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MT bucket
06-11-2009, 08:21 AM
I have my tires on my pickup at 60 psi ( higher than recommended here I know) but I like the lower rolling resistance and actually like the feel of sensing every little crack in the pavement. it also makes me more diligent about avoiding potholes.
anyhow, after a couple of days my left front will be down in the 50s and after a week the 40s. any good way to fix this? i would prefer not to have to go to the filling station every day to top it off.

hunter44102
06-11-2009, 08:47 AM
Try this:

Remove wheel, fill to 60PSI and put in small tub of soapy water.

Spin the tire slowly in the water and look for bubbles/air.

Once you find the leak, mark and use one of those $5-$10 plug kits at any parts store

This is how the gas stations do it.

If the leak is on the sides it cannot be plugged. If its a rim leak, I think they might have to re-install the tire

CapriRacer
06-11-2009, 08:52 AM
I have my tires on my pickup at 60 psi ( higher than recommended here I know) but I like the lower rolling resistance and actually like the feel of sensing every little crack in the pavement. it also makes me more diligent about avoiding potholes.
anyhow, after a couple of days my left front will be down in the 50s and after a week the 40s. any good way to fix this? i would prefer not to have to go to the filling station every day to top it off.

First you need to find out where the leak is. There are several possibilities.

1) Normal passenger car tire valves are rated to 60 psi. However, as time goes on, they may develop some seepage, either though the valve core itself, or where the rubber in the valve contacts the rim.

2) Alloy rims are essentially a loose cystalline matrix and are naturally porous. As a result ALL alloy rims are clear coated - partially to maintain their appearance over time, but mostly to seal those pores. Over time the clearcoat can be rubbed off or crack (miscroscopically) and allow air to escape through the metal matrix.

3) Alloy rims also corrode when in contact with steel. It is fairly common for the steel clips that hold the balance weights on scratch through the clear coat and corrode the alloy.

4) You may have a pinhole (or worse) leak somewhere in the tire. Needless to say, using higher pressure will not only force the air out more rapidly, but the tension on the tire due to the pressure will expand the hole more.

There are other scenarios.

So you need to find the source of the leak.

One way is to use a soapy solution in a spray bottle. When sprayed onto a leak, the solution will bubble where there is a leak. However, this will not work for leaks that are slow or from a large area - like the alloy rim porosity would be.

In those cases, immersing the tire in water is more effective. Kiddy pools work very well for this purpose, but the tire / rim has to be weighted down to keep it from floating. The problem is that you have to take the tire and rim off the car and it sometimes takes a few hours for the leak to become apparent.

Taliesin
06-11-2009, 09:30 AM
Another option (that my room mate would kill me for making) is a can of fix-a-flat. It would seal any small leaks, but you will have a heck of a time getting the tire off when it comes time for new ones.

EXPIOWA
06-11-2009, 12:22 PM
Take it to the tire store and have somebody do it for you. It is the easiest and most reliable way. I believe Discount Tire will do it for almost nothing. I wouldn't mess around with it.

Btw you are not gaining that much from over-inflating. In my opinion it is foolish, and definitely dangerous. You could even be considered negligent in a crash by exceeding the posted limitations of your tires. If you keep doing it I will make sure that they put how many gallons of gas you saved on your tombstone.

ksstathead
06-11-2009, 12:29 PM
...yet I keep wondering how I survive on my road bike at the recommended 145 psi.

EXPIOWA
06-11-2009, 12:41 PM
Maybe it's because that is the recommended pressure. No limitations have been exceeded. Pump it up to 200 and let me know how its going next fall.

Hypermilers are quick to say that AAA is wrong about how safe hypermilers are and we have a Dangerous Drafters thread. I think we should have a Dangerous Over-inflaters watchdog thread as well. It is proven that over-inflating decreases your margin of safety.

You all probably already think that I can be a jerk but this has to do with safety and I will not apologize for that. Even if you didn't crash you can buy a lot of miles for the price of one destroyed tire even at $4/gallon.

ksstathead
06-11-2009, 12:51 PM
Define overinflation, giving examples of ...what? crashes, exploding tires, extended stopping distances, increased/uneven wear?

At the pressures we run we are seeing the opposite. Granted we don't operate at the edge of the tire performance capability, where such things MIGHT show up, but that is part of the point: We drive slow, pay attention, and see BETTER handling, wear, performance.

The ride is stiff, but again, we are not psl+10.

I welcome your perspective; keep it coming.

PaleMelanesian
06-11-2009, 12:58 PM
Show me an example of tire failure due to overinflation.

digidug
06-11-2009, 01:09 PM
...It is proven that over-inflating decreases your margin of safety.

Questions to research before jumping to conclusions about safety:

How much margin of safety is built into that max sidewall rating?

How much are we decreasing it by over-inflating by say 15%?

MT bucket
06-11-2009, 08:23 PM
Thanks for the tips everyone. i think I am going to go with EXPIOWAs and just take it in to a tire store, i don't want to deal with removing the wheel, etc...;)

Take it to the tire store and have somebody do it for you. It is the easiest and most reliable way. I believe Discount Tire will do it for almost nothing. I wouldn't mess around with it.

Thank you for raising the safety concerns regarding high tire pressures. I drive for a living so that is very important to me. I read this article and that changed my mind about tire pressure.
http://www.cleanmpg.com/forums/showthread.php?t=11652

read it and let me know what you think.
MT

Btw you are not gaining that much from over-inflating. In my opinion it is foolish, and definitely dangerous. You could even be considered negligent in a crash by exceeding the posted limitations of your tires. If you keep doing it I will make sure that they put how many gallons of gas you saved on your tombstone.

nervousmini
06-12-2009, 01:10 AM
Another option (that my room mate would kill me for making) is a can of fix-a-flat. It would seal any small leaks, but you will have a heck of a time getting the tire off when it comes time for new ones.

PLEASE! PLEASE! PLEASE!

Don't ever use that stuff unless you are really stranded and have no other options. I have had to work on tires after this stuff is installed and the mess it makes is unreal! They also usually use PROPANE or ISOBUTANE or some other typically flammable/explosive gas as a propellant - not fun when you're the guy that has to hope you don't spark anything as you are breaking the tire down.

run2w8s
06-12-2009, 01:13 AM
Had a slow leak on a Sienna minivan with alloy wheels. Turned out to be corrosion along the bead. Shop removed the tire, cleaned off the corrosion, problem fixed.

drimportracing
06-12-2009, 01:23 AM
Show me an example of tire failure due to overinflation.


Yesterday I went down a gravel road for about 1 mile and upon leaving I noticed my passenger front was going flat fast. I got to the end of the gravel road and pumped it up somewhat until I could find the hole, it was a tear between the treads caused by a rock, I plugged it with 2 plugs and went into town, calling ahead to the tire store, $36.00 and I was back on the road in an hour.

I believe that if I had 35psi when I went down that rocky road I would have had a much better chance of not busting a tire. I will continue to keep 60psi in my tires unless I have to go country driving again and then I'm deflating for the trip. Stuff happens. :D - Dale

Yaris Hilton
06-12-2009, 06:43 AM
You really don't want to use Fix-A-Flat if you have a Tire Pressure Monitoring System.

EXPIOWA
06-12-2009, 09:56 AM
Third attempt to post this. My internet provider in this hotel sucks and I am posting from an ipod. I will create this post in stages then edit it to add more informaion.

MT bucket, wise choice. Thank you.

I second not using fix-a-flat. Some of that stuff is also flamable. It's nothing to worry about under most circumstances though. I just don't want that crud inside of my tires. Some service stations don't like having to deal with it. I have been to a few that charge more to fix a puncture if you used it.

A previous reply was correct about a margin of safety being built into our tires. I will explain why you may exceed it and not know until it fails. For starters most people don't know how or when to inflate their tires. It should be done within the first mile of driving. After that tire pressure will be effected by the temperature of the tire. A tire is to be considered overinflated if you exceed the Max Inflation shown on the side wall of the tire itself. I have never seen one with the word "recommended". Like it or not that is how it is.

If you fill your tires in the morning when it is 65 degrees then it gets up to 95 that afternoon your pressure will increase by 1 psi for every 10 degrees. Then you decide to go for a drive. Friction with the hot road will increase your pressure even more.

Walk on blacktop with bare feet and you can tell that the temp can be signifficant. That adds heat to the tire again through convective heat transfer. As you can already see, your tires have to be safe over an already wide range of conditions. An overinflation of 15 percent can turn into much more.

Now let's talk about the tire itself. They are not all the same. There is a world of difference between an H rated tire and a Z rated tire for example. A new tire may be able to handle overinflation for a while if it was built properly. Over time tires wear out. The tread blocks wear down and no longer provide the cushioning effect that they had when they were new. Now the core structure will take more abuse. Some tires have a softer compound that the tire wears into so that it maintains the same grip over the life of the tire as well. Did you know that a high speed rated tire looses it's speed rating if it has been patched? True, with very few excepions.

Another thing to think about is the fact that your tires were built to a cost to accomidate the average driver under a certain set of conditions. I don't want to find out the hard way what part of my tires they decided to save a nickel on. Remember the Wilderness fiasco with the SUVs back around 2000? Believe it or not the failure rate of that tire was not that far from the average for all tires. The press jumped onto the bandwagon and went to town with it.

Most of of do not have expansion resistant nitrogen in our tires and they won't stay new forever. Your tires were designed to provide a margin of safety over their entire serviceble life provided that their use falls into a specific set of conditions. Tire manufacturers have gone through a lot of trouble to design, test, produce, and market safe, low rolling resistance tires specifically for people like the ones here at this forum who's goal it is to maximize mileage. Please for the sake of those around you don't overinflate your tires. It is dangerous.

PaleMelanesian
06-12-2009, 10:34 AM
Remember the Wilderness tire fiasco? I sure do. A major factor in that case was the Explorer's LOW recommended inflation pressure. Since that event, Explorers come with a higher recommended pressure. Why might that be?

Nitrogen is a gas just like any other. It must obey the same pressure-temperature laws.

Taliesin
06-12-2009, 10:40 AM
PLEASE! PLEASE! PLEASE!

Don't ever use that stuff unless you are really stranded and have no other options. I have had to work on tires after this stuff is installed and the mess it makes is unreal! They also usually use PROPANE or ISOBUTANE or some other typically flammable/explosive gas as a propellant - not fun when you're the guy that has to hope you don't spark anything as you are breaking the tire down.

And that's the whole reason my room mate would kill me for bringing it up. It's definately not the best option.

EXPIOWA
06-12-2009, 12:47 PM
Why that might be is not that much of a mystery. Off road vehicles typically use a lower pressure to increase the footprint of the tread. I believe the auto manufacturer recommended around 28 psi, which is well below the pressure limitation set by the tire manufacturer. It will ride smoother and grip better when used off road, the purpose for which they were designed.

Guess who drives most of these types of vehicles? I'll give you a hint, suburban moms who want the space and crash protection for their children and there is nothing wrong with that. The problem arises from the fact that these types are not doing regular checks on their vehicle's condition, if ever.

Knowing that, if you were a service station owner who only saw the vehicle every 5,000 miles for the oil change wouldn't you want to make sure that the pressure would be sufficient until the next visit?

People will sue for anything and Tires can loose around 5 lbs./month. It was a case of the manufacturer shifting the blame from their design to individual's improper maintenance. Starting from a higher pressure was a simple fix. We now have tire pressure monitoring systems that you have to pay for when you buy a new car because you can't trusted to use a tire gague on a regular basis.

Btw, nitrogen is very different. It does not expand as much as regular air due to temperature or ambient pressure changes. It us used exclusively in large aircraft tires because it does not expand as the pressure drops with altitude. If you do some research you will also see that it is the gas of choice for inflating the tires of every elite form of auto racing. I don't think that you could even buy an exotic car anymore that didn't have nitrogen filled tires. It is that much better and it will not corrode alloy rims like air will.

R.I.D.E.
06-12-2009, 01:08 PM
A note on fix a flat.

A service station owner in Texas settled for just under 1 million dollars with one of the manufacturers who used volatile propellants in their fix a flat.

He was plugging a tire and when he pushed the rasp through the nail hole, a spark ignited the mixture of air and fix a flat that was just about the perfect mixture.

The resulting explosion was estimated to be about the same as two sticks of dynamite. It did 40k damage to the station and the owner's skull injury almost killed him. After repeated surgeries his skull still was caved in almost an inch on the left side, a really nasty sight to look at.

Most of the fix a flat today is non flammable, and it may also be a good reason to actually have nitrogen in your tires is you ever intend to use a similar product.

regards
gary

R.I.D.E.
06-12-2009, 01:15 PM
We had a customer who brought his car in for a wheel balance. I balanced the wheels put them back on the car and they were not right. Took them off and checked and they were all off by at least 1.5 ounces.

No freakin way could I have been that wrong on every wheel with a new Snap-On balancer that had never failed me before.

Took the newly balanced tire-wheel assembly, right off the balancer, and bounced it off the ground twice. It was off by 1.5 ounces again!!!!!

GRRRRRRRRRRRRRRRRRRR!

The guy had put fix a flat in every tire, JUST IN CASE HE HAD A FLAT!!!!!!!!!

regards
gary

jkp1187
06-12-2009, 01:37 PM
Thank you for raising the safety concerns regarding high tire pressures. I drive for a living so that is very important to me. I read this article and that changed my mind about tire pressure.
http://www.cleanmpg.com/forums/showthread.php?t=11652

read it and let me know what you think.
MT

That article really doesn't carry much weight with me as a source.

The link's dead, I've never heard of the author (anyone can claim to be a police sgt - or a Hollywood consultant - in fact, I've never heard of the website. What is Officer.com? What is their agenda? Is it a police special interest website? Is it just some online rag that tries to sell stuff to police?) The article itself is just a straight narrative and doesn't cite to any outside sources beyond the personal experience of the author, which really isn't good enough. (Certainly, there are no numbers mentioned that could be validated or invalidated.) And why was the article removed?

Too many questions there. That article is no better than an anonymous forum posting as a source. I wouldn't put any real reliance on it.

I am interested in hearing if anyone has a source that involves serious research-not just personal anecdotal experiences-on the affects/advisability of increased tire pressure and safety/longevity - above manufacturer's recommended pressures, up to Max Sidewall pressure, and beyond.

EXPIOWA
06-12-2009, 02:37 PM
Give me a day or two and I will find the post from a tire engineer who is also a member here or at eccomodder.com who was personally involved with testing tire pressure vs failure rates for one of the manufacturers.

Why it is so hard for some people to believe that exceeding max tire inflation limits isn't dangerous? It would be easier to get people to believe in aliens.

ksstathead
06-12-2009, 02:51 PM
Need one or more examples of people driving the way we do who have had negative results.

phoebeisis
06-12-2009, 03:04 PM
EXPIOWA-I know your question was rhetorical, but folks believe what they want to believe.
On the forum folks know that increased tire pressure improves mpg, and this is a mg forum. They don't want to believe that ,after a point, it is dangerous to overinflate.
Of course it makes sense that overinflation can be dangerous. But, I doubt that a40 psi in a 35 psi "door panel) tire is dangerous. In fact, it is probably safer to run at 40 psi(under sidewall usually) than at 35 psi( door panel numbers).

It is just a question of at what psi does it become dangerous-say more risky that door panel pressure-5 psi over, 7 psi over?

I doubt that there are any studies showing exactly where exceeding the door panel #'s becomes dangerous. I wouldn't feel safe with 60 psi in a 45 psi (sidewall max).If a couple of steel cords get nicked they are more likely to suddenly fail at 60 psi than at 45 psi.

People everywhere believe what they want to believe-that will never change.
Charlie
PS In general my guess is that 5 psi over door panel is safer than door panel( because of increased heat and wear)-but I can't prove that.

jkp1187
06-12-2009, 03:42 PM
EXPIOWA-I know your question was rhetorical, but folks believe what they want to believe.
On the forum folks know that increased tire pressure improves mpg, and this is a mg forum. They don't want to believe that ,after a point, it is dangerous to overinflate.
Of course it makes sense that overinflation can be dangerous. But, I doubt that a40 psi in a 35 psi "door panel) tire is dangerous. In fact, it is probably safer to run at 40 psi(under sidewall usually) than at 35 psi( door panel numbers).

It is just a question of at what psi does it become dangerous-say more risky that door panel pressure-5 psi over, 7 psi over?

I doubt that there are any studies showing exactly where exceeding the door panel #'s becomes dangerous. I wouldn't feel safe with 60 psi in a 45 psi (sidewall max).If a couple of steel cords get nicked they are more likely to suddenly fail at 60 psi than at 45 psi.



I'm skeptical, too, but I wanted to ask in case there was some publicly-available study (as opposed to private tire company papers.) I do get nervous when people cite the article mentioned above from OFFICER.COM as though it settles everything. For the reasons I mentioned above, I don't think it does. (And I've seen it cited in different places, not just here - including an email from a friend of mine who owns a Camry Hybrid.)

For my money, and unless I see a valid study establishing otherwise (i.e., a real engineering study, not anecdotal evidence,) inflating the tires to a point where max sidewall pressure is not exceeded when the tires are hot is probably the best place to be. If the engineers who designed the tires are perhaps overly conservative in their safety specs, that's fine by me. I can live within those specs, because I'm pretty conservative about safety, too.

Right Lane Cruiser
06-12-2009, 06:48 PM
One note here -- the number listed on the sidewall is maximum cold PSI. Worrying about that number being exceeded when the tires are heated up is not something you need to do.

MT bucket
06-12-2009, 07:06 PM
Ok, mabye I will let a little air out, but just a little ;) I will never go below sidewall max though! :p thanks everyone for the posts and info, may the debate continue! :)

EXPIOWA
06-13-2009, 02:09 AM
You don't have to go below molded sidewall inflation. That fits within the tire limitations and should provide a level of safety. I run mine at that pressure.

I will still try to find the post that I spoke of earlier but as far as I am concerned the debate is over. Some people will never change their beliefs and it would be a waste of time to continue to try to convince them. Enough of an arguement was presented to convince a few with open minds to alter their behavior. That is all I could have hoped for.

CapriRacer
06-13-2009, 08:03 AM
Some thoughts on inflation pressure:

Let's start with this as a reference:

http://www.geocities.com/barrystiretech/loadtables.html

What you should get out of this is:

1) That the RATED inflation pressure of a standard load passenger car tire (the type most of us have on our cars) is 35 or 36 psi depending on whether the English system of measurements or the metric system is being used.

2) That what is written on the sidewall of a tire is a MAXIMUM

3) That what is written on the sidewall is controlled by a government regulation

4) That there disagreement among tire manufacturers as to what is supposed to be written on the sidewall of a tire

5) That if something other than 35 or 36 psi is written on the sidewall of a tire, it is a PERMISSIBLE inflation pressure.

6) That when tires are tested, they are tested based on the RATED inflation pressure of 35 or 36 psi.

And given the following:

7) That when a vehicle manufacturer specifies the tire size and inflation pressure, he is not only specifying the load carrying capacity of the tire, but also the spring rate and the approximate size of the footprint.

8) That the spring rate of a tire is an important consideration for vehicle handling

9) That footprint size has an effect on the ultimate grip (race cars use wide tires)

10) That footprint size is both a function of load (more load = larger footprint) and inflation pressure (more pressure = smaller footprint)


As a result, I tend to think that when inflation pressure is referred to, it should be referenced against the placard pressure (for spring rate and footprint size) and the rated pressure of 35 or 36 psi (as the pressure tire tests are based on), and not what is written on the sidewall (since it doesn't have a sound technical basis).

psyshack
06-13-2009, 10:14 AM
The question was about a small leak. The the thread went right down the toilet over psi. LMFAO!

EXPIOWA
06-13-2009, 11:29 AM
This has been a great thread and it is far from the toilet. Off the original topic, yes, but one have I have found very interesting. Great discussion.

jkp1187
06-13-2009, 11:47 AM
I agree. This has been informative. If the admins want to bifurcate the thread and put the tire PSI discussion in a different thread, that's fine. Psyshack, do you disagree with something that has been said vis-a-vis tire PSI? If so, please feel free to express that disagreement so that it can be evaluated in the mix.

@Right Lane Cruiser - I was not aware that the max pressure listed on the sidewall was cold, not hot. I'd always assumed it was hot. Thanks.

@Capriracer: I actually am aware of some owner's manuals for higher-performance vehicles that recommend higher pressures if higher speeds (in excess of 90/100 MPH) are going to be maintained. Just an exception to your point, which I assume is: the placard pressures are the ones that have been tested for this specific vehicle and the sort of driving it is likely to encounter. Yes?

basjoos
06-13-2009, 10:46 PM
Btw, nitrogen is very different. It does not expand as much as regular air due to temperature or ambient pressure changes. It us used exclusively in large aircraft tires because it does not expand as the pressure drops with altitude. If you do some research you will also see that it is the gas of choice for inflating the tires of every elite form of auto racing. I don't think that you could even buy an exotic car anymore that didn't have nitrogen filled tires. It is that much better and it will not corrode alloy rims like air will.

This is a new one to me. I wasn't aware that there was a gas that didn't follow Charles's and Boyle's Laws. I guess I naively thought that all gases would follow the ideal gas laws (Boyle's, Charles's, Gay-Lussac's) that I learned in physics class. So, of every gas in existence, nitrogen is the only one that doesn't follow the ideal gas laws. Somehow I have doubts about this unique exception to the laws of physics.

EXPIOWA
06-14-2009, 12:28 AM
This is a new one to me. I wasn't aware that there was a gas that didn't follow Charles's and Boyle's Laws. I guess I naively thought that all gases would follow the ideal gas laws (Boyle's, Charles's, Gay-Lussac's) that I learned in physics class. So, of every gas in existence, nitrogen is the only one that doesn't follow the ideal gas laws. Somehow I have doubts about this unique exception to the laws of physics.

I am guessing that you went to a public school. They only teach you what they want you to know. :) (I am just having some fun with you).

Check this link out http://www.getnitrogen.org/ You may even read something there about how it might even help you save gas. It was one of the first links google popped up. (Nitrogen in tires is not a new concept for me so I didn't spend that much time finding the perfect website to explain it.)

Nitrogen is an element that is not as affected by temperature or pressure changes and it is inert so it is non-corrosive.

If you don't like my link google your own until you find a source that you can trust let us know what you found.

Google "nitrogen in airliner tires", "nitrogen in sr-71 tires", or "nitrogen in car tires".

EXPIOWA
06-14-2009, 12:36 AM
Btw, there may someday be a higher max inflation pressures listed on sidewalls for nitrogen only tires. The tire would be at the max operating pressure hot or cold. Expansion will not be as large of a factor when determining the safe limits of a given tire.

CapriRacer
06-14-2009, 06:02 AM
This is a new one to me. I wasn't aware that there was a gas that didn't follow Charles's and Boyle's Laws. I guess I naively thought that all gases would follow the ideal gas laws (Boyle's, Charles's, Gay-Lussac's) that I learned in physics class. So, of every gas in existence, nitrogen is the only one that doesn't follow the ideal gas laws. Somehow I have doubts about this unique exception to the laws of physics.

You are correct.

The difference between nitrogen and air (with 78% nitrogen) is 3% - not enough to worry about:

http://www.engineeringtoolbox.com/individual-universal-gas-constant-d_588.html

To verify this Walter Waddell actually tested this and presented this to the California Air Resources Board in June, 2008. You'll want to look at Slide #8:

http://www.arb.ca.gov/cc/tire-pressure/meetings/060408/060408exxonpresentation.pdf

Looking at the data, it appears there is more measurement error than anything else.

So, no, there will NOT be a separate nitrogen value imprinted on the sidewall of tire in the future. In fact, the government agency that writes the regulation (NHTSA) is now convinced that nitrogen has no effect on anything that is in their perview.

CapriRacer
06-14-2009, 06:16 AM
..........

@Capriracer: I actually am aware of some owner's manuals for higher-performance vehicles that recommend higher pressures if higher speeds (in excess of 90/100 MPH) are going to be maintained. Just an exception to your point, which I assume is: the placard pressures are the ones that have been tested for this specific vehicle and the sort of driving it is likely to encounter. Yes?

Actually, no!

The owner's manuals are following the "permissble" part of the tire standard, so that's OK within the situation specifically outlined in the manual. So there isn't an exception to what I wrote.

But to continue your train of thought: I am convinced that those folks who will want to hyperinflate their tires will do so regardless of what I post. However, I want to make sure they have as many facts as possible - particularly about where the sidewall pressure maximum comes from. That way when there is a problem, they will be more likely to attribute it to the pressure they are using and be able to learn from the experience. But as you can see, there are lots of folks who are not afraid of posting stuff and not all of it is factual.

MT bucket
06-14-2009, 09:36 AM
I think I will leave the tires hyperinflated in my Mirage, since I can get much longer glides with hard tires.
I avoid highways and go so rediculously slow that i really am in very little danger of getting hurt or crashing into anyone or anything.
If a tire fails, yeah it will negate gas money saved, but I would rather support my local tire business than OPEC any day!

cpeter38
06-14-2009, 11:18 AM
I am guessing that you went to a public school. They only teach you what they want you to know. :) (I am just having some fun with you).

Check this link out http://www.getnitrogen.org/ You may even read something there about how it might even help you save gas. It was one of the first links google popped up. (Nitrogen in tires is not a new concept for me so I didn't spend that much time finding the perfect website to explain it.)

Nitrogen is an element that is not as affected by temperature or pressure changes and it is inert so it is non-corrosive.

If you don't like my link google your own until you find a source that you can trust let us know what you found.

Google "nitrogen in airliner tires", "nitrogen in sr-71 tires", or "nitrogen in car tires".
I love their "SCIENTIFIC PROOF":Driving on underinflated tires? If you are, it’s like driving your car through sand!
The engine has to work harder, burning more fuel and adding wear to engine components.
It’s also dangerous. Almost all tire blowouts are caused by underinflated tires. Tires lose 1-2 PSI every month!. That’s 6 PSI low by the time you have your oil changed!

[SNIP]

But don't just take our word for it. Look at these test results performed by a variety of groups, from private studies to research labs. They all agree that nitrogen tire inflation reaps benefits. If you'd like to see how much you can save, go to our home page and use the handy savings calculator (http://www.getnitrogen.org/index.php).

How the heck is that scientific?

The fact is that Nitrogen does behave like all other gases with respect to expansion when heated. The big differences are that N2 does not diffuse through rubber as quickly as water vapor due to its molecular weight/configuration and it is an inert (non-reactive) molecule. Oxygen reacts with the tire components (no big surprise - it oxidizes the hydrocarbons and steel in a tire). Water vapor diffuses quicker because it is a much smaller molecule.

Here is a more detailed description of pressure decay:As far as pressure is concerned, there will be little measurable (air vs N2) short term difference in FE if you check your tires on a weekly basis. N2 filled tires should have a very minor additional pressure due to the diffusion of O2 across the membrane (tire wall) into the inside of the tire (yes, you read correctly - INTO the N2 filled tire). This diffusion stops when the partial pressure of O2 is equal on both sides of the membrane (approximately 2.9 psia).

Similar in principle to O2 diffusion, but opposite in direction, the N2 diffuses across the membrane to the atmosphere. Again, like O2, the diffusion rate is governed by the partial pressure differential. In this case, the partial pressure of N2 in the atmosphere is approximately 11.8 psia.

Back to my beginning summary paragraph. The biggest problem with air filled tires according to the research I have seen (and from the chemistry/physics aspect) is that O2 reacts with the tire. This causes measurable (http://www.nitrofill.com/documents/Rubber-News-Nitrogen-Tire-Study1.pdf) degradation of the tire. It is also responsible for a slight decrease in tire pressure (when the compounds oxidize, the O2 is pulled out of the air and is now part of a solid molecule). However, you have to ask yourself a more important question. Which usually fails first, Tread wear or blowout? Unless you run over something or buy a REALLY bad tire without a protective inner coating, the answer is nearly always going to be tread wear.

One other minor factor is that rubber is not a "true solid". Instead, it retains some behavioral similarities to liquids. Depending on the rubber compound, O2 is 2-3 time more soluble than N2 is in rubber (I mention this because traditional diffusion properties do not completely describe the behavior of rubber).

Conclusion for those who were willing to stick through my poorly written, caffeine deprived dissertation:1.) What you use to inflate your tires does not matter if you check them on a regular basis (every hypermiler should).
2.) In general, what your tire is inflated with will not affect your leak rate.
3.) As mentioned above by others. Fix-a-Flat and similar fillers are a temporary tool of last resort. 9 out of 10 times it will affect the balance of your tires and in the case of some products, can cause hazardous situations.
4.) Discount tire, Costco, and other places will often fix small tire leaks for a nominal fee (or free if you are nice and find a nice person) and will do a great job.
5.) A significant amount of tire wear is caused by misaligned suspensions (a problem w/my SVT), jackrabbit burnout starts, and FLEXING TIRES. As long as the sidewalls are not starting to yield under the most significant load points, "fully inflating" your tires will reduce flexing and increase your tire life (it is of course up to you to decide what is "fully inflating" your tire).

phoebeisis
06-14-2009, 12:46 PM
Eventually you should end up with higher than ATM concentrations just from normal leaking and refilling-why pay for it.

N2 is bigger than O2 because N outer electrons are better shielded from the protons than O atoms-and they are more repulsed by their fellow electrons.. This makes/allows them stray farther from the nucleus-so they are bigger.
Left to right-same horizontal line-atoms get smaller, and the molecules they form get smaller.

Save your money- use air -it is 80% N2 AND OVER TIME YOUR TIRES CONCENTRATION OF N2 WILL INCREASE ANYWAY.
Paying for N2 is for suckers(or racers).

Charlie

lightfoot
06-14-2009, 02:02 PM
I agree with cpeter38 above and would like to add that no one seems to have thought about what a tire place does when they "fill your tire with nitrogen": they open the valve to let air escape, and when air stops coming out they inflate the tire to say 34psi with nitrogen.

BUT WAIT, THERE WAS STILL AIR IN THE TIRE WHEN THEY STARTED FILLING! They did not pull a vacuum, so there was air at atmospheric pressure in the tire. Atmospheric pressure is 14.7psi, and the 34psi is the pressure ABOVE atmospheric. To reach 34psi, they added 34/14.7 = 2.3 volumes of nitrogen. This dilutes the 22% of other gases in the tire by a factor of 3.3. So what is in the tire is NOT 100% nitrogen, it is 93% nitrogen, 7% other gases.

Repeated fill/vent cycles would bring the number closer to 100%, and this may be what is done for aircraft. As for racers, their tires have such a short lifetime and come on and off so frequently that it is doubtful that O2 or water vapor from air would have much time to act. So it may be a case of using N2 because that's what the other guys are doing.

lightfoot
06-14-2009, 02:50 PM
For starters most people don't know how or when to inflate their tires. It should be done within the first mile of driving. After that tire pressure will be effected by the temperature of the tire.
I have some interesting data on this. Last summer I had to drop the tire pressures on my Subaru from sidewall rating (51psi) to door placard (32psi) during the day. I set the tires to 51psi (Accu-Gage) in the morning before leaving home. I drove about 50 miles on I-95 at around 55mph and then stopped at a gas station. Using the same gauge, I checked the pressures BEFORE bleeding them down and they were all at 51-52psi!! It was a warm sunny summer day, but the ambient temperature may have risen only 10 degrees since morning.

I suspect that a tire inflated to sidewall rating will experience only a small pressure rise during driving because the higher pressure will reduce flexing. Whereas a tire inflated to the lower door placard pressure will flex more, heat up more, and show a greater pressure increase above the initial pressure setting.

Damionk
06-14-2009, 06:21 PM
I have some interesting data on this. Last summer I had to drop the tire pressures on my Subaru from sidewall rating (51psi) to door placard (32psi) during the day. I set the tires to 51psi (Accu-Gage) in the morning before leaving home. I drove about 50 miles on I-95 at around 55mph and then stopped at a gas station. Using the same gauge, I checked the pressures BEFORE bleeding them down and they were all at 51-52psi!! It was a warm sunny summer day, but the ambient temperature may have risen only 10 degrees since morning.

I suspect that a tire inflated to sidewall rating will experience only a small pressure rise during driving because the higher pressure will reduce flexing. Whereas a tire inflated to the lower door placard pressure will flex more, heat up more, and show a greater pressure increase above the initial pressure setting.

I have done something similar, and less than 1.5 PSI increase. I may do it at the recommended 32 PSI and drive just to see how much of an increase there is.

Heat is a by-product of friction, if the side-wall, along with the tread, flex less there is less friction and less resulting heat.

EXPIOWA
06-15-2009, 12:51 AM
Repeated fill/vent cycles would bring the number closer to 100%, and this may be what is done for aircraft..

I believe that three vent/fill cycles is common practice. I will admit that after reading the the replies here and doing more research on my own I probably gave nitrogen a little more credit than it deserves but I still want it, but not $10 /wheel bad. I can admit when I am wrong.

MT bucket
06-22-2009, 10:15 PM
Finally got the leak fixed today! I thought it fixed itself at first. I backed off some on the PSI from 60 to around 48, it didn't seem to make a difference in my fuel use, but the leak seemed to stop. I checked it every day and it was not going down any, so i was thinking too high pressure was causing it?
well today I was struggling to get decent fe on what seemed like it should be a great fe day, hot dry roads and light breezes, plus decent routes, i barely got above 34 mpg, and i noticed I was getting alot more tire squeel around tight corners, plus more than usual difficulty getting up to speed on steep on ramps
I thought mabye its the heat, but i better check the tires. well something distracted me so I didnt. then i stopped at the store, and when i came out and was walking toward my truck i could see it was noticably low. Got out my gauge and checked...20 psi!:eek:
I can't belive i drove on it like that today! the heat must have cooked my brain! oh well I made it safely to the shop and they found the culprit quickly...

http://img.photobucket.com/albums/v630/Cyberfish8/mt%20pilgrims%20pics/nail.jpg

They could tell it had been in there for a while because the end that was sticking out of the tire was flattened and poilished smooth from hitting the road a zillion times! I just can't figure out why it stopped leaking for a few days???



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