Tire inflation

"---MIKE---" <twinmountain@webtv.net> wrote in message
news:3633-421E6713-25@storefull-3254.bay.webtv.net...[color=blue]
> Everyone says that tires should be inflated to the recommended pressure
> when "cold". Does this mean cold at a reasonable outside temperature?
> How about when the car has been sitting all night at ten below zero
> Fahrenheit? Wouldn't this cause the pressure to read lower than normal?
>
> ---MIKE---
>[/color]
Cold means approximately 68 F or 20 C.

I always thought of "cold" as not driven, like overnight.I never heard it
associated with an actual ambient temperature. Is that generally accepted?
jor
"Mark A" <nobody@nowhere.com> wrote in message
news:S_6dnbAIs6Bh7oPfRVn-3g@comcast.com...[color=blue]
> "---MIKE---" <twinmountain@webtv.net> wrote in message
> news:3633-421E6713-25@storefull-3254.bay.webtv.net...[color=green]
>> Everyone says that tires should be inflated to the recommended pressure
>> when "cold". Does this mean cold at a reasonable outside temperature?
>> How about when the car has been sitting all night at ten below zero
>> Fahrenheit? Wouldn't this cause the pressure to read lower than normal?
>>
>> ---MIKE---
>>[/color]
> Cold means approximately 68 F or 20 C.
>
>[/color]

"jor" <jor@jor.com> wrote in message
news:KPudnWTV0d4Q6IPfRVn-jA@giganews.com...[color=blue]
>I always thought of "cold" as not driven, like overnight.I never heard it
>associated with an actual ambient temperature. Is that generally accepted?
>[/color]

That's what I would assume. If I filled up my tires at 20ºC and drove them
in -30ºC weather, I think there would be issues.. There are calculations for
this.....

Regards,

Robin

[email]twinmountain@webtv.net[/email] (---MIKE---) wrote in news:3633-421E6713-
[email]25@storefull-3254.bay.webtv.net[/email]:
[color=blue]
> Everyone says that tires should be inflated to the recommended pressure
> when "cold". Does this mean cold at a reasonable outside temperature?
> How about when the car has been sitting all night at ten below zero
> Fahrenheit? Wouldn't this cause the pressure to read lower than normal?[/color]



"Cold" means "not driven for the last 4 hours or so."

You lose or gain roughly one psi for every ten degrees Fahrenheit.

Fill to 32psi at 32 degrees, and that drops to 28 at -10F. Still safe to
drive on.

--
TeGGeR®

"Robin S." <lasernerd@hotmail.com> wrote:
[color=blue]
>
>"jor" <jor@jor.com> wrote in message
>news:KPudnWTV0d4Q6IPfRVn-jA@giganews.com...[color=green]
>>I always thought of "cold" as not driven, like overnight.I never heard it
>>associated with an actual ambient temperature. Is that generally accepted?
>>[/color]
>
>That's what I would assume. If I filled up my tires at 20ºC and drove them
>in -30ºC weather, I think there would be issues.. There are calculations for
>this.....
>
>Regards,
>
>Robin
>[/color]
I don't agree with you, I've been driving cars etc for more years
than I care to count and wrongly or rightly I put in 32 PSI
whenever I notice a tire looking low...that's it...haven't had
any problem yet...
--

-Gord.
(use gordon in email)

"jor" <jor@jor.com> wrote in message
news:KPudnWTV0d4Q6IPfRVn-jA@giganews.com...[color=blue]
> I always thought of "cold" as not driven, like overnight.I never heard it
> associated with an actual ambient temperature. Is that generally accepted?
> jor[/color]

Cold tire pressure does mean "not driven" because the tire heats up quickly
when driven due to the rapid flexing of the belts under the tread as the
vehicle moves. This causes the air inside the tire to heat up and expand.

However, ambient temperature also affects the calculation as to how much the
air inside a tire heats up and how much it expands.

Nominal air temperature is usually considered to be 20 C or 68 F. This is
basic chemistry 101.

---MIKE--- wrote:
[color=blue]
> Everyone says that tires should be inflated to the recommended pressure
> when "cold". Does this mean cold at a reasonable outside temperature?
> How about when the car has been sitting all night at ten below zero
> Fahrenheit? Wouldn't this cause the pressure to read lower than normal?
>
>
> ---MIKE---
>
>[/color]

For the final answer:
[url]http://www.tirerack.com/tires/tiretech/general/pressure.jsp[/url]

Read this article and see if you have ANY unanswered questions. They
even tested the effects on "cold" tire pressure from parking the car
with one side exposed to the sun.

On Thu, 24 Feb 2005 21:45:51 -0700, "Mark A" <nobody@nowhere.com>
wrote:
[color=blue]
>"jor" <jor@jor.com> wrote in message
>news:KPudnWTV0d4Q6IPfRVn-jA@giganews.com...[color=green]
>> I always thought of "cold" as not driven, like overnight.I never heard it
>> associated with an actual ambient temperature. Is that generally accepted?
>> jor[/color]
>
>Cold tire pressure does mean "not driven" because the tire heats up quickly
>when driven due to the rapid flexing of the belts under the tread as the
>vehicle moves. This causes the air inside the tire to heat up and expand.
>
>However, ambient temperature also affects the calculation as to how much the
>air inside a tire heats up and how much it expands.
>
>Nominal air temperature is usually considered to be 20 C or 68 F. This is
>basic chemistry 101.
>[/color]
I agree with you, Mark, that "cold" means the ambient temperature. I
would also add Jor's definition that the tire itself be not driven.
Even at 68F, the tire pressure would not be accurate if the tire has
been driven due to the heat build-up as you mentioned above.

> For the final answer:[color=blue]
> [url]http://www.tirerack.com/tires/tiretech/general/pressure.jsp[/url]
>
> Read this article and see if you have ANY unanswered questions. They
> even tested the effects on "cold" tire pressure from parking the car
> with one side exposed to the sun.
>[/color]
They forgot to include the affects of altitude changes. For most purposes,
cold tire pressure is measured at 20C or 68F at sea level.

"Viperkiller" <nothing@nothing.net> wrote in message
news:o0gt11lf9pknr5mbbh71rjcub8idkj09rj@4ax.com...[color=blue]
> On Thu, 24 Feb 2005 21:45:51 -0700, "Mark A" <nobody@nowhere.com>
> wrote:
>[color=green]
> >"jor" <jor@jor.com> wrote in message
> >news:KPudnWTV0d4Q6IPfRVn-jA@giganews.com...[color=darkred]
> >> I always thought of "cold" as not driven, like overnight.I never heard[/color][/color][/color]
it[color=blue][color=green][color=darkred]
> >> associated with an actual ambient temperature. Is that generally[/color][/color][/color]
accepted?[color=blue][color=green][color=darkred]
> >> jor[/color]
> >
> >Cold tire pressure does mean "not driven" because the tire heats up[/color][/color]
quickly[color=blue][color=green]
> >when driven due to the rapid flexing of the belts under the tread as the
> >vehicle moves. This causes the air inside the tire to heat up and expand.
> >
> >However, ambient temperature also affects the calculation as to how much[/color][/color]
the[color=blue][color=green]
> >air inside a tire heats up and how much it expands.
> >
> >Nominal air temperature is usually considered to be 20 C or 68 F. This is
> >basic chemistry 101.
> >[/color]
> I agree with you, Mark, that "cold" means the ambient temperature. I
> would also add Jor's definition that the tire itself be not driven.
> Even at 68F, the tire pressure would not be accurate if the tire has
> been driven due to the heat build-up as you mentioned above.[/color]

Yes I agree. I thought that I made that clear. I said ambient temperature
ALSO affects ... (right after I described how driving the car heats up the
air inside the tire).

The pressure will be different than manufacturer recommended for any of the
following reasons:

Car is driven, which heats up tires
Ambient temp is not 68 F
Altitude is not sea level

However, on a very cold day, if you drive it a short time, the temperature
of the gas (air) inside the tire could be 68 F.

On Thu, 24 Feb 2005 18:45:23 -0500, [email]twinmountain@webtv.net[/email]
(---MIKE---) wrote:
[color=blue]
>Everyone says that tires should be inflated to the recommended pressure
>when "cold". Does this mean cold at a reasonable outside temperature?
>How about when the car has been sitting all night at ten below zero
>Fahrenheit? Wouldn't this cause the pressure to read lower than normal?
>
>
> ---MIKE---[/color]


IMHO: Cold meaning you haven't driven in a while(few hours). Since
car tired flex and warm up while driving.

hth,


tom @ [url]www.CarFleaMarket.com[/url]

On 25 Feb 2005 01:58:34 GMT, "TeGGer®" <tegger@istop.c0m> wrote:

snip[color=blue]
>
>"Cold" means "not driven for the last 4 hours or so."
>
>You lose or gain roughly one psi for every ten degrees Fahrenheit.
>
>Fill to 32psi at 32 degrees, and that drops to 28 at -10F. Still safe to
>drive on.[/color]

Fully agree.

For those interested in the calculation, the so-called gas law using
absolute temperatures and pressures applies:

PV = nR T

where P = absolute pressure (gauge pressure + ambient atmospheric
pressure), V = volume of container, n = quantity of gas, R = the gas
"constant" and T = absolute temperature (degrees F + 460).

Since nR remains unchanged as temp and pressure change, we can write:

P1V1/T1 = P2V2/T2

Assuming tire interior volume does not change, that is V1 = V2, this
becomes:

P1/T1 = P2/T2

Thus:

P2 = P1T2/T1

For TeGGer's 32 F and 32 psig (gauge) and assuming ambient atmospheric
(barometric) pressure = 14.7 psia (absolute) we get:

T1 = 32 + 460 = 492 degrees Rankine
P1 = 32 + 14.7 = 46.7 psia
T2 = -10 + 460 = 450 degrees Rankine

P2 = (46.7 * 450)/492 = 42.7 psia

Or in gauge pressure:

P2 = (42.7 - 14.7) = 28 psig

TeGGer's rule is sufficiently accurate, easy to remember, and a lot
easier to use.

Thanks, TeGGer.

Rod

Rod wrote:[color=blue]
> On 25 Feb 2005 01:58:34 GMT, "TeGGer®" <tegger@istop.c0m> wrote:
>
> snip[color=green]
>>
>> "Cold" means "not driven for the last 4 hours or so."
>>
>> You lose or gain roughly one psi for every ten degrees Fahrenheit.
>>
>> Fill to 32psi at 32 degrees, and that drops to 28 at -10F. Still
>> safe to drive on.[/color]
>
> Fully agree.[/color]

snipped the arcane formulae
[color=blue]
> TeGGer's rule is sufficiently accurate, easy to remember, and a lot
> easier to use.
>
> Thanks, TeGGer.
>
> Rod[/color]

And remember ... if you spell tire with a 'y' that you need to rotate the
air in your tyres annually.
--

- Philip ;^)

"anon" <none@whatever.com> wrote in message
news:cvmupe$s9h$1@hercules.btinternet.com...[color=blue]
>
> tyre pressures are a compromise between safety and performance anyway.[/color]
less[color=blue]
> pressure gives more surface contact, therefore more grip, (to a point[/color]
where[color=blue]
> too less pressure will compromise road control etc)
> more pressure will increase fuel economy but compromise surface area[/color]
contact[color=blue]
> and therefore grip.
> top fuel dragster tyres run at low pressures to increase grip, you will[/color]
see[color=blue]
> the tyre twisting on the rim under acceleration but the grip to the road
> surface remains good.
> for maximum fuel economy though very high tyre pressure will be required[/color]
to[color=blue]
> reduce friction caused by surface area contact.
> the other issue in the equation is of course tyre wear, and depending on
> tyre size, width, and design too much pressure will cause the outer edges[/color]
to[color=blue]
> wear prematurely, and the opposite if under inflated.
> but you all knew that anyway right.
>[/color]
You forgot to mention several important safety factors.

When a tire has less air, it often (up to a point) reduces the chances of a
rollover. This is more important to SUV's and other vehicles with a high
center of gravity.

But when a tire has less pressure, the chances of a tire failure are greater
(up to a point).

If you think these points are trivial, just remember the Firestone / Ford
Explorer Fiasco a few years ago. Peoples lives have been lost regarding this
issue, and billions of dollars have been lost (and many jobs lost at
Firestone). The law suits are far from over.

On Fri, 25 Feb 2005 08:03:02 -0600, Rod <nobody@home.com> wrote:
[color=blue]
>On 25 Feb 2005 01:58:34 GMT, "TeGGer®" <tegger@istop.c0m> wrote:
>
>snip[color=green]
>>
>>"Cold" means "not driven for the last 4 hours or so."
>>
>>You lose or gain roughly one psi for every ten degrees Fahrenheit.
>>
>>Fill to 32psi at 32 degrees, and that drops to 28 at -10F. Still safe to
>>drive on.[/color]
>
>Fully agree.
>
>For those interested in the calculation, the so-called gas law using
>absolute temperatures and pressures applies:
>
>PV = nR T
>
>where P = absolute pressure (gauge pressure + ambient atmospheric
>pressure), V = volume of container, n = quantity of gas, R = the gas
>"constant" and T = absolute temperature (degrees F + 460).
>
>Since nR remains unchanged as temp and pressure change, we can write:
>
>P1V1/T1 = P2V2/T2
>
>Assuming tire interior volume does not change, that is V1 = V2, this
>becomes:
>
>P1/T1 = P2/T2
>
>Thus:
>
>P2 = P1T2/T1
>
>For TeGGer's 32 F and 32 psig (gauge) and assuming ambient atmospheric
>(barometric) pressure = 14.7 psia (absolute) we get:
>
>T1 = 32 + 460 = 492 degrees Rankine
>P1 = 32 + 14.7 = 46.7 psia
>T2 = -10 + 460 = 450 degrees Rankine
>
> P2 = (46.7 * 450)/492 = 42.7 psia
>
>Or in gauge pressure:
>
>P2 = (42.7 - 14.7) = 28 psig
>
>TeGGer's rule is sufficiently accurate, easy to remember, and a lot
>easier to use.
>
>Thanks, TeGGer.
>
>Rod[/color]


Before you get all hopped up on your brain power, you need to add the
disclaimer, these are only for ideal gases, and need to be compensated
for nonideal gases. Factor in that the container's (this case a tire)
volume isn't constant, than you have real problems if you don't
compensate for those changes. That's why your math might look pretty,
but aren't accurate to really oriented people like the rest of us.
:-P

BTW, rankine is good for steam systems, plant efficiencies, but
personally I've liked the metric system and kelvin for gas laws. Much
cleaner and more standard to people who usually work with compressed
gases.

later,

tom