effect on tire pressure

Callistus Valerius said:

I forgot everything I learned in my physics class, so I need your help.

If I'm going from 2000' to 8000' what would be the effect on my tire
pressure? And at 8000' do I keep the tire pressure that I normally do at
120 psi.

I would expect your tire pressure to go up about 3 psi.

HTH,
Ernie

Callistus Valerius said:

I forgot everything I learned in my physics class, so I need your help.

If I'm going from 2000' to 8000' what would be the effect on my tire
pressure? And at 8000' do I keep the tire pressure that I normally do at
120 psi.

If you go from sea level to outer space the pressure only changes by
14-15 psi. Don't worry about it.

Peter Cole said:

If you go from sea level to outer space the pressure only changes by
14-15 psi. Don't worry about it.

But think of the time trial PB with no air resistance!

Callistus Valerius said:

I forgot everything I learned in my physics class, so I need your help.

If I'm going from 2000' to 8000' what would be the effect on my tire
pressure? And at 8000' do I keep the tire pressure that I normally do at
120 psi.

Let's see now. How much would the volume of the tire change? Since the
tire casing does not stretch, that would be 0. How much would the
temperature change?  No more than usual changes of temperature. So, why
is it that the tire pressure would change?

--

David L. Johnson

__o | Enron's slogan: Respect, Communication, Integrity, and
_`\(,_ | Excellence.
(_)/ (_) |

Callistus Valerius said:

I forgot everything I learned in my physics class, so I need your help.

If I'm going from 2000' to 8000' what would be the effect on my tire
pressure? And at 8000' do I keep the tire pressure that I normally do at
120 psi.

Dear CV,

Here's a calculator:

http://www.srh.noaa.gov/elp/wxcalc/pressurealtitude.shtml

For 29.9212 inches of mercury, it will hint at sea level.

For 27.82 inches of mercury, it will suggest 2,000 feet,
2.10 inches less.

For 22.22 inches of mercury, it will predict 8,000 feet,
7.70 inches less.

For 17.57 inches of mercury, it will wheeze at 14,000 feet,
12.35 inches less.

The difference of 5.60 inches of mercury between 2,000 and
8,000 feet corresponds to about 2.46 psi, or 0.1693 bar, or
127.0 mm Hg.

So if you pumped your tire to 120 psi at 2000 feet, it might
feel an exuberant 122 to 123 psi at 8000 feet.

If you pumped your tire to 120 psi at the beach, flew to
Colorado, and climbed the 14,000 foot mountain of your
choice, your tire pressure might increase dangerously to 126
psi.

Weather and heat change the pressure, too, so don't take
such figures too literally.

When James Bond wrote his touching farewell note to his
one-night stand in "The Spy Who Loved Me" about her Vespa's
tyre pressures being too high for her intended travel south
from Lake George, New York (2041 feet), he was showing how
little a naval officer might know about air pressure. She
would have had to lower her tire pressure approximately 1
psi if she descended to sea level.

Of course, Ian Fleming was the sort of writer who was
untroubled by the idea that his hero's letter suggested that
Bond had slipped out that cold morning and checked the
woman's tire pressure before sneaking off.

Carl Fogel

David L. Johnson said:

Let's see now. How much would the volume of the tire change? Since the
tire casing does not stretch, that would be 0. How much would the
temperature change? No more than usual changes of temperature. So, why
is it that the tire pressure would change?

If only airlines could follow this logic (and the holds are pressurised
anyway!)

Zog The Undeniable said:

David L. Johnson said:

Let's see now. How much would the volume of the tire change?

Since the

Quoted message said:

Quoted message said:

tire casing does not stretch, that would be 0. How much would the
temperature change? No more than usual changes of temperature. So,

why

Quoted message said:

Quoted message said:

is it that the tire pressure would change?

If only airlines could follow this logic (and the holds are

pressurised

Quoted message said:

anyway!)

The tires pressure relative to the suurounding atmosphere has changed
and that is what could cause a blowout. It's a good thing the airline
people have that figured out.

Cam

Cam said:

The tires pressure relative to the suurounding atmosphere has changed
and that is what could cause a blowout. It's a good thing the airline
people have that figured out.

But (even if it were possible; in an unpressurised hold the differential
pressure only goes up 14.7 psi) an exploding bicycle tyre would be
unlikely to threaten the safety of an aircraft. I've had enough tyres
go off in my face to know that they're pretty harmless. Bead unseats
from rim, tube pokes out, tube pops, tyre falls back onto rim. All
about as dangerous as a party balloon, unless you're riding the bike at
the time.

Zog The Undeniable said:

Cam said:

The tires pressure relative to the suurounding atmosphere has

changed

Quoted message said:

Quoted message said:

and that is what could cause a blowout. It's a good thing the

airline

Quoted message said:

Quoted message said:

people have that figured out.

But (even if it were possible; in an unpressurised hold the

differential

Quoted message said:

pressure only goes up 14.7 psi) an exploding bicycle tyre would be
unlikely to threaten the safety of an aircraft. I've had enough

tyres

Quoted message said:

go off in my face to know that they're pretty harmless. Bead unseats

Quoted message said:

from rim, tube pokes out, tube pops, tyre falls back onto rim. All
about as dangerous as a party balloon, unless you're riding the bike

at

Quoted message said:

the time.

While they don't like the sound of anything "harmlessly popping" in the
hold I'm sure they're even less keen to listen to clients pop off on
them when they find that they need new tubes (and/or tires). Much
easier to deflate before shipping and pump up at the destination.

Cam

On Wed, 04 May 2005 12:12:07 -0600, [email hidden]

Quoted message said:

Callistus Valerius said:

I forgot everything I learned in my physics class, so I need your help.

If I'm going from 2000' to 8000' what would be the effect on my tire
pressure? And at 8000' do I keep the tire pressure that I normally do at
120 psi.

Dear CV,

Here's a calculator:

http://www.srh.noaa.gov/elp/wxcalc/pressurealtitude.shtml

For 29.9212 inches of mercury, it will hint at sea level.

For 27.82 inches of mercury, it will suggest 2,000 feet,
2.10 inches less.

For 22.22 inches of mercury, it will predict 8,000 feet,
7.70 inches less.

For 17.57 inches of mercury, it will wheeze at 14,000 feet,
12.35 inches less.

The difference of 5.60 inches of mercury between 2,000 and
8,000 feet corresponds to about 2.46 psi, or 0.1693 bar, or
127.0 mm Hg.

So if you pumped your tire to 120 psi at 2000 feet, it might
feel an exuberant 122 to 123 psi at 8000 feet.

If you pumped your tire to 120 psi at the beach, flew to
Colorado, and climbed the 14,000 foot mountain of your
choice, your tire pressure might increase dangerously to 126
psi.

Weather and heat change the pressure, too, so don't take
such figures too literally.

When James Bond wrote his touching farewell note to his
one-night stand in "The Spy Who Loved Me" about her Vespa's
tyre pressures being too high for her intended travel south
from Lake George, New York (2041 feet), he was showing how
little a naval officer might know about air pressure. She
would have had to lower her tire pressure approximately 1
psi if she descended to sea level.

Of course, Ian Fleming was the sort of writer who was
untroubled by the idea that his hero's letter suggested that
Bond had slipped out that cold morning and checked the
woman's tire pressure before sneaking off.

Carl Fogel

[A messenger delivered the following telegram from Universal
Exports, a wholly owned subsidiary of Transworld
Consortium.]

Carl,

It wasn't my fault--remember, she was the one who wrote the
book, not me.

What the devil was that bimbo thinking, anyway? She fooled
you--the tyre pressure needed to be raised 1 psi, not
lowered, if she was going to ride her silly scooter down
from the thin air of Lake George to near sea level in the
American South.

And you're wrong--it's the mountain near Lake George that's
2041 feet. The lake itself is only 353 feet.

Hmmm . . . maybe she was going to climb some mighty rise in
the South? That would reverse things, and make Bond's fuss
about the scooter's tires more plausible. Maybe she was
going to watch a baseball game at Fulton Stadium in Atlanta,
which is 1050 feet, a full 700 feet higher. The difference
amounts to 0.26 inches of mercury, a full 0.13 psi.

Who knows if her tyres might have burst if Bond hadn't
warned her of the danger?

"Blest isle! with matchless beauty crowned,
And manly hearts to guard the fair."

Rule Britannia!

I. Fleming

P.S. Oops. Fulton Stadium wasn't built until 1965 and the
Braves didn't play there until 1966, and I--er, she wrote
the book in 1962. Never mind. I.F.

Cam said:

Zog The Undeniable said:

David L. Johnson said:

Let's see now. How much would the volume of the tire change? Since the
tire casing does not stretch, that would be 0. How much would the
temperature change? No more than usual changes of temperature. So, why
is it that the tire pressure would change?

If only airlines could follow this logic (and the holds are pressurised
anyway!)

The tires pressure relative to the suurounding atmosphere has changed
and that is what could cause a blowout. It's a good thing the airline
people have that figured out.

If you launch your bicycle into space, the pressure differential will
change by approximately 14.7 psi (air pressure at sea level). For more
typical cruising altitudes, the difference will be closer to 10-12 psi, in
a completely unpressurized hold. In real holds of commercial airplanes
(you can put your pets in these things!) the difference will be
*much* smaller.

If this change is enough to blow your tires off, you're pumping them way
too high to begin with. Your tires and rims are more likely to sustain
damage if they're uninflated.

--
Benjamin Lewis

Although the moon is smaller than the earth, it is farther away.

Cam said:

While they don't like the sound of anything "harmlessly popping" in the
hold I'm sure they're even less keen to listen to clients pop off on
them when they find that they need new tubes (and/or tires). Much
easier to deflate before shipping and pump up at the destination.

But entirely unnecessary. Airliners (incl. the baggage compartment) are
pressurized to an equivalent altitude of at most 8000 feet. Compared to
sea level this represents a pressure drop of about 3 psi, so the effect
on the bike tire is to increase the pressure by no more than that
amount. This is an insignificant increase for a bike tire and therefore
there is no need to make any modification to the normal inflation pressure.

If the effects on tire pressure are so insignificant at higher altitudes,
then how come I remember having to suck some air out of tennis balls with a
syringe when I used to play tennis at high altitudes when I was a kid?

If we didn't do that, the balls were way too bouncy.

Ed Chait

Peter said:

But entirely unnecessary. Airliners (incl. the baggage compartment)
are pressurized to an equivalent altitude of at most 8000 feet.

Quite. An acquaintance travelling with bike from Oz to the BRITONS' England
was once asked to deflate his tyres. He asked whether it was airline policy
to ask the owners of animals travelling in the hold to defalte their cats
and dogs, at which point the airline munchkin decided not to argue any
further...

--
Dave Larrington - <http://www.legslarry.beerdrinkers.co.uk/>
Stop it! You're scarin' the Hippo...

Ed Chait said:

If the effects on tire pressure are so insignificant at higher altitudes,
then how come I remember having to suck some air out of tennis balls with a
syringe when I used to play tennis at high altitudes when I was a kid?

If we didn't do that, the balls were way too bouncy.

Ed Chait

That's a good question. Imagine you are at sea level and the atmospheric
pressure is 100 KPa. You pump your tyre up to 700 KPa (100 PSI).
You ride up a high mountain where the atmospheric pressure drops to say
50 KPa, the tyre pressure relative to atmospheric is now 750 KPa. Your
tyre is now overinflated.
Conversely, if you pump up your tyre to 700 kPa at the top of a mountain
and ride down to sea level your tyre will be under inflated.
I wonder if this is noticeable in the real world by the top cyclists?
Comments anyone?

Marty

Dave Larrington said:

Quoted message said:

But entirely unnecessary. Airliners (incl. the baggage
compartment) are pressurized to an equivalent altitude of at most
8000 feet.

Quoted message said:

Quite. An acquaintance travelling with bike from Oz to the BRITONS'
England was once asked to deflate his tyres. He asked whether it
was airline policy to ask the owners of animals travelling in the
hold to deflate their cats and dogs, at which point the airline
munchkin decided not to argue any further...

When asked whether I let the air out of the tires when I flew with my
bicycle as baggage on commercial air, I have often noted that messing
with the tires on an aircraft is a federal offense. I wouldn't do
that.

Besides, Air France requires tires on shipped bicycles to be inflated
so tires and rims won't get damaged by handling.

[email hidden]

Quoting Ed Chait <[email hidden]>:

Quoted message said:

If the effects on tire pressure are so insignificant at higher altitudes,
then how come I remember having to suck some air out of tennis balls with a
syringe when I used to play tennis at high altitudes when I was a kid?
If we didn't do that, the balls were way too bouncy.

A tennis ball doesn't have several atmospheres of pressure in it to begin
with, so the change is proportionately larger.
--
David Damerell <[email hidden]> flcl?
Today is First Thursday, May.

Quoted message said:

Quoted message said:

Let's see now. How much would the volume of the tire change? Since the
tire casing does not stretch, that would be 0. How much would the
temperature change? No more than usual changes of temperature. So, why
is it that the tire pressure would change?

If only airlines could follow this logic (and the holds are pressurised
anyway!)

I was told (by an airline employee) that the reason for deflating the tires
was so they could make sure you weren't smuggling anything in them. People
have apparently smuggled clandestine substances inside of inner tubes in the
past. With the tire deflated, you can feel if there's anything in the tube.
For what it's worth, I leave my tires inflated partially (maybe 40psi) as an
air-cushion against shipping damage. If some customs guy wants to deflate it
the rest of the way, fine.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA

Mike Jacoubowsky said:

Quoted message said:

Quoted message said:

Let's see now. How much would the volume of the tire change?
Since the tire casing does not stretch, that would be 0. How much
would the temperature change? No more than usual changes of
temperature. So, why is it that the tire pressure would change?

Quoted message said:

Quoted message said:

If only airlines could follow this logic (and the holds are
pressurised anyway!)

Quoted message said:

I was told (by an airline employee) that the reason for deflating
the tires was so they could make sure you weren't smuggling anything
in them. People have apparently smuggled clandestine substances
inside of inner tubes in the past. With the tire deflated, you can
feel if there's anything in the tube. For what it's worth, I leave
my tires inflated partially (maybe 40psi) as an air-cushion against
shipping damage. If some customs guy wants to deflate it the rest of
the way, fine.

I'm amazed at the cover stories people can come up with for stupid
procedures. Smuggling is a function of customs, not baggage handles.
I have taken inflated tires to Europe for many years with no questions
asked either by baggage or customs. The deflate tires story is myth
and lore that gets passed on by baggage mashers who like to give
minorities (bicyclists) a hard time.

[email hidden]