Why do some forks and frames have brake rotor size limits?
 

On Sat, 28 Oct 2017 21:41:38 -0300, Joy Beeson
wrote:

On Sun, 29 Oct 2017 07:53:49 +0700, John B.
wrote:

I was thinking of air brakes configured more like a bird's wings. When
folded they would provide a certain amount of streamlining for the
rear of the bike and when actuated have a substantial amount of
stopping power.

When I lived in Albany County, I used air brakes all the time. Sitting
up straight and spreading yourself out will slow you quite a lot.

Once I left the top of a hill at the same time as another rider -- he
tucked, I, less confident, sat up. He reached the bottom when I was
about half-way down. And I had better bearings.

In Kosciusko County, going too fast is hardly ever a problem.

Frank, I believe went into some detail abut this phenomena some time
ago.

One problem with the sit up straight and spread your wings scheme is
sometimes it isn't enough :-)
--
Cheers,

John B.

Why do some forks and frames have brake rotor size limits?
 

On Sat, 28 Oct 2017 23:13:20 -0400, Frank Krygowski
wrote:

On 10/28/2017 9:11 PM, John B. wrote:

A great deal snipped.



I live at a whopping 400 feet (about) elevation. The garage in my building is probably 0 feet. That minor elevation change sometimes means the difference between ice and no ice -- so I walk outside in the morning and say f*** this! And then I jump in the car and half-way to work, creeping along in traffic, there is no ice -- and then I regret not riding. So, in order to avoid that regret, I have done some pretty stupid sh** spinning around on ice or hoofing it in my SPDs to get out of my neighborhood and then being freaked out riding over the slick bridges and viaducts into town. I met up with another guy on a bike who was fish-tailing down the road on one of those mornings, and we looked at each other and shook our heads -- "we're a couple of idiots." So, now I'm working on not feeling regret or guilt if I drive. And don't get me going about the dopes who jump into their Malibus with no-season/no-tread tires and crash on the ice and/or snow. I'll slap on the snow tires in
November. I really miss studs, but I'm doing penance with studless.

-- Jay Beattie.

Are studded auto tires legal? I seem to remember that back in the
1960's when I was in Maine that it was illegal to drive studded tires
on bare roads. It was a long time ago and memory is always
questionable but I'm sure that I remember people getting a ticket for
using studded tires under certain conditions.

I don't know if they're legal in Oregon now (Jay can tell us) but I've
driven out there in the summer and experienced the weirdness of a
freeway with two troughs worn in it by thousands of studded tires.

Our cars track (i.e. left to right wheel span) didn't quite match the
trough widths, and our car had a disturbing tendency to "hunt" back and
forth as I drove.

I was curious. As I had said I'm sure it was illegal to drive with
either chains or studs on bare roads back then. The subject was of
some interest as being in the Service I had to be out and about by
about 0600 in order to get to work on time and frequently the snow
plows hadn't gotten all the streets plowed that early.
--
Cheers,

John B.

Why do some forks and frames have brake rotor size limits?
 

John B. wrote:
On Sun, 29 Oct 2017 01:45:50 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 15:12:37 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 06:23:59 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 03:54:43 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 01:13:54 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Fri, 27 Oct 2017 09:32:04 -0700, Joerg
wrote:

On 2017-10-27 09:25, Frank Krygowski wrote:
On 10/27/2017 9:58 AM, Joerg wrote:

Finally after many decades the bicycle industry woke up and adopted
what the automotive guys had all along, disc brakes. Why should I
accept an inferior brake system on a new bike when there is a much
better one?

sigh There are advantages and disadvantages to this equipment choice,
just as with other equipment choices. The disadvantages of discs have
been discussed. If they don't matter or apply to you, fine; but they
matter to others.


Many others just don't know any better. I have witnessed several people
riding a bike with hydraulic disc brakes for the first time and the
reaction was usually "WHOA!". Same with me, it almost sent me over the bar.


But I'll note that you're currently in a project to increase your disc's
diameter from something like 160mm or 180mm up to 200mm or more. You
seem to feel bigger diameter is better.


Because bigger is better here.


Well, even "better," why not go up to roughly 622mm? That's what lots
of us prefer, with cable actuation.


The disadvantages have been discussed ad nauseam. A rim brake is not a
disc brake. Not even close.

Care to explain the mechanical difference? I mean a rotating surface
and two friction pads that are tightened against it....
--
Cheers,

John B.

As far as I can tell, the differences between a rim brake and a 622 mm disk
a

1) The disk doesn't have to provide tire clearance, so the pads can sit
closer, facilitating higher mechanical advantage.

I'm not sure that is correct. After all some old Greek guy was
supposed to have said, "Give me a lever and a place to stand and I
will move the earth". Nothing about being close.

No. I'm pretty certain I'm right here. Let's say that you can pull 100 lbs
on your brake lever and the lever has 2" of play before it hits your bars.
You can fiddle with leverage many places in the system, but the product of
that initial 100 lbs and 2" will be constant in the system. If the final
travel of the brake pads is 1/2", then you can apply 400 lbs force to the
pads. If you tighten up your tolerances such that the pads only have to
move 1/16", then you can increase the leverage to the point where you can
apply 3200 lbs force to the pads. In disk brake systems this reduction in
pad-disk distance allow the MA to be increased to compensate for the
decreased leverage of the disk on the wheel. The increases brake pad
pressure at a given bike deceleration is what gives disk brakes more
consistent performance in the wet.

Movement of the parts doesn't make any difference the efficiency is
the pressure applied to the brake lever versus the pressure applied to
the braking device, usually the pads themselves.

A lever that is 1 foot long and moves, lets say, one quarter of the
diameter of a 2 foot circle applies the same force to a load located 1
foot from the fulcrum as a 100 ft lever which moves 1/4 of the
diameter of a 200 ft circle applies to a load that is 100 ft. from the
fulcrum. The first lever moves 19 inches and the second moves 157
feet.

Sure. But the distance you can move your brake lever is limited by the
length of your fingers, and so the distance you can move at the lever end
is essentially fixed. To increase the mechanical advantage in THAT system,
you have to reduce the distance the brake pads move. No ifs, ands, buts or
maybes.

You are talking about two different things. Mechanical efficiency and
how long your fingers are.

They aren't really related.
--
Cheers,

John B.

Theoretically, the mechanical advantage of a brake system and the length of
your fingers aren't related, but practically, in this example of the
mechanical advantage of a bicycle brake system, the two quantities are
chained together at the ankles. You can't have high brake pad travel and
high mechanical advantage unless the travel of the brake lever is very
large, and human hand dimensions just won't allow that.

Well you can continue to equate mechanical advantage with long, or
short, fingers but it doesn't make it true :-)

But you keep talking about the large clearance between the rim brake
pads and the rim versus the disc pads and the disc which isn't
necessarily true.

I use brifters - Shimano STI brake&shifters - on two of my bikes and
considering the rather limited travel of the brake levers the pads
need to be fitted very closely to the rims, and of course, the rims
need to be very straight. The two bikes are about 1,000 km from where
I'm presently located so I'm going much by memory but I think that the
pad to rim clearance is about 1mm. The two bikes I have here both have
down tube shifting and the brake pad clearance is largely determined
by where I want the brake levers to be when the brakes are applied,
but measuring one bike shows that the clearance is about 6mm.

I can sense no appreciable difference in the pressure I feel against
my fingers when stopping any of the four bikes.
--
Cheers,

John B.

I think we're pretty close to a standoff here, so I'll invoke the name of
Sheldon, and then give up. Read through

https://www.sheldonbrown.com/cantilever-geometry.html

and tell me if it changes your opinion about what I've been saying.

To summarize my position
1) The mechanical advantage of a brake system (ie: the ratio of pad force
to lever force) is the inverse of the ratio of pad travel to lever travel.

2) bike brakes are made for humans and not orangutans or aliens, so they
all tend to have about the same amount of lever travel.

3) because of 1 and 2, the travel of the brake pad is pretty much inversely
proportional to the mechanical advantage.

4) because of 1, 2 and the fact that brakes need to actually touch the
rim/disk in order to work, the mechanical advantage of a bicycle brake
system is approximately inversely proportional to how far you can set the
pads away from the rim/disk and still have the system work (non-linear
systems excepted).

If you still doubt what I say, you may have to continue the discussion with
somebody else, as I have obviously failed in my attempts to communicate.


Yes, Sheldon says just what I've been saying that mechanical advantage
is the relationship between force in and force out and he describes
it, as I did, two ways. One as a ratio of forces and two a ratio of
distances. i.e., a lever that has a ratio of two to one will exert
twice the force on the shorter end as applied to the longer end and by
the same token that the long end will travel twice as far as the short
end.

It has nothing to do with finger length or brake pad clearance.
--
Cheers,

John B.

Theoretically, yes, but practically, no. Try to design a brake system with
a 10:1 mechanical advantage and 1" of brake pad travel and you will soon
discover that your fingers are about 8" too short for it to work because
you will have to pull 10" at the lever.

So yeah, theory says nothing about finger length, but pretty much every
brake lever out there doesn't move more than about 3". Therefore,
practically, the travel of your brake pads can't be any more than 3"
divided by your MA.

So then, if you NEED or WANT a certain amount of brake pad to rim
clearance, then that sets a practical limit on the MA you can have in that
system before you run out of lever travel.

For a real world example, I have cantilever brakes on my Surly. I can lower
the straddle cable to increase the MA of the system, but then I get lower
pad travel. To ensure that I don't bottom out my levers while braking, I
then have to keep the pads closer to the rim. However, I can't just keep
doing that forever, since I also have to accommodate runout and warpage in
my rim. I also need to maintain a certain pad to rim distance to allow me
to unhook the straddle cable so that I can remove my wheel. If I was
running a disk setup, my minimum pad to disk clearance would be smaller,
which would allow the use of a brake system with higher MA. I can't
consider MA and pad to disk/rim clearance independently because I have
normal human fingers that only allow 3" or less of lever travel. And
that's how finger length becomes part of the equation.

Why do some forks and frames have brake rotor size limits?
 

On Sun, 29 Oct 2017 05:11:13 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sun, 29 Oct 2017 01:45:50 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 15:12:37 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 06:23:59 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 03:54:43 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 01:13:54 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Fri, 27 Oct 2017 09:32:04 -0700, Joerg
wrote:

On 2017-10-27 09:25, Frank Krygowski wrote:
On 10/27/2017 9:58 AM, Joerg wrote:

Finally after many decades the bicycle industry woke up and adopted
what the automotive guys had all along, disc brakes. Why should I
accept an inferior brake system on a new bike when there is a much
better one?

sigh There are advantages and disadvantages to this equipment choice,
just as with other equipment choices. The disadvantages of discs have
been discussed. If they don't matter or apply to you, fine; but they
matter to others.


Many others just don't know any better. I have witnessed several people
riding a bike with hydraulic disc brakes for the first time and the
reaction was usually "WHOA!". Same with me, it almost sent me over the bar.


But I'll note that you're currently in a project to increase your disc's
diameter from something like 160mm or 180mm up to 200mm or more. You
seem to feel bigger diameter is better.


Because bigger is better here.


Well, even "better," why not go up to roughly 622mm? That's what lots
of us prefer, with cable actuation.


The disadvantages have been discussed ad nauseam. A rim brake is not a
disc brake. Not even close.

Care to explain the mechanical difference? I mean a rotating surface
and two friction pads that are tightened against it....
--
Cheers,

John B.

As far as I can tell, the differences between a rim brake and a 622 mm disk
a

1) The disk doesn't have to provide tire clearance, so the pads can sit
closer, facilitating higher mechanical advantage.

I'm not sure that is correct. After all some old Greek guy was
supposed to have said, "Give me a lever and a place to stand and I
will move the earth". Nothing about being close.

No. I'm pretty certain I'm right here. Let's say that you can pull 100 lbs
on your brake lever and the lever has 2" of play before it hits your bars.
You can fiddle with leverage many places in the system, but the product of
that initial 100 lbs and 2" will be constant in the system. If the final
travel of the brake pads is 1/2", then you can apply 400 lbs force to the
pads. If you tighten up your tolerances such that the pads only have to
move 1/16", then you can increase the leverage to the point where you can
apply 3200 lbs force to the pads. In disk brake systems this reduction in
pad-disk distance allow the MA to be increased to compensate for the
decreased leverage of the disk on the wheel. The increases brake pad
pressure at a given bike deceleration is what gives disk brakes more
consistent performance in the wet.

Movement of the parts doesn't make any difference the efficiency is
the pressure applied to the brake lever versus the pressure applied to
the braking device, usually the pads themselves.

A lever that is 1 foot long and moves, lets say, one quarter of the
diameter of a 2 foot circle applies the same force to a load located 1
foot from the fulcrum as a 100 ft lever which moves 1/4 of the
diameter of a 200 ft circle applies to a load that is 100 ft. from the
fulcrum. The first lever moves 19 inches and the second moves 157
feet.

Sure. But the distance you can move your brake lever is limited by the
length of your fingers, and so the distance you can move at the lever end
is essentially fixed. To increase the mechanical advantage in THAT system,
you have to reduce the distance the brake pads move. No ifs, ands, buts or
maybes.

You are talking about two different things. Mechanical efficiency and
how long your fingers are.

They aren't really related.
--
Cheers,

John B.

Theoretically, the mechanical advantage of a brake system and the length of
your fingers aren't related, but practically, in this example of the
mechanical advantage of a bicycle brake system, the two quantities are
chained together at the ankles. You can't have high brake pad travel and
high mechanical advantage unless the travel of the brake lever is very
large, and human hand dimensions just won't allow that.

Well you can continue to equate mechanical advantage with long, or
short, fingers but it doesn't make it true :-)

But you keep talking about the large clearance between the rim brake
pads and the rim versus the disc pads and the disc which isn't
necessarily true.

I use brifters - Shimano STI brake&shifters - on two of my bikes and
considering the rather limited travel of the brake levers the pads
need to be fitted very closely to the rims, and of course, the rims
need to be very straight. The two bikes are about 1,000 km from where
I'm presently located so I'm going much by memory but I think that the
pad to rim clearance is about 1mm. The two bikes I have here both have
down tube shifting and the brake pad clearance is largely determined
by where I want the brake levers to be when the brakes are applied,
but measuring one bike shows that the clearance is about 6mm.

I can sense no appreciable difference in the pressure I feel against
my fingers when stopping any of the four bikes.
--
Cheers,

John B.

I think we're pretty close to a standoff here, so I'll invoke the name of
Sheldon, and then give up. Read through

https://www.sheldonbrown.com/cantilever-geometry.html

and tell me if it changes your opinion about what I've been saying.

To summarize my position
1) The mechanical advantage of a brake system (ie: the ratio of pad force
to lever force) is the inverse of the ratio of pad travel to lever travel.

2) bike brakes are made for humans and not orangutans or aliens, so they
all tend to have about the same amount of lever travel.

3) because of 1 and 2, the travel of the brake pad is pretty much inversely
proportional to the mechanical advantage.

4) because of 1, 2 and the fact that brakes need to actually touch the
rim/disk in order to work, the mechanical advantage of a bicycle brake
system is approximately inversely proportional to how far you can set the
pads away from the rim/disk and still have the system work (non-linear
systems excepted).

If you still doubt what I say, you may have to continue the discussion with
somebody else, as I have obviously failed in my attempts to communicate.


Yes, Sheldon says just what I've been saying that mechanical advantage
is the relationship between force in and force out and he describes
it, as I did, two ways. One as a ratio of forces and two a ratio of
distances. i.e., a lever that has a ratio of two to one will exert
twice the force on the shorter end as applied to the longer end and by
the same token that the long end will travel twice as far as the short
end.

It has nothing to do with finger length or brake pad clearance.
--
Cheers,

John B.

Theoretically, yes, but practically, no. Try to design a brake system with
a 10:1 mechanical advantage and 1" of brake pad travel and you will soon
discover that your fingers are about 8" too short for it to work because
you will have to pull 10" at the lever.

So yeah, theory says nothing about finger length, but pretty much every
brake lever out there doesn't move more than about 3". Therefore,
practically, the travel of your brake pads can't be any more than 3"
divided by your MA.

So then, if you NEED or WANT a certain amount of brake pad to rim
clearance, then that sets a practical limit on the MA you can have in that
system before you run out of lever travel.

For a real world example, I have cantilever brakes on my Surly. I can lower
the straddle cable to increase the MA of the system, but then I get lower
pad travel. To ensure that I don't bottom out my levers while braking, I
then have to keep the pads closer to the rim. However, I can't just keep
doing that forever, since I also have to accommodate runout and warpage in
my rim. I also need to maintain a certain pad to rim distance to allow me
to unhook the straddle cable so that I can remove my wheel. If I was
running a disk setup, my minimum pad to disk clearance would be smaller,
which would allow the use of a brake system with higher MA. I can't
consider MA and pad to disk/rim clearance independently because I have
normal human fingers that only allow 3" or less of lever travel. And
that's how finger length becomes part of the equation.

The point is that the mechanical advantage of a lever system is
determine by the relative lengths of the levers. A 2::1 mechanical
advantage remains a 2::1 mechanical advantage regardless of what is
attached to it... just as I've been saying.

You seem to be arguing that because you have short fingers that
somehow the mechanical advantage of the brake lever changes in some
way. But in fact, if you take the brake lever off the handlebar and
throw it in the "spares" box the mechanical advantage of that brake
lever hasn't changed a bit.


--
Cheers,

John B.

Why do some forks and frames have brake rotor size limits?
 

On 2017-10-28 21:32, John B. wrote:
On Sat, 28 Oct 2017 23:13:20 -0400, Frank Krygowski
wrote:

On 10/28/2017 9:11 PM, John B. wrote:

A great deal snipped.



I live at a whopping 400 feet (about) elevation. The garage in my building is probably 0 feet. That minor elevation change sometimes means the difference between ice and no ice -- so I walk outside in the morning and say f*** this! And then I jump in the car and half-way to work, creeping along in traffic, there is no ice -- and then I regret not riding. So, in order to avoid that regret, I have done some pretty stupid sh** spinning around on ice or hoofing it in my SPDs to get out of my neighborhood and then being freaked out riding over the slick bridges and viaducts into town. I met up with another guy on a bike who was fish-tailing down the road on one of those mornings, and we looked at each other and shook our heads -- "we're a couple of idiots." So, now I'm working on not feeling regret or guilt if I drive. And don't get me going about the dopes who jump into their Malibus with no-season/no-tread tires and crash on the ice and/or snow. I'll slap on the snow tires in
November. I really miss studs, but I'm doing penance with studless.

-- Jay Beattie.

Are studded auto tires legal? I seem to remember that back in the
1960's when I was in Maine that it was illegal to drive studded tires
on bare roads. It was a long time ago and memory is always
questionable but I'm sure that I remember people getting a ticket for
using studded tires under certain conditions.

I don't know if they're legal in Oregon now (Jay can tell us) but I've
driven out there in the summer and experienced the weirdness of a
freeway with two troughs worn in it by thousands of studded tires.


Sounds like truck grooves. We have those in California a lot even
without truckers using studded tires. Courtesy of corruption where tax
Dollar mostly do not reach their destination.


Our cars track (i.e. left to right wheel span) didn't quite match the
trough widths, and our car had a disturbing tendency to "hunt" back and
forth as I drove.

I was curious. As I had said I'm sure it was illegal to drive with
either chains or studs on bare roads back then. The subject was of
some interest as being in the Service I had to be out and about by
about 0600 in order to get to work on time and frequently the snow
plows hadn't gotten all the streets plowed that early.


In Germany they made studs illegal altogether some time in the 70's. I
remember sitting there with my dad prying out the studs from the tires
so they could still be used as regular snow tires.

AFAIK that does not apply to bicycles and prople use Nokian tires and
such over there in winter.

--
Regards, Joerg

http://www.analogconsultants.com/

Why do some forks and frames have brake rotor size limits?
 

On 10/29/2017 2:05 AM, John B. wrote:
On Sun, 29 Oct 2017 05:11:13 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sun, 29 Oct 2017 01:45:50 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 15:12:37 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 06:23:59 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 03:54:43 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sat, 28 Oct 2017 01:13:54 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Fri, 27 Oct 2017 09:32:04 -0700, Joerg
wrote:

On 2017-10-27 09:25, Frank Krygowski wrote:
On 10/27/2017 9:58 AM, Joerg wrote:

Finally after many decades the bicycle industry woke up and adopted
what the automotive guys had all along, disc brakes. Why should I
accept an inferior brake system on a new bike when there is a much
better one?

sigh There are advantages and disadvantages to this equipment choice,
just as with other equipment choices. The disadvantages of discs have
been discussed. If they don't matter or apply to you, fine; but they
matter to others.


Many others just don't know any better. I have witnessed several people
riding a bike with hydraulic disc brakes for the first time and the
reaction was usually "WHOA!". Same with me, it almost sent me over the bar.


But I'll note that you're currently in a project to increase your disc's
diameter from something like 160mm or 180mm up to 200mm or more. You
seem to feel bigger diameter is better.


Because bigger is better here.


Well, even "better," why not go up to roughly 622mm? That's what lots
of us prefer, with cable actuation.


The disadvantages have been discussed ad nauseam. A rim brake is not a
disc brake. Not even close.

Care to explain the mechanical difference? I mean a rotating surface
and two friction pads that are tightened against it....
--
Cheers,

John B.

As far as I can tell, the differences between a rim brake and a 622 mm disk
a

1) The disk doesn't have to provide tire clearance, so the pads can sit
closer, facilitating higher mechanical advantage.

I'm not sure that is correct. After all some old Greek guy was
supposed to have said, "Give me a lever and a place to stand and I
will move the earth". Nothing about being close.

No. I'm pretty certain I'm right here. Let's say that you can pull 100 lbs
on your brake lever and the lever has 2" of play before it hits your bars.
You can fiddle with leverage many places in the system, but the product of
that initial 100 lbs and 2" will be constant in the system. If the final
travel of the brake pads is 1/2", then you can apply 400 lbs force to the
pads. If you tighten up your tolerances such that the pads only have to
move 1/16", then you can increase the leverage to the point where you can
apply 3200 lbs force to the pads. In disk brake systems this reduction in
pad-disk distance allow the MA to be increased to compensate for the
decreased leverage of the disk on the wheel. The increases brake pad
pressure at a given bike deceleration is what gives disk brakes more
consistent performance in the wet.

Movement of the parts doesn't make any difference the efficiency is
the pressure applied to the brake lever versus the pressure applied to
the braking device, usually the pads themselves.

A lever that is 1 foot long and moves, lets say, one quarter of the
diameter of a 2 foot circle applies the same force to a load located 1
foot from the fulcrum as a 100 ft lever which moves 1/4 of the
diameter of a 200 ft circle applies to a load that is 100 ft. from the
fulcrum. The first lever moves 19 inches and the second moves 157
feet.

Sure. But the distance you can move your brake lever is limited by the
length of your fingers, and so the distance you can move at the lever end
is essentially fixed. To increase the mechanical advantage in THAT system,
you have to reduce the distance the brake pads move. No ifs, ands, buts or
maybes.

You are talking about two different things. Mechanical efficiency and
how long your fingers are.

They aren't really related.
--
Cheers,

John B.

Theoretically, the mechanical advantage of a brake system and the length of
your fingers aren't related, but practically, in this example of the
mechanical advantage of a bicycle brake system, the two quantities are
chained together at the ankles. You can't have high brake pad travel and
high mechanical advantage unless the travel of the brake lever is very
large, and human hand dimensions just won't allow that.

Well you can continue to equate mechanical advantage with long, or
short, fingers but it doesn't make it true :-)

But you keep talking about the large clearance between the rim brake
pads and the rim versus the disc pads and the disc which isn't
necessarily true.

I use brifters - Shimano STI brake&shifters - on two of my bikes and
considering the rather limited travel of the brake levers the pads
need to be fitted very closely to the rims, and of course, the rims
need to be very straight. The two bikes are about 1,000 km from where
I'm presently located so I'm going much by memory but I think that the
pad to rim clearance is about 1mm. The two bikes I have here both have
down tube shifting and the brake pad clearance is largely determined
by where I want the brake levers to be when the brakes are applied,
but measuring one bike shows that the clearance is about 6mm.

I can sense no appreciable difference in the pressure I feel against
my fingers when stopping any of the four bikes.
--
Cheers,

John B.

I think we're pretty close to a standoff here, so I'll invoke the name of
Sheldon, and then give up. Read through

https://www.sheldonbrown.com/cantilever-geometry.html

and tell me if it changes your opinion about what I've been saying.

To summarize my position
1) The mechanical advantage of a brake system (ie: the ratio of pad force
to lever force) is the inverse of the ratio of pad travel to lever travel.

2) bike brakes are made for humans and not orangutans or aliens, so they
all tend to have about the same amount of lever travel.

3) because of 1 and 2, the travel of the brake pad is pretty much inversely
proportional to the mechanical advantage.

4) because of 1, 2 and the fact that brakes need to actually touch the
rim/disk in order to work, the mechanical advantage of a bicycle brake
system is approximately inversely proportional to how far you can set the
pads away from the rim/disk and still have the system work (non-linear
systems excepted).

If you still doubt what I say, you may have to continue the discussion with
somebody else, as I have obviously failed in my attempts to communicate.


Yes, Sheldon says just what I've been saying that mechanical advantage
is the relationship between force in and force out and he describes
it, as I did, two ways. One as a ratio of forces and two a ratio of
distances. i.e., a lever that has a ratio of two to one will exert
twice the force on the shorter end as applied to the longer end and by
the same token that the long end will travel twice as far as the short
end.

It has nothing to do with finger length or brake pad clearance.
--
Cheers,

John B.

Theoretically, yes, but practically, no. Try to design a brake system with
a 10:1 mechanical advantage and 1" of brake pad travel and you will soon
discover that your fingers are about 8" too short for it to work because
you will have to pull 10" at the lever.

So yeah, theory says nothing about finger length, but pretty much every
brake lever out there doesn't move more than about 3". Therefore,
practically, the travel of your brake pads can't be any more than 3"
divided by your MA.

So then, if you NEED or WANT a certain amount of brake pad to rim
clearance, then that sets a practical limit on the MA you can have in that
system before you run out of lever travel.

For a real world example, I have cantilever brakes on my Surly. I can lower
the straddle cable to increase the MA of the system, but then I get lower
pad travel. To ensure that I don't bottom out my levers while braking, I
then have to keep the pads closer to the rim. However, I can't just keep
doing that forever, since I also have to accommodate runout and warpage in
my rim. I also need to maintain a certain pad to rim distance to allow me
to unhook the straddle cable so that I can remove my wheel. If I was
running a disk setup, my minimum pad to disk clearance would be smaller,
which would allow the use of a brake system with higher MA. I can't
consider MA and pad to disk/rim clearance independently because I have
normal human fingers that only allow 3" or less of lever travel. And
that's how finger length becomes part of the equation.

The point is that the mechanical advantage of a lever system is
determine by the relative lengths of the levers. A 2::1 mechanical
advantage remains a 2::1 mechanical advantage regardless of what is
attached to it... just as I've been saying.

You seem to be arguing that because you have short fingers that
somehow the mechanical advantage of the brake lever changes in some
way. But in fact, if you take the brake lever off the handlebar and
throw it in the "spares" box the mechanical advantage of that brake
lever hasn't changed a bit.

My wife has shorter fingers than I do - short enough that on her touring
bike, I bent her brake levers so her fingers could reach them more
comfortably. This did reduce the distance her brake levers would move
before hitting the handlebars.

Her bike has center pull cantilever brakes, which means the overall
mechanical advantage is adjustable. Other things being equal, I could
not adjust her brake system to have the same mechanical advantage as my
brake system. The distance available for force input is smaller on her bike.

--
- Frank Krygowski

Why do some forks and frames have brake rotor size limits?
 

On 2017-10-28 17:18, John B. wrote:
On Sat, 28 Oct 2017 08:09:28 -0700, Joerg
wrote:

On 2017-10-27 17:11, John B. wrote:
On Fri, 27 Oct 2017 06:58:27 -0700, Joerg
wrote:

On 2017-10-27 01:11, John B. wrote:
On Wed, 25 Oct 2017 07:53:11 -0700, Joerg
wrote:

On 2017-10-24 17:21, John B. wrote:
On Tue, 24 Oct 2017 11:47:12 -0700, Joerg
wrote:

On 2017-10-24 07:27, wrote:
On Tuesday, October 24, 2017 at 2:19:48 AM UTC-7, John B. wrote:
On Mon, 23 Oct 2017 10:09:20 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 12:48:29 +0700, John B.
wrote:

On Sun, 22 Oct 2017 20:51:15 -0700, Jeff Liebermann
wrote:

On Mon, 23 Oct 2017 07:02:08 +0700, John B.
wrote:

But re disc brake cooling F1 car brakes appear to work with
the discs red hot. In the 1,000 degree (F) range. And they
use Carbon Fiber discs too :-) And everyone knows that CF
is better.

"Thermal Conductivity of Carbon Fiber, and other Carbon
Based Materials"
http://www.christinedemerchant.com/carbon_characteristics_heat_conductivity.html


"So...Is Carbon Fiber a good heat conductor?
As usual the answer is "it depends." The short answer is NO
not when regular carbon fiber is made up in regular epoxy and
expected to conduct heat across the thickness. IF a highly
carbonized pan fiber with graphite or diamond added, is
measured for heat transmission in the length of the fiber it
is very good and can rival and exceed copper."

On the other hand, they seem to work pretty well :-) See
https://www.youtube.com/watch?v=h5JcHAEmIYM for a visual
indication of heat dissipation. :-)

Impressive. I'll assume it's a carbon-carbon rotor, since all F1
cars seem to using them.

Undoubtedly so. But if the advantage of "carbon" bikes can be
extolled that a carbon-carbon frame must have twice the bragging
rights :-)


http://www.racecar-engineering.com/technology-explained/f1-2014-explained-brake-systems/


(4 pages)
"A typical road car uses a cast iron brake disc with an organic
brake pad. In an F1 car, though, the same material is used for
both disc and pad, and this material is known as carbon-carbon -
a significantly different material to the carbon-fibre
composites used in the rest of the car" In other words, the F1
brakes are NOT made from CF.

Some detail on Formula 1 brakes:
https://www.youtube.com/watch?v=ev6XTdlKElw

Fun destroying brakes:
https://www.youtube.com/watch?v=KslGsXMgmqg The brake starting
at 4:45 sure looks like CF but I'm not sure.

Maybe twin disk brakes would be easier?
http://nuovafaor.it//public/prodotto/75/nccrop/DOPPIO_FRENO_CROSS_ENDURO.jpg


https://i.ytimg.com/vi/Pvwj-WWlKkg/maxresdefault.jpg
https://gzmyu4ma9b-flywheel.netdna-ssl.com/wp-content/uploads/2011/09/Gatorbrake-dual-hydraulic-front-disc-brakes-carbon-rotors01.jpg


https://lh4.googleusercontent.com/-cDfAFWrGR6Q/VHKPsm-f6YI/AAAAAAAAX10/2FCyj87xs0g/s640/14%2520-%25201.jpg
https://www.minibikecraze.co.uk/wp-content/uploads/bs0978.jpg
https://endless-sphere.com/forums/viewtopic.php?f=28&t=56268

Given the coefficient of friction between a 1.25" wide rubber tire
(32mm) and a wet road probably dragging the feet will work. :-)

Joerg's experience is with full suspension MTB's. These things are
incredibly heavy and long wheelbased. He has his judgement of disks
and it is no doubt quite accurate for his experience and riding.

I have disks on a much lighter and shorter wheelbased bike. I know
the failings up close and personal. I simply cannot imagine WHY a
person would want a more complicated system than that offered by the
Campy Skeleton brakes.


The reason can be summed up in one word: Rain :-)

But last Sunday I started out my "weekend" ride in the rain. It had
been raining nearly all night and the roads had a lot of water on them
- note we have been having floods here in Bangkok lately - but it
appeared that the rain was ending so off I went.

Unfortunately my weather forecasting facility wasn't working very well
and I rode 20 Km of a 30 Km ride in light rain and flooded roads in
many places. I was splashing through water in some places and cars
were splashing through (and splashing me) in others.

Of course, Sunday is much lighter traffic then on work days but still,
Bangkok is rated as one of the cities with the most chaotic traffic
in the world, and I did have to stop suddenly several time, on flooded
roads with wet wheels and brakes.

My brakes worked just as they do in the dry. Back brake stops me
somewhat slowly and front brake stops rather suddenly, both brakes
together provides best stopping. No long wait after grabbing a brake
lever although I did think of you with your stopping problems and I
have the feeling that the brake lever pressure might be a tiny bit
more to stop in the rain but if it was it was so little that it
couldn't be quantified.

But of course I am using quality brake pads. Why it costs me US$12.12
a wheel just for pads alone.... but they do last a year or more.


It seems Californian rain and Thai rain aren't the same. When it rains
heavily and I have to do a surprise emergency stop after not having used
the brakes for a while there is 1-2sec of nada, absolutely nothing. It
makes no difference whatsoever whether I use $17 high-falutin Koolstop
rain-rated pads or $4 Clarks pads. The experience of other riders around
here and in this NG is similar.

Which, to be honest, I find a little mystifying as I've had pretty
constant success with conventional brakes.

Frankly, I can't believe this is solely because I'm somehow so
uniquely skilled or that y'all are all in the awkward squad

I do see a number of people here and many who are not here who seem to
have ridden for years using conventional brakes without complaint and
some of the blogs I read don't even talk about brakes. Dave Moulton,
for example. An old fellow, used to race bikes, came to the U.S. in
about 1979 and built frames commercially for years, now retired, has
one entry in his blog about brakes - "centering side pull brakes".

Another blog from the long distance side of the bicycleing world, The
Blayleys, who are into Audex's and who apparently each ride in the
neighborhood of 10,000 miles annually, mentions Vee brakes in
reference to a Tandem while a photo of them on a tandem on their web
page shows disc brakes. On the other hand, when she discusses a "good
brevet bike she simply says that the "brakes must clear the fenders
and probably long reach caliper brakes will suffice".

In short, it seems that brakes just don't seem to be a hot subject in
much of the cycling fraternity.


To a large part that is because most cyclist will not ride in driving
rain. Some do and those know exactly how that delay with rim brakes
feels. Occasionally it is called "free fall" because that's how it feels
like.

Well, the Blayleys state that the husband, John, has ridden 10 - 17
thousand miles a year for the past 25 years and the wife, Pamela, has
ridden from 10 - 14 thousand miles a year for the past 20 years, or
another way to put it might be that together they have ridden from 20
- 30 thousand miles a year for the past 20 years.

Somehow I suspect that they may have encountered rain in that period.


And grandpa has driven his cars without safety belts yet survived ...


Well, since you mentioned it. My two grandfathers, neither of whom
ever had a road accident. One died at 92 and the other at 87. My
father never had a road accident although he did get a speeding ticket
once, died at 87. My mother had one "accident", a guy ran a red light
and tee-boned her car, no speeding tickets, died at 86. All deaths
were considered "natural".

Do you really believe that safety belts would have benefited them?


Counting on luck alone is not smart. The father of a friend's wife died
from the consequences of a minor fender bender at an intersection
because he didn't wear a belt. That accident was 100% survivable. Or
would have been ...

--
Regards, Joerg

http://www.analogconsultants.com/

Why do some forks and frames have brake rotor size limits?
 

On Friday, October 27, 2017 at 4:25:11 PM UTC-7, Sir Ridesalot wrote:
On Friday, October 27, 2017 at 5:40:05 PM UTC-4, wrote:
Snipped
Exactly how do you plan ahead for someone opening their door? Especially these days when people will pull over to consult their cell phones and then drive off again? And narrow bike lanes in heavy traffic always brings out the jerk in drivers. Yesterday I was almost hit by two drivers as I was pulling across a three lane into the left turn lane when there was a red light for them and they could see me crossing.

I have so much less problems with long haul truckers who know the rules and know that losing 5 seconds here means nothing.

Rather simple Old Boy. (giggling) You look aheadand if cars are parked right beside your bicycle lane you move left out of the bicycle lane when it's safe to merge into the motor traffic stream. I do that every day.

You make me think that you are nothing more than Frank posting under a different identity. Let me inform someone that probably refuses to be informed - you are not allowed to move out into the car lane if you have a bike lane that is usable. And until you get to a car blocking the lane it is usable. And if you DO try you have cars behind you honking their horns.

It is pretty obvious that for someone that thinks of themselves as "ridesalot" that you don't ride much at all.

Why do some forks and frames have brake rotor size limits?
 

On Friday, October 27, 2017 at 4:37:38 PM UTC-7, Joerg wrote:
On 2017-10-27 16:15, Sir Ridesalot wrote:
The more I read of your posts the more I think you're a really big Usenet Troll.


Well, think what you want.

I think it's pretty easy to detect who the troll is.

Why do some forks and frames have brake rotor size limits?
 

On Friday, October 27, 2017 at 5:11:29 PM UTC-7, John B. wrote:

Well, the Blayleys state that the husband, John, has ridden 10 - 17
thousand miles a year for the past 25 years and the wife, Pamela, has
ridden from 10 - 14 thousand miles a year for the past 20 years, or
another way to put it might be that together they have ridden from 20
- 30 thousand miles a year for the past 20 years.

Somehow I suspect that they may have encountered rain in that period.

For three years while between jobs I road almost continuously including several long distance tours each year. I barely made 10,000 miles per year and usually only cleared that hurdle with a last minute sprint. So unless the Blayley's are on a continuous tour I would question those miles.