What exactly does cold pressure mean?

I help maintain a Ford E350 used for a vanpool.

The door panel spec says that the rear tires require 80 psi.

The sidewall specs on the rear tires say that the maximum pressure is
80 psi.

So, what does cold pressure mean exactly?

If I check the tires on a cold morning (say 35 degrees) I will end up
putting in a few extra pounds more that I would at 70 degrees. But I
bet the operating temperature of a tire is largely independent of
whether the ambient temperature is 35 or 70.

"Tom Adams" > wrote in message
...
>I help maintain a Ford E350 used for a vanpool.
>
> The door panel spec says that the rear tires require 80 psi.
>
> The sidewall specs on the rear tires say that the maximum pressure is
> 80 psi.
>
> So, what does cold pressure mean exactly?
>
> If I check the tires on a cold morning (say 35 degrees) I will end up
> putting in a few extra pounds more that I would at 70 degrees. But I
> bet the operating temperature of a tire is largely independent of
> whether the ambient temperature is 35 or 70.

The difference in pressure between 35F and 70F is no more than about
3-4 psi.

The "cold" pressure to be that which is measured on a tire which is
has not been heated by road use. It is the ambiental temperature
whether it is 35F or 70F.

On Nov 29, 4:12*pm, "hls" > wrote:
> "Tom Adams" > wrote in message
>
> ...
>
> >I help maintain a Ford E350 used for a vanpool.
>
> > The door panel spec says that the rear tires require 80 psi.
>
> > The sidewall specs on the rear tires say that the maximum pressure is
> > 80 psi.
>
> > So, what does cold pressure mean exactly?
>
> > If I check the tires on a cold morning (say 35 degrees) I will end up
> > putting in a few extra pounds more that I would at 70 degrees. * But I
> > bet the operating temperature of a tire is largely independent of
> > whether the ambient temperature is 35 or 70.
>
> The difference in pressure between 35F and 70F is no more than about
> 3-4 psi.
>
> The "cold" pressure to be that which is measured on a tire which is
> has not been heated by road use. * It is the ambiental temperature
> whether it is 35F or 70F.

Seems like that 3-4 psi would lead to a higher operating temperature
and pressure
when you got up to speed and fully warmed up the tire. Correct?

Are you saying that should be ignored even when you are operating at
the
maximum pressure specified on the tire wall?

"Tom Adams" > wrote in message
...
On Nov 29, 4:12 pm, "hls" > wrote:
> "Tom Adams" > wrote in message
>
> ...
>
> >I help maintain a Ford E350 used for a vanpool.
>
> > The door panel spec says that the rear tires require 80 psi.
>
> > The sidewall specs on the rear tires say that the maximum pressure is
> > 80 psi.
>
> > So, what does cold pressure mean exactly?
>
> > If I check the tires on a cold morning (say 35 degrees) I will end up
> > putting in a few extra pounds more that I would at 70 degrees. But I
> > bet the operating temperature of a tire is largely independent of
> > whether the ambient temperature is 35 or 70.
>
> The difference in pressure between 35F and 70F is no more than about
> 3-4 psi.
>
> The "cold" pressure to be that which is measured on a tire which is
> has not been heated by road use. It is the ambiental temperature
> whether it is 35F or 70F.

Seems like that 3-4 psi would lead to a higher operating temperature
and pressure
when you got up to speed and fully warmed up the tire. Correct?

Are you saying that should be ignored even when you are operating at
the
maximum pressure specified on the tire wall?

I didnt say you should ignore anything.
If the tire is specified at 80 psi max COLD, then that is what it means.
The pressure will rise as the tire heats up, but then that is not a cold
pressure reading.

If you are going to be on the highway, then you can stop and measure
the hot pressure when you fuel. You can reduce them to 80PSI if
you tire says 80psi maximum pressure.

Tom Adams > wrote in news:2438871f-28ff-443d-ab57-
:

> I help maintain a Ford E350 used for a vanpool.
>
> The door panel spec says that the rear tires require 80 psi.
>
> The sidewall specs on the rear tires say that the maximum pressure is
> 80 psi.
>
> So, what does cold pressure mean exactly?



Ambient temperature, or estimated middle of an ambient range.

I'm wondering if those tires are correct for the vehicle. Seems to me that
you ought to be running tires with a max pressure of more like 100 psi, to
allow for seasonal changes in ambient.

Are these truck tires (LT instead of P)?


>
> If I check the tires on a cold morning (say 35 degrees) I will end up
> putting in a few extra pounds more that I would at 70 degrees.



That's correct. You're supposed to adjust the cold temperatures regularly,
as ambient changes with the seasons, adding or bleeding-off as needed.

Roughly, every 10F in ambient temperature changes tire pressures by 1 psi,
up and down. Since ambient won't ever be exactly the same all the time,
you guess the average ambient temperature range for your time of year in
your area, then set cold-pressure tire pressures for the middle of that
range.

Suppose ambient tends to be between 20F and 40F. You'd set the pressures to
be 80 psi at 30F. At 20F, you're 1 psi underinflated, and at 40F, you're 1
psi overinflated.

If you happened to check the pressures when the ambient was at its high of
40, you would need to make sure the tire read 81 psi, so that it would be
80 when ambient dropped to 30, or 79 when it dropped to 20.



> But I
> bet the operating temperature of a tire is largely independent of
> whether the ambient temperature is 35 or 70.


Probably is, but it's still starting from that cold-pressure setting. And
an underinflated tire is going to generate a lot more heat at 90F than it
would at 20F, even with the same number of psi underinflation.



--
Tegger

"Tegger" > wrote in message
...
> Tom Adams > wrote in news:2438871f-28ff-443d-ab57-
> :
>
>> I help maintain a Ford E350 used for a vanpool.
>>
>> The door panel spec says that the rear tires require 80 psi.
>>
>> The sidewall specs on the rear tires say that the maximum pressure is
>> 80 psi.
>>
>> So, what does cold pressure mean exactly?
>
>
>
> Ambient temperature, or estimated middle of an ambient range.
>
> I'm wondering if those tires are correct for the vehicle. Seems to me that
> you ought to be running tires with a max pressure of more like 100 psi, to
> allow for seasonal changes in ambient.
>
> Are these truck tires (LT instead of P)?
>
>
>>
>> If I check the tires on a cold morning (say 35 degrees) I will end up
>> putting in a few extra pounds more that I would at 70 degrees.
>
>
>
> That's correct. You're supposed to adjust the cold temperatures regularly,
> as ambient changes with the seasons, adding or bleeding-off as needed.
>
> Roughly, every 10F in ambient temperature changes tire pressures by 1 psi,
> up and down. Since ambient won't ever be exactly the same all the time,
> you guess the average ambient temperature range for your time of year in
> your area, then set cold-pressure tire pressures for the middle of that
> range.
>
> Suppose ambient tends to be between 20F and 40F. You'd set the pressures
> to
> be 80 psi at 30F. At 20F, you're 1 psi underinflated, and at 40F, you're 1
> psi overinflated.
>
> If you happened to check the pressures when the ambient was at its high of
> 40, you would need to make sure the tire read 81 psi, so that it would be
> 80 when ambient dropped to 30, or 79 when it dropped to 20.
>
>
>
>> But I
>> bet the operating temperature of a tire is largely independent of
>> whether the ambient temperature is 35 or 70.
>
>
> Probably is, but it's still starting from that cold-pressure setting. And
> an underinflated tire is going to generate a lot more heat at 90F than it
> would at 20F, even with the same number of psi underinflation.
>

That is essentially what I told him.. Maybe he is a little slow to get up
to temperature.

Tom Adams wrote:
> I help maintain a Ford E350 used for a vanpool.
>
> The door panel spec says that the rear tires require 80 psi.

That is great IF the tires on the van are the same ones that came from
the factory. Otherwise it's basically crap.

>
> The sidewall specs on the rear tires say that the maximum pressure is
> 80 psi.

And what does the chart for that tire say the operating pressure should
be given the load you carry? If your not driving around at the GVW all
day then you probably also don't need the maximum pressure.

>
> So, what does cold pressure mean exactly?

Cold pressure means NO drive time on the tire. What it reads after the
van has sat long enough for the tires to reach ambient air temperature.
So you come out in the AM, Start the engine so it warms up and check the
tire air pressure. (Don't forget to check the spare)

>
> If I check the tires on a cold morning (say 35 degrees) I will end up
> putting in a few extra pounds more that I would at 70 degrees. But I
> bet the operating temperature of a tire is largely independent of
> whether the ambient temperature is 35 or 70.

That is why you check the pressure at whatever the "normal" temp is for
the given season. So if you normally see 35-40 degrees during the winter
check it at 37 degrees. The small amount of change won't make much
difference.

Same in the spring and summer. If the "normal" temps are around 80
degrees then check it at that temp.

--
Steve W.

On 11/29/2010 06:57 PM, Steve W. wrote:
> Tom Adams wrote:
>> I help maintain a Ford E350 used for a vanpool.
>>
>> The door panel spec says that the rear tires require 80 psi.
>
> That is great IF the tires on the van are the same ones that came from
> the factory. Otherwise it's basically crap.

well, it might be crap for the tire, but it's not for the van's
stability. you certainly don't want the pressure to be less than that
if it's loaded - and vanpools usually are.


>
>>
>> The sidewall specs on the rear tires say that the maximum pressure is
>> 80 psi.
>
> And what does the chart for that tire say the operating pressure should
> be given the load you carry? If your not driving around at the GVW all
> day then you probably also don't need the maximum pressure.
>
>>
>> So, what does cold pressure mean exactly?
>
> Cold pressure means NO drive time on the tire. What it reads after the
> van has sat long enough for the tires to reach ambient air temperature.
> So you come out in the AM, Start the engine so it warms up and check the
> tire air pressure. (Don't forget to check the spare)
>
>>
>> If I check the tires on a cold morning (say 35 degrees) I will end up
>> putting in a few extra pounds more that I would at 70 degrees. But I
>> bet the operating temperature of a tire is largely independent of
>> whether the ambient temperature is 35 or 70.
>
> That is why you check the pressure at whatever the "normal" temp is for
> the given season. So if you normally see 35-40 degrees during the winter
> check it at 37 degrees. The small amount of change won't make much
> difference.
>
> Same in the spring and summer. If the "normal" temps are around 80
> degrees then check it at that temp.
>


--
nomina rutrum rutrum

jim beam wrote:
> On 11/29/2010 06:57 PM, Steve W. wrote:
>> Tom Adams wrote:
>>> I help maintain a Ford E350 used for a vanpool.
>>>
>>> The door panel spec says that the rear tires require 80 psi.
>>
>> That is great IF the tires on the van are the same ones that came from
>> the factory. Otherwise it's basically crap.
>
> well, it might be crap for the tire, but it's not for the van's
> stability. you certainly don't want the pressure to be less than that
> if it's loaded - and vanpools usually are.
>
>

No it is crap all around. That number is based on the OEM tire and GVW.
It is only valid for the same tire.

Say I buy the same van, Say it comes OEM with a 245 75 16. So I decide
to replace the tires with something like a 265 35 20 (or whatever fits
in the rubber band sizes).
Does the tire pressure apply? NOPE.

Noww if the tire is the same ply rating, same type of construction and
same size as OEM then it could be used as a guide IF those tires are
rated the same way.


--
Steve W.
(\___/)
(='.'=)
(")_(")

On 11/29/2010 08:23 PM, Steve W. wrote:
> jim beam wrote:
>> On 11/29/2010 06:57 PM, Steve W. wrote:
>>> Tom Adams wrote:
>>>> I help maintain a Ford E350 used for a vanpool.
>>>>
>>>> The door panel spec says that the rear tires require 80 psi.
>>>
>>> That is great IF the tires on the van are the same ones that came from
>>> the factory. Otherwise it's basically crap.
>>
>> well, it might be crap for the tire, but it's not for the van's
>> stability. you certainly don't want the pressure to be less than that
>> if it's loaded - and vanpools usually are.
>>
>>
>
> No it is crap all around. That number is based on the OEM tire and GVW.
> It is only valid for the same tire.
>
> Say I buy the same van, Say it comes OEM with a 245 75 16. So I decide
> to replace the tires with something like a 265 35 20 (or whatever fits
> in the rubber band sizes).

don't be ridiculous - nobody's going to be monkeying about with
non-stock wheels on an f350 carpool.


> Does the tire pressure apply? NOPE.

same pressures apply - see above.


>
> Noww if the tire is the same ply rating, same type of construction and
> same size as OEM then it could be used as a guide IF those tires are
> rated the same way.
>
>


--
nomina rutrum rutrum