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

On Mon, 13 Nov 2017 10:10:05 -0800, Joerg
wrote:

On 2017-11-12 17:46, John B. wrote:

[...]


As an aside, I just measured the front discs on my wife's Honda Jazz
(I think it is called a "Fit"in the U.S.) and to my horror I find that
they are only 240mm (9.4") in diameter. As the nominal weight of the
car is about 1100 Kg (2400lb), as opposed to (probably) an all up
weight of less then 250 lbs for a bicycle, it is obvious that they
can't possibly be large enough to be safe. And Horrors, there isn't
any room to fit larger :-(


Of course, you didn't bother to measure the rotor thickness and didn't
notice the fact that it is rather solid.

Whatever are you talking about? Does the thickness of the disc matter?
If so why are bicycle (and motorcycle) disc such puny little things
hardly thicker then a piece of paper?
--
Cheers,

John B.

John B. wrote:
On Mon, 13 Nov 2017 14:57:49 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Mon, 13 Nov 2017 03:41:11 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Mon, 13 Nov 2017 02:24:55 +0000 (UTC), Ralph Barone
wrote:

John B. wrote:
On Sun, 12 Nov 2017 12:10:38 -0500, Frank Krygowski
wrote:

On 11/11/2017 7:39 PM, Joerg wrote:

Yes, if 10" were more mainstream I'd probably have taken those but 8"
seems fine because I am not towing a brake-less trailer. A friend of
mine does though.

The extra cost is minimal. The adapters cost me $5.56 for both. The
rotors were around $23.70 each and the cost difference towards the
smaller versions will almost be made up by extended service life.

BTW there is a new bike shop in Placerville and one of the owners had
his MTB there the other day. 10" rotors on both wheels. He weighs less
than I do and said 8" was too iffy on some of his rides. These guys know
their stuff.

Let's look at the big picture. How do we decide which disc size is big
enough? And how do we decide how much how much tire puncture protection
is enough? How do we decide how bright one's lights need to be? How do
we decide how strong wheels need to be, how strong frames need to be, etc.?

In each of those categories (as well as in everything else being
designed) there is a tradeoff of benefits vs. detriments. Everyone else
recognizes this, and shoots for some optimal compromise. Example: I had
a flat about three days ago, but I prefer dealing with a few flats per
year rather than riding tires that noticeably slow me.

In each of those categories, Joerg's claim has been: if it's not as
robust as an automobile it's not good enough. But A) that's total
nonsense, because bikes and cars have very different uses and
parameters. And B) he really doesn't believe it anyway; otherwise he'd
be pedaling the de-motorized motorcycle that Sir Ridesalot has proposed
many times.

Joerg's real attitude is different. He's decided that the only
acceptable equipment is what he desires or approves, and that the entire
bicycle industry should cater to his wishes.

But in its wisdom, the bicycling industry realizes there's only one Joerg.

I don't think that you understand :-) You see, if it is "mine" then it
must be better then anyone. My brakes are better; my legs are
stronger; my beer is better; and on and on and on.

As an aside, I just measured the front discs on my wife's Honda Jazz
(I think it is called a "Fit"in the U.S.) and to my horror I find that
they are only 240mm (9.4") in diameter. As the nominal weight of the
car is about 1100 Kg (2400lb), as opposed to (probably) an all up
weight of less then 250 lbs for a bicycle, it is obvious that they
can't possibly be large enough to be safe. And Horrors, there isn't
any room to fit larger :-(
--
Cheers,

John B.

Bah... Think outside the box. You can probably rig up some cantilever rim
brakes on there. That will probably get you up to 14" or so. :-)

I probably could but I think I'd have to change the rims to a
different brand to get a wide enough rim for the caliper pads to be
effective.

Another thing that might enter into the equation. They refer to the
wheels as "Mag Wheels". If they are in fact magnesium wheels they I'd
have to be careful not to get them too hot. I knew that they made a
movie called "Blazing Saddles" and I suspect that "blazing brakes"
might be even more exciting :-(
--
Cheers,

John B.

It's a safety feature. When the magnesium catches on fire, it emits a
blinding white light that signals other road users to get the hell out of
your way.

So... no requirement for a helmet if using Mag wheels :-)

--
Cheers,

John B.

Well, to be fair, it's only a safety feature for other people, so you may
wish to keep the helmet on. Unless your line of thinking is that you would
prefer NOT to be conscious after crashing your flaming vehicle

I'm not sure I'd want to be conscious WHEN I'm crashing my flaming
vehicle :-)

--
Cheers,

John B.

That too!

On 2017-11-13 15:50, John B. wrote:
On Mon, 13 Nov 2017 10:06:52 -0800, Joerg
wrote:

On 2017-11-12 17:58, John B. wrote:
On Sun, 12 Nov 2017 09:37:54 -0800, Joerg
wrote:

On 2017-11-12 09:10, Frank Krygowski wrote:
On 11/11/2017 7:39 PM, Joerg wrote:

Yes, if 10" were more mainstream I'd probably have taken those but 8"
seems fine because I am not towing a brake-less trailer. A friend of
mine does though.

The extra cost is minimal. The adapters cost me $5.56 for both. The
rotors were around $23.70 each and the cost difference towards the
smaller versions will almost be made up by extended service life.

BTW there is a new bike shop in Placerville and one of the owners had
his MTB there the other day. 10" rotors on both wheels. He weighs less
than I do and said 8" was too iffy on some of his rides. These guys
know their stuff.

Let's look at the big picture. How do we decide which disc size is big
enough?


Big enough so they won't overheat on the longest descent on the usual
routes on a 105F day without overheating. Now that was simple.


I guess I'd have to ask "what is over heating"? You see a F1 car's
brakes work perfectly when they are red hot, around 1200 degrees (C),
in fact I understand that at ambient temperatures they are less
effective then when hot.

So, what is too hot?


Simple: When the point comes where the brake fades away, as happened to
an MTB rider in front of me at the last sharp turn down a long hill. If
he hadn't been a seasoned dirt bike rider he probably would have gone off.

[...]


It must be a problem with small discs as I've never had that problem
with my 700C rim brakes which operate quite similar to disc, i.e. a
rotating surface with pads that squeeze against both sides of the
rotating surface. Although, of course, my "discs" are about 27 inches
in diameter, not little puny 10 inch discs.


And they quite working in the rain. Mine don't.

Anyhow, ask people who had tire blow-outs when overheating the rim. On
the front that's not funny at all.



BTW, the most common excuse I hear from cyclists not to have made a
particular trip by bike is "It's got a flat right now". I have never
heard that from a motor vehicle user, ever.

But to be honest, I never heard a bicyclist say that, or a
motorcyclist say that, or a auto driver say that, or even a big 18
wheel trucker say that.

Is that something they say in Germany?


In California, Washington State, and so on. In Germany the standard
excuse is "Es ist gerade platt" which isn't logically correct but
common. "C'mon, let's fix it and ride" ... "Ahm, maybe next time".

Seriously? California cyclists can't fix a flat tire?


Most can but they won't. I'd hoped it had become clear by now that this
is a commonly used excuse, not an admittance of incompetence. They just
don't want to ride.

Although, I have met cyclists who could not fix a flat. One couldn't
even get the rear wheel out. He had an expensive new CF bike and was
clad in fancy Lycra. I couldn't believe it and then fixed it for him.
Oh, and the pump he had with him was totally useless for anything more
than a kid's tricycle.

There also are Californians who cart their bike to the LBS in their car,
drop it off to have a flat fixed and pick it up next day. No qualms at
all to drive 40mi and blow away almost two gallons of gasoline for that,
and more than a whole hour. No kidding. That dawned on me when I saw
"Flat fixing" on the standard price list at a bike shop. I asked the
owner whether that's a joke. "Oh no!"

--
Regards, Joerg

http://www.analogconsultants.com/

On 2017-11-13 15:53, John B. wrote:
On Mon, 13 Nov 2017 10:10:05 -0800, Joerg
wrote:

On 2017-11-12 17:46, John B. wrote:

[...]


As an aside, I just measured the front discs on my wife's Honda Jazz
(I think it is called a "Fit"in the U.S.) and to my horror I find that
they are only 240mm (9.4") in diameter. As the nominal weight of the
car is about 1100 Kg (2400lb), as opposed to (probably) an all up
weight of less then 250 lbs for a bicycle, it is obvious that they
can't possibly be large enough to be safe. And Horrors, there isn't
any room to fit larger :-(


Of course, you didn't bother to measure the rotor thickness and didn't
notice the fact that it is rather solid.

Whatever are you talking about? Does the thickness of the disc matter?


sigh

I thought you were an engineer. No, I am not going to answer this
because it should be easy to figure that out for yourself.


If so why are bicycle (and motorcycle) disc such puny little things
hardly thicker then a piece of paper?


Have you ever wondered why a motorcycle rotor weighs over a pound?

https://i2.wp.com/www.yamahar3racing...9/IMG_4199.jpg

Now _that_ would be the dream for the front wheel of my MTB.

--
Regards, Joerg

http://www.analogconsultants.com/

On Mon, 13 Nov 2017 16:03:57 -0800, Joerg
wrote:

On 2017-11-13 15:50, John B. wrote:
On Mon, 13 Nov 2017 10:06:52 -0800, Joerg
wrote:

On 2017-11-12 17:58, John B. wrote:
On Sun, 12 Nov 2017 09:37:54 -0800, Joerg
wrote:

On 2017-11-12 09:10, Frank Krygowski wrote:
On 11/11/2017 7:39 PM, Joerg wrote:

Yes, if 10" were more mainstream I'd probably have taken those but 8"
seems fine because I am not towing a brake-less trailer. A friend of
mine does though.

The extra cost is minimal. The adapters cost me $5.56 for both. The
rotors were around $23.70 each and the cost difference towards the
smaller versions will almost be made up by extended service life.

BTW there is a new bike shop in Placerville and one of the owners had
his MTB there the other day. 10" rotors on both wheels. He weighs less
than I do and said 8" was too iffy on some of his rides. These guys
know their stuff.

Let's look at the big picture. How do we decide which disc size is big
enough?


Big enough so they won't overheat on the longest descent on the usual
routes on a 105F day without overheating. Now that was simple.


I guess I'd have to ask "what is over heating"? You see a F1 car's
brakes work perfectly when they are red hot, around 1200 degrees (C),
in fact I understand that at ambient temperatures they are less
effective then when hot.

So, what is too hot?


Simple: When the point comes where the brake fades away, as happened to
an MTB rider in front of me at the last sharp turn down a long hill. If
he hadn't been a seasoned dirt bike rider he probably would have gone off.

[...]


It must be a problem with small discs as I've never had that problem
with my 700C rim brakes which operate quite similar to disc, i.e. a
rotating surface with pads that squeeze against both sides of the
rotating surface. Although, of course, my "discs" are about 27 inches
in diameter, not little puny 10 inch discs.


And they quite working in the rain. Mine don't.

As I've often written, my rim brakes work in the rain. Given that I'm
living in a country where the term Monsoon Rains may have been coined
I suggest that I probably ride in the rain as much as someone from
California.

But then, I can't remember but once that a tire sidewall failed and
that was because I hit a nail that went in the tread and out the
sidewall :-)


Anyhow, ask people who had tire blow-outs when overheating the rim. On
the front that's not funny at all.

Many? Strange, in all the years I've ridden a bike I never actually
have seen such a thing. Which is not to say it never happened of
course, but I've even stopped a number of times on very steep hills to
feel the temperature of the aluminum rims and have never seen
temperatures hot enough that I couldn't hold my hand on the rim.

But perhaps my braking technique is better then the hot rim crowd?





BTW, the most common excuse I hear from cyclists not to have made a
particular trip by bike is "It's got a flat right now". I have never
heard that from a motor vehicle user, ever.

But to be honest, I never heard a bicyclist say that, or a
motorcyclist say that, or a auto driver say that, or even a big 18
wheel trucker say that.

Is that something they say in Germany?


In California, Washington State, and so on. In Germany the standard
excuse is "Es ist gerade platt" which isn't logically correct but
common. "C'mon, let's fix it and ride" ... "Ahm, maybe next time".

Seriously? California cyclists can't fix a flat tire?


Most can but they won't. I'd hoped it had become clear by now that this
is a commonly used excuse, not an admittance of incompetence. They just
don't want to ride.

Although, I have met cyclists who could not fix a flat. One couldn't
even get the rear wheel out. He had an expensive new CF bike and was
clad in fancy Lycra. I couldn't believe it and then fixed it for him.
Oh, and the pump he had with him was totally useless for anything more
than a kid's tricycle.

There also are Californians who cart their bike to the LBS in their car,
drop it off to have a flat fixed and pick it up next day. No qualms at
all to drive 40mi and blow away almost two gallons of gasoline for that,
and more than a whole hour. No kidding. That dawned on me when I saw
"Flat fixing" on the standard price list at a bike shop. I asked the
owner whether that's a joke. "Oh no!"

I knew a guy like that and was actually in the bike shop when he
dropped a wheel off. I said something like, "Oh! Can't fix a flat?" He
replied that he reckoned that in the time he might spend fixing a flat
he might make more money working.

Given that he worked for a group that sells yachts he might well be
correct.
--
Cheers,

John B.

On 11/13/2017 7:03 PM, Joerg wrote:
On 2017-11-13 15:50, John B. wrote:
Seriously? California cyclists can't fix a flat tire?

Most can but they won't. I'd hoped it had become clear by now that this
is a commonly used excuse, not an admittance of incompetence.

There are many people who can't fix a flat bike tire. It's sad but true,
and it's not going to get any better.

The denizens of this group tend to be people who love bikes and are at
least reasonably competent with tools. But as I've described in the
past, I've done simple bike repairs for otherwise very intelligent
people (including engineering PhDs) who were baffled by the simplest
mechanical things.

They just don't want to ride.

This is true. Again, we're an unusual group. If you gave every American
a perfectly safe, absolutely level, completely separated bike path
directly from their house to their favorite grocery store one mile away,
I doubt more than 3% would ride bikes to shop.

--
- Frank Krygowski

On 11/13/2017 7:09 PM, Joerg wrote:
On 2017-11-13 15:53, John B. wrote:
On Mon, 13 Nov 2017 10:10:05 -0800, Joerg
wrote:

On 2017-11-12 17:46, John B. wrote:

[...]


As an aside, I just measured the front discs on my wife's Honda Jazz
(I think it is called a "Fit"in the U.S.) and to my horror I find that
they are only 240mm (9.4") in diameter. As the nominal weight of the
car is about 1100 Kg (2400lb), as opposed to (probably) an all up
weight of less then 250 lbs for a bicycle, it is obvious that they
can't possibly be large enough to be safe. And Horrors, there isn't
any room to fit larger :-(


Of course, you didn't bother to measure the rotor thickness and didn't
notice the fact that it is rather solid.

Whatever are you talking about? Does the thickness of the disc matter?


sigh

I thought you were an engineer. No, I am not going to answer this
because it should be easy to figure that out for yourself.


If so why are bicycle (and motorcycle) disc such puny little things
hardly thicker then a piece of paper?


Have you ever wondered why a motorcycle rotor weighs over a pound?

https://i2.wp.com/www.yamahar3racing...9/IMG_4199.jpg


Now _that_ would be the dream for the front wheel of my MTB.

So why aren't you using it? I thought you were an engineer.


--
- Frank Krygowski

On 2017-11-13 19:02, Frank Krygowski wrote:
On 11/13/2017 7:03 PM, Joerg wrote:
On 2017-11-13 15:50, John B. wrote:
Seriously? California cyclists can't fix a flat tire?

Most can but they won't. I'd hoped it had become clear by now that
this is a commonly used excuse, not an admittance of incompetence.

There are many people who can't fix a flat bike tire. It's sad but true,
and it's not going to get any better.

The denizens of this group tend to be people who love bikes and are at
least reasonably competent with tools. But as I've described in the
past, I've done simple bike repairs for otherwise very intelligent
people (including engineering PhDs) who were baffled by the simplest
mechanical things.


A lot of folks are scared to break something expensive. Many simply
aren't used to do anything manual on any vehicle or other technical
equipment. Their only tools for fixing stuff are the yellow pages, the
Internet and their smart phone.


They just don't want to ride.

This is true. Again, we're an unusual group. If you gave every American
a perfectly safe, absolutely level, completely separated bike path
directly from their house to their favorite grocery store one mile away,
I doubt more than 3% would ride bikes to shop.


They would if you gave them an E-bike with a throttle-only mode. And if
it had an A/C button.

I know you don't believe it but I know it for a fact that there is a
number of people who will ride when there is a bike path. It may be only
1-3% but for America that is a lot and as you wrote yourself that alone
presents a tremendous cost savings for our health care network.

--
Regards, Joerg

http://www.analogconsultants.com/

On 2017-11-13 19:04, Frank Krygowski wrote:
On 11/13/2017 7:09 PM, Joerg wrote:
On 2017-11-13 15:53, John B. wrote:
On Mon, 13 Nov 2017 10:10:05 -0800, Joerg
wrote:

On 2017-11-12 17:46, John B. wrote:

[...]


As an aside, I just measured the front discs on my wife's Honda Jazz
(I think it is called a "Fit"in the U.S.) and to my horror I find that
they are only 240mm (9.4") in diameter. As the nominal weight of the
car is about 1100 Kg (2400lb), as opposed to (probably) an all up
weight of less then 250 lbs for a bicycle, it is obvious that they
can't possibly be large enough to be safe. And Horrors, there isn't
any room to fit larger :-(


Of course, you didn't bother to measure the rotor thickness and didn't
notice the fact that it is rather solid.

Whatever are you talking about? Does the thickness of the disc matter?


sigh

I thought you were an engineer. No, I am not going to answer this
because it should be easy to figure that out for yourself.


If so why are bicycle (and motorcycle) disc such puny little things
hardly thicker then a piece of paper?


Have you ever wondered why a motorcycle rotor weighs over a pound?

https://i2.wp.com/www.yamahar3racing...9/IMG_4199.jpg


Now _that_ would be the dream for the front wheel of my MTB.

So why aren't you using it? I thought you were an engineer.


For the umpteenth time:

1. I don't have a lathe and other tools.

2. It requires adapting the fork mounts to a motorcycle caliper and the
handle has to come from a Yamaha.

3. I just don't have that much time right now. For example, this
afternoon I get to modify an RF amp from my EMC set-up where the
rechargeable battery size has become unobtanium. Not my favorite job but
as John Wayne said "Man's got to do what man's got to do".

4. I just converted the MTB to 8" rotors for both wheels. Any engineer
woth his salt will recognize when good enough is good enough. I shall
try that out extensively but I think that'll do the trick.

BTW, #2 wouldn't be so bad because that would eliminate the dreaded
(messy) burping procedure. Bike brake systems have no extra reservoir
tank for whatever reason.

--
Regards, Joerg

http://www.analogconsultants.com/

On 11/14/2017 3:43 PM, Joerg wrote:
On 2017-11-13 19:04, Frank Krygowski wrote:
On 11/13/2017 7:09 PM, Joerg wrote:

https://i2.wp.com/www.yamahar3racing...9/IMG_4199.jpg

Now _that_ would be the dream for the front wheel of my MTB.

So why aren't you using it? I thought you were an engineer.


For the umpteenth time:

1. I don't have a lathe and other tools.

I thought you were an engineer.

2. It requires adapting the fork mounts to a motorcycle caliper and the
handle has to come from a Yamaha.

I thought you were an engineer.

3. I just don't have that much time right now.

You spend too much time whining on Usenet.

4. I just converted the MTB to 8" rotors for both wheels. Any engineer
woth his salt will recognize when good enough is good enough.

Then why did you say " Now _that_ would be the dream for the front wheel
of my MTB" ?

I agree that any engineer worth his salt will recognize when good enough
is good enough.

Failing to do that is your entire schtick.


--
- Frank Krygowski