Automotive Forums .com - the leading automotive community online! Automotive Forums .com - the leading automotive community online!
Automotive Forums .com - the leading automotive community online! 
-
Latest | 0 Rplys
Go Back   Automotive Forums .com Car Chat > Engineering/Technical
Engineering/Technical Ask technical questions about cars. Do you know how a car engine works?
Reply Show Printable Version Show Printable Version | Email this Page Email this Page | Subscription Subscribe to this Thread
 
Thread Tools
Old 09-12-2021, 10:26 AM   #16
Blue Bowtie
Registered Offender
 
Blue Bowtie's Avatar
 
Join Date: Mar 2006
Location: Rural
Posts: 6,513
Thanks: 6
Thanked 341 Times in 336 Posts
Re: Is This Tire Pressure Chart Legit?

That chart is, at best, very confusing, and at worst, incorrect. It also apparently ignores the fact that 70°F is not the highest temperature ever achieved on the surface of Earth. I guess we just run them overinflated and ignore that, as per the table.

Charles' Law and Boyles Law are physical LAWS. They are not theroies, conjectures, musings, nor axioms.

The Standard Temperature and Pressure (STP) for atmospheric air measurement is to have everything equalized to 68°F (20°C), 36% RH, and 14.696 PSIA (1.013 BAR). The linked table seems to make an attempt at that, but fails miserably. As a general guide, it is better than nothing, but also close to nothing of value.

The formula to correct for STP is simple. I can accurately predict the pressure of a given mass of air contained within a fixed volume (tire) at any practical temperaures from near absolute zero to the point of auto-ignition of the tire rubber compounds.

A substantial wildcard is the relative humidity of the air in the tire. That changes with temperature - Thus the term "relative" humidity. This is one reason for the popularity of dry nitrogen being used as tire fill, in addition to some other minor benefits.

Overall, the table is an attempt of someone to partially educate the populus about pressure variations, but doesn't quite meet the need.
__________________
Permanent seat assignment on the Group W bench...
Automotive Forums Survival Guide
Blue Bowtie is offline   Reply With Quote
Old 09-12-2021, 11:59 AM   #17
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by Blue Bowtie View Post
That chart is, at best, very confusing, and at worst, incorrect. It also apparently ignores the fact that 70°F is not the highest temperature ever achieved on the surface of Earth. I guess we just run them overinflated and ignore that, as per the table.

Charles' Law and Boyles Law are physical LAWS. They are not theroies, conjectures, musings, nor axioms.

The Standard Temperature and Pressure (STP) for atmospheric air measurement is to have everything equalized to 68°F (20°C), 36% RH, and 14.696 PSIA (1.013 BAR). The linked table seems to make an attempt at that, but fails miserably. As a general guide, it is better than nothing, but also close to nothing of value.

The formula to correct for STP is simple. I can accurately predict the pressure of a given mass of air contained within a fixed volume (tire) at any practical temperaures from near absolute zero to the point of auto-ignition of the tire rubber compounds.

A substantial wildcard is the relative humidity of the air in the tire. That changes with temperature - Thus the term "relative" humidity. This is one reason for the popularity of dry nitrogen being used as tire fill, in addition to some other minor benefits.

Overall, the table is an attempt of someone to partially educate the populus about pressure variations, but doesn't quite meet the need.
Could the chart - and the website it comes from - be suggesting that at an ambient temp. of F70° or warmer, it's acceptable to match the recommended cold tire pressure on the door frame decal? That is, assuming the temperature first thing at dawn is F70°.

Below that temperature, say, if the ambient dawn temperature is 60°, then inflate the tires to door frame sticker plus one psi. 50° outside? add two psi to door frame sticker cold pressure, until you get down to F20°

So to simplify, if you live where the lowest summer temperatures in your part of the world are between 65-75°F, it's ok to inflate to the door sticker value exactly.
IE: Me - 32psi cold.


If your winter lows in your part of the world average 30°F early in the day, then add 4psi to the door placard values, to compensate for differences in air density at the colder temperatures.
IE: Me - 36psi(32 + 4) cold.

That's my understanding, on the face of it.

My aforementioned retired engineer customer at work feels that 36psi cold, in summer or winter, is a bad idea for a car which Honda specifies 32psi cold, "seasonal air density differences be damned!" lol

Last edited by RidingOnRailz; 09-14-2021 at 10:29 AM.
RidingOnRailz is online now   Reply With Quote
Old 12-24-2021, 02:39 PM   #18
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Re: Is This Tire Pressure Chart Legit?

REDUX:

Here is the same chart, revised for clarity of meaning. The original, the subject of this thread, was the property of the RMA(Rubber Manufacturers Assn).
Attached Images
File Type: jpg IMG_2435.JPG (199.9 KB, 13 views)
RidingOnRailz is online now   Reply With Quote
Old 12-25-2021, 06:20 AM   #19
CapriRacer
AF Enthusiast
 
Join Date: May 2003
Location: Somewhere in the US
Posts: 504
Thanks: 0
Thanked 34 Times in 32 Posts
Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
REDUX:

Here is the same chart, revised for clarity of meaning. The original, the subject of this thread, was the property of the RMA(Rubber Manufacturers Assn).
I'm going to challenge you on the origin of this document. I don't think the RMA (Now the US Tire Manufacturers Association - USTMA) would publish such a document. It implies that the inflation pressure listed on the vehicle tire placard is only valid at 70°F - which is wrong.

Can you provide a link?

(Just a side note: I tried to google for it and couldn't find it.)
__________________
CapriRacer

Visit my website: http://www.barrystiretech.com/
CapriRacer is offline   Reply With Quote
Old 12-25-2021, 07:18 AM   #20
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
I'm going to challenge you on the origin of this document.
I don't think the RMA (Now the US Tire Manufacturers Association -
USTMA) would publish such a document. It implies that the inflation
pressure listed on the vehicle tire placard is only valid at 70°F -
which is wrong.

Can you provide a link?

(Just a side note: I tried to google for it and couldn't find it.)
Good morning and Merry Christmas, et al.

Here is the link to the Tire Inflation sub-page of AA1 Car repair.

https://www.aa1car.com/library/tirepres.htm

Note that the blue tire inflation table in the above link is now the revised edition(which I shared in post #18).

The webmaster of that site himself stated, in our e-mail exchange, that the original chart(in my first post) was from RMA/TMA. He might have had to recreate the table himself owing possibly to legal reasons for simply not being able to include the original there.

For me, the revised table makes much more sense, and the original is suggesting something entirely different.

As for the temperature, it is common practice in the scientific and engineering communities to use a temperature of C°20(F°68), and a barometric pressure of 29.94"(or something in the ballpark of mean sea level) as baseline atmospheric conditions for experiments and testing.

So the producers of the original table probably just rounded up - to F°70 - for underscoring the effect on inflation pressure every positive or negative ten degrees F.
RidingOnRailz is online now   Reply With Quote
Old 12-26-2021, 07:26 AM   #21
CapriRacer
AF Enthusiast
 
Join Date: May 2003
Location: Somewhere in the US
Posts: 504
Thanks: 0
Thanked 34 Times in 32 Posts
Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
....... The webmaster of that site himself stated, in our e-mail exchange, that the original chart(in my first post) was from RMA/TMA. He might have had to recreate the table himself owing possibly to legal reasons for simply not being able to include the original there. .......
When I said link, I meant to an RMA or USTMA webpage. What you just said is that the webmaster SAID it came from the RMA - and I find NO evidence to support that - which why I made the challenge.

Quote:
Originally Posted by RidingOnRailz View Post
.......As for the temperature, it is common practice in the scientific and engineering communities to use a temperature of C°20(F°68), and a barometric pressure of 29.94"(or something in the ballpark of mean sea level) as baseline atmospheric conditions for experiments and testing.....
Yes, yes, but that is NOT how tire pressure works. Tires are supposed to be inflated at ambient conditions. STP just doesn't apply.
__________________
CapriRacer

Visit my website: http://www.barrystiretech.com/
CapriRacer is offline   Reply With Quote
Old 12-26-2021, 10:14 AM   #22
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
When I said link, I meant to an RMA or USTMA webpage.
What you just said is that the webmaster SAID it came from the
RMA - and I find NO evidence to support that - which why I made
the challenge.


Yes, yes, but that is NOT how tire pressure works. Tires are supposed
to be inflated at ambient conditions. STP just doesn't apply.

1) Larry's(from AA1Car) words, verbatim:

"Thanks for the feedback. I agree that chart is
confusing. I am going to redo it to make it less
confusing. The chart was originally provided by
the Rubber Mfrs Assn. and lists pressures up to 90
PSI which is for heavy-duty over the road trucks.


What the chart is trying to indicate is how much
additional tire pressure it takes to provide the
same weight carrying capacity as the temperature
drops.
"

2) How tire pressure works:
You are saying, if I read you correctly, that all I have to do, monthly or otherwise, is adjust my tires to the correct/recommended cold pressures.

IE: If 33psi cold is recommended, just maintain that 33psi, from August high temperatures to February lows, and that's enough.

Do I have that correct?
RidingOnRailz is online now   Reply With Quote
Old 12-27-2021, 07:26 AM   #23
CapriRacer
AF Enthusiast
 
Join Date: May 2003
Location: Somewhere in the US
Posts: 504
Thanks: 0
Thanked 34 Times in 32 Posts
Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
1) Larry's(from AA1Car) words, verbatim:

"Thanks for the feedback. I agree that chart is
confusing. I am going to redo it to make it less
confusing. The chart was originally provided by
the Rubber Mfrs Assn. and lists pressures up to 90
PSI which is for heavy-duty over the road trucks.


What the chart is trying to indicate is how much
additional tire pressure it takes to provide the
same weight carrying capacity as the temperature
drops.
" ......
Again he SAID it came from the RMA, but I find no supporting evidence - you know, like the chart he referred to at the RMA website! I can not find ANYTHING that even resembles that chart - let alone one from the RMA. So I don't believe he got it from the RMA. He may have gotten it from somewhere else and misremembers.

Quote:
Originally Posted by RidingOnRailz View Post
.......2) How tire pressure works:
You are saying, if I read you correctly, that all I have to do, monthly or otherwise, is adjust my tires to the correct/recommended cold pressures.

IE: If 33psi cold is recommended, just maintain that 33psi, from August high temperatures to February lows, and that's enough.

Do I have that correct?
Allow me to state this in a different way:

Tire pressures are supposed to be set at ambient conditions when the tire is at those conditions. We refer to that as "Cold".

So if it is 50°F outside and your car is going to be driven in those conditions, the tire pressure should be set such that they are 33 psi (or whatever is specified) when the tire is at 50°F. Now you could let the car sit outside for an hour and a half so that it reaches ambient conditions or calculate what is needed at the temperature the car is at (like a 70°F garage).

The problem in winter is that usually tire pressures are set in a warm environment (like a garage or an autumn-like day), but the tire later is going to operate in much colder conditions. The procedure I recommend is to set the pressures such that they are what you want them to be when the temperature drops - which means that you have to estimate what the worst condition is going to be.

As an example, let's assume you want 33 psi when the temperature is going as low as -10°F. You are setting the pressures in your garage and it is 50°F inside the garage. So you are targeting for a temperature drop of 60°F = 6 psi, so you set the pressures at 39 psi.
__________________
CapriRacer

Visit my website: http://www.barrystiretech.com/
CapriRacer is offline   Reply With Quote
Old 12-27-2021, 07:56 AM   #24
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
Again he SAID it came from the RMA, but I find no supporting evidence - you know, like the chart he referred to at the RMA website! I can not find ANYTHING that even resembles that chart - let alone one from the RMA. So I don't believe he got it from the RMA. He may have gotten it from somewhere else and misremembers.



Allow me to state this in a different way:

Tire pressures are supposed to be set at ambient conditions when the tire is at those conditions. We refer to that as "Cold".

So if it is 50°F outside and your car is going to be driven in those conditions, the tire pressure should be set such that they are 33 psi (or whatever is specified) when the tire is at 50°F. Now you could let the car sit outside for an hour and a half so that it reaches ambient conditions or calculate what is needed at the temperature the car is at (like a 70°F garage).

The problem in winter is that usually tire pressures are set in a warm environment (like a
garage or an autumn-like day), but the tire later is
going to operate in much colder conditions. The procedure I recommend
is to set the pressures such that they are what you want them to be
when the temperature drops - which means that you have to estimate
what the worst condition is going to be.

As an example, let's assume you want 33 psi when the temperature
is going as low as -10°F. You are setting the pressures in your garage
and it is 50°F inside the garage. So you are targeting for a
temperature drop of 60°F = 6 psi, so you set the pressures
at 39 psi.

Understood completely.

Now, please understand this: Where I live, our cars are in "ambient conditions" year-round, as in, parked out on a driveway. Our garage is detached and unheated, used for storage. So it's a lot more straightforward for me to adjust cold tire pressures. Tire gauges are kept inside, in a kitchen "miscellaneous" drawer, if that means anything.

During the half hour before sunrise, coolest time of day, before our cars have been driven anywhere, I just go out, check, and adjust.

During the cooling months around here(October, November, December, etc), I overinflate the tires the evening before when it's relatively warm outside, maybe 5psi over door pillar placard. Next morning, just before sunrise, bleed them down to specification. No lingering outside forever waiting for the 12V pump to fill them up.

During the warming up months(April, May, June, etc), it's just a simple matter of bleeding off pressure that has built up from the month before.

Am I doing it right?


And in any case, the producer of the table that is the topic of this thread probably tried to explain what we both understand, in a most round-about and confusing way.
RidingOnRailz is online now   Reply With Quote
Old 12-28-2021, 06:32 AM   #25
CapriRacer
AF Enthusiast
 
Join Date: May 2003
Location: Somewhere in the US
Posts: 504
Thanks: 0
Thanked 34 Times in 32 Posts
Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
...... Am I doing it right? .......
Yes

If you want a better understanding of why all inflation pressures are set at ambient conditions, consider that the stiffness of a material does not change with temperature (within the range of ambient temperatures humans inhabit) and that a tire's load carrying capacity is therefore not dependent on temperature, but it is dependent on inflation pressure.
__________________
CapriRacer

Visit my website: http://www.barrystiretech.com/
CapriRacer is offline   Reply With Quote
Old 12-28-2021, 07:45 AM   #26
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
Yes

If you want a better understanding of why all inflation
pressures are set at ambient conditions, consider that
the stiffness of a material does not change with temperature
(within the range of ambient temperatures humans inhabit)
and that a tire's load carrying capacity is therefore not
dependent on temperature, but it is dependent on inflation
pressure.
Well, I would beg to differ when it came to the stiffness of the vinyl upholstered bench seat in my old 1981 Buick in winter, lol! Like rocks.

In summer, it was soft and supple by comparison.

So rubber, like the composition in tires at least, is less susceptible to such variations?

Additionally Barry, I have forward the original table to the USTMA:

“Greetings:

I am writing to inquire if the attached tire pressure table
originated from the USTMA or its predecessor, the RMA
(Rubber Manufs).

I found it on a car repair site/blog, and it seems to be
generating lots of confusion, and outright hostility, among
those who have viewed it, regarding what the chart might
be suggesting.

I interpret it as suggesting that operators of cars and light
trucks inflate their tires, during colder temperature months,
to pressures up to 7psi higher than they would during
hotter months.

I would appreciate your assessment of this table, its origins,
the intent of information displayed, and succinctly, its
overall validity.

Thanks and kind regards,”


I should hopefully have a response from them by next week, as much of their office are on traditional Christmas-New Years holiday break this week

Last edited by RidingOnRailz; 12-28-2021 at 08:56 AM.
RidingOnRailz is online now   Reply With Quote
Old 12-29-2021, 07:06 AM   #27
CapriRacer
AF Enthusiast
 
Join Date: May 2003
Location: Somewhere in the US
Posts: 504
Thanks: 0
Thanked 34 Times in 32 Posts
Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
Well, I would beg to differ when it came to the stiffness of the vinyl upholstered bench seat in my old 1981 Buick in winter, lol! Like rocks.

In summer, it was soft and supple by comparison.

So rubber, like the composition in tires at least, is less susceptible to such variations?

Additionally Barry, I have forward the original table to the USTMA:

“Greetings:

I am writing to inquire if the attached tire pressure table
originated from the USTMA or its predecessor, the RMA
(Rubber Manufs).

I found it on a car repair site/blog, and it seems to be
generating lots of confusion, and outright hostility, among
those who have viewed it, regarding what the chart might
be suggesting.

I interpret it as suggesting that operators of cars and light
trucks inflate their tires, during colder temperature months,
to pressures up to 7psi higher than they would during
hotter months.

I would appreciate your assessment of this table, its origins,
the intent of information displayed, and succinctly, its
overall validity.

Thanks and kind regards,”


I should hopefully have a response from them by next week, as much of their office are on traditional Christmas-New Years holiday break this week
Do not be surprised if USTMA doesn't respond.

First, they are very wary of potential lawsuits and this query kind of sounds like a lawyer trolling.

Second, the source of this table said he got it FROM a similar table from the RMA. He didn't even credit the RMA on the chart in any way. So it's not the exact table RMA is reported to have published. If I were in their shoes, the only response I would give is to point out that the table didn't come from the USTMA and make no more comment than that!

Third, Here's a copy of USTMA's manual for truck and bus tires: https://www.ustires.org/sites/defaul...BusTires_0.pdf

If that chart (or some form of it) isn't in there, then either the RMA never published it, or they feel it is obsolete. I've looked through this and don't find anything that resembles the chart. That and the fact that I didn't find the chart (or something similar) doing a google image search convinces me that the webmaster is wrong about where he got the chart - and I'll bet he is misremembering. I certainly don't want to accuse him of falsifying the source to give it more credibility - which he has only done in an email to you.
__________________
CapriRacer

Visit my website: http://www.barrystiretech.com/
CapriRacer is offline   Reply With Quote
Old 12-30-2021, 05:39 AM   #28
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
Do not be surprised if USTMA doesn't respond.

First, they are very wary of potential lawsuits and this query kind of sounds like
a lawyer trolling.

Second, the source of this table said he got it FROM a similar table from
the RMA. He didn't even credit the RMA on the chart in any way. So it's
not the exact table RMA is reported to have published. If I were in
their shoes, the only response I would give is to point out that the
table didn't come from the USTMA and make no more comment
than that!

Third, Here's a copy of USTMA's manual for truck and bus tires: https://www.ustires.org/sites/defaul...BusTires_0.pdf

If that chart (or some form of it) isn't in there, then either the
RMA never published it, or they feel it is obsolete. I've looked
through this and don't find anything that resembles the chart.
That and the fact that I didn't find the chart (or something similar)
doing a google image search convinces me that the webmaster
is wrong about where he got the chart - and I'll bet he is
misremembering. I certainly don't want to accuse him of
falsifying the source to give it more credibility - which he
has only done in an email to you.
Yes, I looked through all the free TMA PDF documents and found nothing resembling either table - the original, or his revision of it.

I don't know why he would quote such an authority as the source of the table. Otherwise, the automotive information on AA1, not just in the tire section, seems to be accurate and informative.

Re: "lawyer trolling" Well I'm certainly not a lawyer, but in my twenty plus years of participating in Usenet news groups, forums like this one, and social media until last year, I have often been described, either as, a "troll" or "trolling".

Seekers of verification and of the truth often get branded as such, lol!
RidingOnRailz is online now   Reply With Quote
Old 12-30-2021, 08:27 AM   #29
CapriRacer
AF Enthusiast
 
Join Date: May 2003
Location: Somewhere in the US
Posts: 504
Thanks: 0
Thanked 34 Times in 32 Posts
Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
...... Seekers of verification and of the truth often get branded as such, lol!
I think it's your approach. It seems like you accept what is printed and aren't skeptical of what people write. Perhaps if you worded things differently.
__________________
CapriRacer

Visit my website: http://www.barrystiretech.com/
CapriRacer is offline   Reply With Quote
Old 12-30-2021, 08:53 AM   #30
RidingOnRailz
AF Enthusiast
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 761
Thanks: 44
Thanked 15 Times in 15 Posts
Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
I think it's your approach. It seems like you accept what is printed and aren't skeptical of what people write. Perhaps if you worded things differently.
1) Isn't that a bit backwards?

I'm questioning things because I don't accept, all the time, what is printed and am skeptical of some things.

2) "Wording things differently"

I was just trying to sound professional in my e-mail to the USTMA
RidingOnRailz is online now   Reply With Quote
 
Reply

POST REPLY TO THIS THREAD


Tags
gauge , placard , pressure , tire , vehicle
Go Back   Automotive Forums .com Car Chat > Engineering/Technical

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 01:37 PM.

Community Participation Guidelines | How to use your User Control Panel

Powered by: vBulletin | Copyright Jelsoft Enterprises Ltd.
 
 
no new posts