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Posted: 5/31/2019 11:30:12 AM EDT
[#1]
Quote HistoryQuoted:
I looked it up: pressure is equal to force divided by area. So if the area changed then yes the pressure would change. But simply making a tire lay flatter is not changing the volume just the shape. So the answer for a vehicle tire is no. It's not like stuffing a balloon in a square box. |
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Posted: 5/31/2019 11:30:34 AM EDT
[#2]
Quote HistoryQuoted:
The answer is Yes. How? PV=nRT |
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Posted: 5/31/2019 11:31:24 AM EDT
[#3]
Quote HistoryQuoted: If you change the shape of something with a rigid carcass like a steel belted radial, then you are going to change the volume. It's not like stuffing a balloon in a square box. 
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Posted: 5/31/2019 11:32:10 AM EDT
[#4]
Quote HistoryQuoted: There's no "slightly" about it. I inflate the rear tires of my truck to 71 PSI, per the door sticker. When I hitch up my trailer with 1100 lbs of tongue weight, and then I get on the highway, the tires will go up to 82 psi after 30 minutes or so. This is according to the TPMS display on my dash. Total weight on the rear axle is about 5500 lbs. And to the OP's question, no, the pressure does not change by simply adding the weight while parked. Again, the TPMS shows 71 psi before hitching IP, and 71 psi after. |
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Posted: 5/31/2019 11:35:49 AM EDT
[#5]
Quote HistoryQuoted:
Tire isn't rigid, otherwise it wouldn't bulge |
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Posted: 5/31/2019 12:11:53 PM EDT
[#6]
In this thread we learn about people who can use a lot of words proving that they don’t know what they are talking about.
We also learn about people who think a small number is the same as zero. |
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Posted: 5/31/2019 12:15:51 PM EDT
[#7]
Quote HistoryQuoted:
In this thread we learn about people who can use a lot of words proving that they don't know what they are talking about. We also learn about people who think a small number is the same as zero. Is this a scientific exercise or a real-world effect exercise? |
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Posted: 5/31/2019 12:16:09 PM EDT
[#8]
Quote HistoryQuoted:
Pretty rigid compared to a balloon. Quote HistoryQuoted:
Quoted:
Tire isn't rigid, otherwise it wouldn't bulge 
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Posted: 5/31/2019 12:21:13 PM EDT
[#9]
30 psi and full load of 1000 lbs?
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Posted: 5/31/2019 12:24:54 PM EDT
[#10]
Quote HistoryQuoted:
30 psi and full load of 1000 lbs? |
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Posted: 5/31/2019 12:26:35 PM EDT
[#11]
Quote HistoryQuoted:
30 psi and full load of 1000 lbs? ST175/80R13 trailer tires 
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Posted: 5/31/2019 12:28:03 PM EDT
[#12]
Quote HistoryQuoted:
What's up? Quote HistoryQuoted:
Quoted:
30 psi and full load of 1000 lbs? Maybe I'm wrong idk. When I have a good load or loaded trailer I will run higher psi. When fully loaded I will run it as high as what the tire states, not the door sticker. |
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Posted: 5/31/2019 12:29:21 PM EDT
[#13]
Quote HistoryQuoted:
Not significantly. Temperature is a larger contributor usually. But more weight = more deformity on road contact portion of tire = less volume = greater pressure. |
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Posted: 5/31/2019 12:30:46 PM EDT
[#14]
pv=nrt
p1v1 = p2v2 |
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Posted: 5/31/2019 12:32:58 PM EDT
[#15]
Quote HistoryQuoted: I alway assumed the recommended tire pressure was for an unloaded vehicle. Maybe I'm wrong idk. When I have a good load or loaded trailer I will run higher psi. When fully loaded I will run it as high as what the tire states, not the door sticker. That was the whole deal with the Ford/Firestone debacle from some years ago. Everybody blamed the tire for having blowout issues, when it was Ford who de-flated the tires to meet roll requirements. As you can see from the chart I just posted, the same tire has different load carrying capacities at different pressures. Running your tires at maximum PSI when empty can:
ETA: running too LOW of psi in your tires for the given conditions can results in:
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Posted: 5/31/2019 12:36:26 PM EDT
[#16]
Only if there's a treadmill and magnets involved.
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Posted: 5/31/2019 12:43:39 PM EDT
[#17]
Quote HistoryQuoted:
Lots of people smoking something this evening. Yes. Pressure increases. It is not a linear increase to match the load, as the tire itself will deform as pressure increases. Doesn't anyone trailer? Empty trailers wear out the center of the tire all the time because they are over-pressured empty and correct when full. The load smashes the tire making a larger contact patch, and increasing tire pressure. |
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Posted: 5/31/2019 12:47:00 PM EDT
[#18]
Quote HistoryQuoted:
I'm just making my way through this thread, but here's the first correct answer. Doesn't anyone trailer? Empty trailers wear out the center of the tire all the time because they are over-pressured empty and correct when full. The load smashes the tire making a larger contact patch, and increasing tire pressure. Quote HistoryQuoted:
Quoted:
Lots of people smoking something this evening. Yes. Pressure increases. It is not a linear increase to match the load, as the tire itself will deform as pressure increases. Doesn't anyone trailer? Empty trailers wear out the center of the tire all the time because they are over-pressured empty and correct when full. The load smashes the tire making a larger contact patch, and increasing tire pressure. Part in red: BY HOW MUCH??? I've never seen it enough to even register on a tire pressure gauge under normal loads. The tire changing shape a bit does not mean volume inside the tire (or the air pressure) was effected in any significant manor. |
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Posted: 5/31/2019 12:53:20 PM EDT
[#19]
After reading through this thread, the common misnomer I am seeing is the belief a load on a tire actually decreases the volume; this is incorrect. In fact, the opposite is true since the rubber in the tire will stretch ever so slightly increasing volume. A change of shape (sidewall bulge) does not mean there is a change of volume. The only variables that will affect pressure within a tire is temperature and volume. (see below) As others have stated, a load can cause a tire to heat up hence changing the pressure, but the mass of the load on the tire will not.
Why do we add air to tires that are bulging under a load? To increase the pressure. If the load on tire actually increased the pressure, wouldn’t the tire inflate itself? Boyle’s Law: Constant=temperature. Volume increases, pressure decreases or volume decreases, pressure increases. Inversely proportional Charles’ Law: Constant=pressure. Temperature increases, Volume increases or Temperature decreases, Volume decreases. Directly proportional. Gay Lussac’s Law: Constant=volume. Temperature increases, Pressure increases. Directly proportional. |
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Posted: 5/31/2019 12:53:44 PM EDT
[#20]
What size coal is in the truck?
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Posted: 5/31/2019 12:54:41 PM EDT
[#21]
Yes
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Posted: 5/31/2019 1:07:55 PM EDT
[#22]
I would guess no air pressure change with more weight on the tire. If you load a whole week of groceries into your F 350 the air in the tires isn't really transferring that weight to the Walmart parking lot. The tire walls are. The tire walls can only hold so much, just like anything else they will fail if too many Cheezey Poofs are loaded on.
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Posted: 5/31/2019 1:15:58 PM EDT
[#23]
Yes, pressure does increase as long as the resulting resulting strain is staying within the elastic range of the tire's material properties.
The rigid tire carcass means that the relationship between load and pressure is not linear (stand on a bare tire with no rim, for example) Just because you don't notice the pressure increase with imprecise instruments does not mean it is not there, nor that it is not repeatable or quantifiable. |
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Posted: 5/31/2019 1:16:29 PM EDT
[#24]
Quote HistoryQuoted:
The answer is Yes. How? PV=nRT P=nRT/V |
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Posted: 5/31/2019 1:18:43 PM EDT
[#25]
Quote HistoryQuoted:
Tire pressures on the door are primarily for stability ratings and ride quality. ETA: And expected/rated load on pickup trucks. That was the whole deal with the Ford/Firestone debacle from some years ago. Everybody blamed the tire for having blowout issues, when it was Ford who de-flated the tires to meet roll requirements. As you can see from the chart I just posted, the same tire has different load carrying capacities at different pressures. Running your tires at maximum PSI when empty can:
ETA: running too LOW of psi in your tires for the given conditions can results in:
OEM:euro-metric 265/70/16/112 @ 30 psi=2,149 lbs inflated load capacity Aftermarket tire: LT265/75/16/123(E) @ 37 psi=1,954 lbs inflated load capacity(after P/euro-metric to LT de-rating factor of 1.1) Truck has a curb weight of 4,500 lbs and GVWR of 5,600 lbs. What I'm getting at is, there's more being considered than straight GVWR when their calculating the recommended psi. |
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Posted: 5/31/2019 1:19:35 PM EDT
[#26]
Geez, freshman high school physics, what a statement to the failure of public education. Boyle's Gas Law even high school Chemistry should have covered this. And to think Common Core was suppose to make this better.
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Posted: 5/31/2019 1:25:12 PM EDT
[#27]
Quote HistoryQuoted:
Seems to me, if you sit on a balloon, it's going to pop.  |
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Posted: 5/31/2019 1:30:23 PM EDT
[#28]
Quote HistoryQuoted:
After reading through this thread, the common misnomer I am seeing is the belief a load on a tire actually decreases the volume; this is incorrect. In fact, the opposite is true since the rubber in the tire will stretch ever so slightly increasing volume. A change of shape (sidewall bulge) does not mean there is a change of volume. The only variables that will affect pressure within a tire is temperature and volume. (see below) As others have stated, a load can cause a tire to heat up hence changing the pressure, but the mass of the load on the tire will not. Why do we add air to tires that are bulging under a load? To increase the pressure. If the load on tire actually increased the pressure, wouldn’t the tire inflate itself? Boyle’s Law: Constant=temperature. Volume increases, pressure decreases or volume decreases, pressure increases. Inversely proportional Charles’ Law: Constant=pressure. Temperature increases, Volume increases or Temperature decreases, Volume decreases. Directly proportional. Gay Lussac’s Law: Constant=volume. Temperature increases, Pressure increases. Directly proportional. 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 1:30:48 PM EDT
[#29]
Quote HistoryQuoted:
I have the same tire on my Tacoma; runs at 37 psi. OEM:euro-metric 265/70/16/112 @ 30 psi=2,149 lbs inflated load capacity Aftermarket tire: LT265/75/16/123(E) @ 37 psi=1,954 lbs inflated load capacity(after P/euro-metric to LT de-rating factor of 1.1) Truck has a curb weight of 4,500 lbs and GVWR of 5,600 lbs. What I'm getting at is, there's more being considered than straight GVWR when their calculating the recommended psi. Quote HistoryQuoted:
Quoted:
Tire pressures on the door are primarily for stability ratings and ride quality. ETA: And expected/rated load on pickup trucks. That was the whole deal with the Ford/Firestone debacle from some years ago. Everybody blamed the tire for having blowout issues, when it was Ford who de-flated the tires to meet roll requirements. As you can see from the chart I just posted, the same tire has different load carrying capacities at different pressures. Running your tires at maximum PSI when empty can:
ETA: running too LOW of psi in your tires for the given conditions can results in:
OEM:euro-metric 265/70/16/112 @ 30 psi=2,149 lbs inflated load capacity Aftermarket tire: LT265/75/16/123(E) @ 37 psi=1,954 lbs inflated load capacity(after P/euro-metric to LT de-rating factor of 1.1) Truck has a curb weight of 4,500 lbs and GVWR of 5,600 lbs. What I'm getting at is, there's more being considered than straight GVWR when their calculating the recommended psi. The fact that you went from a passenger tire to an LT tire changes handling quite a bit. The sidewalls are far stiffer. |
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Posted: 5/31/2019 1:32:05 PM EDT
[#30]
Quote HistoryQuoted:
Geez, freshman high school physics, what a statement to the failure of public education. Boyle's Gas Law even high school Chemistry should have covered this. And to think Common Core was suppose to make this better. |
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Posted: 5/31/2019 1:35:07 PM EDT
[#31]
Pressure doesn't change dramatically.
IE; when I set a tractor/trailer to 100/90D/90T, then it get's loaded with 50K lbs of product, pressure is still relatively 100/90/90. |
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Posted: 5/31/2019 1:44:34 PM EDT
[#32]
Quoted:
You guys seem to enjoy physics questions. How about this? You inflate your vehicles tires to 30psi just as the manual and door frame label recommend, then you add 1000 lbs of weight in cargo (gravel, firewood, whatever). You can SEE your tires look different. When measured, do you think the pressure has changed? Because the door sticker doesn't know what tires you run, what weight those tires can carry, and what payload you are carrying. _ |
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Posted: 5/31/2019 1:48:34 PM EDT
[#33]
The pressure doesn't change much. The tire deforms to increase the contact patch while keeping it's volume nearly constant. It will obviously be compressed a bit, not enough to notice on a gauge.
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Posted: 5/31/2019 1:57:38 PM EDT
[#34]
Yes, but not a meaningful amount under normal loads.
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Posted: 5/31/2019 2:01:16 PM EDT
[#35]
Yes the pressure will increase under load if significant enough.
What the fuck kind of nonsense is going on in here? Jack up a tire. Fill tire to 5psi Remove jack. Measure psi Oh my goodness it higher. Rocket science. |
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Posted: 5/31/2019 2:09:23 PM EDT
[#36]
Quote HistoryQuoted:
Yes the pressure will increase under load if significant enough. What the fuck kind of nonsense is going on in here? Jack up a tire. Fill tire to 5psi Remove jack. Measure psi Oh my goodness it higher. Rocket science. |
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Posted: 5/31/2019 2:12:16 PM EDT
[#37]
Quote HistoryQuoted:
I dare you to try exactly that with a truck/car tire and non +-.001 gauge. Quote HistoryQuoted:
Quoted:
Yes the pressure will increase under load if significant enough. What the fuck kind of nonsense is going on in here? Jack up a tire. Fill tire to 5psi Remove jack. Measure psi Oh my goodness it higher. Rocket science. Lift tire off floor. Fill to 5 psi. Sit on bike. Record PSI I've done it to measure psi for mud riding with a full load. |
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Posted: 5/31/2019 2:15:41 PM EDT
[#38]
Quote HistoryQuoted:
Back when I was working for a different company, were were installing a ballasted roof on a school. The roof was almost complete - we only had about 17-ish more tons of gravel on order at the pit. They sent this total numbskull of a truck driver to go pick up some gravel and take it to the jobsite. His single-axle dump truck could only hold about five tons of weight, so when he got to the gravel pit and they asked him how much of the remaining rock he wanted, he just said, "Hell, give me all of it." He made it about a half mile before all six tires exploded and he was left sitting by the roadside on his rims. So yes, if you put a shit-ton of weight on a truck, it DOES change the air pressure in the tires. The pressure decreases to zero. 
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Posted: 5/31/2019 2:18:36 PM EDT
[#39]
Pressure increases to some extent because volume decreases. A cross section of the tire before the load would show it being closer to round. After the load, it will be more oval. The relationship of volume per unit of surface area decreases as the shape changes from round towards flat.
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Posted: 5/31/2019 2:19:27 PM EDT
[#40]
Quote HistoryQuoted:
Geez, freshman high school physics, what a statement to the failure of public education. Boyle's Gas Law even high school Chemistry should have covered this. And to think Common Core was suppose to make this better. 
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Posted: 5/31/2019 2:25:59 PM EDT
[#41]
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Posted: 5/31/2019 2:27:48 PM EDT
[#42]
Quote HistoryQuoted:
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. |
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Posted: 5/31/2019 2:30:10 PM EDT
[#43]
Quote HistoryQuoted:
Know how I know that this story is 100% fabrication? Quote HistoryQuoted:
Quoted:
Back when I was working for a different company, were were installing a ballasted roof on a school. The roof was almost complete - we only had about 17-ish more tons of gravel on order at the pit. They sent this total numbskull of a truck driver to go pick up some gravel and take it to the jobsite. His single-axle dump truck could only hold about five tons of weight, so when he got to the gravel pit and they asked him how much of the remaining rock he wanted, he just said, "Hell, give me all of it." He made it about a half mile before all six tires exploded and he was left sitting by the roadside on his rims. So yes, if you put a shit-ton of weight on a truck, it DOES change the air pressure in the tires. The pressure decreases to zero. |
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Posted: 5/31/2019 2:31:02 PM EDT
[#44]
Headed out to the skatepark with my boys. I'm gonna try out my new found wizardry skills.
I'll post my results. |
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Posted: 5/31/2019 2:33:15 PM EDT
[#45]
Yes. The tires compress because of the weight. And then there is a temperature increase because of the deformity when you drive.
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Posted: 5/31/2019 2:36:18 PM EDT
[#46]
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. 
Accuracy vs precision will add a few pages of jibber-jabber. |
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Posted: 5/31/2019 2:37:11 PM EDT
[#47]
go put a tire gauge on your truck take a reading, record your results
fill it up with heavy stuff and take another reading, record your results,compare results. |
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Posted: 5/31/2019 2:45:15 PM EDT
[#48]
Quote HistoryQuoted:
Headed out to the skatepark with my boys. I'm gonna try out my new found wizardry skills. I'll post my results. I've done this with tractor tires and semi truck tires and no change was ever recorded (on a standard stick gauge). And also please report if you squat the tire to the rims (damaging your tire ) or just bulge a bit from weight. There is a difference, as I don't know *many* arfcommers who would run their truck fully loaded on the rims 
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Posted: 5/31/2019 2:46:47 PM EDT
[#49]
Yes, pressure increases.
Imagine the cross section of the bottom part of the tire as a rough circle. As you put more weight on the tire, that shape becomes more of a flattened oval. Tires are not very elastic, so the circumference of the circle won't change (very much) as it's squished into an oval. Therefore, the area of the cross section decreases. Now imagine the tire as a 3D shape again, and you can see that the tire volume decreases as it's squished by more weight. The mass of air in the tire does not change.... so as the volume of the container decreases, the pressure must increase. |
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Posted: 5/31/2019 2:48:37 PM EDT
[#50]
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. Quote HistoryQuoted:
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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