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Old 05-18-2006, 02:09 PM   #1
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We have all heard that we should check our tire air pressure when the tires are cool, not hot. What is the recommended outside air temperature. Cool means different things to different people.

Also, my home base is in Denver. Does altitude make a difference?
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Old 05-18-2006, 02:09 PM   #2
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We have all heard that we should check our tire air pressure when the tires are cool, not hot. What is the recommended outside air temperature. Cool means different things to different people.

Also, my home base is in Denver. Does altitude make a difference?
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Old 05-18-2006, 06:54 PM   #3
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"Cool" means in the morning before you do any driving, whatever that air temp is. (Check 'em cool means the tires are not heated by driving ...it is not considering air temp). Yes, that does mean you will need to add some air in colder weather and then maybe let some out when summer comes based on ambient temperature. Theoretically, I suppose altitude could make some difference but you set the tire pressure according to your tire mfg charts and you rig weight wherever you are in the AM before hitting the road, so you don't really need to think about any small changes based on changes in altitude.
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Old 05-19-2006, 05:27 AM   #4
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Rex - I asked this very question on rv.net a couple of weeks ago. Got the usual gamut of responses - most answers had little value and didn't directly answer the question. One poster had a link that addressed the topic fron tirerack.com, but even that detailed dissertation did not give temperatures or altitudes as a standard.

Everybody and every source keeps saying to check them while the tires are cold, as in before driving. However there are a few pounds of difference among the matrix of sea level, 5,000 feet of altitude, 30 degrees and 100 degrees of temperature.

Maybe an email to Michelin would be in order? Let us know what they say
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Old 05-19-2006, 06:04 PM   #5
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Hi LK23,
I found this article on tire care that explains the effect of temperature on tire inflation and the proper way to account for it. Atmospheric pressure is mentioned but not dealt with. The change in absolute pressure from sea level to 10,000 feet is from 14.69 PSI to 10.11 PSI. Less than 5 PSI and easily accounted for by checking pressures occasionally as you go cross country. With altitude changes of 1,000 to 2,000 feet, I can't see adjusting the pressures for the one PSI change that this would cause. Remember that PSIG (gradient) rises with altitude ie. tire pressure goes up. The hint about 1 PSI rise / 10 degrees Fahrenheit is probably the most important when checking pressures, and the hint on checking cold before driving and then accounting for the temperature difference is handy.

http://www.discounttire.com/dtcs/infoAirPressure.dos
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Old 05-19-2006, 06:56 PM   #6
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The difference of tire pressure to altitude is not even a consideration for aircraft tire pressure at sea level to 30,000 feet AGL. When the airlines build up a tire wheel unit the unit is filled with nitrogen at room temp. It is then installed on the aircraft and the pressure is re-checked and released for flight service.
Motorhome tires are just fine with recomended and adjusted by weight recomendations of the manufactor of the tire at any altitude you can drive at in the USA. But temp will effect the pressure some what. As already stated cool means that the tire is not hot from highway or road use.
A tire that is up to 120 to 140 degrees from driving on it will appear to look fine and will show more pressure then when it is at air ambient temp, so always try and check the tires at air ambient temp when possible.
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Old 05-20-2006, 05:20 AM   #7
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">article on tire care </div></BLOCKQUOTE>
There is some decent info the article, but it's an interesting recommendation that you should "refill your tires every other time you fill up at the gas station." There is no way for you to know what air their need unless you were parked at the gas station overnight! Just check your tires each morning before you hit the road. I never check pressures during the day unless I have an overheating tire or one looks low.
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Old 10-19-2006, 03:09 PM   #8
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Used 100% Nitrogen in my F-250 and 35'FW for two years. Got rid of tire problems and had great service from 100% Nitrogen in and out of desert..mountains..Lost about 1#N/tire over 6 mos. Switched to 100%N in my 2006 35U foot Sucruiser. Using door placard pressures. 100% Nitrogen gives a good, consistent ride-performance and virtually eliminates daily tire checks...assuming good tires, rims and stems are on the vehicle.
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Old 10-19-2006, 03:28 PM   #9
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Pubtym:
Used 100% Nitrogen in my F-250 and 35'FW for two years. Got rid of tire problems and had great service from 100% Nitrogen in and out of desert..mountains..Lost about 1#N/tire over 6 mos. Switched to 100%N in my 2006 35U foot Sucruiser. Using door placard pressures. 100% Nitrogen gives a good, consistent ride-performance and virtually eliminates daily tire checks...assuming good tires, rims and stems are on the vehicle. </div></BLOCKQUOTE>

Why not use "air" in your tires?....since air contains 80% nitrogen?
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Old 10-20-2006, 05:58 AM   #10
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In the old days standard temerature used to be 25'C but I did some research and found that there are several different temps that are now considered "standard". See:http://en.wikipedia.org/wiki/Standar...e_and_pressure
for a good summary.
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Old 10-20-2006, 02:55 PM   #11
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FrontRangeRVer: You are correct. Under standard conditions, air in most automotive tire is 20% Oxygen and 80% Nitrogen. However, it's the Oxygen molucules that are smaller than Nitrogen molecules and Oxygen is more affected by temperature and pressure changes. Eliminating the oxygen molecule provides a more stable total gas pressure in the tire.
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Old 10-21-2006, 04:17 AM   #12
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Why not use "air" in your tires?....since air contains 80% nitrogen? </div></BLOCKQUOTE>

Our local Ford dealer offers 100% nitrogen in your tires for $8.95 per wheel. For a passenger car. They claim you get a better ride (?) more fuel mileage, less tire failures, contant tire pressures, and longer life out of your tires.

The data is true about 20% oxygen has smaller particles. When I asked the dealer what to do IF tire pressures ever drop he answered, "Noo problem - you just fill them up with AIR at any service station (?)

I am missing what, here ?
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Old 10-21-2006, 06:11 AM   #13
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From my experience, ride is better and more consistent. Generally, expect maybe 2-5 # initial pressure drop the first 6 mos to year. This initial pressure drop is sometimes connected with the unpurged oxygen from the initial fill with Nitrogen. Costco offers Nitrogen tops offs-refills nationwide on any of the tires they sell with Nitrogen service. Many car dealers are investing in Nitrogen generator-service units for their shop...and the cost-benefit lights are starting to come on for these service shops. Initial outlay for Nitrogen service unit is still fairly high for low customer traffic shops.

With the pickup truck and motorhome..I have a total of 10 tires to occasionally maintain with 100% N. I'm in Sioux Falls SD and I solved that problem for about$230 by buying a 40 cubic foot portable Nitrogen bottle and needed pressure gauge-hose all from the local Linweld (weld shop supply) dealer. 40 cubic feet did all initial serivce on 6 motorhome tires and two of the F-150 tires. Refill on the 40 cubic foot bottle was $16. You can also purchase just the bottle guage and valve assembly and borrow (deposit) an 80 cubic foot bottle (cheaper way) for home weekend inititial service..then return bottle. Any very minor follow-on service can be from a loaner 40 cubic bottle. Since I'm not a fulltimer,,I check and minor service tires with 100% Nitrogen.. as/if needed before any trip. The 40 cubic foot portable tank is workable for transport in motorhome for fulltiming or just carry the guage-valve service assembly hose...and minor reservice with loaner bottles along the way. Again, my experience shows very little (2-3 #) to none continued Nitrogen service needed over 6 month - 12 month interval. Works for me...and I have much more safety confidence in my motorhome tire health and performance using the 100% Nitrogen.
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Old 10-21-2006, 06:31 AM   #14
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NR4A:

Our local Ford dealer offers 100% nitrogen in your tires for $8.95 per wheel. I am missing what, here ? </div></BLOCKQUOTE>

Nothing......100% Nitrogen in tires has been going around the internet for years now, and generally is concieved as a waste of money with no difference in tire wear or longevity.

Save your money....put AIR in your tires
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Old 10-21-2006, 07:30 AM   #15
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FrontRangeRVr: In Columbus times...had the internet been there..I'm sure the "internet" would have said the world was flat.

For the past few years I have understood why COSTCO and many car service dealers...and nitrogen generator fabrication companies.. are investing millions..thousands in the Nitrogen service capability for customers...because I understand the principals and safety benefits (priceless) of correctly using/maintaining 100% Nitrogen in my vehicle tires. To me..optimum tire safety and performance is not a waste of money by using 100% Nitrogen. I do not think COSTCO and other major auto service business providers think it is a waste of money either because it (100%N)is not "snake oil". The challenge these companies have is to convince current customers of the safety and enhanced-sustained tire performance of 100% Nitrogen.
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Old 10-21-2006, 08:00 AM   #16
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Huumm: Just a thought here. If oxygen leaks out at a greater rate than nitrogen (and it does), then one might assume that after time you would have close to 100% nitrogen after the continuous leaking and topping off with air.
Just a thought to ponder.
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Old 10-21-2006, 08:54 AM   #17
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Pubtym:
I do not think COSTCO and other major auto service business providers think it is a waste of money either because it (100%N)is not "snake oil". The challenge these companies have is to convince current customers of the safety and enhanced-sustained tire performance of 100% Nitrogen. </div></BLOCKQUOTE>

Exactly...it's 100% PROFIT for COSCO for the unknowing public.. Has nothing to do with them caring about "safety"...it's about them getting $10/tire profit and making someone THINK they are getting value....A good COSTCO "salesman" can talk some people in to buying this un-needed product.

Same with "Siping" your tires...you think Discount Tire is pushing this for your safety? Nope...they do it for $10/tire....If the tire manufacturers thought so much for this "added" feature, they would already by siped....

So...do you REALLY think that these discount tire places are thinking about your SAFETY or their bottom line?

Hey...it's your money!
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Old 10-21-2006, 09:47 AM   #18
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">claim you get a better ride (?) more fuel mileage, less tire failures, contant tire pressures, and longer life out of your tires. </div></BLOCKQUOTE>
"Better ride" is a pretty subjective thing. As for the rest, checking your tires regularly and keeping them properly inflated based on the weight you are carrying will take care of those things. The point is that too many people ignore their tires until one of them has a problem. If you ignore your tires, I believe some of those claims about using Nitrogen might be true.
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Old 10-21-2006, 10:05 AM   #19
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Here are some other comments I located on another website Engineering Tips Forum.

The follwing are some of the key points:

The question about nitrogen in tires has come up in other lists on the web as well. Let me clarrify a few points.

1. Air is 78% nitrogen, N2, and 21% oxygen, O2. So even if you put air in the tire, it's already 78% nitrogen. Many of the so called nitrogen generators don't produce much more than 90% nitrogen.

2. At relatively low pressures (ie tire pressures) N2, O2 and water vapor will all behave as ideal gases, and follow PV=nRT. Pressure will increase or decrease to the same extent as the temperature increases or decreases regardless of which gas is in the tire. (Even at 300 psi, which is about 20 atm, there is little deviation from ideality.) Therefore the comments about N2 not changing in pressure as the temperature changes are without merit.

3. The rate of effusion (or diffusion) of a gas through a porous membrane depends on the molar mass and to some degree on the molecular diameter. N2 and O2 are almost the same size and N2 is lighter than O2 (28 g/mol vs 32 g/mol) so if either gas were to effuse out of the tire, nitrogen would do it more quickly. Luckily, tires are designed not to be porous membranes.

4. N2 and O2 both have essentially the same specific heat capacity, about 1.0 J/gK, and thermal conductivity, about 0.00026 W/cmK. Water vapor has a specific heat capacity of about 2 J/gK. But remember, water vapor will constitute less than 1% of the air in the tire. So the idea that N2 has different heat handling properties is also without merit.

5. The ozone, O3, in the atmosphere, which is a ground level pollutant, will do a great deal more damage to your tires than the O2 inside the tire. For instance, don't leave a condom out in the air in Los Angeles for a few days. It will develop lots of tiny holes and weaken.

It has been said that dry air is preferably to air with a lot of water vapor. As a tire heats up, the very small amount of H2O present will be in the vapor state which may contribute to the overall pressure very slightly.

Several have suggested that N2 in a high pressure tank is more portable and requires no electricity. That would make sense, particularly for aircraft tires.

I find no reason to believe that N2 is going to produce a "better ride" or "better handling".

The bottom line is that for general passenger car tires or truck tires there is nothing to be gained (other than portability) by using nitrogen rather than air. The biggest gain will be $$$ by the companies that sell nitrogen handling equipment and the tire merchants that appeal to ignorant customers. And who is the biggest loser? Yep, the consumer.
Regardless of how much you want a gas not to increase in pressure when heated, it's just not going to happen. The laws of chemistry and physics apply all the time. PV=nRT is true all the time, for every gas, be it air, nitrogen or water vapor. Saying that a gas does not increase in pressure as temperature increases is nonsense.

Also, don't worry about the "water" in the air. It exists as water vapor, a gas, and is simply part of the total pressure in the tire. As the tire heats up, the water vapor will continue to be a gas and be governed by the equation PV=nRT, just like air, which is 78% nitrogen.

Every gas is going to escape from a tire, regardless, as long as the pressure inside the tire is greater than the pressure outside the tire. The gas molecules are going to diffuse through the walls of the tire at a very slow rate. It doesn't make any difference what the gas is, although there are small differences between the diffusion rates of oxygen and nitrogen. Since nitrogen is slightly less massive than oxygen (28 g/mol vs 32 g/mol) Graham's law predicts that nitrogen will diffuse slightly more rapidly than oxygen.

The bottom line is that you can't set aside science in favor of hype and wishful thinking.

This was copied from a post by Mike Jones on www.eng-tips.com.
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Old 10-21-2006, 10:16 AM   #20
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Exactly. I have confidently chosen... with my money.. to... in my opinion, better manage the gasses in my tires with the 100% Nitrogen process...and therefore almost elimate the number 1 cause of tire failure (under in flation) for my vehicles. Those choosing the daily/regular hassel to do daily/regular tire checks of their motorhome tires with air in them..can choose to do so too. I sure don't see any hazards being posted by experienced forum users of 100% Nitrogen. Guess the civil, military and private aviation community has been using this snake oil in their tires for years too. Maybe the world is still flat.
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