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gayanath

Tire Inflation Pressure Compensation and Adjustment

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Posted (edited)

This is an excerpt from an old technical service bulletin (TSB). Although the main purpose of the TSB is not relevant to us (we are a tropical country), there is a valuable part in it that is relevant to us.
Everyone knows that tire pressure increases when a tire heats up, but we do not know its numerical value. This graph is a good solution for that ..... (Its true that this is for few Toyota models but we could use this until we find a most suitable one for other models)
Let us forget the ambient temperature difference axis (Axis 5) in this graph and consider only the points where the 0 F line intersects (0 F line along the axis 4). This gives a clear idea of how much more air pressure needed depending on the temperature variation of the tire in the three cases 1,2,3 when we inflate the tires.
For example:
In case of Cold Tire - Recommended psi value is required
In case of Warm Tire - 2 psi more than recommended is required
In case of Hot Tire - 4.5 psi more than recommended is required

Note: Normally, the sticker pasted on door jamb shows the recommended "cold tire pressure" . 

FB_IMG_1595310758598.thumb.jpg.ec87e76a957c4db0d07405806574db74.jpg

 

Please find full TSB by this link for your further reference. 

https://attachments.priuschat.com/attachment-files/2015/10/96267_T-SB-0345-08.pdf

Edited by gayanath
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On 7/21/2020 at 11:52 AM, gayanath said:

This is an excerpt from an old technical service bulletin (TSB). Although the main purpose of the TSB is not relevant to us (we are a tropical country), there is a valuable part in it that is relevant to us.
Everyone knows that tire pressure increases when a tire heats up, but we do not know its numerical value. This graph is a good solution for that ..... (Its true that this is for few Toyota models but we could use this until we find a most suitable one for other models)
Let us forget the ambient temperature difference axis (Axis 5) in this graph and consider only the points where the 0 F line intersects (0 F line along the axis 4). This gives a clear idea of how much more air pressure needed depending on the temperature variation of the tire in the three cases 1,2,3 when we inflate the tires.
For example:
In case of Cold Tire - Recommended psi value is required
In case of Warm Tire - 2 psi more than recommended is required
In case of Hot Tire - 4.5 psi more than recommended is required

Note: Normally, the sticker pasted on door jamb shows the recommended "cold tire pressure" . 

FB_IMG_1595310758598.thumb.jpg.ec87e76a957c4db0d07405806574db74.jpg

 

Please find full TSB by this link for your further reference. 

https://attachments.priuschat.com/attachment-files/2015/10/96267_T-SB-0345-08.pdf

One day I pumped air to 34 psi (in the morning). On the same day I checked the air pressure again at evening after normal city driving. ( Checked by the same tire shop, same air pump). Pressure gauge raised up to 41 psi. Then I lowered the pressure again to 34 psi. Next day morning I checked the tire pressure again and pressure was 26 psi. Then I removed all pressurized air in the tire and filled with nitrogen (34 psi).  

Then I checked the tyre pressure according to above way. Tyre pressure only varies about 1-1.5 psi.

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Posted (edited)
14 hours ago, Sadeepa Dilhara said:

One day I pumped air to 34 psi (in the morning). On the same day I checked the air pressure again at evening after normal city driving. ( Checked by the same tire shop, same air pump). Pressure gauge raised up to 41 psi. Then I lowered the pressure again to 34 psi. Next day morning I checked the tire pressure again and pressure was 26 psi. Then I removed all pressurized air in the tire and filled with nitrogen (34 psi).  

Then I checked the tyre pressure according to above way. Tyre pressure only varies about 1-1.5 psi.

Your difference is 7 psi. Let's do backward a calculation using same chart.

The fare case: If both of your morning and evening conditions are 2, then ambient temperature difference should be at-least 80 F = 44 C

More optimistic case: If your morning condition is 2 and evening condition is 3, then ambient temperature difference should be at-least 54 F = 30 C

Extreme case: If your morning condition is 1 and evening condition is 3, then ambient temperature difference should be at-least 33 F = 18 C

Which country/city you are living?

Edited by gayanath

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9 hours ago, gayanath said:

Your difference is 7 psi. Let's do backward a calculation using same chart.

The fare case: If both of your morning and evening conditions are 2, then ambient temperature difference should be at-least 80 F = 44 C

More optimistic case: If your morning condition is 2 and evening condition is 3, then ambient temperature difference should be at-least 54 F = 30 C

Extreme case: If your morning condition is 1 and evening condition is 3, then ambient temperature difference should be at-least 33 F = 18 C

Which country/city you are living?

 

2 minutes ago, Sadeepa Dilhara said:

Kurunegala, Sri Lanka 

Can we expect such a large ambient temperature change in Kurunegala in the morning and afternoon?? 

What I just feel is, either Toyota is wrong or your data is incorrect or both. Isn't it? 

Trust me, I live in both Colombo and Matara and I have a habit of doing various tests as a hobby when time permits. I never observed such an air pressure difference ether for same pump or different pumps when I pumping air in the morning and afternoon. (using normal air)

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Posted (edited)
1 hour ago, gayanath said:

What I just feel is, either Toyota is wrong or your data is incorrect or both. Isn't it? 

Well..if you read the TSB and look at where the TSB is issued at and for what...Toyota is not wrong.

image.thumb.png.19ecd6e76cd946c951a6b12993cb988a.png

The TSB is issued for cold climate countries in order to address drastic tire pressure differences that would occur when a car has been worked on in a workshop and then driven out. This can very well happen in winter countries when cars are worked on in heated workshops and are driven to be used in a cold snowy environment. I remember in Utah the outside temperature would easily hit -20/-10 degrees (or even more) celsius during winter and we always kept are sheds at about 15-20 degrees. 

Edited by iRage
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16 minutes ago, iRage said:

Well..if you read the TSB and look at where the TSB is issues...Toyota is not wrong.

I also didn't think Toyota was wrong. I let him rethink his data without directly saying he was wrong ... 😃😃. That’s why I show him a backwards calculation assuming his different running conditions to show how an ambient temperature change could occur to get his results.

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13 minutes ago, gayanath said:

I also didn't think Toyota was wrong. I let him rethink his data without directly saying he was wrong ... 😃😃. That’s why I show him a backwards calculation assuming his different running conditions to show how an ambient temperature change could occur to get his results.

Hmm... I think it's better to do that experiment again. Someway it can be a error of the pressure gauge of that pump. But it is a relatively new pump. 

Now I only pump nitrogen into tires because of less pressure variations (1 psi-1.5 psi according to my experience). So I'm sticking to it.

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