Potential good news for Mt. Washington access. - Page 19 - Cycling Mob: Road Cycling, Mountain Biking and More

01-10-2005, 05:22 PM

Frank Krygowski wrote:

> Mark and Christine wrote:
>
>> I am coming into this discussion a little late, so if I am
>> repeating something that has already been pointed out then I
>> appologize in advance. There have been a couple of "factual
>> errors" in recent posts. If no one with an engineering
>> background has corrected them then...
>
> Several people with strong engineering backgrounds have been following
> this thread. Your "corrections" have grevious factual errors, which is
> why nobody else has brought them up. Comments below:
>
>> Expanding air cools, compressing air heats. When you fill a tire you
>> are expanding the air (cooling) and then as the tire inflates the amount
>> of expansion decreases. It does not compress and heat. For all
>> practical purposes the tire "might" cool slightly.
>
> When you take atmospheric air at zero gage pressure and pump a tire to
> 100 psi gage pressure, you are _certainly_ compressing the air, not
> expanding it. During the pump compression stroke, the air within the
> pump is at a higher pressure still; but this is largely immaterial.

PV = NkT. Assuming volume inside the tire remains relatively constant
(once the tire is mostly inflated), and that the pressure is directly
proportional to the number of molecules, shouldn't the temperature remain
constant? (Once it has entered the tube, that is). I'm not sure what
"Mark and Christine" had in mind; perhaps that the volume inside the tube
is increasing as it inflates.

--
Benjamin Lewis

Luke, I'm yer father, eh. Come over to the dark side, you hoser.
-- Dave Thomas, "Strange Brew"

01-10-2005, 05:27 PM

Mark and Christine writes:

> I am coming into this discussion a little late, so if I am repeating
> something that has already been pointed out then I appologize in
> advance. There have been a couple of "factual errors" in recent
> posts. If no one with an engineering background has corrected them
> then...

> Expanding air cools, compressing air heats. When you fill a tire
> you are expanding the air (cooling) and then as the...

This has got to be a troll, it is so bizarre. Let's not get carried
away by it. This is not the place to review high school physics for
those who missed it.

Jobst Brandt
[Only registered and activated users can see links. ]

01-10-2005, 05:27 PM

Mark and Christine writes:

> I am coming into this discussion a little late, so if I am repeating
> something that has already been pointed out then I appologize in
> advance. There have been a couple of "factual errors" in recent
> posts. If no one with an engineering background has corrected them
> then...

> Expanding air cools, compressing air heats. When you fill a tire
> you are expanding the air (cooling) and then as the...

This has got to be a troll, it is so bizarre. Let's not get carried
away by it. This is not the place to review high school physics for
those who missed it.

Jobst Brandt
[Only registered and activated users can see links. ]

01-10-2005, 05:27 PM

Mark and Christine writes:

> I am coming into this discussion a little late, so if I am repeating
> something that has already been pointed out then I appologize in
> advance. There have been a couple of "factual errors" in recent
> posts. If no one with an engineering background has corrected them
> then...

> Expanding air cools, compressing air heats. When you fill a tire
> you are expanding the air (cooling) and then as the...

This has got to be a troll, it is so bizarre. Let's not get carried
away by it. This is not the place to review high school physics for
those who missed it.

Jobst Brandt
[Only registered and activated users can see links. ]

01-10-2005, 06:21 PM

On Mon, 10 Jan 2005 19:53:20 -0500, Frank Krygowski
<[Only registered and activated users can see links. ]> wrote:

>
>Several people with strong engineering backgrounds have been following
>this thread. Your "corrections" have grevious factual errors, which is
>why nobody else has brought them up. Comments below:
>

Since I was trying to be nice and add something, and you
were obviously doing the opposite...

Boyles law only works in absolutes. If you use C for the
temp then you must add 273 to your temp on each side, but
only 14.7 for pressure and nothing for volume. You do the
math and see if temp will do anything to the pressure of a
tire in a temperature range that would not first weaken the
tire.

As for friction, you simply do not understand real world
friction applications if you do not think that friction
occurs unless the tire is skiding. Max heating of a tire
occurs at the speed just before the tire stops rotating.
The moment a tire skids friction drops significantly.
Anti-lock brakes?

Mark

PS, Why am I, and bunch of others, double posting
everything to the group tonight?

01-10-2005, 06:21 PM

On Mon, 10 Jan 2005 19:53:20 -0500, Frank Krygowski
<[Only registered and activated users can see links. ]> wrote:

>
>Several people with strong engineering backgrounds have been following
>this thread. Your "corrections" have grevious factual errors, which is
>why nobody else has brought them up. Comments below:
>

Since I was trying to be nice and add something, and you
were obviously doing the opposite...

Boyles law only works in absolutes. If you use C for the
temp then you must add 273 to your temp on each side, but
only 14.7 for pressure and nothing for volume. You do the
math and see if temp will do anything to the pressure of a
tire in a temperature range that would not first weaken the
tire.

As for friction, you simply do not understand real world
friction applications if you do not think that friction
occurs unless the tire is skiding. Max heating of a tire
occurs at the speed just before the tire stops rotating.
The moment a tire skids friction drops significantly.
Anti-lock brakes?

Mark

PS, Why am I, and bunch of others, double posting
everything to the group tonight?

01-10-2005, 06:21 PM

On Mon, 10 Jan 2005 19:53:20 -0500, Frank Krygowski
<[Only registered and activated users can see links. ]> wrote:

>
>Several people with strong engineering backgrounds have been following
>this thread. Your "corrections" have grevious factual errors, which is
>why nobody else has brought them up. Comments below:
>

Since I was trying to be nice and add something, and you
were obviously doing the opposite...

Boyles law only works in absolutes. If you use C for the
temp then you must add 273 to your temp on each side, but
only 14.7 for pressure and nothing for volume. You do the
math and see if temp will do anything to the pressure of a
tire in a temperature range that would not first weaken the
tire.

As for friction, you simply do not understand real world
friction applications if you do not think that friction
occurs unless the tire is skiding. Max heating of a tire
occurs at the speed just before the tire stops rotating.
The moment a tire skids friction drops significantly.
Anti-lock brakes?

Mark

PS, Why am I, and bunch of others, double posting
everything to the group tonight?

01-10-2005, 07:39 PM

Mark and Christine <[Only registered and activated users can see links. ]> writes:

> As for friction, you simply do not understand real world
> friction applications if you do not think that friction
> occurs unless the tire is skiding.

We understand the real world quite well, however, that
triple-negative is a bit hard to parse.

Your original (incorrect) point was that the friction of the road
against the tire somehow heated up the air in the tube. It doesn't,
essentially all the heat is generated in the brake/rim interface. The
tire friction is significant only in that without we couldn't generate
the braking friction, however, no significant amount of heat is being
generated at the tire/road interface unless the tire is skidding. And
a skidding tire is not of interest to this discussion (for several
reasons).

> Max heating of a tire
> occurs at the speed just before the tire stops rotating.

That makes no sense. There is no given speed at which a tire stops
rotating. Anyhow, the velocity at which maximum power generation
occurs is not the worst-case for temperature rise under steady-state
braking, one has to consider convection cooling at the rim. A
calculation I did some time ago suggests that the worst-case velocity
is Vterm/sqrt(5), where Vterm is the terminal velocity of the rider.

Joe

01-10-2005, 07:39 PM

Mark and Christine <[Only registered and activated users can see links. ]> writes:

> As for friction, you simply do not understand real world
> friction applications if you do not think that friction
> occurs unless the tire is skiding.

We understand the real world quite well, however, that
triple-negative is a bit hard to parse.

Your original (incorrect) point was that the friction of the road
against the tire somehow heated up the air in the tube. It doesn't,
essentially all the heat is generated in the brake/rim interface. The
tire friction is significant only in that without we couldn't generate
the braking friction, however, no significant amount of heat is being
generated at the tire/road interface unless the tire is skidding. And
a skidding tire is not of interest to this discussion (for several
reasons).

> Max heating of a tire
> occurs at the speed just before the tire stops rotating.

That makes no sense. There is no given speed at which a tire stops
rotating. Anyhow, the velocity at which maximum power generation
occurs is not the worst-case for temperature rise under steady-state
braking, one has to consider convection cooling at the rim. A
calculation I did some time ago suggests that the worst-case velocity
is Vterm/sqrt(5), where Vterm is the terminal velocity of the rider.

Joe

01-10-2005, 07:39 PM

Mark and Christine <[Only registered and activated users can see links. ]> writes:

> As for friction, you simply do not understand real world
> friction applications if you do not think that friction
> occurs unless the tire is skiding.

We understand the real world quite well, however, that
triple-negative is a bit hard to parse.

Your original (incorrect) point was that the friction of the road
against the tire somehow heated up the air in the tube. It doesn't,
essentially all the heat is generated in the brake/rim interface. The
tire friction is significant only in that without we couldn't generate
the braking friction, however, no significant amount of heat is being
generated at the tire/road interface unless the tire is skidding. And
a skidding tire is not of interest to this discussion (for several
reasons).

> Max heating of a tire
> occurs at the speed just before the tire stops rotating.

That makes no sense. There is no given speed at which a tire stops
rotating. Anyhow, the velocity at which maximum power generation
occurs is not the worst-case for temperature rise under steady-state
braking, one has to consider convection cooling at the rim. A
calculation I did some time ago suggests that the worst-case velocity
is Vterm/sqrt(5), where Vterm is the terminal velocity of the rider.

Joe