Capri Racer: Here's Another Wrench In the Works

Capri:

http://cdn.differencebetween.net/wp-content/uploads/2018/09/PSI-vs-PSIG.jpg

It postulates that the pressure the tire gauge shows is only the pressure according to the gauge(PSIG) and differs from the actual pressure inside the tire(PSI) or other such container.

Your thoughts?

Cat/Holiday got everyone's tongue?

Put down the Fakebook and let's talk shop! :D

Cat/Holiday got everyone's tongue?

Put down the Fakebook and let's talk shop! :D


LOL things ain't fast here no mo'.


The chart you posted is technically correct. PSIG is what you're taking when you check your tire pressure.....because you're measuring the difference between ambient pressure and what's in the tire. Take that tire into a vacuum and the pressure would indicate MUCH higher....and match PSI as well.

LOL things ain't fast here no mo'.


The chart you posted is technically correct. PSIG is what you're taking
when you check your tire pressure.....because you're measuring the
difference between ambient pressure and what's in the tire. Take that
tire into a vacuum and the pressure would indicate MUCH higher....and
match PSI as well.


So you mean the atmospheric pressure pressing on the tire also. Got it.

Remove that atmosphere, like put that same tire on the moon(negligible atmospheric pressure) and it might explode.

But here on Earth, if I need 32psi in my tires at dawn, and my gauge indicates 32, that's all that matters, right?

So you mean the atmospheric pressure pressing on the tire also. Got it.

Remove that atmosphere, like put that same tire on the moon(negligible atmospheric pressure) and it might explode.

But here on Earth, if I need 32psi in my tires at dawn, and my gauge indicates 32, that's all that matters, right?

Yes. Your gauge shows 32, that's the difference between outside and inside the tire and what you need to support the weight of the vehicle.

On the moon (wrongly assuming gravity is the same), starting with a vacuum and mounting the tire, you would also need 32psig, but it would take a LOT less air.

Fred Jackson san is correct, but here is another way of explaining it:

If you are using a gauge to measure pressure, it is always psig.

However, if you are using one of the gas laws, like the Ideal Gas Law: PV = nRT, both the temperature and pressure are absolute. Put another way, one would have to add 14.7 psi to any gauge measurement and 460° to any Fahrenheit temperature measurement. (273° for Celsius)

Oh, and I only look at this website using the search function: "tire". Your initial post didn't have that. It only showed up today because Fred used the word yesterday.

Also, it is pretty common for folks to use psia (for absolute) and psig when there might be confusion.

Fred Jackson san is correct, but here is another way of explaining it:

If you are using a gauge to measure pressure, it is always psig.

However, if you are using one of the gas laws, like the Ideal Gas Law: PV = nRT, both the temperature and pressure are absolute. Put another way, one would have to add 14.7 psi to any gauge measurement and 460° to any Fahrenheit temperature measurement. (273° for Celsius)

Oh, and I only look at this website using the search function: "tire". Your initial post didn't have that. It only showed up today because Fred used the word yesterday.

Also, it is pretty common for folks to use psia (for absolute) and psig when there might be confusion.


Barryyyyyy! :D

Nice of you to join the party - away for the long weekend? Hope you and all concerned are fine.

Thanks for the additional explanation, I knew you'd come through.

But here on Earth, in an ordinary passenger vehicle, with a decent mid-tier($40-60) tire pressure gauge, I really don't have to worry about that difference, right?

Until I drive the car on Mars or somewhere... http://staticaf.com/vbulletin/images/smilies/grinyes.gif

Barryyyyyy! :D

Nice of you to join the party - away for the long weekend? Hope you and all concerned are fine.

Thanks for the additional explanation, I knew you'd come through.

But here on Earth, in an ordinary passenger vehicle, with a decent mid-tier($40-60) tire pressure gauge, I really don't have to worry about that difference, right?

Until I drive the car on Mars or somewhere... http://staticaf.com/vbulletin/images/smilies/grinyes.gif

There is a difference in psia between sea level and high elevations. Google is your friend here! Atmospheric pressure at elevation

Hint: Denver is only 2 1/2 psi different than NYC. IMHO, not enough to worry about.

There is a difference in psia between
sea level and high elevations.

Hint: Denver is only 2 1/2 psi different than NYC.
IMHO, not enough to worry about.

In which direction, higher pressure or lower?

2 1/2psi is a big deal to me. I aim for less than half psi, cold, between all four tires on any car I drive, or when setting someone elses. If my Honda Accord indicates 32 in one tire, 33 in another, 31 in another and 34 in the other, that's a problem. ;) I try to get them all as close to 33psi, that pointer as close as possible to the third tick above 30psi, or two ticks below 35, on that dial gauge.

I have the time to do this, and I guess it's not fair in light of the fact that I don't have a dozen other work orders, that need to be completed between 8am and 5pm today, stacked up behind the car I'm so meticulously adjusting cold tire pressure on - as many garage mechs do.

2 thoughts:

You're being overly fussy about things - including inflation pressure. It's not that big of a deal. Ya' see, even 10°F change in temperature will change the inflation pressure 1 psi. that's more than the temperature swing within a day!

Second, the pressure of the air is a function of altitude because of the amount of air sitting on top of it. In the vacuum of space, the pressure is very near zero, so the ambient pressure in Denver is LESS than it is in NYC. Needless to say, the gauge pressure would increase! The gauge is measuring the difference.

And consider the water pressure at the bottom of the Marianas trench. The water sitting on top of the water there is pressing down much, much more than it is at the surface - over 15,000 psi.

2 thoughts:

You're being overly fussy about things - including inflation pressure.
It's not that big of a deal. Ya' see, even 10°F change in temperature
will change the inflation pressure 1 psi. that's more than the
temperature swing within a day!

Second, the pressure of the air is a function of altitude because of
the amount of air sitting on top of it. In the vacuum of space, the
pressure is very near zero, so the ambient pressure in Denver is LESS
than it is in NYC. Needless to say, the gauge pressure would increase!
The gauge is measuring the difference.

And consider the water pressure at the bottom of the Marianas trench.
The water sitting on top of the water there is pressing down much,
much more than it is at the surface - over 15,000 psi.

Hearing that I'm "being overly fussy" from you, of all people with knowledge of this subject, is disconcerting.

You speak from a position of science, which I agree with and respect, and your website supports that. So I don't understand your assessment.

What is wrong with making sure all the tires on a given vehicle are as close as possible to the recommended/required cold pressures?

From a handling standpoint, it means that the vehicle will react predictably, to ordinary and extraordinary maneuvers, during the course of daily driving. A turn to one side can be commenced as predictably as a turn to the other. Also, the vehicle will accelerate, track, and brake more evenly from side to side.

With all due respect Barry, and with me owning the caliber of gauges I do, I cannot accept, in my case, having four different pressured tires on my car. (Unless, of course, I'm intentionally staggering them for the race track)

With my digital gauge, why wouldn't I want them to all indicate 33.0 exactly? With my analog dial, why wouldn't I want that needle to point as close to 33psi on it as possible? To me that's just common sense. If that's considered being 'anal', well, that's the culture's problem - not mine.

As I explained before, I'm not a Town Fair, or Costco Auto, with a dozen vehicles queued up behind the one I'm servicing. So I can take the extra five minutes to make sure our two household vehicles' tires are properly filled.

Hearing that I'm "being overly fussy" from you, of all people with knowledge of this subject, is disconcerting.

You speak from a position of science, which I agree with and respect, and your website supports that. So I don't understand your assessment.

What is wrong with making sure all the tires on a given vehicle are as close as possible to the recommended/required cold pressures?

From a handling standpoint, it means that the vehicle will react predictably, to ordinary and extraordinary maneuvers, during the course of daily driving. A turn to one side can be commenced as predictably as a turn to the other. Also, the vehicle will accelerate, track, and brake more evenly from side to side.

With all due respect Barry, and with me owning the caliber of gauges I do, I cannot accept, in my case, having four different pressured tires on my car. (Unless, of course, I'm intentionally staggering them for the race track)

With my digital gauge, why wouldn't I want them to all indicate 33.0 exactly? With my analog dial, why wouldn't I want that needle to point as close to 33psi on it as possible? To me that's just common sense. If that's considered being 'anal', well, that's the culture's problem - not mine.

As I explained before, I'm not a Town Fair, or Costco Auto, with a dozen vehicles queued up behind the one I'm servicing. So I can take the extra five minutes to make sure our two household vehicles' tires are properly filled.

One of the classes I took in college involved engineering as practiced in the real world. One of the segments involved unnecessary precision.

The story that illustrated the point was the $10,000 hammer (I'm not sure of the details). The story was that the US Air Force had specifications for a hammer that was to be carried as part of an on board tool box - and they were sooooo precise that it cost that much to certify it. Had they used normal, everyday specifications, they could have bought one from the corner hardware store for under $10.00 and it would have functioned just as well.

I think that's what you are doing. Close enough is close enough. If you want to fuss over precision, don't be surprised that you spend a lot of time doing so. I don't think it is necessary and don't practice it myself.

However, when I was racing, that was a different story. Some precision yielded better lap times. I paid real close attention to inflation pressure.

And as it turned out, it was all for naught! I just didn't have the talent to utilize that level of precision. Again, unnecessary precision!

One of the classes I took in college involved engineering as practiced in the real world. One of the segments involved unnecessary precision.

The story that illustrated the point was the $10,000 hammer (I'm not sure of the details). The story was that the US Air Force had specifications for a hammer that was to be carried as part of an on board tool box - and they were sooooo precise that it cost that much to certify it. Had they used normal, everyday specifications, they could have bought one from the corner hardware store for under $10.00 and it would have functioned just as well.

I think that's what you are doing. Close enough is close enough. If you want to fuss over precision, don't be surprised that you spend a lot of time doing so. I don't think it is necessary and don't practice it myself.

However, when I was racing, that was a different story. Some precision yielded better lap times. I paid real close attention to inflation pressure.

And as it turned out, it was all for naught! I just didn't have the talent to utilize that level of precision. Again, unnecessary precision!

I remember something about a toilet seat costing the DoD that much, lol!

Because I have been gauging tires for at least thirty years of my life, it now takes me probably only a few seconds more to get "32, 32, 32, and 32"psi, than it would for some shlamile to get "30, 33, 32.5, and 31" psi on their four tires.

And I acknowledge that the gauge itself is not perfect: even if the tires all indicate 32.0 on a digital piece, they might all in actuality be a half psi off in different directions, due to gauge discrepancy.

But at least I tried, and that's why most gauges these days have a bleeder button on them. Over-inflate the tire by a few psi, and then keep repeatedly pressing the air bleeder until the needle points to exactly your target pressure.

I don't consider that to be "over-precision", or even precise. I call it a job well done. And I feel the results: in the corners and in the ride quality. Want precision? There's a couple gauges out there, digital models, that read down to the hundredth of one PSI! Who the heck would need to be that exact? lol

Come on Capri, never surrender quality and giving a damn! ;)

I remember something about a toilet seat costing the DoD that much, lol!

Because I have been gauging tires for at least thirty years of my life, it now takes me probably only a few seconds more to get "32, 32, 32, and 32"psi, than it would for some shlamile to get "30, 33, 32.5, and 31" psi on their four tires.

And I acknowledge that the gauge itself is not perfect: even if the tires all indicate 32.0 on a digital piece, they might all in actuality be a half psi off in different directions, due to gauge discrepancy.

But at least I tried, and that's why most gauges these days have a bleeder button on them. Over-inflate the tire by a few psi, and then keep repeatedly pressing the air bleeder until the needle points to exactly your target pressure.

I don't consider that to be "over-precision", or even precise. I call it a job well done. And I feel the results: in the corners and in the ride quality. Want precision? There's a couple gauges out there, digital models, that read down to the hundredth of one PSI! Who the heck would need to be that exact? lol

Come on Capri, never surrender quality and giving a damn! ;)

Let me put it like this:

Precision costs money. As a responsible employee, I should spend the company's money prudently. If I am working for an F1 team, I would use a different approach than if I am in the company's garage servicing pool vehicles. Using the right approach to the situation is not surrendering quality.

Let me put it like this:

Precision costs money. As a responsible employee, I should spend
the company's money prudently. If I am working for an F1 team,
I would use a different approach than if I am in the company's garage
servicing pool vehicles. Using the right approach to the situation is
not surrendering quality.


To each their own!

All I know is, those friends of mine whose tires I have properly inflated have used the terms "smoother", "better gas mleage", and "feels like a new car" to describe what they felt the next day when they went to work or wherever.

A scientific guy telling me as close to desired pressure as possible is "not necessary" or being "overly fussy"?

Takes all kinds to make this world go round I guess!