Tire Pressure increases 5 lbs in one ride
#51
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Nope. At -50°F (227K), the pressure would be 30 psi. The tires might go flat because the rubber isn’t flexible anymore and may crack but the pressure wouldn’t be zero. You’d need to condense the air to get to near zero pressure which is -320°F (196°C). The rubber will definitely shatter at that temperature. But notice that the pressure change is only 10 psi.
I’ve done demonstrations with balloons in liquid nitrogen where I can show liquid air (and zero pressure in the balloon). It’s very cool to watch the balloon collapse and a pool of liquid form in the bottom. It’s also very cool to watch the balloon expand as the liquid air boils off.
I’ve done demonstrations with balloons in liquid nitrogen where I can show liquid air (and zero pressure in the balloon). It’s very cool to watch the balloon collapse and a pool of liquid form in the bottom. It’s also very cool to watch the balloon expand as the liquid air boils off.
I'm not sure what you're contradicting with your "Nope.", but it's offensive, either way. Are you one of those posters who always has to be right?
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You said the tire would be “flat”. That implies zero pressure. I don’t go out and look at a tire that is low and say it is “flat”. It may be going flat but it isn’t flat yet. A 10psi pressure drop due to temperature isn’t even close to being “flat”. It may be low but it isn’t “flat”.
I’m contradicting your assertion that the tire is flat. The rest of the post relates back to that assertion. It’s not an “offense”. It’s just a introduction to the rest of the post. “Nope” and “no” are equivalent statements
I'm not sure what you're contradicting with your "Nope.", but it's offensive, either way.
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Do we have an IGNORE feature? How-to, please.
You said the tire would be “flat”. That implies zero pressure. I don’t go out and look at a tire that is low and say it is “flat”. It may be going flat but it isn’t flat yet. A 10psi pressure drop due to temperature isn’t even close to being “flat”. It may be low but it isn’t “flat”.
I’m contradicting your assertion that the tire is flat. The rest of the post relates back to that assertion. It’s not an “offense”. It’s just a introduction to the rest of the post. “Nope” and “no” are equivalent statements
I’m contradicting your assertion that the tire is flat. The rest of the post relates back to that assertion. It’s not an “offense”. It’s just a introduction to the rest of the post. “Nope” and “no” are equivalent statements
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We also have rules against profanity…even stuff that is “starred” out.
Please tell me how my first two sentences above…taken together or separately…constitute bovine excrement (that’s how you do profanity). Did you change the tire at -50°F because it was “flat” or did you just drive along on a low(er) pressure tire? Of course, the pressure is lower. Is the tire “flat”…i.e zero pressure? Obviously not.
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A tire pressure gauge is not calibrated to be zero at sea level atmospheric pressure. It is calibrated for zero when the pressure on the inside of the tire is equal to the pressure outside the tire (atmospheric pressure). That could be at sea level or at 20,000 feet. A flat tire reads zero in either situation.
All tire pressure gauges are designed to read the pressure inside the tire ABOVE the actual atmospheric pressure. This is why measured pressure in a tire increase with altitude, even thought the absolute pressure does not. The pressure in the tire remains the same, but the atmospheric pressure drops. Thus the difference increases, thus the tire measures (and behaves) higher in pressure.
For a simple explanation, read the 4th and 5th paragraphs: https://www.tirerack.com/tires/tiret...jsp?techid=167
You can do all the gas law calculation you want, but it does not change the fact of what tire gauges are actually measuring.
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Sea level pressure comes in handy when doing volumetric conversions to STP.
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All gauges measure relative pressure. Absolute gauges measure relative pressure and then use a trick or adjustment to convert it to absolute.
Other pressure gauges use springs and cylinders for the measurement but they are still calibrated against sea level (usually poorly).
Yeah that's hooey... a gauge calibrated for sea level pressure would read actual 0 psig as a negative value at altitude.
Sea level pressure comes in handy when doing volumetric conversions to STP.
Sea level pressure comes in handy when doing volumetric conversions to STP.
I read Kapusta’s statement as a change in pressure of a filled vessel with altitude. That would depend on the vessel. A cylinder of gas filled at sea level is going to have the same pressure at altitude as at sea level. A tire filled at sea level and taken to altitude might show a slight change in pressure but that is because the “vessel” in that case is elastic. That is going to complicate the problem because the tire expands (slightly) which would result in a decrease in pressure (Boyles’ Law).
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Yes.
Pressure gauges are calibrated to read zero at sea level. “Gauge” in psig means standard pressure. Yes, it will read zero at any altitude but it is calibrated to read zero at sea level. We use it as a differential but it is designed to read compared to sea level.
By the way, thank you for saying that “flat” means zero pressure.
It’s more complicated than just due to an increase in altitude, especially where tires are concerned. A tire is at least partly elastic. The pressure differential between altitudes is most likely to be due to that elastic nature than any change in external pressure. A rigid metal cyclinder will not measure a decrease in pressure with a change in altitude because the cylinder is rigid. A tire expands slightly which means that the volume increases. Increased volume with the same amount of gas will cause the pressure to decrease.
They aren’t taking into account the decrease in pressure on the outside of the elastic tire, however. That could easily account for the pressure difference. It’s not a simple problem.
A tire pressure gauge is not calibrated to be zero at sea level atmospheric pressure. It is calibrated for zero when the pressure on the inside of the tire is equal to the pressure outside the tire (atmospheric pressure). That could be at sea level or at 20,000 feet. A flat tire reads zero in either situation.
By the way, thank you for saying that “flat” means zero pressure.
All tire pressure gauges are designed to read the pressure inside the tire ABOVE the actual atmospheric pressure. This is why measured pressure in a tire increase with altitude, even thought the absolute pressure does not. The pressure in the tire remains the same, but the atmospheric pressure drops. Thus the difference increases, thus the tire measures (and behaves) higher in pressure.
For a simple explanation, read the 4th and 5th paragraphs: https://www.tirerack.com/tires/tiret...jsp?techid=167
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The term “moles” is a description of the number of molecules. A “mole” is defined as 6.02 x 10^23 particles of a substance. The number of particles can be a fraction of a mole or a multiple of a mole. To say the number of particles is the same as saying the number of moles. To say “the number of moles of particles” is redundant.
A Bourdon tube gauge is a closed, flattened copper tube that tries to straighten out when pressure is applied to the tube by some system. An absolute gauge is zeroed against a vacuum (with a little bit of calculation because you can’t get a perfect vacuum) while a “gauge” pressure gauge is zeroed at atmospheric pressure. A gear system is connected to the dial to serve as an indicator. The actual calibration is done with a dead weight system or some kind of digital reference gauge but both are adjusted for standard pressure. You could build the gauge at any altitude but it is calibrated against sea level pressure.
This is fun bickering - but defining mole and bourdon tube to an engineer is condescending... (that means talking to people like they're stupid).
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Yes.
Pressure gauges are calibrated to read zero at sea level. “Gauge” in psig means standard pressure. Yes, it will read zero at any altitude but it is calibrated to read zero at sea level. We use it as a differential but it is designed to read compared to sea level.
By the way, thank you for saying that “flat” means zero pressure.
It’s more complicated than just due to an increase in altitude, especially where tires are concerned. A tire is at least partly elastic. The pressure differential between altitudes is most likely to be due to that elastic nature than any change in external pressure. A rigid metal cyclinder will not measure a decrease in pressure with a change in altitude because the cylinder is rigid. A tire expands slightly which means that the volume increases. Increased volume with the same amount of gas will cause the pressure to decrease.
They aren’t taking into account the decrease in pressure on the outside of the elastic tire, however. That could easily account for the pressure difference. It’s not a simple problem.
Pressure gauges are calibrated to read zero at sea level. “Gauge” in psig means standard pressure. Yes, it will read zero at any altitude but it is calibrated to read zero at sea level. We use it as a differential but it is designed to read compared to sea level.
By the way, thank you for saying that “flat” means zero pressure.
It’s more complicated than just due to an increase in altitude, especially where tires are concerned. A tire is at least partly elastic. The pressure differential between altitudes is most likely to be due to that elastic nature than any change in external pressure. A rigid metal cyclinder will not measure a decrease in pressure with a change in altitude because the cylinder is rigid. A tire expands slightly which means that the volume increases. Increased volume with the same amount of gas will cause the pressure to decrease.
They aren’t taking into account the decrease in pressure on the outside of the elastic tire, however. That could easily account for the pressure difference. It’s not a simple problem.
Tire pressure gauges measure the pressure difference between the the inside of the tire and surrounding atmospheric pressure. This is incredibly basic stuff and anyone with the most basic understanding of how a simple tire pressure gauge works knows this. They are not calibrated to "sea level" that does not even make sense to say.
In fact, I am fairly certain that you know this as well. You are clearly a smart guy. Unfortunately for reasons that nobody but you can understand, you decided to disagree for the sake of argument, and are now trying to defend a nonsensical point by changing the subject and making arguments that do not even relate to the topic.
I don't know why you dig yourself into these holes, but it gets old.
Oh, and I did NOT say that there was zero pressure in a flat tire. I said that a tire pressure gauge would READ zero (because the pressure inside and outside the flat tire is the same). But I think you actually know this already. You’re just trying to confuse things.
Last edited by Kapusta; 05-31-22 at 08:47 PM.
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The term “moles” is a description of the number of molecules. A “mole” is defined as 6.02 x 10^23 particles of a substance. The number of particles can be a fraction of a mole or a multiple of a mole. To say the number of particles is the same as saying the number of moles. To say “the number of moles of particles” is redundant.
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Bourdon tube gauges are less susceptible to ambient pressures, but not immune - and I've never seen a Bourdon tube gauge that reads psia... show me one and I'll eat my comment. Most Pabs gauges are for use in highly sensitive lab instruments and use a reference chamber that is not susceptible to atmospheric fluctuations. This has nothing to do with bike tires of course.
Me too, doing mechanical engineering. I've also used them at XXXX feet below sea level (confidential information). Do your gauges have a pin that keeps the dial from going below zero?
This is fun bickering - but defining mole and bourdon tube to an engineer is condescending... (that means talking to people like they're stupid).
My redefining a mole to you was to point out you are in error about the concept. “n” in the ideal gas law is the number of moles. But, because the number of particles is equivalent to the number of moles, “particles” can be substituted for moles. Of course, the units on the gas constant would have to be changed in a calculation. “Moles” is a short hand that is easier to deal with but stating the number of particles is correct.
From a historical context, Avogadro’s Law states the “amount of gas”. Avogadro develop his law in 1812 but the Avogadro’s number (6.02 x10^23 particles) wasn’t established until 1909. The Ideal Gas Law was described in 1834. The concept of a “mole” wasn’t described until 1900. People used other units prior to the discovery of the mole and Avogadro’s number. We just use the mole as short hand.
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How bout them digital pressure gauges. Don't the transducer sense tire pressure independently from atmosphere? I use a digital one. Tospeak or something. I don't like how it attaches to the valve stem but otherwise it is rock solid repeatable.
I measured pressure before yesterday's ride, it was 80 psi at 72F. It got to 98F on my Garmin during my ride, the BMW said 100F. I should have written down my numbers but I was so hot and tired, I forgot. But I seem to recall confirming that tire pressure rises with temperature and my tires were more than 100F. Getting old and cranky with poor eyes and memory has its limitations.
I measured pressure before yesterday's ride, it was 80 psi at 72F. It got to 98F on my Garmin during my ride, the BMW said 100F. I should have written down my numbers but I was so hot and tired, I forgot. But I seem to recall confirming that tire pressure rises with temperature and my tires were more than 100F. Getting old and cranky with poor eyes and memory has its limitations.
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No, actually, "particles" is the superset of "molecules" when you're showing off Avogadro's number, because it's also possible to have a mole of atoms (whether gaseous or solid). You know that, of course. So can we lay this tedious argument for the sake of argument to the side for a while, please?
To be clear, I was not the one who drug the discussion off into the weeds. I pointed out that the Ideal Gas Law is a poor tool for calculating the effect that temperature has on pressure.
Nor did I say that temperature has no influence on pressure. It does. rbrides’ increase in pressure could be related to a temperature increase but it also could be related to a reading error or some combination of the two.
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I read Kapusta’s statement as a change in pressure of a filled vessel with altitude. That would depend on the vessel. A cylinder of gas filled at sea level is going to have the same pressure at altitude as at sea level. A tire filled at sea level and taken to altitude might show a slight change in pressure but that is because the “vessel” in that case is elastic. That is going to complicate the problem because the tire expands (slightly) which would result in a decrease in pressure (Boyles’ Law).
If you are going to argue with me, at least argue with what I am actually saying.
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You should be glad you weren't in my class or lab -- you'd have a zero for the day. You forgot the factors that scale between mole and number of particles or grams, and you were sloppy with using mass.
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The reason I am careful about pressure on tubeless tires goes back to 2016 when my Compass tubeless tires blew off 15 psi under the labeled max pressure and the recent podcast where Silca's Josh Poertner said he had tires blow off at 80 psi that I believe would be rated for 75 psi. I am just an old mediocre engineer who doesn't really want to get into the technical side of this matter, but I believe 100% what Josh said because I observed a similar blow off. (Yes, I reported it to the seller)
Personally, I would run a 30-32mm wide hookless at lower pressure but not 25mm at required pressure (75 psi) and maybe not even 28 mm unless I was really confident in my guage or I lost some weight.
Personally, I would run a 30-32mm wide hookless at lower pressure but not 25mm at required pressure (75 psi) and maybe not even 28 mm unless I was really confident in my guage or I lost some weight.
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My Topeak Smart gauge measures at half pound increments. 80.5 front and 80 rear psi at 50°. Starting temp was about 70° for 25 miles on blacktop. Temp gauge read over 90, but it was more like 85. The tires came in at 82 psi. Not the 5 pound increase, but temperatures did increase. Not worth worrying about.
Good reason to go for a ride on a nice day.
Good reason to go for a ride on a nice day.
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You mean like like this one?
Also, your sentence doesn't even make sense... the vast majority of people with a passing exposure have never had any exposure?
My redefining a mole to you was to point out you are in error about the concept. “n” in the ideal gas law is the number of moles. But, because the number of particles is equivalent to the number of moles, “particles” can be substituted for moles. Of course, the units on the gas constant would have to be changed in a calculation.
I have no idea who you are or what you do.
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Well, I'd say something, but this comes to mind...ultracrepidarian.
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