disc brake fundamentals please

jim beam wrote:
wrote:


Cable shortcomings are mimimal. Fatigue is a non-issue if you take a
few minutes to install new cables once every couple years.

but why change them at all? hydraulics are fit and forget.

One should always consider advantages vs. disadvantages. For my bikes,
I'd be completely uninterested in spending significant extra money and
giving up field repairability for the minor advantages of hydraulics.
And the overwhelming majority of cyclists agree with me, judging by
their purchasing choices. Those that agree with you tend to have
extreme needs - including, in many cases, the need to be seen with the
fanciest equipment!


If a cable does break, it can be repaired in deserted areas using only
normal, tiny tools.

only if it breaks in a way that's convenient.

What do you mean? I've never seen a cable broken in such an
"inconvenient" way that it couldn't be easily traded for a new cable of
the same length and diameter.


Spare cables are trivial to carry. And in many
applications, leaving a couple inches of extra cable at the end allows
temporary "get you home" cable repair without even an extra cable.

no. cables break at the ends.

True. And convenient! ;-)

that means any "spare" is either on the
free end that's broken off and therefore utterly useless or it's
furthest away from the nipple end that's broken off and is still utterly
useless.

Here's what you do, Jim. When you install a new cable, you leave it
about two inches longer than necessary at the clamp end. Tie it into a
loose circle, if needed, to keep it contained.

If the nipple breaks off, you loosen the clamp bolt, push the extra
length back through to the lever, and knot it to form a temporary
"nipple."

Of course, you don't have to bother with that if you choose to carry a
spare cable. Your choice.

Personally, I like bike components to be field-repairable.

so do i. example: pee can be used as hydraulic fluid in emergencies.

um... Have you actually done that??

Hydraulic problems are much more difficult to deal with, especially if,
as you say, a line has broken (although I doubt that's common). The
advantages of hydraulics - primarily minimizing friction - are as
minimal as the disadvantages of cables.

i've never cited supposed benefits regarding friction and don't intend
to. i've cited reliability, modulation and self-adjustment, all of
which are substantial.

Reduced friction and modulation are the "cause and effect" aspects of
one phenomenon, at least in a reasonably well-designed brake. Self
adjustment is possible with either actuation method, whether or not
it's presently employed. (If manual adjustment is easy enough, it's a
very minor issue.)

And the difference in reliablity is minimal, and a bit difficult to
quantify. We're comparing two systems. One system fails perhaps once
in three to five years when given no maintenance, but is easily field
repaired. The other fails perhaps once in ten years, but can't be
repaired at all in the field. I'd say it's a wash.

the
only real stronghold for bowden cable these days is bikes, and imo,
that's more a function of emotional inertia than rational analysis.

That final bit of logic could be used to argue for elimination of
foot-powered cranks, derailling gearshifts, and even dual inline
wheels!

only if you want to twist out of context. when is the last time you saw
a car with cable brakes?

You want to limit it to brakes? OK: ten minutes ago - i.e. last time
I saw a car pass. (Ever examine your car's emergency brake?)

But your actual statement was not limited to brakes. So let's see:
two cars live here, both with cable actuated emergency brakes, hood
latches, filler door latches, and clutch cables. One also has a cable
operated throttle, rear hatch lock and HVAC controls. Then there's the
motorcycle, with cable brakes, clutch, throttle and "choke". I could
get into the other machines with cables around this house, but those
should suffice.

Bikes are unusual machines. Technology doesn't have to be common
elsewhere to be appropriate for them.

bicycles don't have to ignore good engineering. rear mounted front
brake calipers for example.

:-) Rather than change the subject, you should stick to losing one
argument at a time!

(Although my cars and my motorcycle have multiple cables that have
worked fine for many, many years! )

and they have cable brakes? i think not. there aren't even many modern
cars retaining throttle cables come to that - fly-by-wire is the order
of the day.

Jim, if we went outside and opened the hood of the next 100 cars we
came to, you'd doubtlessly learn a lot. Although I suspect you'd
merely put a very, very rigid definition on "modern" in an attempt to
save face.

- Frank Krygowski

jim beam wrote:
Tom Ace wrote:

If the nipple breaks off, you can make a
surrogate nipple by tying that end in a knot--
which some extra cable length makes possible.


that's not a repair to trust your life to.

:-) Is ****ing into your hydraulic line any better?

cable steel is near "full
hard" and the physical deformation incurred in that situation can easily
surpass the ductility of the material, hence it can break again.

You _must_ have never knotted a cable! The problem isn't breaking the
cable. It's merely getting the knot small enough. But it's just not
that bad!

if it doesn't slip of course. i'll walk, never ride a repair like that.

In over 30 years of cycling, I've done that to only one brake cable.
(I've done it to shift cables three times, I think.) If I didn't ride
that brake repair, I'd have walked something like fifteen miles!

As it was, it held perfectly. Still, I replace my brake cables more
frequently now.

- Frank Krygowski

wrote:
jim beam wrote:
wrote:

Cable shortcomings are mimimal. Fatigue is a non-issue if you take a
few minutes to install new cables once every couple years.
but why change them at all? hydraulics are fit and forget.

One should always consider advantages vs. disadvantages. For my bikes,
I'd be completely uninterested in spending significant extra money and
giving up field repairability for the minor advantages of hydraulics.

cable brakes are no more repairable than hydraulics. you're trying to
fudge the issue by sliding replacement into the equation for cables only
instead of repair for both.

And the overwhelming majority of cyclists agree with me, judging by
their purchasing choices. Those that agree with you tend to have
extreme needs - including, in many cases, the need to be seen with the
fanciest equipment!

do we have hydraulics for road bikes yet? and don't b.s. about "fancy".
hydraulics are great on mtb's, where they're most commonly sold. they
are much superior in mtb riding conditions. i know that for fact
because i've used both extensively. armchair quarterbacking engineering
solutions doesn't work.



If a cable does break, it can be repaired in deserted areas using only
normal, tiny tools.
only if it breaks in a way that's convenient.

What do you mean? I've never seen a cable broken in such an
"inconvenient" way that it couldn't be easily traded for a new cable of
the same length and diameter.

there you go again - by that rationale, i can /replace/ hydraulics and
call those "repairs" too, right?


Spare cables are trivial to carry. And in many
applications, leaving a couple inches of extra cable at the end allows
temporary "get you home" cable repair without even an extra cable.
no. cables break at the ends.

True. And convenient! ;-)

eh? it's convenient that cables break???


that means any "spare" is either on the
free end that's broken off and therefore utterly useless or it's
furthest away from the nipple end that's broken off and is still utterly
useless.

Here's what you do, Jim. When you install a new cable, you leave it
about two inches longer than necessary at the clamp end. Tie it into a
loose circle, if needed, to keep it contained.

but all that means is that you lose those extra inches when the cable
breaks at the clamp bolt. you could have 10' of spare cable, but it
makes no difference to where the break is.


If the nipple breaks off, you loosen the clamp bolt, push the extra
length back through to the lever, and knot it to form a temporary
"nipple."

and kill yourself when it slips as you're trying to avoid the speeding
big rig - great idea.


Of course, you don't have to bother with that if you choose to carry a
spare cable. Your choice.

i carry spare emergency hydraulic fluid with me all the time.


Personally, I like bike components to be field-repairable.
so do i. example: pee can be used as hydraulic fluid in emergencies.

um... Have you actually done that??

not on a bike, but i have on an off-road vehicle stuck in the
wilderness, yes.


Hydraulic problems are much more difficult to deal with, especially if,
as you say, a line has broken (although I doubt that's common). The
advantages of hydraulics - primarily minimizing friction - are as
minimal as the disadvantages of cables.
i've never cited supposed benefits regarding friction and don't intend
to. i've cited reliability, modulation and self-adjustment, all of
which are substantial.

Reduced friction and modulation are the "cause and effect" aspects of
one phenomenon, at least in a reasonably well-designed brake. Self
adjustment is possible with either actuation method, whether or not
it's presently employed. (If manual adjustment is easy enough, it's a
very minor issue.)

minor issue??? ridiculous argument.


And the difference in reliablity is minimal, and a bit difficult to
quantify. We're comparing two systems. One system fails perhaps once
in three to five years when given no maintenance, but is easily field
repaired. The other fails perhaps once in ten years, but can't be
repaired at all in the field. I'd say it's a wash.

rubbish - difference in reliability is orders of magnitude. that's why
hydraulics are used for the most mission critical heavy usage
applications throughout the world, and have been used so for the better
part of a century.


the
only real stronghold for bowden cable these days is bikes, and imo,
that's more a function of emotional inertia than rational analysis.
That final bit of logic could be used to argue for elimination of
foot-powered cranks, derailling gearshifts, and even dual inline
wheels!
only if you want to twist out of context. when is the last time you saw
a car with cable brakes?

You want to limit it to brakes? OK: ten minutes ago - i.e. last time
I saw a car pass. (Ever examine your car's emergency brake?)

But your actual statement was not limited to brakes. So let's see:
two cars live here, both with cable actuated emergency brakes, hood
latches, filler door latches, and clutch cables. One also has a cable
operated throttle, rear hatch lock and HVAC controls. Then there's the
motorcycle, with cable brakes, clutch, throttle and "choke". I could
get into the other machines with cables around this house, but those
should suffice.

want to compare apples with oranges too? they're both round i guess...
bottom line, bikes use cables as mission critcal, no other application
does because of reliability issues and need for adjustment.


Bikes are unusual machines. Technology doesn't have to be common
elsewhere to be appropriate for them.
bicycles don't have to ignore good engineering. rear mounted front
brake calipers for example.

:-) Rather than change the subject, you should stick to losing one
argument at a time!

eh? would you seriously argue that a rear mounted caliper is not safer
than front mounted????


(Although my cars and my motorcycle have multiple cables that have
worked fine for many, many years! )
and they have cable brakes? i think not. there aren't even many modern
cars retaining throttle cables come to that - fly-by-wire is the order
of the day.

Jim, if we went outside and opened the hood of the next 100 cars we
came to, you'd doubtlessly learn a lot. Although I suspect you'd
merely put a very, very rigid definition on "modern" in an attempt to
save face.

a throttle cable has no load frank. a parking brake cable is not used
to stop the vehicle. a gas cap retainer as an example is a joke. now,
go to any bmw, mercedes, vw, honda, toyota, subaru dealership... no
throttle cables there, even for base models. oh, wait, detroit's not on
the list, but hey, that's another debate.

On 2006-12-17, jim beam wrote:
Tom Ace wrote:
jim beam wrote:

no. cables break at the ends. that means any "spare" is either on the
free end that's broken off and therefore utterly useless or it's
furthest away from the nipple end that's broken off and is still utterly
useless.

If the nipple breaks off, you can make a
surrogate nipple by tying that end in a knot--
which some extra cable length makes possible.

Tom Ace

that's not a repair to trust your life to. cable steel is near "full
hard" and the physical deformation incurred in that situation can easily
surpass the ductility of the material, hence it can break again. if it
doesn't slip of course. i'll walk, never ride a repair like that.

If a brake cable breaks you can just ride home carefully using only the
other brake. But a hydraulic leak that's letting in air will affect both
brakes, unless bikes have split circuits like cars?

Ben C wrote:
On 2006-12-17, jim beam wrote:

Tom Ace wrote:

jim beam wrote:


no. cables break at the ends. that means any "spare" is either on the
free end that's broken off and therefore utterly useless or it's
furthest away from the nipple end that's broken off and is still utterly
useless.

If the nipple breaks off, you can make a
surrogate nipple by tying that end in a knot--
which some extra cable length makes possible.

Tom Ace


that's not a repair to trust your life to. cable steel is near "full
hard" and the physical deformation incurred in that situation can easily
surpass the ductility of the material, hence it can break again. if it
doesn't slip of course. i'll walk, never ride a repair like that.


If a brake cable breaks you can just ride home carefully using only the
other brake. But a hydraulic leak that's letting in air will affect both
brakes, unless bikes have split circuits like cars?

Why do you think they don't have split systems? Get your fundamentals
right ;-).

Lou
--
Posted by news://news.nb.nu

On 2006-12-17, jim beam wrote:
[snip]
Personally, I like bike components to be field-repairable.
so do i. example: pee can be used as hydraulic fluid in emergencies.

um... Have you actually done that??

not on a bike, but i have on an off-road vehicle stuck in the
wilderness, yes.

Is it preferable to water in any way?

[snip]

a throttle cable has no load frank. a parking brake cable is not used
to stop the vehicle. a gas cap retainer as an example is a joke. now,
go to any bmw, mercedes, vw, honda, toyota, subaru dealership... no
throttle cables there, even for base models.

I'm sure the reason for that is not the inherent unreliability of
cables. After all, as you pointed out, there's very little force on a
throttle cable anyway. It's presumably so they can interpose electronics
to do things like improve fuel economy and emissions, and in the case of
automatics, decide when to shift gears without requiring additional
throttle position sensors.

On Sun, 17 Dec 2006 08:49:32 -0800, jim beam
wrote:

Tim McNamara wrote:
In article ,
jim beam wrote:

wrote:
jim beam wrote:
i understand that some people are concerned about hydraulic
leakage, but i don't see how snagging and breaking an hydraulic
line is any different from breaking a bowden cable. in fact, the
bowden cable is probably the worse bet because if fatigue,
susceptibility to clogging, etc.
Cable shortcomings are mimimal. Fatigue is a non-issue if you take
a few minutes to install new cables once every couple years.
but why change them at all? hydraulics are fit and forget.

But how about if it leaks?

it shouldn't leak unless damaged or incorrectly fitted.

Cables will not break unless damaged or incorrectly fitted.

Hydraulics are fine on cars and trucks, although interestingly the
emergency backup brake is cable-activated on many vehicles.

that's so you have a fully independent back-up. cables are /never/ used
as the service brake.


Morris Minor.

On 17 Dec 2006 08:55:16 -0800, wrote:

Jim, if we went outside and opened the hood of the next 100 cars we
came to, you'd doubtlessly learn a lot. Although I suspect you'd
merely put a very, very rigid definition on "modern" in an attempt to
save face.



Already done, when he claimed that no brake bolts or qr skewers were
made using cut threads, but they were without exception rolled;
multiple examples to the contrary were posted, whereupon numerous
evasive tactics were employed by jim beam, ending with the threat of
trial by combat as a means of deciding the truth.

In article ,
jim beam wrote:

Tim McNamara wrote:
In article ,
jim beam wrote:

wrote:
jim beam wrote:
i understand that some people are concerned about hydraulic
leakage, but i don't see how snagging and breaking an hydraulic
line is any different from breaking a bowden cable. in fact,
the bowden cable is probably the worse bet because if fatigue,
susceptibility to clogging, etc.

Cable shortcomings are mimimal. Fatigue is a non-issue if you
take a few minutes to install new cables once every couple years.
but why change them at all? hydraulics are fit and forget.

But how about if it leaks?

it shouldn't leak unless damaged or incorrectly fitted.

That makes sense, of course. Damage is what I had in mind. On a car,
the brake lines are inflexible tubes mounted along the chassis in a way
that they are well protected from impact and the like. There's a
flexible part connecting to the brakes themselves that allows for
suspension movement. On a bike, the housing sticks out in various
places where it can be bent or snagged. I don't know how often damage
like this actually happens, of course, not having used them (and not
mountain biking any more, either; I do remember snagging brake cables on
singletrack a few times on my MTB and my 'cross bike but other than
causing a spill on a couple of occasions, no damage was done).

vehicle systems leak sometimes at very high mileage, master cylinders
on cars for example, but even if it does leak, it can still be used
and fluid refilled to get you home for repair.

Can the leak be repaired on the road or trail so that you have
brakes?

if it's something like a loose fitting, sure, just re-tighten. if
something's broken, i don't see how that's different from a cable
brake.

A brake cable is easy to carry and easy to replace if it gets broken.
Is the same true with hydraulics? Can one carry spare housing and fluid
conveniently, or some other type of repair kit? I would think that the
volume of fluid is pretty small and should be packable.

I've never used these (bike) brakes so I've got no idea about how
susceptible to failure or how repairable they are. Hydraulics are
fine on cars and trucks, although interestingly the emergency
backup brake is cable-activated on many vehicles.

that's so you have a fully independent back-up. cables are /never/
used as the service brake.

True, it's there for parking or in case of brake failure. It was just
interesting to me that it's a cable system and not a second independent
hydraulic system.

In 40 years of riding bikes, I've never had a brake cable break or
clog or rust solid (although I have seen the latter a number of
times before lined brake cable housing was normal, back in my bike
shop days). I've yet to see a compelling reason to change to
hydraulics or disk brakes. As far as I can tell, it's bling factor
that sells these.

no, you should try using them some time - hydraulics are quite
wonderful. they're also a lot more reliable both in terms of service
interval and failure rate.

More reliable than mechanical disk brakes (e.g., Avids, which I have
tried and did not like- grabby and non-progressive)? Or more reliable
than sidepulls, dual pivots, cantilevers or centerpulls?

broken/frayed cables are common as dirt. i sometimes ride with a guy
that has three strands left on his rear and refuses to swap the cable
out. i make sure i'm always behind him. mine get swapped out every
year or so.

I wouldn't want him riding behind me either. Jeez. As Jesse Ventura
said, "you can't legislate against stupidity."

In article ,
jim beam wrote:

wrote:
jim beam wrote:
wrote:

Cable shortcomings are mimimal. Fatigue is a non-issue if you
take a few minutes to install new cables once every couple years.
but why change them at all? hydraulics are fit and forget.

One should always consider advantages vs. disadvantages. For my
bikes, I'd be completely uninterested in spending significant extra
money and giving up field repairability for the minor advantages of
hydraulics.

cable brakes are no more repairable than hydraulics. you're trying
to fudge the issue by sliding replacement into the equation for
cables only instead of repair for both.

Ummm. At the risk of getting sucked into another jim beam-vs-Krygowski
match, which is just where I don't want to be.... that's how brake
cables are repaired: you replace them if they break or show obvious
signs of failure. I mean, nobody rebraids them or replaces the nipple
on brake cables. I have no idea how hydraulic brake lines are repaired
and whether that is possible out in the field.

And the overwhelming majority of cyclists agree with me, judging by
their purchasing choices. Those that agree with you tend to have
extreme needs - including, in many cases, the need to be seen with
the fanciest equipment!

do we have hydraulics for road bikes yet?

Well, I've seen disk brakes on road bikes. I don't know if they were
hydraulic. The one owner I asked was quite enthusiastic about them,
especially on his commute in wet/freezing winter weather (he doesn't own
a car and lives here in Minnesota).