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Old 09-17-2019, 06:29 AM   #1
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Cool Is This Tire Pressure Chart Legit?

Since this isn't getting any attention over in the tire sub-forum, I'll ask here.


This chart I found online suggests that in winter we should increase the indicated tire pressure anywhere from 2-6psi during the cold months:




IE my vehicle's door sticker specifies 33psi cold. Does that mean I should keep them at 37-38psi indicated, in January and February?

I also do not subscribe to that ancient myth about lowering indicated pressures 'for better traction' during winter weather. I just make sure that they are at 33psi from July to January here in CT.

Which is correct: moi, or the attached chart?
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Old 09-17-2019, 10:25 PM   #2
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Re: Is This Tire Pressure Chart Legit?

I can't believe that they would want you to run with the higher pressures listed in the chart during colder weather. Yes as it gets colder your pressure drops in your tires. That is why you add more air to compensate and bring the pressure back up to the correct amount but not the higher pressure listed in the chart. Wouldn't the manufacture list this information on the placard as well if it was correct? I think maybe the chart has a baseline of 70 degrees and if you were to fill a tire to say 32 lbs at 70 degrees it would lose roughly a pound for every 10 degree drop in temperature. Now if at 70 degrees you over filled the tire to 39 lbs and then lowered the temperature to 0 degrees it would be at 32 lbs. That is how I interpret it anyway.
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Old 09-17-2019, 11:29 PM   #3
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Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by jerryg2112 View Post
I can't believe that they would want you to run with the higher pressures listed in the chart during colder weather. Yes as it gets colder your pressure drops in your tires. That is why you add more air to compensate and bring the pressure back up to the correct amount but not the higher pressure listed in the chart. Wouldn't the manufacture list this information on the placard as well if it was correct? I think maybe the chart has a baseline of 70 degrees and if you were to fill a tire to say 32 lbs at 70 degrees it would lose roughly a pound for every 10 degree drop in temperature. Now if at 70 degrees you over filled the tire to 39 lbs and then lowered the temperature to 0 degrees it would be at 32 lbs. That is how I interpret it anyway.

Thanks for replying!

The site in which this chart resides claims that air is "less dense" at lower temperatures. Thus, they contend, that 32psi at, IE 20F is not the same as 32psi at higher(Summer) temperatures.

The way I interpret it is that if your tires indicate 32psi at 70F, that one should add 1psi for ever ten degrees F drop in ambient temperature, then maintain the same pressure for ambient temperatures 0F and below. So at 60F inflate your tires to indicate 33psi, 40F: 35psi, etc.

Since my car rides rough even at factory 33psi, I could not imagine running any more than 1-2psi over that - at any time of the year!
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Old 09-18-2019, 05:01 AM   #4
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Re: Is This Tire Pressure Chart Legit?

Here is the link for their explanation for that chart:

https://www.aa1car.com/library/tirepres.htm
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Old 09-18-2019, 07:21 AM   #5
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Re: Is This Tire Pressure Chart Legit?

Tire engineer here.

The link didn't actually say HOW to use the chart. I suspect what you are supposed to do is if you fill your tires at a certain ambient temperature, use the chart to tell you how much to fill it to. That way at 70F, you will have the proper pressure.

Alternatively, if you are filling your tires at 70F, then use the chart to make sure you have enough tire pressure when it gets down to the temperature indicated.

Either way, I think this creates more confusion than is needed.

So there is a bit of wrong information on the page. For every 10F change in ambient temperature, the pressure inside a passenger car tire changes about 1 psi. For other tires, use 3% for every 10F. (Note: 3% of 30 psi is about 1 psi)

Please note that the tire manufacturers want you to inflate your tires to the vehicle manufacturer's specified pressure for whatever the operating conditions are. That means that if you are operating at 10F, they want you to use the specified pressure, not one specified for another temperature. That also means if you fill your tires at 70F, then they will be too low at 10F (about 6 psi low).

Yes. yes, it is confusing.

Now allow me to express my opinion: Winter tires would benefit from a few extra psi. (3 to 5 psi) That extra pressure helps push the footprint through the snow to reach the pavement. The pavement will always have better traction than snow.

Some people will argue that over inflating your tires will cause the center of the tread to wear faster that the shoulders. That is true, BUT that effect is small compared to most other things that cause rapid wear, such as alignment and the drive vs steering effect.

Drive vs steering effect? Steering tires tend to wear the shoulders and drive tires tend to wear the center. You can see this clearly on a RWD car - where the wear rates are about the same front to rear but in different portions of the tread. That's why rotating tires gets you longer tread life.

On a FWD car, you can't see the steering vs drive difference as the front tires are doing both - BUT - that also means that the front tires are going to wear more rapidly that the rears. I've measured about 2 1/2 times faster. Again rotating tires helps even out the wear.
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Old 08-13-2021, 10:26 PM   #6
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Cool Re: Is This Tire Pressure Chart Legit?

CAPRI RACER!

Scroll down to Table (3) in this link....

https://patents.google.com/patent/WO2009036547A1/en

It is similar to the blue one linked to here, and discussed above:

https://s19526.pcdn.co/wp-content/up...tion_chart.jpg



The explanation following my first link explains how such a chart might be used - for adjusting tire pressure in an environment unlike actual operating conditions! - IE: a WARM GARAGE DURING COOLER AUTUMN OR WINTER OUTDOOR TEMPERATURES.

Think about it - it makes sense after reading the explanation that follows my first link-to.

So if I did regularly garage my Honda Accord(recommended tire pressure 32psi) in an attached space that was heated to, IE, F60, and the January avg. dawn temperature was F20, it would behoove me to set my Acccord 'cold' tire pressures to 36psi while in that heated garage.

Once I drove out of the garage, the tires would 'settle down' to, approximately, the Honda-recommended 32psi.

Makes more sense now! Too bad the providers of the blue chart did not make clear that intended purpose. Duhhh.. It implies an enclosed service space heated to F70, and calculates pressure recommended to compensate for setting it inside of said space, before driving out into lower ambient temps.

Actually, it works out for the better that, in reality, our cars reside in our driveway, so no worries about cold-vs-compensated pressures. Just go outside at dawn, regardless of outdoor ambient temperature, and set to carmaker recommended cold pressure. If that pressure is too high, remove air, if too low, add.
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Old 08-14-2021, 06:56 AM   #7
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Re: Is This Tire Pressure Chart Legit?

I didn't go into this in my first reply of this thread - BUT - there are some folks who incorrectly believe that the tire load tables are based on STP (Standard Temperature and Pressure) - they are NOT!!

STP is used in the scientific world for testing purposes where the testing environment is different from the specified test environment. Folks doing testing would need to adjust the results to STP so they can do comparisons.

Tires work on a different principle. Tire pressures should be set for ambient conditions.

That presents a problem for situations where the environment the tire will be operating in is different than the environment when the pressures are adjusted - like moving from the seashore to the mountains, or from a cold morning to the hottest part of the day on a desert floor.

There's another aspect that isn't fully understood - tires are fairly forgiving - that is, if you are within a few psi of the target pressure, that will be good enough. Too many people think that if you are off a few psi, that is significant. And by a few, I mean 2 or 3 psi for passenger car tires.

In theory, the tire pressure specified by the vehicle tire placard includes enough extra capacity that 2 or 3 psi will not matter. This is the opposite of what is argued for the Ford Explorer back in the 2000/2001 time frame. Some argue that the pressure specification CAUSED the tire failure - and that is not the case. The specified pressure was adequate - although, it would be better engineering to have specified a higher pressure. What is misunderstood is that the Firestone tires involved had a design problem that wasn't revealed until the tire started failing. Then Firestone stonewalled in issue until forced to recall the tires.
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Old 08-14-2021, 07:51 AM   #8
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Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
I didn't go into this in my first reply of this thread - BUT - there are
some folks who incorrectly believe that the tire load tables are based on STP
(Standard Temperature and Pressure) - they are NOT!!

STP is used in the scientific world for testing purposes where the testing environment
is different from the specified test environment. Folks doing testing would need to
adjust the results to STP so they can do comparisons.

Tires work on a different principle. Tire pressures should be set for ambient conditions.

That presents a problem for situations where the environment the tire will be operating
in is different than the environment when the pressures are adjusted - like moving
from the seashore to the mountains, or from a cold morning to the hottest part of the
day on a desert floor.

There's another aspect that isn't fully understood - tires are fairly forgiving - that is, if
you are within a few psi of the target pressure, that will be good enough. Too many
people think that if you are off a few psi, that is significant. And by a few, I mean 2
or 3 psi for passenger car tires.

In theory, the tire pressure specified by the vehicle tire placard includes enough extra
capacity that 2 or 3 psi will not matter. This is the opposite of what is argued for the
Ford Explorer back in the 2000/2001 time frame. Some argue that the pressure
specification CAUSED the tire failure - and that is not the case. The specified pressure
was adequate - although, it would be better engineering to have specified a higher
pressure. What is misunderstood is that the Firestone tires involved had a design
problem that wasn't revealed until the tire started failing. Then Firestone stonewalled
in issue until forced to recall the tires.
So how does all that relate to the tables and explanations I shared?

Like I recently stated, at our place we keep our cars in our "standard operating environment" - our driveway! Plus or minus 100feet(33m) variation in local altitudes. So bi-weekly predawn pressure checks - and adjustments if necessary - are the norm here, and our shops have exclaimed accordingly: "Very even wear for 3-5 year old tires!"
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Old 08-14-2021, 10:11 AM   #9
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Cool Re: Is This Tire Pressure Chart Legit?

CapriRacer wrote:
Quote:
On a FWD car, you can't see the steering vs drive difference as the
front tires are doing both - BUT - that also means that the front tires
are going to wear more rapidly that the rears. I've measured about
2 1/2 times faster. Again rotating tires helps even out the wear.
Are you kidding?

I can see different wear pattern(more shoulder wear) on the front tires of my Honda Accord, and on the fronts of other front-drivers I've owned.

Same as with my rear-wheel drivers from ages ago - my Chevelle and Buick Century
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Old 08-15-2021, 06:55 AM   #10
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Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
So how does all that relate to the tables and explanations I shared?

Like I recently stated, at our place we keep our cars in our "standard operating environment" - our driveway! Plus or minus 100feet(33m) variation in local altitudes. So bi-weekly predawn pressure checks - and adjustments if necessary - are the norm here, and our shops have exclaimed accordingly: "Very even wear for 3-5 year old tires!"
As I explained, it is very common in scientific circles to reference STP (Standard Temperature and Pressure - 0C, 100 kPa = 32F, 14.7 psi) for testing purposes. Every experimental result is adjusted back to those conditions so they can be compared to other test results.

For tires, STP isn't used or referenced - however many people are used to the idea of a reference temperature and pressure, so they try to apply it EVERYWHERE - even when it isn't appropriate - and that is the case with the tables you referenced.

Quote:
Originally Posted by RidingOnRailz View Post
Are you kidding?

I can see different wear pattern(more shoulder wear) on the front tires of my Honda Accord, and on the fronts of other front-drivers I've owned.

Same as with my rear-wheel drivers from ages ago - my Chevelle and Buick Century
The problem here is that some alignment settings will result in uneven wear patterns rather than even wear. For a reason I don't quite understand, many vehicle manufacturers specify lots of camber - and when coupled with a bit of toe, the result is one-sided wear and/or diagonal wear.

Then there is the issue of how a vehicle is used. Vehicles that do a lot of city driving will experience more shoulder wear. So even though the front tires on a FWD SHOULD wear evenly, both the actual alignment and how the vehicle is used will impact evenness of wear. One way to put it is: Your mileage may vary.
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Old 08-15-2021, 07:28 AM   #11
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Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
Tire engineer here.

The link didn't actually say HOW to use the chart. I suspect what you are supposed to do is if you fill your tires at a certain ambient temperature, use the chart to tell you how much to fill it to. That way at 70F, you will have the proper pressure.

Alternatively, if you are filling your tires at 70F, then use the chart to make sure you have enough tire pressure when it gets down to the temperature indicated.

Either way, I think this creates more confusion than is needed.

So there is a bit of wrong information on the page. For every 10F change in ambient temperature, the pressure inside a passenger car tire changes about 1 psi. For other tires, use 3% for every 10F. (Note: 3% of 30 psi is about 1 psi)

Please note that the tire manufacturers want you to inflate your tires to the vehicle manufacturer's specified pressure for whatever the operating conditions are. That means that if you are operating at 10F, they want you to use the specified pressure, not one specified for another temperature. That also means if you fill your tires at 70F, then they will be too low at 10F (about 6 psi low).

Yes. yes, it is confusing.

Now allow me to express my opinion: Winter tires would benefit from a few extra psi. (3 to 5 psi) That extra pressure helps push the footprint through the snow to reach the pavement. The pavement will always have better traction than snow.

Some people will argue that over inflating your tires will cause the center of the tread to wear faster that the shoulders. That is true, BUT that effect is small compared to most other things that cause rapid wear, such as alignment and the drive vs steering effect.

Drive vs steering effect? Steering tires tend to wear the shoulders and drive tires tend to wear the center. You can see this clearly on a RWD car - where the wear rates are about the same front to rear but in different portions of the tread. That's why rotating tires gets you longer tread life.

On a FWD car, you can't see the steering vs drive difference as the front tires are doing both - BUT - that also means that the front tires are going to wear more rapidly that the rears. I've measured about 2 1/2 times faster. Again rotating tires helps even out the wear.
Quote:
Originally Posted by CapriRacer View Post
As I explained, it is very common in scientific circles to reference STP (Standard Temperature and Pressure - 0C, 100 kPa = 32F, 14.7 psi) for testing purposes. Every experimental result is adjusted back to those conditions so they can be compared to other test results.

For tires, STP isn't used or referenced - however many people are used to the idea of a reference temperature and pressure, so they try to apply it EVERYWHERE - even when it isn't appropriate - and that is the case with the tables you referenced.



The problem here is that some alignment settings will result in uneven
wear patterns rather than even wear. For a reason I don't quite
understand, many vehicle manufacturers specify lots of camber - and
when coupled with a bit of toe, the result is one-sided wear and/or
diagonal wear.

Then there is the issue of how a vehicle is used. Vehicles that do a
lot of city driving will experience more shoulder wear. So even
though the front tires on a FWD SHOULD wear evenly, both the actual
alignment and how the vehicle is used will impact evenness of
wear. One way to put it is: Your mileage may vary.

I just naturally assumed - and expected - varying degrees of additional shoulder wear(or at least, more outer tread wear) - on the steer tires, owing to the complex stew of angles occurring during the act of steering, as compared to tires on non-steering axles. Regardless of front- vs rear- vs all-wheel drive.

Variables could include specific tire compound, inflation pressure, steering geometry specific to a given vehicle, condition of those components, and of course, driving style(Earnhardt vs Sundee driver, lol!)
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Old 08-16-2021, 06:24 AM   #12
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Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by RidingOnRailz View Post
I just naturally assumed - and expected - varying degrees of additional shoulder wear(or at least, more outer tread wear) - on the steer tires, owing to the complex stew of angles occurring during the act of steering, as compared to tires on non-steering axles. Regardless of front- vs rear- vs all-wheel drive.

Variables could include specific tire compound, inflation pressure, steering geometry specific to a given vehicle, condition of those components, and of course, driving style(Earnhardt vs Sundee driver, lol!)
As you point out, there are lots of variables. That is why it is difficult to convinced people of the basic principles involved - their own experiences and what they read on the internet don't include such subtleties as what has the biggest effect and what can be ignored (not having a significant effect).
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Old 08-16-2021, 08:09 AM   #13
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Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
As you point out, there are lots of variables.
That is why it is difficult to convinced people of the basic
principles involved - their own experiences and what they
read on the internet don't include such subtleties as what
has the biggest effect and what can be ignored (not having
a significant effect).

So based, probably, on the topmost three statements in this link, regarding pressure, density, and temperature of air:

http://msrc.sunysb.edu/~chang/atm205...ter_1_txtb.pdf

The providers of that blue chart are suggesting that, for every F10 below F70, one should increase their cold tire pressures according to the grid.

IE: The vehicle placard on my Honda Accord recommends 32PSI cold, as long as same size and speed rating of tire are kept on it when replacing.

For temperatures from 70F up, that cold pressure can be maintained.

However, when first thing in the morning temperatures start to average 60F, I should add a pound - to 33psi cold. And so on...

Until the average morning temperature, say in February around here, averages only 20F, then I should be maintaining 37psi cold. Come April, with average dawn Temps around 40F, then it's OK to deflate them back to 35psi cold.

Again, based on the principles, concerning air pressure, density, and temperature, in the above link.

So if I had a big old Econoline or Express van, proper light truck tires, and recommended rear axle cold pressure(80psi) = Max cold pressure on the tires, is it ok, per those principles and that chart, to keep them at 85-87psi cold, in winter?

But, if colder air is more dense than warm air - the opposite of what I assumed for most of my 51 years, why are they suggesting increasing cold tire pressures at lower ambient temperatures?

Barry you can probably tell I spent many years in special ed schools - they never taught us any of the above stuff! lol
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Old 08-17-2021, 09:18 AM   #14
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Re: Is This Tire Pressure Chart Legit?

Allow me to start in a different place:

What to ignore:

Elevation: Even at 5,000 feet (Denver), the amount of inflation pressure change from sea level is only 2 1/2 psi - not enough to worry about.

Humidity: Just not a factor

So we are only talking about temperature vs pressure.

In summer, we can expect at 20F change from early morning to the hottest point of the day. That would be a 4% change - 80 psi to 83 psi - again, not enough to worry about.

The problem in winter is 2 fold:

1) Water vapor can freeze about of humid air at as little as 37F. That means that one should avoid check inflation pressures when it gets below - say - 40F. That also means that, in winter, one should anticipate colder temperatures and set the tire inflation pressures to cover the worst temperatures in the coming months. When I lived in Michigan, the worst temperature I anticipated was -20F, but I would set the pressures for 0F, reasoning that if it got to -20F, I was not going to travel fast (which causes additional stresses) nor for very long.

Which brings me to:

2) Setting the pressure in a warn environment, with the expectation of operating in a cold environment.

So lets say the pressures are set at 50F, and the expect operating temperature is 0F, then the expect loss of pressure would be 10%. So an 80 psi tire should be set at 88 psi.

Doesn't that exceed the max pressure on the sidewall? Yes, but not only are tires designed for a much higher pressure (long story why that is!), but the tire isn't expected to operate at that pressure - the tire will cool down to a lower pressure.

You can use that chart to help set pressure for anticipated conditions - except that the chart doesn't show what I just outlined above. Ergo, I would recommend NOT using this chart.
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Old 08-17-2021, 11:03 AM   #15
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Cool Re: Is This Tire Pressure Chart Legit?

Quote:
Originally Posted by CapriRacer View Post
Allow me to start in a different place:

What to ignore:

Elevation: Even at 5,000 feet (Denver), the amount of inflation pressure change
from sea level is only 2 1/2 psi - not enough to worry about.

Humidity: Just not a factor

So we are only talking about temperature vs pressure.

In summer, we can expect at 20F change from early morning to the hottest
point of the day. That would be a 4% change - 80 psi to 83 psi - again, not
enough to worry about.

The problem in winter is 2 fold:

1) Water vapor can freeze about of humid air at as little as 37F. That means
that one should avoid check inflation pressures when it gets below - say - 40F.
That also means that, in winter, one should anticipate colder temperatures and
set the tire inflation pressures to cover the worst temperatures in the coming
months. When I lived in Michigan, the worst temperature I anticipated was
-20F, but I would set the pressures for 0F, reasoning that if it got to -20F, I
was not going to travel fast (which causes additional stresses) nor for very long.


Which brings me to:

2) Setting the pressure in a warn environment, with the expectation of
operating in a cold environment.

So lets say the pressures are set at 50F, and the expect operating temperature
is 0F, then the expect loss of pressure would be 10%. So an 80 psi tire should
be set at 88 psi.

Doesn't that exceed the max pressure on the sidewall? Yes, but not only are
tires designed for a much higher pressure (long story why that is!), but the tire
isn't expected to operate at that pressure - the tire will cool down to a lower
pressure.

You can use that chart to help set pressure for anticipated conditions -
except that the chart doesn't show what I just outlined above. Ergo,
I would recommend NOT using this chart.
Neither does a customer I showed it to where I work.

He said if my car specified 32psi cold tire pressures, setting them to the 37psi the grid suggests, even during below freezing dawn temperatures, would, in his own words, "... f - k up the tires! ..." I told him you got most idiots these days running anywhere from 40psi up to what's stamped on their tire sidewalls, and you might be risking your life to suggest they do otherwise!

I do maintain 34psi though, from December through March, and 33psi the rest of the year - primarily to account for possible tire gauge discrepancy. This Accord, even with the 50-series low profile rubber OEM at its trim level, seems to do everything and handle most predictably and securely, at those pressures, even on the rare occasion I push things, IE: take a corner a little faster than I usually do, etc.

So I think Honda does its homework when it comes to what's on their door frame decals.

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