Brake pad question

Helmut Springer said:

jim beam said:

air brakes on buses & trucks are sensitive only to stroke,
not force.

Not the ones I drove.

well, the actuator valve is spring loaded, but that's it.
take a valve apart and check for yourself - all you're
doing is pressing spring - you're not compressing air with
your foot like you are compressing fluid in a hydraulic
brake system.

bendix.com03812.pdfOpen ↗
for a diagram.

Quoted message said:

Would be a counter-intuitive concept, btw.

that's why car drivers have trouble with air brakes when
they first start driving them!

Tim McNamara said:

Bruce Graham said:

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

Tom Sherman writes:

<snip>

Quoted message said:

> I have driven older cars without power brakes and did
> not find the effort excessive: certainly nothing out
> of the normal range for fit cyclist.

What "older cars" did you drive that had unassisted disc
brakes?

VW beetles from the late 60's early 70's.

Sorry, drum brakes. At least if my wife's '72 Super Beetle
was anything to go by.

I've just checked my VW 1500 beetle out the back (which I
bought new on 2 July 1968). And yes, it still has
(unassisted) front discs.

John

Old Crow / Wild Turkey said:

Quoted message said:

Quoted message said:

Having driven 135,000+ miles in cars with 4-wheel disc
brakes and power assist but no anti-lock, I feel that I
am quite familiar with that type of system. I have also
driven plenty of pickups and vans with rear wheel drum
brakes, so I am all too aware of their poor modulation
and "self-energizing" effect.

Quoted message said:

actually, the two reasons brakes have gone to disk from
drum are:

Quoted message said:

1. disks cool much quicker so therefore are much more fade
resistant. ask any big rig driver about fade in drum
brakes.

Quoted message said:

2. if they get wet, drums are hard to dry out - disks dry
almost immediately so disks are much safer.

Quoted message said:

and it's too simplistic to claim "poor modulation" on a
rear drum brakes - it takes no account of load
compensation or proportioning devices.

The main reason for changing to disc brakes from drums is
linearity of application pressure and braking effect. I can
say this with great certainty, having designed brakes in the
1960's when those decisions were made. Brake fade and lock-
up were common and was caused mainly by the self servo of
leading shoes on which drum brake performance depended.
Decoupling braking force from application force by having
applied pad pressure at right angles to braking force is the
main reason for getting rid of drum brakes. Trucks use drum
brakes today because they can dissipate more power for a
given volume and cost than discs.

This subject has been hammered to death here in the past and
I suggest you review that in the archives. The effects you
mention as 1. & 2. are derivatives of linear braking that
does not use servo action of drum brakes but rather a
decoupled response. It is the instability of response of
drum brakes that get their effectiveness in a narrow range
of friction coefficient whose response is greatly amplified
by the servo effect.

Quoted message said:

Quoted message said:

Just because you drive cars doesn't qualify you as
understanding the works of the brakes. I'm sure you can
strike up a conversation with a truck driver at a truck-
stop cafe and get all sorts of testimonials on the
benefits of various equipment, some of which is pure
folklore and other parts that happen to coincide with
fact. Mileage does not an automotive engineer make, so
take it easy on the mileage claims.

Quoted message said:

Quoted message said:

Quoted message said:

The point is that power assisted braking and steering
(not to mention automatic transmissions) are used in
cars because they are designed for lazy people who
expect to put out no effort, not out of necessity.

Quoted message said:

Quoted message said:

Tell that to Michael Schumacher and his competitors. The
power brake is an essential part of good braking and cars
that don't use it are either light enough to squeak by or
too cheap to use it.

Quoted message said:

Quoted message said:

The basic concept of a brake is that it is a force
transducer,

Quoted message said:

Technically, it's an energy transducer - turns the energy
of motion into heat.

I think you have your idea of a definition confused. A
transducer transmits a function of the same kind through
some multiplier to a destination. There is no energy input
to a brake pedal, only position and force and the position
is irrelevant. For instance, on a bicycle, braking would be
ideal if the hand lever controlled braking entirely by how
hard the lever was squeezed with no travel. That is a force
transducer. The brake converts kinetic energy to heat.

Quoted message said:

Quoted message said:

A brake pedal is not a position transducer as steering
is. Good Brake response is proportional to pedal
pressure, not stroke. In fact the stroke involved is
counterproductive because it changes the leverage of the
leg and the feel of how hard the brake is being applied.
Stroke on power assisted brakes is a necessary evil of
having to also work (with diminished capacity) without
assist.

Quoted message said:

Air brakes on buses & trucks are sensitive only to stroke,
not force. You can bottom the pedal on an air braked
vehicle no problem. A common mistake make by people
learning to drive an air braked vehicle is to brake much
too fiercely because they're expecting the pedal to stop
going down as they reach some kind of bite point.

So what does this have to do with disc brakes. Pedal
activated air brakes respond the same as other brakes except
that the resistance is not a feedback from the brakes
because the brakes are not a constant depending on what the
vehicle complement is (semi-trailer or semi-trailer and full
tailer) so a fixed pseudo load is provided, but it is a
force rather than just position. Are you perhaps thinking of
hand operated railway air brakes where feedback is a
pressure gauge?

Jobst Brandt [email hidden]

Jim Adney said:

Quoted message said:

What "older cars" did you drive that had unassisted disc
brakes?

Quoted message said:

VW type 3s came with unassisted front disks from '66 to
the end of production in '73. They certainly require more
pedal effort than a car with power brakes, but that's
really only because power brakes require virtually no
effort. I've never had any problem getting one of mine to
stop, but I keep the brakes in good condition. In general,
I've always considered their brakes to be excellent.

Yes and 356Porsches had no power assist but required more
pedal pressure that is standard today. They were just under
the limit of excessive pedal pressure and not adding power
was far less expensive. In those days people were not as
ready to splurge on automotive toys as today.

Quoted message said:

People who are used to power brakes are often surprised by
the pedal effort, but I have always assumed that this was
simply because they were used to the zero effort that
power brakes required.

That's true and right there the question arises, how hard
should a driver need to push on the brake pedal to lock the
wheels (approach that condition)? It is definitely less that
those cars demanded from the average driver. Since power
brakes make that force optional, a force in the range of
comfort zones of many drivers has been chosen. That is why
the brand of car (rental) makes no difference to the driver
who, today, knows what to expect.

Jobst Brandt [email hidden]

Quoted message said:

Old Crow / Wild Turkey said:

Quoted message said:

>Having driven 135,000+ miles in cars with 4-wheel disc
>brakes and power assist but no anti-lock, I feel that I
>am quite familiar with that type of system. I have also
>driven plenty of pickups and vans with rear wheel drum
>brakes, so I am all too aware of their poor modulation
>and "self-energizing" effect.

Quoted message said:

actually, the two reasons brakes have gone to disk from
drum are:

Quoted message said:

1. disks cool much quicker so therefore are much more fade
resistant. ask any big rig driver about fade in drum
brakes.

Quoted message said:

2. if they get wet, drums are hard to dry out - disks dry
almost immediately so disks are much safer.

Quoted message said:

and it's too simplistic to claim "poor modulation" on a
rear drum brakes - it takes no account of load
compensation or proportioning devices.

The main reason for changing to disc brakes from drums is
linearity of application pressure and braking effect. I
can say this with great certainty, having designed brakes
in the 1960's when those decisions were made. Brake fade
and lock-up were common and was caused mainly by the self
servo of leading shoes on which drum brake performance
depended.

didn't i say fade? and i remain to be convinced on the
lock-up. i've never experienced a problem with it, and
i've had a number of vintage vw's. any significant self-
actuation swould surely cause instant hard lock-up under
even minor braking operations, and this is clearly not
what we see in practice.

Quoted message said:

Decoupling braking force from application force by having
applied pad pressure at right angles to braking force is
the main reason for getting rid of drum brakes. Trucks
use drum brakes today because they can dissipate more
power for a given volume and cost than discs.

on the face of it, that would apear to be true, but it's
more complicated than that. some lighter trucks & coaches
use air over hydraulic. in that case, disks are used, often
with multiple calipers, to get around fade. in that case,
cost does not seem to be an issue.

for vehicles that use all air, they still use drum because
they are "fail safe", i.e. their unpressurized position is
"full on". when the brake lines are pressurized with
compressed air, actuators balance the brakes in the "just
off" position. when the driver presses the pedal, it reduces
the pressure in the brake circuits and the springs that
force the shoes hard against the drums are allowed to do
some work. fail safe is not a feature on normal caliper
brake systems.

Quoted message said:

This subject has been hammered to death here in the past
and I suggest you review that in the archives. The effects
you mention as 1. & 2. are derivatives of linear braking
that does not use servo action of drum brakes but rather a
decoupled response. It is the instability of response of
drum brakes that get their effectiveness in a narrow range
of friction coefficient whose response is greatly
amplified by the servo effect.

Quoted message said:

Quoted message said:

Just because you drive cars doesn't qualify you as
understanding the works of the brakes. I'm sure you can
strike up a conversation with a truck driver at a truck-
stop cafe and get all sorts of testimonials on the
benefits of various equipment, some of which is pure
folklore and other parts that happen to coincide with
fact. Mileage does not an automotive engineer make, so
take it easy on the mileage claims.

Quoted message said:

Quoted message said:

>The point is that power assisted braking and steering
>(not to mention automatic transmissions) are used in
>cars because they are designed for lazy people who
>expect to put out no effort, not out of necessity.

Quoted message said:

Quoted message said:

Tell that to Michael Schumacher and his competitors. The
power brake is an essential part of good braking and cars
that don't use it are either light enough to squeak by or
too cheap to use it.

Quoted message said:

Quoted message said:

The basic concept of a brake is that it is a force
transducer,

Quoted message said:

Technically, it's an energy transducer - turns the energy
of motion into heat.

I think you have your idea of a definition confused. A
transducer transmits a function of the same kind through
some multiplier to a destination. There is no energy
input to a brake pedal, only position and force and the
position is irrelevant. For instance, on a bicycle,
braking would be ideal if the hand lever controlled
braking entirely by how hard the lever was squeezed with
no travel. That is a force transducer. The brake converts
kinetic energy to heat.

Quoted message said:

Quoted message said:

A brake pedal is not a position transducer as steering
is. Good Brake response is proportional to pedal
pressure, not stroke. In fact the stroke involved is
counterproductive because it changes the leverage of the
leg and the feel of how hard the brake is being applied.
Stroke on power assisted brakes is a necessary evil of
having to also work (with diminished capacity) without
assist.

Quoted message said:

Air brakes on buses & trucks are sensitive only to stroke,
not force. You can bottom the pedal on an air braked
vehicle no problem. A common mistake make by people
learning to drive an air braked vehicle is to brake much
too fiercely because they're expecting the pedal to stop
going down as they reach some kind of bite point.

So what does this have to do with disc brakes. Pedal
activated air brakes respond the same as other brakes
except that the resistance is not a feedback from the
brakes because the brakes are not a constant depending on
what the vehicle complement is (semi-trailer or semi-
trailer and full tailer) so a fixed pseudo load is
provided, but it is a force rather than just position. Are
you perhaps thinking of hand operated railway air brakes
where feedback is a pressure gauge?

it's got everything to do with disks if it's an air over
hydraulic system. see above.

the only pedal resistance is the spring in the actuator
valve. that's not "force" because it has nothing to do
with the pressure in the air lines - only pedal position
affects pressure.

Quoted message said:

Jobst Brandt [email hidden]

jim beam said:

[email hidden] wrote:

...

Quoted message said:

Quoted message said:

The main reason for changing to disc brakes from drums is
linearity of application pressure and braking effect. I
can say this with great certainty, having designed brakes
in the 1960's when those decisions were made. Brake fade
and lock-up were common and was caused mainly by the self
servo of leading shoes on which drum brake performance
depended.

didn't i say fade? and i remain to be convinced on the lock-
up. i've never experienced a problem with it, and i've had
a number of vintage vw's. any significant self-actuation
swould surely cause instant hard lock-up under even minor
braking operations, and this is clearly not what we see in
practice.

It was absolutely critical to chamfer the leading edge of
the brake linings to minimize "grabbing" of VW drum brakes.
Otherwise the effect could be dramatic.

Another supposed advantage of discs was the lower proportion
of resin binder in the rigid pads compared with the
necessarily more flexible linings for drums. This resin was
supposed to act as a lubricant when it got very hot, but
maybe that's a myth.

John

jim beam said:

well, the actuator valve is spring loaded, but that's it.

Which means you get more resistance the more you open the
valve, which comes to the same effect: harder braking needs
a harder push.

Quoted message said:

take a valve apart and check for yourself - all you're
doing is pressing spring - you're not compressing air with
your foot like you are compressing fluid in a hydraulic
brake system.

BTDT.

Quoted message said:

that's why car drivers have trouble with air brakes when
they first start driving them!

Doesn't match my experience. People tended to brake hard on
an unloaded truck when they started, but did the same in a
car with high(er) ratio ("aggressive brakes"😉.

--
MfG/Best regards helmut springer

SNIP...

Quoted message said:

The main reason for changing to disc brakes from drums is
linearity of application pressure and braking effect. I
can say this with great certainty, having designed brakes
in the 1960's when those decisions were made. Brake fade
and lock-up were common and was caused mainly by the self
servo of leading shoes on which drum brake performance
depended. Decoupling braking force from application force
by having applied pad pressure at right angles to braking
force is the main reason for getting rid of drum brakes.
Trucks use drum brakes today because they can dissipate
more power for a given volume and cost than discs.

...SNIP...

Oh well, who wants to start off the discussion on the
difficulties of setting up a 4 leading shoe front
motorbike brake or start talking of the aero
industry....... Hugh Fenton

Helmut Springer said:

jim beam said:

well, the actuator valve is spring loaded, but that's it.

Which means you get more resistance the more you open the
valve, which comes to the same effect: harder braking
needs a harder push.

yes, but that resistance is just the return spring, not the
braking system. in hydraulic systems you have both the
return spring back pressure /and/ the brake fluid pressure,
the latter being impossible to overcome without a fault: you
can floor a pedal in an air system, not an hydraulic system.

Quoted message said:

Quoted message said:

take a valve apart and check for yourself - all you're
doing is pressing spring - you're not compressing air with
your foot like you are compressing fluid in a hydraulic
brake system.

BTDT.

Quoted message said:

that's why car drivers have trouble with air brakes when
they first start driving them!

Doesn't match my experience. People tended to brake hard
on an unloaded truck when they started, but did the same
in a car with high(er) ratio ("aggressive brakes"😉.

jim beam said:

Quoted message said:

Which means you get more resistance the more you open the
valve, which comes to the same effect: harder braking
needs a harder push.

yes, but that resistance is just the return spring, not
the braking system.

Doesn't make a difference from the user interface point
of view: the harder you want to brake the harder you
have to push. Intuitive control by force applied, not by
pedal position.

--
MfG/Best regards helmut springer

Helmut Springer said:

jim beam said:

Quoted message said:

Which means you get more resistance the more you open the
valve, which comes to the same effect: harder braking
needs a harder push.

yes, but that resistance is just the return spring, not
the braking system.

Doesn't make a difference from the user interface point of
view: the harder you want to brake the harder you have to
push. Intuitive control by force applied, not by pedal
position.

well, it's good that your experience has been positive, but
my experience of working with learner drivers is that a
significant proportion jump in the cab, sit there trying to
familiarize themselves with the controls, press the brake
pedal, then /freak/ when they find they can press the brake
all the way to the floor! and when they start driving, it's
these same drivers that lock the wheels the first few times
they brake because they're stamping the pedal too hard -
they're trying to find the "hard" resistance point.

not /everyone/ did this, and you're clearly one of the
smarter ones, but the first time i saw it, i dismissed it as
a freak occurance, but when new drivers kept having this
same reaction i realized that different people have
different intuition on the way that brakes "should" work.
once you explain the way the air valve works and why the
pedal has a different feel, they go away happy and never
have a problem again.

Mark South said:

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

Quoted message said:

Mark South said:

>>Today I experienced something new.

Quoted message said:

>>About 20 km into my Sunday morning ride, I was coming
>>up a gentle hill into a tiny village and thinking
>>"Hell, I must be getting weaker every day, why is this
>>incline so hard?"

Quoted message said:

>well, after all that, what was it?

Quoted message said:

Good question. I still am not certain, but it seems to me
that my original explanation based on thermal expansion
of the brake pads was the correct one.

Thermal expansion, even in soft material like bicycle
brake pads cannot take up that clearance unless they were
dragging after they were last adjusted.

They were not dragging, but they were very close. The rim
is laterally true within less than .5 mm and the pads have
only enough clearance to not drag on the rim when
everything is cool.

Let's put some numbers at this problem. If the pads are 10
mm thick, and they expanded by 0.3 mm to cause brake rub,
that's 3% expansion. You were climbing a hill, so I'll
assume that you weren't intentionally dragging the brakes
and making them hot. You were 20 km into a ride, so let's
assume an hour of riding preceded the brakes rubbing.

Further, we'll assume that the temperature was rising very
fast that day
- maybe 5°C per hour. Now that implies that the thermal
expansion coefficient of your brake pads was about 0.03/5
= 0.006 mm/mm/°C. Based on a quick Google, the thermal
expansion coefficient of most materials is a few orders of
magnitude smaller than that. I don't know what the
coefficient is for brake pad material, but I have my
doubts about your theory, Mark.

Here are some tables of thermal expansion coefficients:

foamaliteplastics.comtech11.htmlOpen ↗
tpub.comh1017v2 20.htmOpen ↗
phoenix.phys.clemson.eduexpansionOpen ↗ hyperphysics.phy-hyperphysics.phy-Open ↗
astr.gsu.edu/hbase/tables/thexp.html#c1 physics.nus.edu.sgK 5 26Open ↗
P.htm

Quoted message said:

The brake is and was perfectly centred. When I stopped
and noticed the pads binding, they were both squeezed
onto the rim.

My suspicion is a bit of a sticky cable. The return springs
don't pull the cable taut immediately, but after a while,
the return springs gradually pull the cable through the
sticky spot. I have a rear brake that acts like this myself.
It's not a serious problem, so I haven't done anything about
it just yet.

--
Dave dvt at psu dot edu

dvt ([email hidden]) wrote:
: Mark South wrote:
: > <[email hidden]> wrote in message
: > "]news:[email hidden]...
: >
: >>Mark South writes:
: >>
: >>
: >>>>>Today I experienced something new.
: >>
: >>>>>About 20 km into my Sunday morning ride, I was coming
: >>>>>up a gentle hill into a tiny village and thinking
: >>>>>"Hell, I must be getting weaker every day, why is
: >>>>>this incline so hard?"
: >>
: >>>>well, after all that, what was it?
: >>
: >>>Good question. I still am not certain, but it seems to
: >>>me that my original explanation based on thermal
: >>>expansion of the brake pads was the correct one.
: >>
: >>Thermal expansion, even in soft material like bicycle
: >>brake pads cannot take up that clearance unless they
: >>were dragging after they were last adjusted.
: >
: > They were not dragging, but they were very close. The
: > rim is laterally true within less than .5 mm and the
: > pads have only enough clearance to not drag on the rim
: > when everything is cool.

: Let's put some numbers at this problem. If the pads are 10
: mm thick, and they expanded by 0.3 mm to cause brake rub,
: that's 3% expansion. You were climbing a hill, so I'll
: assume that you weren't intentionally dragging the brakes
: and making them hot. You were 20 km into a ride, so let's
: assume an hour of riding preceded the brakes rubbing.

If one is determined to pursue the theory of thermal
expansion, why assume that it only happens in the pads? Why
not in the rim, the calipers, some length of cable and
casing, and some length of frame that the cable is attached
to? A couple feet of cable is going to change more than 10mm
of pad (which may or may not be cancelled out by changes of
the frame, depending on whether they're dissimilar
materials...).

But I agree that thermal expansion is very unlikely to be
the culprit.

-Ken

Ken Ferschweiler said:

dvt ([email hidden]) wrote:
: Mark South wrote:
: > <[email hidden]> wrote in message
: > "]news:[email hidden]...
: >
: >>Mark South writes:
: >>
: >>
: >>>>>Today I experienced something new.
: >>
: >>>>>About 20 km into my Sunday morning ride, I was
: >>>>>coming up a gentle hill into a tiny village and
: >>>>>thinking "Hell, I must be getting weaker every day,
: >>>>>why is this incline so hard?"
: >>
: >>>>well, after all that, what was it?
: >>
: >>>Good question. I still am not certain, but it seems
: >>>to me that my original explanation based on thermal
: >>>expansion of the brake pads was the correct one.
: >>
: >>Thermal expansion, even in soft material like bicycle
: >>brake pads cannot take up that clearance unless they
: >>were dragging after they were last adjusted.
: >
: > They were not dragging, but they were very close. The
: > rim is laterally true within less than .5 mm and the
: > pads have only enough clearance to not drag on the rim
: > when everything is cool.

: Let's put some numbers at this problem. If the pads are
: 10 mm thick, and they expanded by 0.3 mm to cause brake
: rub, that's 3% expansion. You were climbing a hill, so
: I'll assume that you weren't intentionally dragging the
: brakes and making them hot. You were 20 km into a ride,
: so let's assume an hour of riding preceded the brakes
: rubbing.

If one is determined to pursue the theory of thermal
expansion, why assume that it only happens in the pads?
Why not in the rim, the calipers, some length of cable and
casing, and some length of frame that the cable is
attached to? A couple feet of cable is going to change
more than 10mm of pad (which may or may not be cancelled
out by changes of the frame, depending on whether they're
dissimilar materials...).

Good point.

Thermal expansion of the cables would tend to *open* the
brake rather than close it. OTOH, expansion of the cable
housings would tend to close the brake. But since the cable
housing is shorter than the cable and its stiffest component
(the spiral wrapping) will probably expand about as much as
the cable per unit length, the net effect would probably be
to open the brakes a bit more. Then you factor in the
thermal expansion of the frame, and the net result is
probably about nil. And even if you don't get perfect
cancellation with all of these factors, we're still an order
of magnitude or more away from the required change to make
the brake rub.

Rim width is probably around 20 mm, and based on my
estimates, the thermal expansion of aluminum under those
conditions is a few orders of magnitude smaller than the
observed change. Caliper growth would open the brake, and
we're still talking peanuts compared to the observed change.

--
Dave dvt at psu dot edu

"dvt" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Ken Ferschweiler said:

dvt ([email hidden]) wrote:
: Mark South wrote:
: > <[email hidden]> wrote in message
: > "]news:[email hidden]...
: >
: >>Mark South writes:
: >>
: >>
: >>>>>Today I experienced something new.
: >>
: >>>>>About 20 km into my Sunday morning ride, I was
: >>>>>coming up a gentle hill into a tiny village and
: >>>>>thinking "Hell, I must be getting weaker every
: >>>>>day, why is this incline so hard?"
: >>
: >>>>well, after all that, what was it?
: >>
: >>>Good question. I still am not certain, but it seems
: >>>to me that my original explanation based on thermal
: >>>expansion of the brake pads was the correct one.
: >>
: >>Thermal expansion, even in soft material like
: >>bicycle brake pads cannot take up that clearance
: >>unless they were dragging after they were last
: >>adjusted.
: >
: > They were not dragging, but they were very close.
: > The rim is laterally

true

Quoted message said:

Quoted message said:

: > within less than .5 mm and the pads have only enough
: > clearance to not

drag on

Quoted message said:

Quoted message said:

: > the rim when everything is cool.

: Let's put some numbers at this problem. If the pads
: are 10 mm thick, and they expanded by 0.3 mm to cause
: brake rub, that's 3% expansion. You were climbing a
: hill, so I'll assume that you weren't intentionally
: dragging the brakes and making them hot. You were 20
: km into a ride, so let's assume an hour of riding
: preceded the brakes rubbing.

If one is determined to pursue the theory of thermal
expansion, why assume that it only happens in the pads?
Why not in the rim, the calipers, some length of cable
and casing, and some length of frame that the cable is
attached to? A couple feet of cable is going to change
more than 10mm of pad (which may or may not be cancelled
out by changes of the frame, depending on whether
they're dissimilar materials...).

Good point.

Thermal expansion of the cables would tend to *open* the
brake rather than close it. OTOH, expansion of the cable
housings would tend to close the brake. But since the
cable housing is shorter than the cable and its stiffest
component (the spiral wrapping) will probably expand about
as much as the cable per unit length, the net effect would
probably be to open the brakes a bit more. Then you factor
in the thermal expansion of the frame, and the net result
is probably about nil. And even if you don't get perfect
cancellation with all of these factors, we're still an
order of magnitude or more away from the required change
to make the brake rub.

Rim width is probably around 20 mm, and based on my
estimates, the thermal expansion of aluminum under
those conditions is a few orders of magnitude smaller
than the observed change. Caliper growth would open the
brake, and we're still talking peanuts compared to the
observed change.

Thanks for all your comments. Brake cables (inner and outer)
are new Dura-Ace installed and set up by me 6 weeks ago. Not
enough mileage to wear anything.

I'm going to give up and blame aliens. They probably
abducted me, experimented with the bike, messed with the
gear cables, and then put me back on my bike after wiping
my memory.

That's simpler and more plausible than my theory of thermal
expansion of the pads, and no-one else's suggestions have
checked out.

So let's stick with it being aliens.
--
Mark South: World Citizen, Net Denizen