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Posted: 5/31/2019 2:57:39 PM EDT
[#1]
Quote HistoryQuoted:
Yes Put 1,000,000 lbs in the back of your truck- what happens? The tires pop. Why do they pop? If there is no change in pressure, the tires will not pop.  https://www.youtube.com/watch?v=v0fE8nIt_bY
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Posted: 5/31/2019 3:06:32 PM EDT
[#2]
Quote HistoryQuoted: Now you’ve fone and done it 
Accuracy vs precision will add a few pages of jibber-jabber. |
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Posted: 5/31/2019 3:09:41 PM EDT
[#3]
Quote HistoryQuoted:
What the hell. OK i just did it. Chevy suburban Drivers front / Left front Jack up truck Set to 10 PSI Lower jack Record PSI 11.2 PSI OMG I'm a wizard. Can you try it at 30? For another test, take something with a tall sidewall, jack it up, and let all of the air out until it's at ambient pressure. Cap it and then set the vehicle back down on the ground. I bet that gage pressure won't be "0"... |
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Posted: 5/31/2019 3:17:09 PM EDT
[#4]
If the the tire deforms under additional load the pressure has to go up but since the contact patch area increases significantly faster than volume-decreases/pressure-rises it takes a lot of addition load to see an appreciable increase in pressure.
Using some simplified geometry of a tire to make the math easy and assuming no major stretch of the tire (not a bad assumption given the amount of cording and steel belts in a modern tire) A 265/60R18 tire with 35 psi and 1250 lbs of load has a contact patch of ~ 36 in^2 if you increase that load to 1750 lbs the contact patch goes up to ~50 inch^2 and the internal pressure of the tire would rise to 35.03 psi due to the additional deformation. YMMV |
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Posted: 5/31/2019 3:29:09 PM EDT
[#5]
Quote HistoryQuoted:
Did you use Armor All on them? 
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Posted: 5/31/2019 3:30:28 PM EDT
[#6]
Quote HistoryQuoted:
The volume of air, does not increase, what happens is you have decreased the space that volume of air occupies, 30 PSI is 30 PSI. In a sealed environment, it can exert more or less pressure due to the volume of that sealed environment as it decreases or increases, but the volume of the air will remain the same unless it is heated or cooled. Quote HistoryQuoted:
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But pressure of a gas is related to volume that gas is in (area). If you constrict the volume that a gas is in the pressure will increase. If you increase the volume pressure will decrease. The only other thing I can think of then is the top of the tire is also deforming so the overall volume is remaining the same. What is volume of air if not "space occupied"? And we're not talking about volume, we are talking about pressure. A gas expands to the volume of its container. JFC, this site is like "are you smarter than a 4th Grader?". |
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Posted: 5/31/2019 3:32:32 PM EDT
[#7]
Quote HistoryQuoted:
If the the tire deforms under additional load the pressure has to go up but since the contact patch area increases significantly faster than volume-decreases/pressure-rises it takes a lot of addition load to see an appreciable increase in pressure. Using some simplified geometry of a tire to make the math easy and assuming no major stretch of the tire (not a bad assumption given the amount of cording and steel belts in a modern tire) A 265/60R18 tire with 35 psi and 1250 lbs of load has a contact patch of ~ 36 in^2 if you increase that load to 1750 lbs the contact patch goes up to ~50 inch^2 and the internal pressure of the tire would rise to 35.03 psi due to the additional deformation. YMMV |
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Posted: 5/31/2019 3:37:54 PM EDT
[#8]
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Posted: 5/31/2019 3:51:49 PM EDT
[#9]
Quote HistoryQuoted:
That is a great answer. Quote HistoryQuoted:
Quoted:
If the the tire deforms under additional load the pressure has to go up but since the contact patch area increases significantly faster than volume-decreases/pressure-rises it takes a lot of addition load to see an appreciable increase in pressure. Using some simplified geometry of a tire to make the math easy and assuming no major stretch of the tire (not a bad assumption given the amount of cording and steel belts in a modern tire) A 265/60R18 tire with 35 psi and 1250 lbs of load has a contact patch of ~ 36 in^2 if you increase that load to 1750 lbs the contact patch goes up to ~50 inch^2 and the internal pressure of the tire would rise to 35.03 psi due to the additional deformation. YMMV |
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Posted: 5/31/2019 4:02:02 PM EDT
[#10]
Simple answer, yes. Gas is compressible; as it compresses, the pressure changes. Yes, the tire will deflect some but it is not a 1:1 ratio. The tire is an airspring.
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Posted: 5/31/2019 4:08:57 PM EDT
[#11]
Quote HistoryQuoted:
Wait wat? Adding load increases tire volume and thus decreases tire pressure? I'm gonna need to see some work on this one. Maybe if the tire exceeds it's elasticity range and fails and tears a giant bubble out of the sidewall, but doesn't actually burst. This seems like a perfect experiment for someone with an actual precise (2+ decimal places for PSI) pressure monitor to perform and then chart the pressure with added load. |
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Posted: 5/31/2019 4:16:52 PM EDT
[#12]
Let's do this mathematically.
assume your tires are pressurized to 30 psi. Assume your truck weighs 5000 lbs. I just measured my truck tire in contact with the ground. 81 sq inches. 4 tires makes that 324 sq inches 324 sq inches at 30 pounds per square inch = 9720 lbs what this means I have no idea. 
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Posted: 5/31/2019 4:17:33 PM EDT
[#13]
Quote HistoryQuoted:
Heat will cause pressure to increase, but heavier loads do not, it simply displaces the air into a small volume vessel. If you park your truck in the driveway and do not move it, but add a thousand pounds of ballast you have not increased the overall pressure of the tire, you have simply displaced into a smaller area. Air expands with heat and contracts with cold. 30 PSI is 30 PSI no matter what happens, 30 PSI can be squeezed into a small vessel, which is exactly what happens when you put a load on a truck and that depends on how much side deflection your particular tire has, but is still has 30 PSI in that tire. The tire pressure recommended accounts for heat increase within the designed load rating. That is why it is specified as a cold pressure. The general rule is 1 psi per ten deg F up or down. |
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Posted: 5/31/2019 4:48:25 PM EDT
[#14]
Quote HistoryQuoted:
Let's do this mathematically. assume your tires are pressurized to 30 psi. Assume your truck weighs 5000 lbs. I just measured my truck tire in contact with the ground. 81 sq inches. 4 tires makes that 324 sq inches 324 sq inches at 30 pounds per square inch = 9720 lbs what this means I have no idea. 
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Posted: 5/31/2019 5:30:03 PM EDT
[#15]
Quote HistoryQuoted:
You probably assumed the total area under each tire, you need to subtract the area created by the tire grooves to get the correct contact patch. Quote HistoryQuoted:
Quoted:
Let's do this mathematically. assume your tires are pressurized to 30 psi. Assume your truck weighs 5000 lbs. I just measured my truck tire in contact with the ground. 81 sq inches. 4 tires makes that 324 sq inches 324 sq inches at 30 pounds per square inch = 9720 lbs what this means I have no idea. |
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Posted: 5/31/2019 5:31:13 PM EDT
[#16]
Quote HistoryQuoted:
Heat will cause pressure to increase, but heavier loads do not, it simply displaces the air into a small volume vessel. If you park your truck in the driveway and do not move it, but add a thousand pounds of ballast you have not increased the overall pressure of the tire, you have simply displaced into a smaller area. Air expands with heat and contracts with cold. 30 PSI is 30 PSI no matter what happens, 30 PSI can be squeezed into a small vessel, which is exactly what happens when you put a load on a truck and that depends on how much side deflection your particular tire has, but is still has 30 PSI in that tire. If you change the volume (V) and keep everything else constant the pressure (P) absolutely has to change. Which is exactly what you're saying, that is, changing the volume. |
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Posted: 5/31/2019 6:09:32 PM EDT
[#17]
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Posted: 5/31/2019 6:18:00 PM EDT
[#18]
this is why shot that hauls heavy uses 10+ ply tires and your tacoma and F 150 use glorified car tires
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Posted: 5/31/2019 11:13:35 PM EDT
[#19]
Quote HistoryQuoted:
5psi not 10. The amount of volume to increase past that 5 psi in any significant amount will almost certainly be more than the volume reduction from damaging your tire. ETA: Pics or it didn't happen, as it was only 22 minutes from my post to yours, during work hours. Quote HistoryQuoted:
Quoted:
Quoted:
I dare you to try exactly that with a truck/car tire and non +-.001 gauge. Chevy suburban Drivers front / Left front Jack up truck Set to 10 PSI Lower jack Record PSI 11.2 PSI OMG I'm a wizard. The amount of volume to increase past that 5 psi in any significant amount will almost certainly be more than the volume reduction from damaging your tire. ETA: Pics or it didn't happen, as it was only 22 minutes from my post to yours, during work hours. |
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Posted: 5/31/2019 11:20:19 PM EDT
[#20]
Quote HistoryQuoted:
Hah. It happened. My point as stated is that pressure will go up if the load is significant enough. Will 1000 pounds deform a 30psi truck tire significantly? Depends on the tire. A smooth riding thin sidewall tire, maybe. A 10 ply truck tire...maybe not. |
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