can be true, but not always. On my last bike, a steel one with normal
chainstays, there was visible flex in the chainstays. Now, I have a fat
tubed Klein, and I can't see any flex at all. The steel bike had a mushier
rear brake than the Klein, but the Klein's rear brake is still mushier than
the front, even though the frame flexes less than the Judy fork. So,
something's up with the cables. It may be the cable fibers settling, as I
mentioned. However, as others have pointed out, it's more likely to be the
housing ends settling in the stops, gradually sharpening bends at the
straddle wire, etc., as cable tension increases. There is one piece of
housing between the front lever and brake, and two between the rear lever
and brake, so there's twice the opportunity for play in the rear.
Matt O.
Dave Blake
tyou...@csc.UVic.CA carefully typed:
>> Tom Ace wrote in message <35021A11...@best.comX>...
>> >after the pads are pushing against the rim), what is it?
>My guess is the rear chainstays aren't as rigid as the front forks are in
>a twisting moment. Thus, the fronts feel more rigid because the brake
>pivots move less when the brakes are applied. A brake booster can help
>aliviate this, but will not remidy this completely, since the stays are
>still weaker in the rear than the front.
The front fork brake bosses are almost certainly less rigid
than the rear. In the front, the brake boss experiences twisting
forces from pad contact normal to the rim, and from the braking
force parallel to the rim. The torque of both these forces
is the same in direction in the front, which leads to a twisting
of the front brake boss that is large relative to the rear.
In the rear they partially cancel as they are opposite in
direction.
--
Dave Blake
dbl...@phy.ucsf.edu
Mark McMaster
Tom wrote:
>
> On Sat, 7 Mar 1998, Matt O'Toole wrote:
>
> > >after the pads are pushing against the rim), what is it?
> >
>
> My guess is the rear chainstays aren't as rigid as the front forks are in
> a twisting moment.
How does that explain the extra sponginess of rear brakes with the
sidepull calipers (single or dual pivot) used on road bikes? Cable
tension does not pull on frame at all when these brakes are actuated.
Mark McMaster
MMc...@ix.netcom.com
Karl Frantz
From all accounts, it's not. This is a particularly nasty failure mode
- the most likely time of failure is when you need maximal braking
effort, and there will be no apparent deficiency in the system until
that time...
--
Karl Frantz * fra...@eng.pko.dec.com
+---------------------------------------+
| Good judgement comes from experience. |
| Experience comes from bad judgement. |
+---------------------------------------+
m...@hooked.net
In article <350937...@eng.pko.dec.com>,
Karl Frantz <fra...@eng.pko.dec.com> wrote:
>
> alex wetmore wrote:
> >
> > Todd West wrote in message <6e13vj$1bh$1...@hermes.rdrop.com>...
> > >Umm, not quite. Just about every housing that's sold these days (at
> > >least that I know of) molds a bunch of straight wires into the middle of
> > >the plastic housing. Putting tension on the cable does change housing's
> > >curvature because the cable can't support anything but tensile loads,
> > >and thus the effective distance between the lever and the brakes or
> > >derailleur.
> >
> > This is true of shifter cable housing, but not brake cable housing. All
of
> > the brake cable housing that I've seen is still spiral wound. I don't
> > believe that shifter housing (which is made out of straight wires) is
strong
> > enough to handle the loads of braking.
>
> From all accounts, it's not. This is a particularly nasty failure mode
> - the most likely time of failure is when you need maximal braking
> effort, and there will be no apparent deficiency in the system until
> that time...
I've noticed that some of the "boutique" cable/housing sets are wrapping
straight wires with a sprial winding. Some are going so far as to call
it, "compressionless."
--mc
Mark Chandler m...@hooked.net Concord, CA
http://www.hooked.net/~mpc