Disc brake rotor question

Julian said:

Why are disc brake rotors so wimpy?

troll?

Quoted message said:

Most are drilled until nothing is
left.

slight exaggeration there julian.

Quoted message said:

In tande use they heat up past the boiling point of water.

that's because they're working as they're supposed to - brakes turn your
kinetic energy into heat.

Quoted message said:

Are undrilled rotors better for tandem applications? Seems like there
is more metal there to soak up heat and more surface area to generate
friction.

you don't want the disk to accumulate heat with excess mass - that means
they take longer to recover if they reach fade temp. and drillings help
keep brakes working in mud and rain.

in the future, if you have a serious question, try keeping the troll
factor down.

jim beam said:

in the future, if you have a serious question, try keeping the troll
factor down.

Looks to me like you need to keep your attitude problem down?

On Sat, 16 Dec 2006 14:40:58 GMT, Julian <[email hidden]>

Quoted message said:

Why are disc brake rotors so wimpy? Most are drilled until nothing is
left. In tande use they heat up past the boiling point of water.

Are undrilled rotors better for tandem applications? Seems like there
is more metal there to soak up heat and more surface area to generate
friction.

If your brakes are actually fading (unlikely, unless you're loaded
tandem touring in the alps) the solution is not solid rotors but
bigger ones, and even then only after you've tried a different pad
compound. Stainless steel rotors with the right pads can still be
effective at surface temperatures of >1000F

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

Julian said:

Why are disc brake rotors so wimpy? Most are drilled until nothing is
left. In tande use they heat up past the boiling point of water.

Are undrilled rotors better for tandem applications? Seems like there
is more metal there to soak up heat and more surface area to generate
friction.

What size rotors and what brand are you using?

Julian who? said:

Why are disc brake rotors so wimpy? Most are drilled until nothing
is left. In tandem use they heat up past the boiling point of
water.

Much hotter... red hot!

Quoted message said:

Are undrilled rotors better for tandem applications? Seems like
there is more metal there to soak up heat and more surface area to
generate friction.

And more surface area to cool... We went over all this a month ago or
so and the die hard believers brought up all sorts of specious reasons
for the filigree disks on bicycle. Cars and trucks and railroads do
not have such disks while the spoiler-loud exhaust-tinted window guys
have cross drilled disks. It's like 1960's drillium on bicycles. The
hot rod syndrome.

Jobst Brandt

jim beam said:

Julian said:

Why are disc brake rotors so wimpy?

troll?

Quoted message said:

Most are drilled until nothing is
left.

slight exaggeration there julian.

Quoted message said:

In tande use they heat up past the boiling point of water.

that's because they're working as they're supposed to - brakes turn
your kinetic energy into heat.

Quoted message said:

Are undrilled rotors better for tandem applications? Seems like
there
is more metal there to soak up heat and more surface area to generate
friction.

you don't want the disk to accumulate heat with excess mass - that
means they take longer to recover if they reach fade temp. and
drillings help keep brakes working in mud and rain.

How will removing material reduce the operating temperature
or rate of heat dissipation?

--
Joe Riel

Joe Riel said:

jim beam said:

Julian said:

Why are disc brake rotors so wimpy?

troll?

Quoted message said:

Most are drilled until nothing is
left.

slight exaggeration there julian.

Quoted message said:

In tande use they heat up past the boiling point of water.

that's because they're working as they're supposed to - brakes turn
your kinetic energy into heat.

Quoted message said:

Are undrilled rotors better for tandem applications? Seems like
there
is more metal there to soak up heat and more surface area to generate
friction.

you don't want the disk to accumulate heat with excess mass - that
means they take longer to recover if they reach fade temp. and
drillings help keep brakes working in mud and rain.

How will removing material reduce the operating temperature
or rate of heat dissipation?

surface area/mass. it's a two-edged sword, because low mass heats
quicker, but the other side of it means increasing surface area allows
air flow to carry more heat away more quickly.

This is not a question of mass but rather one of surface area and
integrity when the disk becomes red hot. When a filigreed disk, as we
see often, becomes red hot, its strength is diminished to the point
that it can wrinkle, having so few support arms as the most relieved
ones do (to appear to have low rotating mass for the weight weenies.)
I am surprised to not have heard of crumpled disks that jammed in the
caliper for riders who descend steep roads fast.

Disk mass is irrelevant for heat storage at temperature rise times
that heavy riders cause on steep descents. Disk cooling surface and
strength are the primary concerns. That stainless steel is a poorer
heat conductor is irrelevant for thin disks, but a stainless disk
being "softer" than other steels affects wear. We know that effect
from aluminum rim wear with caliper brakes. However, in the rim
brake, conductivity matters because much of the cooling area is remote
from the braking surface in contrast to the disk brake where the brake
surface is the cooling surface.

Jobst Brandt

translation: affect/effect=impact

Quoted message said:

This is not a question of mass but rather one of surface area and
integrity when the disk becomes red hot.

so which cools quickest, something with a high surface area/mass ratio
or something with a low surface area/mass ratio?

Quoted message said:

When a filigreed disk, as we
see often, becomes red hot,

have you /ever/ seen a red hot mtb disk?

Quoted message said:

its strength is diminished to the point
that it can wrinkle,

that depends on the alloy. you may not be aware that some stainless
steels are used in high temp applications /because/ they retain their
strength.

Quoted message said:

having so few support arms as the most relieved
ones do (to appear to have low rotating mass for the weight weenies.)
I am surprised to not have heard of crumpled disks that jammed in the
caliper for riders who descend steep roads fast.

there's this thing called "testing". it eliminates failures.

Quoted message said:

Disk mass is irrelevant for heat storage

storage? brakes aren't for storing heat - they're for dissipating it.

Quoted message said:

at temperature rise times
that heavy riders cause on steep descents.

it's not just weight, it's speed and rate.

Quoted message said:

Disk cooling surface and
strength are the primary concerns.

indeed.

Quoted message said:

That stainless steel is a poorer
heat conductor is irrelevant for thin disks, but a stainless disk
being "softer" than other steels affects wear.

so?

Quoted message said:

We know that effect
from aluminum rim wear with caliper brakes.

so?

Quoted message said:

However, in the rim
brake, conductivity matters because much of the cooling area is remote
from the braking surface in contrast to the disk brake where the brake
surface is the cooling surface.

that implies that rim brakes cannot dissipate heat through the braking
surface - completely untrue.

Quoted message said:

Jobst Brandt

translation: affect/effect=impact

eh?

Quoted message said:

Julian who? said:

Why are disc brake rotors so wimpy? Most are drilled until nothing
is left. In tandem use they heat up past the boiling point of
water.

Much hotter... red hot!

Quoted message said:

Are undrilled rotors better for tandem applications? Seems like
there is more metal there to soak up heat and more surface area to
generate friction.

And more surface area to cool... We went over all this a month ago or
so and the die hard believers brought up all sorts of specious reasons
for the filigree disks on bicycle. Cars and trucks and railroads do
not have such disks while the spoiler-loud exhaust-tinted window guys
have cross drilled disks. It's like 1960's drillium on bicycles. The
hot rod syndrome.

I think radially vented or solid cast iron disks are going to be a hard
sell. "Just look at the rust on that bike."

Maybe ceramic disks grabbed by aluminum/carbon composite pads will be
the just the ticket for the techno bike crowd. ;-)

Marcus
Me, I'm still boilin' the grease out of the F&S coaster brake.

Johnny Walker said:

Quoted message said:

This is not a question of mass but rather one of surface area and
integrity when the disk becomes red hot.

Quoted message said:

so which cools quickest, something with a high surface area/mass
ratio or something with a low surface area/mass ratio?

That isn't th choice. There is no significant mass to store and
release energy. As I said, the [problem is colling surface and a
holey 50% air disk doesn't do much in that respect.

Quoted message said:

Quoted message said:

When a filigreed disk, as we see often, becomes red hot,

Quoted message said:

have you /ever/ seen a red hot mtb disk?

I see you don't believe the reports given here by users of these
devices. I've seen car and motorcycle disks glow and those who use
bicycles with disks have reported them reaching red heat. What do you
know about maximum temperatures achieved.

Quoted message said:

Quoted message said:

its strength is diminished to the point that it can wrinkle,

Quoted message said:

that depends on the alloy. you may not be aware that some stainless
steels are used in high temp applications /because/ they retain
their strength.

I think you'll find a significant reduction in strength at visibly red
temperatures. I'm thinking of disks that are made of wavy 3/8"
squiggles on six radially slanted fingers with about a 45° incidence
with the brake ring.

http://www.bonthronebikes.co.uk/502-1444?sid=dec684644007e868

Quoted message said:

Quoted message said:

having so few support arms as the most relieved ones do (to appear
to have low rotating mass for the weight weenies.) I am surprised
to not have heard of crumpled disks that jammed in the caliper for
riders who descend steep roads fast.

Quoted message said:

there's this thing called "testing". it eliminates failures.

Oh yes! In th bicycle industry we have experienced many products that
were tested... by the user public where they failed failed. You may
recall that Ralph Nader rose to fame on such testing.

Quoted message said:

Quoted message said:

Disk mass is irrelevant for heat storage

Quoted message said:

storage? brakes aren't for storing heat - they're for dissipating

it.

Oh! To what were you referring when you said: "so which cools
quickest, something with a high surface area/mass ratio or something
with a low surface area/mass ratio?

Quoted message said:

Quoted message said:

Disk mass is irrelevant for heat storage at temperature rise times
that heavy riders cause on steep descents.

Quoted message said:

it's not just weight, it's speed and rate.

Did I say anything else?

Quoted message said:

Quoted message said:

Disk cooling surface and strength are the primary concerns.

Quoted message said:

indeed.

Quoted message said:

Quoted message said:

That stainless steel is a poorer heat conductor is irrelevant for
thin disks, but a stainless disk being "softer" than other steels
affects wear.

Quoted message said:

so?

Quoted message said:

Quoted message said:

We know that effect from aluminum rim wear with caliper brakes.

Quoted message said:

so?

I guess you've never heard of replacing rotors for wear or for that
matter aluminum rims before they break apart.

Quoted message said:

Quoted message said:

However, in the rim brake, conductivity matters because much of the
cooling area is remote from the braking surface in contrast to the
disk brake where the brake surface is the cooling surface.

Quoted message said:

that implies that rim brakes cannot dissipate heat through the
braking surface - completely untrue.

That's your interpretation. At least half the cooling area on
aluminum rims is not the brake track. We know that aluminum rims
reach more then 100°C in descents and they have a cooling area
probably 100x that of the disk shown in the above web site. That
ought to give reason to worry.

Quoted message said:

Quoted message said:

translation: affect/effect=impact

Quoted message said:

eh?

You may not have noticed but the words affect and effect have vanished
from the news media as well as elsewhere. Does that have any impact
on your understanding of the translation?

Jobst Brandt

Quoted message said:

Johnny Walker said:

Quoted message said:

This is not a question of mass but rather one of surface area and
integrity when the disk becomes red hot.

Quoted message said:

so which cools quickest, something with a high surface area/mass
ratio or something with a low surface area/mass ratio?

That isn't th choice.

yes it is - i posed it to you. don't avoid the question.

Quoted message said:

There is no significant mass to store and
release energy.

what's all this "storage" business? you seem very foggy on the braking
concept.

Quoted message said:

As I said, the [problem is colling surface and a
holey 50% air disk doesn't do much in that respect.

eh?

Quoted message said:

Quoted message said:

Quoted message said:

When a filigreed disk, as we see often, becomes red hot,

Quoted message said:

have you /ever/ seen a red hot mtb disk?

I see you don't believe the reports given here by users of these
devices. I've seen car and motorcycle disks glow and those who use
bicycles with disks have reported them reaching red heat. What do you
know about maximum temperatures achieved.

i've seen car disks glow. i've not seen motorcycle or bicycle. and i
own the latter. do the math on the heat generation vs. dissipation
rates, then tell me that bike disks glow.

Quoted message said:

Quoted message said:

Quoted message said:

its strength is diminished to the point that it can wrinkle,

Quoted message said:

that depends on the alloy. you may not be aware that some stainless
steels are used in high temp applications /because/ they retain
their strength.

I think you'll find a significant reduction in strength at visibly red
temperatures.

you "think"? what do you know about high temperature alloys jobst?

Quoted message said:

I'm thinking of disks that are made of wavy 3/8"
squiggles on six radially slanted fingers with about a 45° incidence
with the brake ring.

eh? what has that got to do with whether high temperature alloys are
used??? total red herring.

Quoted message said:

http://www.bonthronebikes.co.uk/502-1444?sid=dec684644007e868

Quoted message said:

Quoted message said:

having so few support arms as the most relieved ones do (to appear
to have low rotating mass for the weight weenies.) I am surprised
to not have heard of crumpled disks that jammed in the caliper for
riders who descend steep roads fast.

Quoted message said:

there's this thing called "testing". it eliminates failures.

Oh yes! In th bicycle industry we have experienced many products that
were tested... by the user public where they failed failed. You may
recall that Ralph Nader rose to fame on such testing.

pathetic straw clutching - spiced with red herrings and your usual
spiteful bleating about an industry that ignores you. if you got your
facts correct, maybe they'd listen. but you don't know what you're
doing and you're vicious with it - hardly a recipe for won friends and
influenced people. all that's left for you is to bray to the
uninitiated and hope you don't get found out. and what a hopeless
exercise that has been. emperor.

Quoted message said:

Quoted message said:

Quoted message said:

Disk mass is irrelevant for heat storage

Quoted message said:

storage? brakes aren't for storing heat - they're for dissipating

it.

Oh! To what were you referring when you said: "so which cools
quickest, something with a high surface area/mass ratio or something
with a low surface area/mass ratio?

do you see where i put the word "storage" in there? maybe you can
explain your own use of the term? and you didn't answer my question.
sometimes jobst, your stupidity is astounding.

Quoted message said:

Quoted message said:

Quoted message said:

Disk mass is irrelevant for heat storage at temperature rise times
that heavy riders cause on steep descents.

Quoted message said:

it's not just weight, it's speed and rate.

Did I say anything else?

well you sure sure didn't say what causes temperatures to rise! but you
certainly did go off track with this incredible concept of "storage"!!!

Quoted message said:

Quoted message said:

Quoted message said:

Disk cooling surface and strength are the primary concerns.

Quoted message said:

indeed.

Quoted message said:

Quoted message said:

That stainless steel is a poorer heat conductor is irrelevant for
thin disks, but a stainless disk being "softer" than other steels
affects wear.

Quoted message said:

so?

Quoted message said:

Quoted message said:

We know that effect from aluminum rim wear with caliper brakes.

Quoted message said:

so?

I guess you've never heard of replacing rotors for wear or for that
matter aluminum rims before they break apart.

jobstian red herring. everybody knows brakes wear. you can't use a
tangential known fact to sustain a fiction about "storage".

Quoted message said:

Quoted message said:

Quoted message said:

However, in the rim brake, conductivity matters because much of the
cooling area is remote from the braking surface in contrast to the
disk brake where the brake surface is the cooling surface.

Quoted message said:

that implies that rim brakes cannot dissipate heat through the
braking surface - completely untrue.

That's your interpretation. At least half the cooling area on
aluminum rims is not the brake track.

er, the web between the brake tracks is not there to cool - it's there
to keep the two sides of the rim separated and the spokes attached.

Quoted message said:

We know that aluminum rims
reach more then 100°C in descents

no, you allege that. show me the math on how you think this can occur -
i want to see the heat in vs. heat out.

Quoted message said:

and they have a cooling area
probably 100x that of the disk shown in the above web site. That
ought to give reason to worry.

why??? rim brakes cooling faster is not a concern. disk brakes getting
hotter than rims is not a concern. you're trying to hide behind smoke
screen.

Quoted message said:

Quoted message said:

Quoted message said:

translation: affect/effect=impact

Quoted message said:

eh?

You may not have noticed but the words affect and effect have vanished
from the news media as well as elsewhere. Does that have any impact
on your understanding of the translation?

jobst, i don't give a flying one about your linguistic hang-ups. i /do/
however give a flying one about your deliberate and consistent
stupidity, refusal to learn, fabrication of data and outright denial of
fact - a more wretched state of mind i cannot imagine.

Quoted message said:

This is not a question of mass but rather one of surface area and
integrity when the disk becomes red hot. When a filigreed disk, as we
see often, becomes red hot, its strength is diminished to the point
that it can wrinkle, having so few support arms as the most relieved
ones do (to appear to have low rotating mass for the weight weenies.)
I am surprised to not have heard of crumpled disks that jammed in the
caliper for riders who descend steep roads fast.

A data point: a friend of mine had a rear disk brake distort on a long
descent, so much so that it did not return to flat when it cooled. The
disk had turned into a cone shape. This was a disk used as a drag brake
on a tandem, so the rider did not have the same feedback about the
disk's condition as on a conventional brake.

The disk was removed so they could proceed (carefully) using only the
front brake.

This was a couple years back, and I can't recall the brand or specs of
the brake.

Jeff

jim beam said:

Quoted message said:

Most are drilled until nothing is
left.

slight exaggeration there julian.

Slight, but not too much. I have some Avid mechanicals that are very
minimal in terms of what's left after drilling.

Quoted message said:

Quoted message said:

In tandem use they heat up past the boiling point of water.

that's because they're working as they're supposed to - brakes turn your
kinetic energy into heat.

That's right. My question is related to keeping peak temperature down
on downhill runs with 400+ lbs. of riders.

Quoted message said:

Quoted message said:

Are undrilled rotors better for tandem applications? Seems like there
is more metal there to soak up heat and more surface area to generate
friction.

you don't want the disk to accumulate heat with excess mass - that means
they take longer to recover if they reach fade temp. and drillings help
keep brakes working in mud and rain.

OK, how about some drilling but not as much as usually seen? The
spider arms contribute to surface area along with scalloped outer
edges. They still don't have a lot of metal. Look at car rotors. For
heavy duty use there are bigger rotors with more metal.

Quoted message said:

in the future, if you have a serious question, try keeping the troll
factor down.

There was no intent to troll or flamebait. It is a serious question.
We had the brakes fade quite severely on a not-too-long (but fast)
downhill.

On Sun, 17 Dec 2006 13:53:21 GMT, Julian <[email hidden]>

Quoted message said:

We had the brakes fade quite severely on a not-too-long (but fast)
downhill.

You might try shopping around for cheap rotors, which are likely to
have more metal in them, and it wouldn't be rocket science to get a
local machinist to make a disc with just the mounting holes and no
other cut outs, but fade is really a pad problem and only a change of
pad compound will cure it. Instantaneous pad surface temperature won't
be greatly affected as long as you're stuck with 2mm thick discs,
which cool almost entirely from the brake track radiation and
conduction to air.You could also try the local sky diving club, who
might be able to give you a drogue chute to throw on downhills :-)

Apart from a couple of specific drag brakes, all bicycle brakes are
designed for solo use by riders not much over 200lb; as such, you
should probably use twice as many of them on a tandem, and dual disc
front hubs aren't widely available yet. Millyard have this set up with
two Hope M4 calipers on a 20mm front hub
http://www.astonhill.com/news278.htm

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

jim beam said:

Joe Riel said:

How will removing material reduce the operating temperature
or rate of heat dissipation?

Quoted message said:

surface area/mass. it's a two-edged sword, because low mass heats
quicker, but the other side of it means increasing surface area allows
air flow to carry more heat away more quickly.

For a circular hole, unless the radius is less than the thickness
of the material, the drilled material has "less" surface area.
Plus, the drilled surface isn't as exposed to the cooling flow.

--
Joe Riel

Julian said:

jim beam said:

Quoted message said:

Most are drilled until nothing is
left.

slight exaggeration there julian.

Slight, but not too much. I have some Avid mechanicals that are very
minimal in terms of what's left after drilling.

Quoted message said:

Quoted message said:

In tandem use they heat up past the boiling point of water.

that's because they're working as they're supposed to - brakes turn your
kinetic energy into heat.

That's right. My question is related to keeping peak temperature down
on downhill runs with 400+ lbs. of riders.

run bigger disks and change the pad material if the current setup is
insufficient.

Quoted message said:

Quoted message said:

Quoted message said:

Are undrilled rotors better for tandem applications? Seems like there
is more metal there to soak up heat and more surface area to generate
friction.

you don't want the disk to accumulate heat with excess mass - that means
they take longer to recover if they reach fade temp. and drillings help
keep brakes working in mud and rain.

OK, how about some drilling but not as much as usually seen? The
spider arms contribute to surface area along with scalloped outer
edges. They still don't have a lot of metal. Look at car rotors. For
heavy duty use there are bigger rotors with more metal.

more metal doesn't mean better braking - more swept area and ability to
dump heat to atmosphere means better braking. cars have bigger rotors
with more metal because they need to withstand higher mechanical loads
and they need to withstand something like 60k miles of abrasion at a
time. true racing rotors for cars are much thinner and lighter, but as
you may imagine, don't last very long.

Quoted message said:

Quoted message said:

in the future, if you have a serious question, try keeping the troll
factor down.

There was no intent to troll or flamebait. It is a serious question.
We had the brakes fade quite severely on a not-too-long (but fast)
downhill.

use different pads. ebc red's don't fade.

jim beam said:

Quoted message said:

Johnny Walker said:

> This is not a question of mass but rather one of surface area and
> integrity when the disk becomes red hot.

Quoted message said:

so which cools quickest, something with a high surface area/mass
ratio or something with a low surface area/mass ratio?

That isn't th choice.

yes it is - i posed it to you. don't avoid the question.

If you start with a cylindrical disk, and then "filigree" it, you will
increase the ratio of surface area to mass, and therefore the heat
dissipation.

If you cut a prism out of a flat cylinder with a cookie cutter, you will
reduce the mass of the cylinder by an amount proportional to the area
removed. But you will add a little bit of surface area back in the form
of the walls around the cookie-shaped hole.

On this reasoning, lots of small holes would work better than the kind
of pattern we see in the disk Jobst posted a link to

http://www.bonthronebikes.co.uk/502-1444?sid=3Ddec684644007e868

But that pattern may just be more fashionable than the "drillium" style.

On 2006-12-17, Julian <[email hidden]> wrote:
[snip]

Quoted message said:

OK, how about some drilling but not as much as usually seen? The
spider arms contribute to surface area along with scalloped outer
edges. They still don't have a lot of metal. Look at car rotors. For
heavy duty use there are bigger rotors with more metal.

Cars often use a duplex disk, supported by a bit filigree in between.
Air passes between the two disks but there's a good surface area for the
pad to grip.