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Old 09-17-2019, 07:29 AM   #1
RidingOnRailz
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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, 11:25 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 09-18-2019, 12:29 AM   #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, 06:01 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, 08:21 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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