Yoke height for Racer Centerpull brakes
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Rene Sterental
Apr 12, 2011, 8:49:44 PM4/12/11
to rbw-owne...@googlegroups.com
Hi all,
I've read all about how high the yoke for the straddle cable should be for regular cantilever brakes depending on their profile. However, I cannot really find any specific info regarding centerpull brakes.
Is it better to have more cable for a higher yoke or less cable for a lower yoke? Paul's instructions state about 2 inches or so higher than the brake arms, I figure that's where the cable attaches, but also states that the height is not critical. If I recall correctly, the same is stated for the Neo-Retro and Canti brakes, although I've learned that they need different heights for optimal performance.
Any feedback is appreciated!
René
benzzoy
Apr 12, 2011, 9:27:39 PM4/12/11
to RBW Owners Bunch
How high you put the straddle cable yoke will affect the system's
overall mechanical leverage. The higher the yoke, the higher the
mechanical advantage. Take a look at this visual calculator:
http://www.circleacycles.com/cantilevers/
-B
overall mechanical leverage. The higher the yoke, the higher the
mechanical advantage. Take a look at this visual calculator:
http://www.circleacycles.com/cantilevers/
-B
Rene Sterental
Apr 12, 2011, 10:14:58 PM4/12/11
to rbw-owne...@googlegroups.com
Saw that online earlier. Still clueless about using it or interpreting it.
Sent from my iPhone 4
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benzzoy
Apr 12, 2011, 11:12:43 PM4/12/11
to RBW Owners Bunch
Well, it's like this:
First, make sure the 4 brake parameters are set correct to reflect
your brake. For example, OP is half the width of the brake bosses, OD
is the brake "reach" that Grant writes about, PA is the effective
length of the "actuated" brake arm.
Once you got those set up, you can toggle the "Y", which is the yoke
height. As you toggle it up (increasing YO on the X-axis), you will
see that the mechanical advantage goes down (on the Y-axis).
Increasing mechanical advantage means that you will need less finger
force to exert more braking force at the pads, at the cost of less pad
clearance when the brakes are released.
You will notice that for a particular set of the 4 brake parameters,
the mechanical advantage curve is the same, and moving the yoke up or
down only changes where in the response curve the brake is adjusted
to, and not the curve itself.
From this neat visual aid, one can verify that all else being equal,
having longer reach brakes will reduce mechanical advantage.
Similarly, having shorter "actuated" arms will also lead to reduced
mechanical advantage.
The visual aid is quite useful in comparing different cantilever
brakes. For example, in the default setting (just reload the URL),
one can see that to get a wide profile brake to feel like a low
profile brake (i.e., have similar mechanical advantage), the wide
profile brake will need to have a much lower yoke height than the low
profile brake (about 60 vs. about 140, respectively).
-B
First, make sure the 4 brake parameters are set correct to reflect
your brake. For example, OP is half the width of the brake bosses, OD
is the brake "reach" that Grant writes about, PA is the effective
length of the "actuated" brake arm.
Once you got those set up, you can toggle the "Y", which is the yoke
height. As you toggle it up (increasing YO on the X-axis), you will
see that the mechanical advantage goes down (on the Y-axis).
Increasing mechanical advantage means that you will need less finger
force to exert more braking force at the pads, at the cost of less pad
clearance when the brakes are released.
You will notice that for a particular set of the 4 brake parameters,
the mechanical advantage curve is the same, and moving the yoke up or
down only changes where in the response curve the brake is adjusted
to, and not the curve itself.
From this neat visual aid, one can verify that all else being equal,
having longer reach brakes will reduce mechanical advantage.
Similarly, having shorter "actuated" arms will also lead to reduced
mechanical advantage.
The visual aid is quite useful in comparing different cantilever
brakes. For example, in the default setting (just reload the URL),
one can see that to get a wide profile brake to feel like a low
profile brake (i.e., have similar mechanical advantage), the wide
profile brake will need to have a much lower yoke height than the low
profile brake (about 60 vs. about 140, respectively).
-B
Rene Sterental
Apr 13, 2011, 12:37:33 AM4/13/11
to rbw-owne...@googlegroups.com
Finally figured out how to use the calculator. However, while I can see the MA go up or down, what is the optimal MA to strive for? I'm still unsure, based on all I've read, whether a lower or a higher MA are better. I thought I understood that lower MA meant more modulation but more force needed to apply the brakes; also a spongier feeling at the lever. Higher MA meant ligher snappier feeling that stops very quickly but looses modulation.
Is it then a matter of finding what you like or is there a number or setting to go for?
René
René
Jeremy Till
Apr 13, 2011, 2:28:37 AM4/13/11
to RBW Owners Bunch
Rene, have you read Sheldon's article on cantilever geometry?
http://sheldonbrown.com/cantilever-geometry.html#mechanical (links to
the section on mechanical advantage)
Of course, the specifics of the article are about cantilevers, but the
information about straddle cable height should be pretty much the same
for centerpull calipers.
The truth is, I don't think there is one "optimal" MA setting for
these types of brakes, it really comes down to the vagaries of your
personal setup and your own preferences in how your brakes feel.
Sheldon points out that the normal instincts of brake feel, coming
from cars--that a firm, stiff response in the lever is optimal--
doesn't necessarily lead to the best brake set up here.
MA is basically the ratio of distances traveled between lever and
pad. At higher MA's, the lever is traveling much farther than the pad
is, and thus it can feel "spongy" and worrisome. However, if you
think about it, high MA means that all that distance being traveled by
the lever is turning into clamping force at the rim, just like when
you use a simple lever and fulcrum, you push the lever a much greater
distance than the load, but produce a greater force than you could
unaided. Thus, "spongy" feeling levers can actually produce
prodigious stopping power, and have great modulation. However, with
too much MA the lever can bottom out on the handlebars. Lower MA's,
conversely, feel firmer at the lever and prevent the lever bottoming
out on the bar, but you will need to squeeze the lever harder within
that smaller range in order to produce the same stopping power as
before. So some of it comes down to hand strength, some to how your
lever interacts with the curve of your bars, and some to how you want
the lever to feel when you pull back on it.
I would set the MA as high as is possible while maintaining what feels
to you like an okay range of motion for the lever, i.e. that doesn't
risk bottoming out on the bars. I took this to the extreme on a bike
i recently sold. It had a traditional medium-profile cantilever
(single front brake on a fixed gear) and a nice old LX mtb (pre-v
brake) lever. I basically set the straddle cable in line with the
bottom of the fork crown, so as low as it could go without affecting
clearance. The lever traveled relatively far, but MAN, could that
thing stop--it shot me forward off the seat the first time i pulled
it.
http://sheldonbrown.com/cantilever-geometry.html#mechanical (links to
the section on mechanical advantage)
Of course, the specifics of the article are about cantilevers, but the
information about straddle cable height should be pretty much the same
for centerpull calipers.
The truth is, I don't think there is one "optimal" MA setting for
these types of brakes, it really comes down to the vagaries of your
personal setup and your own preferences in how your brakes feel.
Sheldon points out that the normal instincts of brake feel, coming
from cars--that a firm, stiff response in the lever is optimal--
doesn't necessarily lead to the best brake set up here.
MA is basically the ratio of distances traveled between lever and
pad. At higher MA's, the lever is traveling much farther than the pad
is, and thus it can feel "spongy" and worrisome. However, if you
think about it, high MA means that all that distance being traveled by
the lever is turning into clamping force at the rim, just like when
you use a simple lever and fulcrum, you push the lever a much greater
distance than the load, but produce a greater force than you could
unaided. Thus, "spongy" feeling levers can actually produce
prodigious stopping power, and have great modulation. However, with
too much MA the lever can bottom out on the handlebars. Lower MA's,
conversely, feel firmer at the lever and prevent the lever bottoming
out on the bar, but you will need to squeeze the lever harder within
that smaller range in order to produce the same stopping power as
before. So some of it comes down to hand strength, some to how your
lever interacts with the curve of your bars, and some to how you want
the lever to feel when you pull back on it.
I would set the MA as high as is possible while maintaining what feels
to you like an okay range of motion for the lever, i.e. that doesn't
risk bottoming out on the bars. I took this to the extreme on a bike
i recently sold. It had a traditional medium-profile cantilever
(single front brake on a fixed gear) and a nice old LX mtb (pre-v
brake) lever. I basically set the straddle cable in line with the
bottom of the fork crown, so as low as it could go without affecting
clearance. The lever traveled relatively far, but MAN, could that
thing stop--it shot me forward off the seat the first time i pulled
it.
MichaelH
Apr 13, 2011, 6:47:40 AM4/13/11
to RBW Owners Bunch
I think you guys are making this way more complicated and confusing
than it needs to be.
If you want to lift something with a cable it is best to pull it in
exactly the direction you want it to move. So a long and nearly
vertical arm, like the neo-retros move upward in a wider, flatter arc
and therefore need a higher cable set pretty close to 90 degrees to
lift the arm upward. A lower profile like the Shimano brake moves
more inward in a narrower arch and so will work better with a shorter
cable, also set close to 90 degrees. I'm not staring at my neo-retros
right now, but I believe Paul recommends a 6" high straddle and I
believe that is about where mine is set. They work great. I also
have both the Racers (on a my tandem) and the Racer Ms on my
Rambouillet. You will get a pretty good angle at about 4" on these.
That is where mine are set and they work quite well.
michael
than it needs to be.
If you want to lift something with a cable it is best to pull it in
exactly the direction you want it to move. So a long and nearly
vertical arm, like the neo-retros move upward in a wider, flatter arc
and therefore need a higher cable set pretty close to 90 degrees to
lift the arm upward. A lower profile like the Shimano brake moves
more inward in a narrower arch and so will work better with a shorter
cable, also set close to 90 degrees. I'm not staring at my neo-retros
right now, but I believe Paul recommends a 6" high straddle and I
believe that is about where mine is set. They work great. I also
have both the Racers (on a my tandem) and the Racer Ms on my
Rambouillet. You will get a pretty good angle at about 4" on these.
That is where mine are set and they work quite well.
michael
William
Apr 13, 2011, 4:19:30 PM4/13/11
to RBW Owners Bunch
The take home from the calculator, I think, is three-fold.
1. Wide profile cantilevers (ones like Mafacs, Tektro CR720, Paul Neo
Retros) behave about the same regardless of straddle yoke height. For
that reason, these brakes are almost impossible to screw up, and give
consistent behavior pretty much every time. At any straddle height
higher than the tire height, you are in the flat part of the curve,
where big changes in straddle height mean small changes in MA. They
can be frustrating if you think lowering the straddle will give you
more power, though, because the payoff will be tiny.
2. Centerpulls have the most pronounced knee in the curve of any of
the brakes listed. If the straddle is really low, then tiny changes
in straddle height mean huge changes in MA. If the straddle is above
~1 inch, then it's almost dead flat, your MA will remain nearly
constant regardless of straddle height.
3. Low profile cantilevers (like most 90's shimanos, Paul Touring
Cantis, IRDs and similar) are hugely sensitive to straddle height.
These are easily screwed up, and are highly tuneable for those who
know what they want to do. The frustration is that if you move
straddle height to clear a fender or a rack or similar, you might be
in a spot where you hate how your brakes feel.
The thing that a lot of people miss is the importance of the OD
dimension in the calculator. It has a pretty big bearing on what MA
you can achieve, but whatever this dimension is, you are basically
stuck with it. The OD dimension depends on where your frame builder
happened to install your canti-posts (and your rim diameter). If your
frame builder mounted the posts a few mm on the low side, you'll get
more MA. If your frame builder mounted them a few mm on the high
side, you'll get less MA. Drag OD back and forth on your brake of
choice and see the dramatic changes in the height of the MA curve.
It's a pretty big deal.
1. Wide profile cantilevers (ones like Mafacs, Tektro CR720, Paul Neo
Retros) behave about the same regardless of straddle yoke height. For
that reason, these brakes are almost impossible to screw up, and give
consistent behavior pretty much every time. At any straddle height
higher than the tire height, you are in the flat part of the curve,
where big changes in straddle height mean small changes in MA. They
can be frustrating if you think lowering the straddle will give you
more power, though, because the payoff will be tiny.
2. Centerpulls have the most pronounced knee in the curve of any of
the brakes listed. If the straddle is really low, then tiny changes
in straddle height mean huge changes in MA. If the straddle is above
~1 inch, then it's almost dead flat, your MA will remain nearly
constant regardless of straddle height.
3. Low profile cantilevers (like most 90's shimanos, Paul Touring
Cantis, IRDs and similar) are hugely sensitive to straddle height.
These are easily screwed up, and are highly tuneable for those who
know what they want to do. The frustration is that if you move
straddle height to clear a fender or a rack or similar, you might be
in a spot where you hate how your brakes feel.
The thing that a lot of people miss is the importance of the OD
dimension in the calculator. It has a pretty big bearing on what MA
you can achieve, but whatever this dimension is, you are basically
stuck with it. The OD dimension depends on where your frame builder
happened to install your canti-posts (and your rim diameter). If your
frame builder mounted the posts a few mm on the low side, you'll get
more MA. If your frame builder mounted them a few mm on the high
side, you'll get less MA. Drag OD back and forth on your brake of
choice and see the dramatic changes in the height of the MA curve.
It's a pretty big deal.
Philip Williamson
Apr 14, 2011, 12:33:04 PM4/14/11
to RBW Owners Bunch
Thanks, William, for the summary. I had thought there was a simple,
linear, correlation of straddle height to mechanical advantage - low
yoke for low profile, high yoke for high profile.
The actual facts as you describe may also explain my disappointment in
my CR720s.
Philip
Philip Williamson
www.biketinker.com
linear, correlation of straddle height to mechanical advantage - low
yoke for low profile, high yoke for high profile.
The actual facts as you describe may also explain my disappointment in
my CR720s.
Philip
Philip Williamson
www.biketinker.com
Rene Sterental
Apr 14, 2011, 1:28:38 PM4/14/11
to rbw-owne...@googlegroups.com
William,
Great actionable summary. Everyone's detailed explanations helped shed
even more light on this topic. Now I'll go and play a bit with the
Racer brakes on the AHH.
It is also fully clear why the Neo and Touring Canti brakes on my
Atlantis feel the way they do and how to fine tune them.
Rene
Sent from my iPhone 4
On Apr 14, 2011, at 9:33 AM, Philip Williamson
<philip.w...@gmail.com> wrote:
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