Tire pressure
Drifting
Joined: Jun 2013
Posts: 1,965
Likes: 343
From: Shell Point (Crawfordville) Florida
In response to the automobile engineer, I mean the retired throat surgeon doctor about his self made theory about air not escaping through rubber...maybe the doc can relate to this>>>sorta like sweat not escaping through skin, but through his pee pee?....heres just an FYI .....
" the principle is called Graham's law.. a well known engineering and scientific principle.. also At GM we have always called that DOT sticker on the door " Idiot Proofing " Since it only keep people out of trouble, people who max out tire pressure based on Max sidewall psi printed on it.
....for that nay sayer or should I say the object of our idiot proofing....
Graham’s Law:
Are Nitrogen Molecules Really Larger Than Oxygen Molecules? The correct answer, with respect to “permeation”, is yes.
There's often confusion associated with the molecular size, molecular weight and permeation properties of oxygen and nitrogen molecules, and GNI is often called to task to explain why nitrogen actually migrates (permeates) out through the rubber of a tire slower than does oxygen but at a much higher rate. both molecules exit through the rubber sidewall .. But the O2 exits much faster.. since air consists of oxygen and Nitrogen. The reason people put pure nitrogen in their tires is because the molecules are larger and there is less swing in the loss of tire pressure.
So for the guy saying BS.. let's see his engineering degree.. or any fact based on his lack of automotive knowledge based on any scientific principles or laws. and also, that door sticker for people just like him.
Fine tuning tires is what every race team in the world does. It separates professionals from amateurs who think they know something about automotive technology.
Since air is made up of 78% nitrogen, 21% oxygen 1% argon and trace amounts of carbon dioxide, the potential of a dry sidewall allowing the small O2 molecule to escape is very relevant. So says Graham's law.. a scientific principle Not BS.
" the principle is called Graham's law.. a well known engineering and scientific principle.. also At GM we have always called that DOT sticker on the door " Idiot Proofing " Since it only keep people out of trouble, people who max out tire pressure based on Max sidewall psi printed on it.
....for that nay sayer or should I say the object of our idiot proofing....
Graham’s Law:
Are Nitrogen Molecules Really Larger Than Oxygen Molecules? The correct answer, with respect to “permeation”, is yes.
There's often confusion associated with the molecular size, molecular weight and permeation properties of oxygen and nitrogen molecules, and GNI is often called to task to explain why nitrogen actually migrates (permeates) out through the rubber of a tire slower than does oxygen but at a much higher rate. both molecules exit through the rubber sidewall .. But the O2 exits much faster.. since air consists of oxygen and Nitrogen. The reason people put pure nitrogen in their tires is because the molecules are larger and there is less swing in the loss of tire pressure.
So for the guy saying BS.. let's see his engineering degree.. or any fact based on his lack of automotive knowledge based on any scientific principles or laws. and also, that door sticker for people just like him.
Fine tuning tires is what every race team in the world does. It separates professionals from amateurs who think they know something about automotive technology.
Since air is made up of 78% nitrogen, 21% oxygen 1% argon and trace amounts of carbon dioxide, the potential of a dry sidewall allowing the small O2 molecule to escape is very relevant. So says Graham's law.. a scientific principle Not BS.
Graham's law, formulated in 1848 (40 years before the inflatable automobile tire was invented), relates to a smaller size molecule diffusing through a membrane or effusing through a pinhole faster than a large size molecule, we all agree on that principle. But the sidewall of a tire is not permeable to atmospheric gas and you have no evidence it is, and that's why inflatable rubber tires have been around since they were first used by Benz in 1888. And they have been much improved in the past 130 years. So again, if you want to try and prove your point about O2 diffusing through the rubber sidewall of a tire faster than N2, as Graham theoretically says it should, then prove it to me with a study showing the increase in N2 and decrease in O2 concentration inside a tire over time. I'll wait. Otherwise, stop spouting non-relevant information which proved absolutely nothing.
Then you go on to say "nitrogen actually migrates (permeates) out through the rubber of a tire slower than does oxygen but at a much higher rate." WTF does that mean? Nitrogen is slower but it's faster? Make up your mind.
And if you'd really like to know, Nitrogen is put into tires to try and displace the water vapor in the air that's in the tires (makes up about 5% of the atmosphere), which is mostly responsible for the pressure fluctuations with temperature.
BTW, I am not a retired throat surgeon, I don't know how you made that up. Also, the analogy you concocted about my self made theory about air not escaping through rubber "sorta like sweat not escaping through skin, but through his pee pee?" How old are you? Did you forget to take your meds today?: You too were an engineer working for GM? On what part of the car, the radio *****?
Try and think a little more or attempt to do a little research before you post garbage like that. We are all here to learn from one another, not to waste time sorting out crap from real sound advice. And this is not my opinion, it was a statement of fact.
Last edited by mrlmd; Feb 20, 2018 at 05:50 PM.
Team Owner
Joined: May 2001
Posts: 25,057
Likes: 1,265
From: Virginia
St. Jude Donor '11
There are so many inaccuracies in your post it's comical. Talking about trying to baffle people with bullshit, you win the prize for today.
Graham's law, formulated in 1848 (40 years before the inflatable automobile tire was invented), relates to a smaller size molecule diffusing through a membrane or effusing through a pinhole faster than a large size molecule, we all agree on that principle. But the sidewall of a tire is not permeable to atmospheric gas and you have no evidence it is, and that's why inflatable rubber tires have been around since they were first used by Benz in 1888. And they have been much improved in the past 130 years. So again, if you want to try and prove your point about O2 diffusing through the rubber sidewall of a tire faster than N2, as Graham theoretically says it should, then prove it to me with a study showing the increase in N2 and decrease in O2 concentration inside a tire over time. I'll wait. Otherwise, stop spouting non-relevant information which proved absolutely nothing.
Then you go on to say "nitrogen actually migrates (permeates) out through the rubber of a tire slower than does oxygen but at a much higher rate." WTF does that mean? Nitrogen is slower but it's faster? Make up your mind.
And if you'd really like to know, Nitrogen is put into tires to try and displace the water vapor in the air that's in the tires (makes up about 5% of the atmosphere), which is mostly responsible for the pressure fluctuations with temperature.
BTW, I am not a retired throat surgeon, I don't know how you made that up. Also, the analogy you concocted about my self made theory about air not escaping through rubber "sorta like sweat not escaping through skin, but through his pee pee?" How old are you? Did you forget to take your meds today?: You too were an engineer working for GM? On what part of the car, the radio *****?
Try and think a little more or attempt to do a little research before you post garbage like that. We are all here to learn from one another, not to waste time sorting out crap from real sound advice. And this is not my opinion, it was a statement of fact.
Graham's law, formulated in 1848 (40 years before the inflatable automobile tire was invented), relates to a smaller size molecule diffusing through a membrane or effusing through a pinhole faster than a large size molecule, we all agree on that principle. But the sidewall of a tire is not permeable to atmospheric gas and you have no evidence it is, and that's why inflatable rubber tires have been around since they were first used by Benz in 1888. And they have been much improved in the past 130 years. So again, if you want to try and prove your point about O2 diffusing through the rubber sidewall of a tire faster than N2, as Graham theoretically says it should, then prove it to me with a study showing the increase in N2 and decrease in O2 concentration inside a tire over time. I'll wait. Otherwise, stop spouting non-relevant information which proved absolutely nothing.
Then you go on to say "nitrogen actually migrates (permeates) out through the rubber of a tire slower than does oxygen but at a much higher rate." WTF does that mean? Nitrogen is slower but it's faster? Make up your mind.
And if you'd really like to know, Nitrogen is put into tires to try and displace the water vapor in the air that's in the tires (makes up about 5% of the atmosphere), which is mostly responsible for the pressure fluctuations with temperature.
BTW, I am not a retired throat surgeon, I don't know how you made that up. Also, the analogy you concocted about my self made theory about air not escaping through rubber "sorta like sweat not escaping through skin, but through his pee pee?" How old are you? Did you forget to take your meds today?: You too were an engineer working for GM? On what part of the car, the radio *****?
Try and think a little more or attempt to do a little research before you post garbage like that. We are all here to learn from one another, not to waste time sorting out crap from real sound advice. And this is not my opinion, it was a statement of fact.
"OccupationRetired CV/Thoracic Surgeon"
Well i'll be darned...below the throat surgeon...chest cavity organ surgeon...idiot surgeon...all the same...
Sir, I think you have some real mental issues, seriously... I guess you didn't see the quote marks around what I copied from another persons post in another thread...those were not my remarks...someone else said it and I quoted them...now calm down and stop forgetting to take your valium...and stop being a hater...move on...I'm out of this discussion...you do what you do best...argue and fight
Advanced
Joined: Jul 2014
Posts: 72
Likes: 6
For those of you that would rather go by the sticker in your door jamb rather than what the actual tire manufacturers recommend, so be it. I've been driving a long time, towed more miles than most of you have put on your precious cars, never ever blew a tire. I'll do things my way, you follow whatever advice you want to. I'm out........ Cold Maximum is printed there for YOU to see, and they know the pressure will rise some with use. I use the cold max as my HOT MAX. Do as you like.
Drifting
Joined: Jun 2013
Posts: 1,965
Likes: 343
From: Shell Point (Crawfordville) Florida
Rage on Yellow but it takes a real man to admit when he's wrong. I am what I said, not what you said, but you won't admit a mistake, you just attack out of immaturity and childlike insecurity.
Your post was inaccurate and your immaturity blasts out, so, like you said, move on, out of this discussion.
And air does not leak out through the rubber sidewalls of a tire, not nitrogen, oxygen, or any other gas, which was the original point made before.
Your post was inaccurate and your immaturity blasts out, so, like you said, move on, out of this discussion.
And air does not leak out through the rubber sidewalls of a tire, not nitrogen, oxygen, or any other gas, which was the original point made before.
Safety Car
Joined: Jun 2017
Posts: 4,786
Likes: 425
From: North Georgia, USA
To the OP, the placard on the door jamb should say "30 PSI cold." and that's the best pressure for tires of the stock size and with the same maximum inflation pressure and maximum load rating as the stock (original factory installed) tires.
Corvettes have had various ratings on the door jamb over the years. You see anything between 30 PSI cold and 35 PSI cold. The specific number depends on the year, and whether GM was focused more on ride quality and handling (30 PSI cold), or whether they were tight on the CAFE requirements that year and were focused more on fuel economy (35 PSI cold).
From experience, for most corvettes since the C4 generation, 30 PSI cold gives the best ride, handling, and the most even tire wear. 35 PSI cold gives a slightly rougher ride, somewhat less grip in cornering, and better fuel economy (between 0.5 mpg and 1.5 mpg higher). At 35 PSI, ,there's also slightly more wear at the center of the tire tread than at the edges.
There's more lateral grip, and a bit more grip for acceleration and braking in lower pressures, and more fuel economy, at the cost of grip and comfort at higher pressures. For track use, or for autocrossing, many folks run lower than 30 PSI cold when they start on track or on the autocross course. I've never experienced any serious problems between 26 PSI cold (track, autocross, or "spirited" driving on mountain twisties) and 35 PSI cold (I use that for long distance, interstate highway trips).
Very bad advice. If anyone is getting away with this, it's only because Murphy (the lawyer) and Darwin are too busy with other fools to get to them.
The maximum load and maximum pressure are related. That's why they are always shown together on the sidewall, in the same typeface and the same size. No vehicle manufacturer ever designs a vehicle with the tires loaded to the absolute maximum safe rating specified by the tire manufacturer. So the maximum safe pressure usually doesn't come into play.
The maximum pressure shown is a "never exceed under any circumstances" pressure. Starting with that pressure cold is a good way to (dangerously) over inflate your tires.
So long as the tire size is the same as the factory installed tires, and the maximum load and maximum pressure shown on the sidewalls is the same or close to the same as the factory installed tires, the placard on the door jamb is the best advice.
If you switch brands, and the maximum inflation pressure changes significantly (more than 10%, for example, if the factory tires said maximum pressure 44PSI, and the replacements say maximum pressure 56 PSI), then call the tire manufacturer for a recommendation. They will need to know the vehicle (to get the curb weight and the maximum loaded weight), the specific model and size of the tire you're using, and from that they can make a recommendation. It will never be the maximum on the sidewall, but it may adjust some in the direction of the change in maximum rated pressure.
Seriously over inflated tires (inflated to the max pressure shown on the sidewall) generally wear excessively on the center of the tread face. You will pick up a bit more fuel economy, and more load capacity (for towing) by going up that high (HOT only), but you need to keep a good measurement of wear across the tread face. The tires are worn out and need to be replaced when any part of the tread is worn down below about 3/32" for most tires (more for "all terrain" types).
To pick up better fuel economy, the most significant gain is in the first 10% to 15% over the factory recommended tire pressure. Beyond that, you're picking up very little, and you're wearing the center of the tread excessively, driving up the cost per mile due to the shortened tire life.
Back to the rest of this thread. Nitrogen (N2) is "better" because it has no moisture. If you vacuum your tires down to completely empty, and then refill with nitrogen, the pressures will act more in line with the ideal gas law. The issue is moisture in the tire (both water vapor in the air, and liquid water, most often present from water based "bead lube" AKA "tire slime), and condensing/evaporating moisture inside the tire causes much more significant pressure changes with temperature.
The down side to nitrogen is that it seems to encourage people to ignore their tires and not check tire pressures regularly. That's dangerous. Even with nitrogen, it's important to check pressures regularly.
Tires are very slightly permeable to the gases in air, and slightly more permeable to O2 than to N2, so there's a very small amount of truth to that statement, though not enough to matter. Some O2 within the tire is also consumed by oxidation of the exposed wheel surface inside the tire, and by oxidation of the inner rubber compounds within the tire. That is probably slightly more significant than O2 lost to permeation, but again, not significant over short timer frames (a few weeks/months). However, pressure variations (losses) from O2 loss are insignificant compared to pressure variations from evaporating/condensing H2O inside the tire. That's far more of an issue.
You should still be checking your tire pressures at a minimum every month, and every fill up is even better. Checking before heading out for cars that are "weekend fair weather drivers" is highly recommended.
Corvettes have had various ratings on the door jamb over the years. You see anything between 30 PSI cold and 35 PSI cold. The specific number depends on the year, and whether GM was focused more on ride quality and handling (30 PSI cold), or whether they were tight on the CAFE requirements that year and were focused more on fuel economy (35 PSI cold).
From experience, for most corvettes since the C4 generation, 30 PSI cold gives the best ride, handling, and the most even tire wear. 35 PSI cold gives a slightly rougher ride, somewhat less grip in cornering, and better fuel economy (between 0.5 mpg and 1.5 mpg higher). At 35 PSI, ,there's also slightly more wear at the center of the tire tread than at the edges.
There's more lateral grip, and a bit more grip for acceleration and braking in lower pressures, and more fuel economy, at the cost of grip and comfort at higher pressures. For track use, or for autocrossing, many folks run lower than 30 PSI cold when they start on track or on the autocross course. I've never experienced any serious problems between 26 PSI cold (track, autocross, or "spirited" driving on mountain twisties) and 35 PSI cold (I use that for long distance, interstate highway trips).
Look at the sidewalls of your tires, not what GM says on the door tag. If you run the same exact tire that GM put on the car in the beginning, then fine, look at the GM tag.
I have a lot of different cars/trucks/trailers. I go by the sidewall on all of them.
When I am not towing, my truck tries are at 60psi. When I am towing, they are at 80psi.
I actually do check tire pressure after driving to see what they are up to when they get hot and adjust from there.
I have a lot of different cars/trucks/trailers. I go by the sidewall on all of them.
When I am not towing, my truck tries are at 60psi. When I am towing, they are at 80psi.
I actually do check tire pressure after driving to see what they are up to when they get hot and adjust from there.
The maximum load and maximum pressure are related. That's why they are always shown together on the sidewall, in the same typeface and the same size. No vehicle manufacturer ever designs a vehicle with the tires loaded to the absolute maximum safe rating specified by the tire manufacturer. So the maximum safe pressure usually doesn't come into play.
The maximum pressure shown is a "never exceed under any circumstances" pressure. Starting with that pressure cold is a good way to (dangerously) over inflate your tires.
So long as the tire size is the same as the factory installed tires, and the maximum load and maximum pressure shown on the sidewalls is the same or close to the same as the factory installed tires, the placard on the door jamb is the best advice.
If you switch brands, and the maximum inflation pressure changes significantly (more than 10%, for example, if the factory tires said maximum pressure 44PSI, and the replacements say maximum pressure 56 PSI), then call the tire manufacturer for a recommendation. They will need to know the vehicle (to get the curb weight and the maximum loaded weight), the specific model and size of the tire you're using, and from that they can make a recommendation. It will never be the maximum on the sidewall, but it may adjust some in the direction of the change in maximum rated pressure.
Seriously over inflated tires (inflated to the max pressure shown on the sidewall) generally wear excessively on the center of the tread face. You will pick up a bit more fuel economy, and more load capacity (for towing) by going up that high (HOT only), but you need to keep a good measurement of wear across the tread face. The tires are worn out and need to be replaced when any part of the tread is worn down below about 3/32" for most tires (more for "all terrain" types).
To pick up better fuel economy, the most significant gain is in the first 10% to 15% over the factory recommended tire pressure. Beyond that, you're picking up very little, and you're wearing the center of the tread excessively, driving up the cost per mile due to the shortened tire life.
Back to the rest of this thread. Nitrogen (N2) is "better" because it has no moisture. If you vacuum your tires down to completely empty, and then refill with nitrogen, the pressures will act more in line with the ideal gas law. The issue is moisture in the tire (both water vapor in the air, and liquid water, most often present from water based "bead lube" AKA "tire slime), and condensing/evaporating moisture inside the tire causes much more significant pressure changes with temperature.
The down side to nitrogen is that it seems to encourage people to ignore their tires and not check tire pressures regularly. That's dangerous. Even with nitrogen, it's important to check pressures regularly.
Tires are very slightly permeable to the gases in air, and slightly more permeable to O2 than to N2, so there's a very small amount of truth to that statement, though not enough to matter. Some O2 within the tire is also consumed by oxidation of the exposed wheel surface inside the tire, and by oxidation of the inner rubber compounds within the tire. That is probably slightly more significant than O2 lost to permeation, but again, not significant over short timer frames (a few weeks/months). However, pressure variations (losses) from O2 loss are insignificant compared to pressure variations from evaporating/condensing H2O inside the tire. That's far more of an issue.
You should still be checking your tire pressures at a minimum every month, and every fill up is even better. Checking before heading out for cars that are "weekend fair weather drivers" is highly recommended.
Last edited by C6_Racer_X; Feb 21, 2018 at 11:42 AM.
Burning Brakes
Joined: Feb 2013
Posts: 904
Likes: 296
From: Sacramento, California
I also run the cold air pressure printed on the door jamb. This has always worked for me on every car I've owned and has given me the best tire wear as well. If you do some spirited driving in hot temps that pressure can rise quite a bit so adjust as necessary. It's funny how this topic has created so many arguments on so many forums. Ask yourself, why does every automobile manufacturer and every tire installation shop use the factory recommended cold inflation pressure? They must all be idiots right? Think about it!
The whole nitrogen filling topic has always been a joke to me especially considering there's almost 80% nitrogen in the air already. Nitrogen is more stable that oxygen if we're talking about expansion and contraction due to temperature, but the small amount of nitrogen that is added on a "nitrogen filled tire" is minimal at best. When you put a tire on a rim there is already normal atmospheric air trapped in the tire, so even if you fill with 100% nitrogen you don't end up with 100%. The only way to have a 100% nitrogen filled tire would be to install the tire in a chamber purged of atmospheric air with 100% nitrogen already inside. Even if this were possible, how do you add nitrogen when you tires get low, carry a bottle with you or try to find a shop with nitrogen? Too much trouble IMO.
My only advice in all of this is invest in a good quality tire gauge, check your tire pressure at least once a month especially when temps are cold, use the recommended cold inflation as a starting point and adjust as neccesaary for good tire wear, gas mileage or performance.
Steve
The whole nitrogen filling topic has always been a joke to me especially considering there's almost 80% nitrogen in the air already. Nitrogen is more stable that oxygen if we're talking about expansion and contraction due to temperature, but the small amount of nitrogen that is added on a "nitrogen filled tire" is minimal at best. When you put a tire on a rim there is already normal atmospheric air trapped in the tire, so even if you fill with 100% nitrogen you don't end up with 100%. The only way to have a 100% nitrogen filled tire would be to install the tire in a chamber purged of atmospheric air with 100% nitrogen already inside. Even if this were possible, how do you add nitrogen when you tires get low, carry a bottle with you or try to find a shop with nitrogen? Too much trouble IMO.
My only advice in all of this is invest in a good quality tire gauge, check your tire pressure at least once a month especially when temps are cold, use the recommended cold inflation as a starting point and adjust as neccesaary for good tire wear, gas mileage or performance.
Steve
Drifting
Joined: Jun 2013
Posts: 1,965
Likes: 343
From: Shell Point (Crawfordville) Florida
The inner surface of all modern tires has a butyl coating, which is designed to block or prevent air from permeating the rubber sidewall and tread. Google tire construction and look it up if you don't believe me. The air permeating into a tire from the inside is minimal, insignificant, and almost non-existent. Have you ever seen an old tire which was cracked or checked on the inside? I bet not, the inside looks almost new after many years of use. Tires get dried out and cracked on the outside from exposure to the UV of the sun much more than oxidized from the O2 in the air, and that's why you see RVs, trailers. and cars sitting around in outdoor storage with covers over the wheels, trying to keep the sunlight off the tires and extend their life.
Nitrogen inside daily driver car tires as beneficial is hype and a myth, only benefiting the service stations and tire places who charge $30 or more to con an unsuspecting car owner into doing this, maybe getting the N2 concentration inside their tires from 78% up to maybe 80-82%. Unless you could either completely and absolutely flush out all the atmospheric air or fill the tires in a vacuum chamber, you are really accomplishing nothing. Even if you got 95-100% nitrogen in your tires, is it worth it? And some day, if your pressure is low, will you stop at a gas station or use your air compressor to fill it up, or will you go back to the station for a nitrogen recharge? So pay your money and take your choice, but buyer beware.
Nitrogen inside daily driver car tires as beneficial is hype and a myth, only benefiting the service stations and tire places who charge $30 or more to con an unsuspecting car owner into doing this, maybe getting the N2 concentration inside their tires from 78% up to maybe 80-82%. Unless you could either completely and absolutely flush out all the atmospheric air or fill the tires in a vacuum chamber, you are really accomplishing nothing. Even if you got 95-100% nitrogen in your tires, is it worth it? And some day, if your pressure is low, will you stop at a gas station or use your air compressor to fill it up, or will you go back to the station for a nitrogen recharge? So pay your money and take your choice, but buyer beware.