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Bert Kemp
11-25-2016, 11:53 PM
I was going to bring this up in the oil check thread but decided to start a new one for what I think is far more critical then checking oil and thats checking your tires air pressure. Its more troublesome to check 4 tires for air but way more important from a safety point. I think low air pressure is a major cause of accidents. I check mine about every 3 or 4 weeks on my car and almost always need a lb or 2 of air. On my Motorcycle Every week I pull into DT and have them check my tires and air. How often do you check your air?

Jim Koepke
11-26-2016, 12:18 AM
I keep an eye on the tires. If they all look same as they do when freshly filled I do not give it much thought.

jtk

Wayne Lomman
11-26-2016, 5:12 AM
I check tyres at least every week. I run pressures at the top end of the recommended range since all my driving is long distances on open roads. When I was about 19 I was told to do this by a tyre fitter in the outback after my car had just blown its second tyre in the space of a day. I have never lost a tyre since. Cheers

John K Jordan
11-26-2016, 7:19 AM
I was going to bring this up in the oil check thread but decided to start a new one for what I think is far more critical then checking oil and thats checking your tires air pressure. Its more troublesome to check 4 tires for air but way more important from a safety point. I think low air pressure is a major cause of accidents. I check mine about every 3 or 4 weeks on my car and almost always need a lb or 2 of air. On my Motorcycle Every week I pull into DT and have them check my tires and air. How often do you check your air?

I give up - what is a DT?

My new Jeep makes it easy to monitor - a diagram on the console shows the pressure of each tire.

I understand underinflated tires also increase rolling resistance which increases fuel use.

With 64 tires here on 19 things monitoring and keeping them aired up is a constant effort, especially as offroad tires age. I keep compressors in three buildings with hoses on retractable reels.

JKJ

Larry Frank
11-26-2016, 7:38 AM
I have one car with the sensors in the tires and that is great. On my older car, I keep an eye on them and check before any longer drives. They are also checked when the tires are rotated.

I also check more often as the temperatures change in the fall. The colder conditions result in lower air pressure.

Robert Engel
11-26-2016, 8:22 AM
I don't see why you need to check them that frequently.

I check when I do oil changes, which is about every 4-5 months or before a long trip.

George Bokros
11-26-2016, 8:27 AM
I have one car with the sensors in the tires and that is great.

The tire pressure sensors that I am familiar with on the cars today ONLY alert you to pressures that at way below the recommended pressures. They are not meant to replace checking the pressures with a tire pressure gauge.

Along with this the last time my truck was serviced the dealer noted that they had filled the tires to the manufacturer recommended pressures which were 5 lbs higher than what it said on the sticker on the vehicles door jamb. I found this interesting since the truck had the factory installed tires so it was not that the tires differed from the manufacturer installed tires. I always ran them at the higher pressure anyway.

Adam Herman
11-26-2016, 8:38 AM
DT = discount tire i am guessing.

i check mine with chalk when i get them to find the best pressure. our volt gets about 40 psi and my truck 38. both higher than the pressure on the door jamb, but also different tires than the cars came with. make a nice wide line of chalk across the tire and back/pull up on a level street. see if the chalk is evenly wore or more in the center or edges. adjust to get it even. more if there is chalk left in the center, and less if there is chalk left on the outsides.

roger wiegand
11-26-2016, 8:39 AM
If you are losing that much pressure in a car tire you have a leak that needs to be fixed.

I check pressure every few months and it almost never varies in the cars. The TPMS system lights a light at about 3 lb under the recommended pressure in my Mini. I check the truck and trailer whenever I leave for a long trip. They are set to 80 lbs and 4 of 10 tires drop 4-5 lb over the course of a month, the rest hold much better. Thats about 25 lb over what the door jamb says, but I run at close to the maximum allowed weight, so pump the tires up to their max capacity.

George Bokros
11-26-2016, 8:58 AM
Static tire pressure varies by the season. Usually in the fall the pressure is lower than it would be static in July at least in the northern climates - northeast Ohio. This being said you should check the pressure as the seasons change.

Kurt Kintner
11-26-2016, 9:11 AM
Don't forget to check the spare..... We ran over a nail in New Mexico, and the spare was flat.... My bad...
But, we carry a 12 volt inflater, and were able to keep enough air in it to get to a tire store ....

Wade Lippman
11-26-2016, 9:13 AM
The system they use on Mazda (we have two Mazdas) only alerts you if one tire is different than the rest. If they are all low you get no warning. So I check once a month or so.
Sad thing is, they frequently need air. Don't know why that is.

But how often do you check the pressure in your spare! My Mazda CX9 is mounted under the car. I checked it after 2 years and found it had half the pressure. I wonder how long it would have taken the little compressor we carry to pump it up to 60psi.

Mike Henderson
11-26-2016, 10:21 AM
I have one car with the sensors in the tires and that is great.

I agree. My car has the tire pressure sensors and I get lots of warning if the pressure goes down. Way better than driving on a tire with low pressure because you didn't notice it.

Mike

Brian Elfert
11-26-2016, 11:35 AM
The tire pressure sensors on my Grand Caravan seem to alert when the pressure is about 10% below normal. I never remember to fill the tires before winter and I usually get a low tire pressure alert once it gets real cold for a few days.

My motor home has add-on sensors that need the tires set to the correct pressure before screwing the sensors on. The display shows the pressure within a few PSI. I was surprised that this year none of the tires had lost any pressure after sitting for months.

Grant Wilkinson
11-26-2016, 11:43 AM
Contrary to George's experience, on my Acura, I can see the individual tire pressures whenever I like. I don't need to wait for a low tire warning. I can actually watch the pressures change as the tires heat up while driving.

George Bokros
11-26-2016, 11:50 AM
Contrary to George's experience, on my Acura, I can see the individual tire pressures whenever I like. I don't need to wait for a low tire warning. I can actually watch the pressures change as the tires heat up while driving.

This is great. All vehicles should have this type of system.

Bert Kemp
11-26-2016, 11:58 AM
Tire pressure can change dramatically with temperature changes, if its cold you can lose pressure if its hot you can get more pressure . My motorcycle is always changing Its 40 in the morning and 80 in the afternoon. The constant up and down over the course of a week really effects how the bike rides and handles. Very easy to feel when my pressure is down even a couple lbs. So its gets checked often the car not as much. I've put 28000 miles on the bike this year and 1200 on the car.



I don't see why you need to check them that frequently.

I check when I do oil changes, which is about every 4-5 months or before a long trip.

Ronald Blue
11-26-2016, 12:02 PM
Both my vehicles tell me exactly what each tire has in it. So at the press of a button I can see where each tire is. It is interesting to see how tire pressure varies by ambient temperature. You will see 2-3 psi difference between 80 degrees and 30 degrees. So you should adjust tire pressures if you are where you see the seasonal changes from summer to winter.

Brian Henderson
11-26-2016, 2:42 PM
Unnecessary, modern cars check them for you.

Mac McQuinn
11-26-2016, 4:00 PM
Both vehicles are checked once a week, more often if there's a large temperature variable. My motorcycle tires are checked twice a week. I tend to get maximum mileage out of a set of tires and owe this to my somewhat anal attention to TP's. I don't check tires after driving or even if car has been sitting in the sun, waste of time imo. My gauge reads in tenths which comes in handy to get a perfect balance to get good tire wear, ride and performance in the rain. I check thread depth once a month and if need be, alter my TP settings to keep the tires wearing correctly. I never use the monitors as I feel they're inaccurate enough to not reply upon.
Mac

Brian Elfert
11-26-2016, 4:22 PM
Both vehicles are checked once a week, more often if there's a large temperature variable. My motorcycle tires are checked twice a week. I tend to get maximum mileage out of a set of tires and owe this to my somewhat anal attention to TP's. I don't check tires after driving or even if car has been sitting in the sun, waste of time imo. My gauge reads in tenths which comes in handy to get a perfect balance to get good tire wear, ride and performance in the rain. I check thread depth once a month and if need be, alter my TP settings to keep the tires wearing correctly. I never use the monitors as I feel they're inaccurate enough to not reply upon.


Check tire pressure in tenths? Is this a race car or a an everyday car? Do you get the gauge calibrated monthly too? How do you have any idea what to change the tire pressure to if they are wearing wrong?

Lee Schierer
11-26-2016, 7:00 PM
The single biggest cause of low tire pressure are the clip on wheel weights on aluminum wheels. Most of those clip on weights use steel clips. When the tire tech pounds them onto the rim, the steel cuts through the anodize that protects the aluminum from corrosion. Add a bit of road salt from either winter roads or dirt roads and some water and you have a galvanic cell that starts eating away the aluminum. This corrosion eventually gets bad enough that the bead will start leaking air. On my Explorer, I would lose 2-3 pounds per week before I got rid of it. Now I only allow the tire techs to use the stick on weights when I have my tires balanced. This keeps the rims free from corrosion in the tire bead area.

Mac McQuinn
11-26-2016, 10:17 PM
Check tire pressure in tenths? Is this a race car or a an everyday car? Do you get the gauge calibrated monthly too? How do you have any idea what to change the tire pressure to if they are wearing wrong?


Brian,
The gauge reads in tenths. That said, my motorcycle is modified with different set-up from stock. The tenths do come in handy in looking for desired contact patch. Since a bike is leaning over in the corners, this is pretty important.

If my car's tires are wearing wrong, say heavier in the middle than the edges, I decrease pressure a bit, the tenths allow me to sneak up on things until I get a consistent wear pattern. You'll also feel the difference in ride if you're careful and get a perfect tire contact. That said, this all assumes your alignment is spot on. You can also check correct pressure by using the chalk test. Quicker to google than explain. I find consistent psi readings more important than total accuracy. I've found different brand tires like different psi settings, the wear pattern is my dictating factor.
Mac

John Terefenko
11-26-2016, 10:38 PM
My Chevy Silverado has a panel readout that I can check all the important things with a push of a button and scroll through them. Oil usage and oil consumption to tire pressure. I go through them at least once a week or if i am bored sitting in traffic.

Kev Williams
11-26-2016, 10:54 PM
i check mine with chalk when i get them to find the best pressure. our volt gets about 40 psi and my truck 38. both higher than the pressure on the door jamb, but also different tires than the cars came with. make a nice wide line of chalk across the tire and back/pull up on a level street. see if the chalk is evenly wore or more in the center or edges. adjust to get it even. more if there is chalk left in the center, and less if there is chalk left on the outsides.
This hits on an issue with tires that simply bugs me, which is the fact that the factory recommended 'door jamb' pressures do NOT refer to which tire types the pressure recommendations refer to. Most tires I've dealt with fall into two basic air pressure ranges, 35psi max and 44psi max. There may be others to be sure, but these 2 seem to be the most common. As an example, my '96 Lincoln MKVIII's door jamb pressure stated 30psi. The original tires that came on the car were 35psi Goodyear tires. I bought the car used, and had to soon change out the original tires. I got the exact same size tires, only they were 44psi max tires, Firestones I think (years ago). The shop put 30 pounds of air in per the door jamb, and the car felt like I was driving on marbles. Oh, what a smooth ride, but it drove horrible. So I did a little math, 30psi was 85.7% of the original tire's 35psi max, and 85.7% of 44psi is 37.7 psi, so I aired them up to 38, and voila, the car drove and handled like a dream. Pretty much exactly like 30psi in the original tires...

The chalk method Adam mentions above works. For one thing, it's 'absolute', it compensates for the actual weight on the tire, the tire itself, and for air gauges that don't work right (does yours? I have 5 that all give different readings! ;) )

My rule of thumb is simple, 3 or 4 psi below the sidewall max, and a snick more up front because of engine weight...

Bill Jobe
11-26-2016, 11:35 PM
I started running my tires on the high side after the Explorer problem identified poorly figured pressure by the manufacturers. As a result, I have a Sable with the 3.0 DOHC V6 that gets 30 mpg on the highway. I make a habit of checking milage every time I drive to my mom's. That's a 300 mile round trip and when I go back home the same day I figure that should give a pretty accurate mpg.
That ain't bad for a car its size.
I'm at a loss as to why car makers can't seem to make midsized SUVs that do that good. My Sable is now 13 years old. So much for progress.

Brian Elfert
11-27-2016, 12:13 AM
For my motor home I have weighed each axle and consult a chart that says what PSI to use based on weight. The vehicle rides better with less air in the tires. I originally ran all tires at max PSI, but it didn't ride all that well. I used to get better MPG back when I ran higher pressure, but I think the new diesel fuel introduced in 2007 has more to do with MPG loss than lower tire pressures.

Jim Becker
11-27-2016, 10:15 AM
My Grand Cherokee Summit has a TPMS system, so "in general" I don't need to manually check things...I just look at the display and can see what the tire pressure on all four corners is at that moment. And the system is reasonably accurate, too. I do adjust tire pressure seasonally and use an electronic pressure tester to zero things in to where I like them...which is 38 psi cold.

Tony Zona
11-27-2016, 12:14 PM
The pressure monitoring system in my wife's car is on the helpful side. It shows individual tire pressures, but there is no indication which pressure goes with which tire.

I consider its reading as telling me to check all tires manually. Then again if I had gotten the air stuff out I would have checked them all anyhow.

Matt Meiser
11-27-2016, 5:43 PM
My 2017 Fusion reads actual PSI First car I've had with that.

When checking pressure I'm partial to these gauges: http://www.ghmeiser.com/ (No idea if I'm related.)

Ole Anderson
11-27-2016, 6:19 PM
Am I correct that TPMS are required on all new cars now? Wife's 2009 Vibe only alerts when a tire (you have to figure out which) is under inflated, I think it goes off at 25% low (26 psi) on a 35 psi normal tire. My 2015 GMC Acadia will send me an email monthly (via Onstar) with all sorts of parameters including tire pressure, and what needs attending to. It cautions to adjust tire pressure if it below 32 psi IIRC. Also miles to next oil change. Of course a low tire (25% low by law I believe) will alert on the dash. Having to check tire pressure on a late model car is a thing of the past.

Myk Rian
11-27-2016, 8:47 PM
I check them with the season changes. I also fine tune the pressures for the best ride and handling.
If tires need air every couple weeks, check the valve stems for leaks around the hole in the wheel. Corrosion does happen there.

Jim Becker
11-28-2016, 10:56 AM
The pressure monitoring system in my wife's car is on the helpful side. It shows individual tire pressures, but there is no indication which pressure goes with which tire.

I consider its reading as telling me to check all tires manually. Then again if I had gotten the air stuff out I would have checked them all anyhow.
Strange that the display doesn't portray the location for each reading...our vehicles do that.

Rod Sheridan
11-28-2016, 11:13 AM
I check tire pressure monthly on the minivan, every couple of weeks on the motorcycle...........Rod.

Bruce Page
11-28-2016, 2:16 PM
The pressure monitoring system in my wife's car is on the helpful side. It shows individual tire pressures, but there is no indication which pressure goes with which tire.
My cars display is the same way, it gives PSI for each tire but no correlation to which tire. I have figured out which is which through trial & error. It has never made any sense to me why they did it that way. My wife's 2012 car is even worse, it'll give you a low pressure warning if a tire is low but that's it - no psi numbers or which tire is low. Both cars are Infiniti brand SUV's

John K Jordan
11-28-2016, 3:53 PM
My cars display is the same way, it gives PSI for each tire but no correlation to which tire. I have figured out which is which through trial & error. It has never made any sense to me why they did it that way. My wife's 2012 car is even worse, it'll give you a low pressure warning if a tire is low but that's it - no psi numbers or which tire is low. Both cars are Infiniti brand SUV's




Maybe the software guys are getting smarter. My wife's Murano, a couple of years old, is like yours but my 2017 Jeep shows which tire has which pressure. Or maybe just slowly release features to encourage dissatisfaction with last year's models. Next will be the the automatic inflation system in use on larger vehicles for years.



JKJ

Ken Combs
11-29-2016, 10:13 AM
Maybe the software guys are getting smarter. My wife's Murano, a couple of years old, is like yours but my 2017 Jeep shows which tire has which pressure. Or maybe just slowly release features to encourage dissatisfaction with last year's models. Next will be the the automatic inflation system in use on larger vehicles for years.



JKJ

The more info the systems display, the more complex maintenance becomes. If the pressure is displayed by position, tire rotation must include a 'relearn' process that requires a special tool.

Owner maintenance is effectively prevented. And, any business, other than a brand dealer, that wishes to do tire maintenance must invest in the tool. Of course, that cost is ultimately passed on to all customers, not just those driving brand 'x'.

My Tundra and Town & Country, both display a warning of low pressure, but no position info. that is fine with me, as I can move tires, change tires etc without having to provide the computer system with an added info.

All conveniences have an associated cost.

Yonak Hawkins
11-29-2016, 10:52 AM
I have three gauges, all of which indicate a different pressure. How do I calibrate or verify what is the correct pressure ?

John K Jordan
11-29-2016, 11:31 AM
I have three gauges, all of which indicate a different pressure. How do I calibrate or verify what is the correct pressure ?

Ha, the age-old question of any instrument. ("The man who has one clock always knows what time it is; the man who has two is never sure.")

I have found horribly poorly calibrated pressure gauges, dial, stick and digital. (Digital were the worst I've had) There are companies that will calibrate anything but it costs money. Do it yourself? My first thought was to use a water column but wasn't sure about the best way to go about it. So Google gave me this: http://www.carsdirect.com/car-repair/how-to-calibrate-a-tire-pressure-gauge A bit of an effort!

I know you can purchase calibrated master gauges but I suspect they are expensive. (a good tire shop may have one and be willing to check your gauges - especially if you are a customer!)

I have a pile of pressure gauges, some cheap and some expensive and supposed to be high quality. One way to check: Compare them all, write down the readings, and throw out those furthest from the average.

This is impossible with some gauges I use, such as those with widely different scales such as the low-pressure gauges for the ATVs and those for my truck which needs 80 psi (for heavy loads). I just buy the best quality I can find and read and try to filter the ratings.

This Consumer Report rated a couple models higher. http://www.consumerreports.org/cro/tire-pressure-gauges/buying-guide.htm

JKJ

Yonak Hawkins
11-30-2016, 12:17 AM
Thanks for the thoughtful response, John, and the link to the Consumer Report ratings. I don't think I'll test using the CarsDirect method.

richard b miller
11-30-2016, 9:16 PM
if checking air pressure in tires is so important, how come they make the psi text soooo small? :)

Curt Harms
12-01-2016, 8:13 AM
My 2017 Fusion reads actual PSI First car I've had with that.

When checking pressure I'm partial to these gauges: http://www.ghmeiser.com/ (No idea if I'm related.)


I'd read that dial gauges are more consistent than the common 'stick' types. I have one gauge on a regulator that is filled with some sort of clear oil so the mechanism shouldn't get sticky with age. The electronic types are interesting (Ooooo, another gadget!!) but yet another battery to go flat at the most inopportune time.

Curt Harms
12-01-2016, 8:21 AM
I have three gauges, all of which indicate a different pressure. How do I calibrate or verify what is the correct pressure ?


Maybe after having tires serviced by a reputable shop, ask what pressure they're inflated to then check with your own gauge? See how far apart the readings are? There'd be no guarantee but you'd hope a professional tire shop would have accurate gauges.

Bert Kemp
12-01-2016, 10:39 AM
Last time I took the bike into DT they checked my tire with the gauge thats hooked to the air hose and he said I had 53 lbs in the back tire. I asked him to check it with another gauge because I knew I didn't have 53 in that tire , he got a dial one from one of the guys and it read 33, much better then he put the hose one back on and checked it at 33 he miss read the pressure DUH. But what happens when Granma comes in and the kid misreads. LOL

Tom Stenzel
12-01-2016, 2:37 PM
I remember some of the GM systems used the ABS rotation sensors to monitor the tire pressure. If one tire spun at a different RPM while driving it was assumed one of the tires was mis-inflated. GM pushed to have that accepted as it used no additional sensors, required only a minor software update to the existing computer, and program one more message in the display system. I think it ended up the highway dept disallowed it as four mis-inflated tires would read as just fine.

When we went shopping for a used car for my daughter there were many cars with the tire monitor system in fault. A sensor would break or a wheel would be changed and the owners just ignored the light. Depending on the price of repair I might be inclined to ignore it too.

-Tom

Gordon Eyre
12-01-2016, 4:43 PM
If this has already been discussed then just ignore my post. I use nitrogen in my tires and it goes a long way towards eliminating the pressure from changing with temperature changes. I maintain a fairly constant 34 lbs. on all four tires and it is monitored and displayed on the dash with a push of a button. Big O tires will check and top off my tires at no charge and I do this prior to any long trip.

Mike Henderson
12-01-2016, 4:52 PM
I remember some of the GM systems used the ABS rotation sensors to monitor the tire pressure. If one tire spun at a different RPM while driving it was assumed one of the tires was mis-inflated. GM pushed to have that accepted as it used no additional sensors, required only a minor software update to the existing computer, and program one more message in the display system. I think it ended up the highway dept disallowed it as four mis-inflated tires would read as just fine.

When we went shopping for a used car for my daughter there were many cars with the tire monitor system in fault. A sensor would break or a wheel would be changed and the owners just ignored the light. Depending on the price of repair I might be inclined to ignore it too.

-Tom
Not only that, but if you replaced one tire with a slightly different size, it would rotate at a different RPM constantly. I had that problem on a car I owned. I had a tire failure on a trip and had to replace it at the nearest tire shop. After that, my cruise control wouldn't work. Eventually found out it was because the two tires on the back were rotating at slightly different RPMs. Had to replace the "new" tire.

Mike

Mike Henderson
12-01-2016, 4:55 PM
If this has already been discussed then just ignore my post. I use nitrogen in my tires and it goes a long way towards eliminating the pressure from changing with temperature changes. I maintain a fairly constant 34 lbs. on all four tires and it is monitored and displayed on the dash with a push of a button. Big O tires will check and top off my tires at no charge and I do this prior to any long trip.
I've heard that before but I don't understand it. Nitrogen expands and contracts with temperature just like air. After all, regular air is almost 80% nitrogen. If there's some truth to this belief it may be because the nitrogen they put in your tires is "dry" while normal air has some level of humidity.

Mike

Bert Kemp
12-01-2016, 6:34 PM
Its not do to expansion and contraction. Air leaks thru the rubber sidewalls on tires and nitrogen leaks a lot slower.


I've heard that before but I don't understand it. Nitrogen expands and contracts with temperature just like air. After all, regular air is almost 80% nitrogen. If there's some truth to this belief it may be because the nitrogen they put in your tires is "dry" while normal air has some level of humidity.

Mike

Mike Henderson
12-01-2016, 8:51 PM
Its not due to expansion and contraction. Air leaks thru the rubber sidewalls on tires and nitrogen leaks a lot slower.
According to this article (http://www.tirebuyer.com/education/nitrogen-vs-air), the difference in leaks through the sidewalls is extremely small. And since air is 80% nitrogen, that's kind of what I'd expect. The only way we'd see a difference is if the oxygen in the air leaked at a rapid rate. Nitrogen and oxygen are next to each other in the periodic table with Oxygen being slightly heavier than nitrogen so we'd expect that oxygen would migrate at a slower rate than nitrogen.

But, in any case, it appears that for ordinary passenger car use, there's not much difference.

Mike

Myk Rian
12-01-2016, 8:53 PM
I have one gauge on a regulator that is filled with some sort of clear oil so the mechanism shouldn't get sticky with age.
Probably Glycerin. It's there for use in applications where there is vibration. Very common in industry.

Curt Harms
12-02-2016, 7:51 AM
I've heard that before but I don't understand it. Nitrogen expands and contracts with temperature just like air. After all, regular air is almost 80% nitrogen. If there's some truth to this belief it may be because the nitrogen they put in your tires is "dry" while normal air has some level of humidity.

Mike

Nitrogen pressure does increase and decrease with temperature, I know that first hand. Certain aircraft use high pressure nitrogen in emergency systems as well as in tires. A system serviced to 2000 p.s.i. in a warm climate may read 1700 p.s.i. after sitting in a cold climate for several hours. Go back to the warm climate, let it sit several hours and the pressure is back up to 2000 p.s.i. with no servicing. There's even a temperature/pressure table next to the gauge.

Malcolm McLeod
12-02-2016, 9:59 AM
Nitrogen in car tires is pure marketing hooey. The ideal gas law makes N2 tire pressure stability impossible. Please note the use of the term 'law', it is not called the 'ideal gas suggestion'.

Putting N2 in your tires allows 2 things: 1. the dealer can charge you $150-$300 over the MSRP (remember dealer's $500 "clear coat protectant" - aka "wax"); and, 2. You can't refill your tires at the local gas station or your shop compressor. So, you have to return to the dealer service bay where they can up-sell you all over again.

Call me a cynic. Or a realist. ...Or even maybe an engineer?:cool:

Bert Kemp
12-02-2016, 11:14 AM
I guess it depends on were you get info from.
From Popular Mechanic's
From the top: Air is 78 percent nitrogen, just under 21 percent oxygen, and the rest is water vapor, CO2 and small concentrations of noble gases such as neon and argon. We can ignore the other gases.There are several compelling reasons to use pure nitrogen in tires.
First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings. That means more consistent inflation pressures during a race as the tires heat up. And when you're tweaking a race car's handling with half-psi changes, that's important.
Passenger cars can also benefit from the more stable pressures. But there's more: Humidity (water) is a Bad Thing to have inside a tire. Water, present as a vapor or even as a liquid in a tire, causes more of a pressure change with temperature swings than dry air does. It also promotes corrosion of the steel or aluminum rim.

Mike Henderson
12-02-2016, 11:55 AM
I guess it depends on were you get info from.
From Popular Mechanic's
From the top: Air is 78 percent nitrogen, just under 21 percent oxygen, and the rest is water vapor, CO2 and small concentrations of noble gases such as neon and argon. We can ignore the other gases.There are several compelling reasons to use pure nitrogen in tires.
First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings. That means more consistent inflation pressures during a race as the tires heat up. And when you're tweaking a race car's handling with half-psi changes, that's important.
Passenger cars can also benefit from the more stable pressures. But there's more: Humidity (water) is a Bad Thing to have inside a tire. Water, present as a vapor or even as a liquid in a tire, causes more of a pressure change with temperature swings than dry air does. It also promotes corrosion of the steel or aluminum rim.

From the same article:
++++++++++++++++++++++
Consumer Reports conducted a study comparing nitrogen versus air loss in tires to determine if this benefit of nitrogen was worth the extra cost. They used 31 pairs of various tire models, filled one tire of each pair to 30 psi with air and the other to the same pressure with nitrogen, then left them outside for a year. At the end of the year, they found that all tires lost pressure. The average pressure loss with air was 3.5 psi; with nitrogen the average loss was 2.2 psi – a difference of only 1.3 psi over a year.
++++++++++++++++

Mike

Malcolm McLeod
12-02-2016, 12:09 PM
I guess it depends on were you get info from.
From Popular Mechanic's
From the top: Air is 78 percent nitrogen, just under 21 percent oxygen, and the rest is water vapor, CO2 and small concentrations of noble gases such as neon and argon. We can ignore the other gases.There are several compelling reasons to use pure nitrogen in tires.
First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings. That means more consistent inflation pressures during a race as the tires heat up. And when you're tweaking a race car's handling with half-psi changes, that's important.
Passenger cars can also benefit from the more stable pressures. But there's more: Humidity (water) is a Bad Thing to have inside a tire. Water, present as a vapor or even as a liquid in a tire, causes more of a pressure change with temperature swings than dry air does. It also promotes corrosion of the steel or aluminum rim.

I try to get my information about the physical world from researchers in the physical sciences, not from the entertainment media. Please spend your money as you feel appropriate.

Curt Harms
12-03-2016, 10:40 AM
I try to get my information about the physical world from researchers in the physical sciences, not from the entertainment media. Please spend your money as you feel appropriate.


I would think (not a chemist) gas mixtures containing oxygen are more chemically reactive than pure nitrogen. Is it enough to matter? I don't know.

John M Wilson
12-03-2016, 11:32 AM
I would think (not a chemist) gas mixtures containing oxygen are more chemically reactive than pure nitrogen. Is it enough to matter? I don't know.

The thing to remember is that your tire is not existing in some isolated world... it is surrounded by the nitrogen/oxygen mixture. If you stop to think about it, most tires do not wear out from the inside. And, if the 21% oxygen mixture were that corrosive to tire rubber, you would still have the problem on the outside of the tire, which is the part that is touching the road, and far more important to operating your vehicle safely.

The thing about the oxygen leakage thing I have never been able to figure out... if over some period of time, the oxygen leaks out of my tires faster than the nitrogen, and I keep refilling them with a mixture that has nearly 5 times as much nitrogen as oxygen, wouldn't my tires eventually become nearly completely filled with nitrogen?

I used that last one on a car salesman one time, and he responded with "Well, I'm not a chemistry teacher, so..." I let him know that I was a chemistry (and physics) teacher, and that caused the conversation to move along to non-chemical ways he could remove money from my pocket and put it into his :rolleyes:.

Ole Anderson
12-03-2016, 12:58 PM
The thing to remember is that your tire is not existing in some isolated world... it is surrounded by the nitrogen/oxygen mixture. If you stop to think about it, most tires do not wear out from the inside. And, if the 21% oxygen mixture were that corrosive to tire rubber, you would still have the problem on the outside of the tire, which is the part that is touching the road, and far more important to operating your vehicle safely.

The thing about the oxygen leakage thing I have never been able to figure out... if over some period of time, the oxygen leaks out of my tires faster than the nitrogen, and I keep refilling them with a mixture that has nearly 5 times as much nitrogen as oxygen, wouldn't my tires eventually become nearly completely filled with nitrogen?

I used that last one on a car salesman one time, and he responded with "Well, I'm not a chemistry teacher, so..." I let him know that I was a chemistry (and physics) teacher, and that caused the conversation to move along to non-chemical ways he could remove money from my pocket and put it into his :rolleyes:.

Ah, that got ya moment. Priceless.

Mike Henderson
12-03-2016, 1:06 PM
At one time, I thought it might be the moisture content in air - while the nitrogen was dry. But think about the compressor in your shop: When you compress air, it can't hold as much moisture as when it's at a lower pressure. That's why you get water in your tank. And the air compressors in a service station probably compress to at least 150 lbs/sq" so the air coming out of the hose is dryer than the ambient air. It isn't completely dry, but it would be very low humidity. So I'd think that moisture in the air in the tire would be a small factor.

Overall, I can't see any significant advantage to all nitrogen in your tires - but I'm willing to listen.

Mike

[I suspect the "nitrogen" that the tire shops put in your tires is not "pure". Getting every last contaminant out of something is extremely difficult and I suspect they buy "cheap" (non-pure) nitrogen, probably because it doesn't matter.]

Mel Fulks
12-03-2016, 2:08 PM
I think the gas station compressors get neglected. After paying as much as .75 cents some years back to get as much water as air I bought one.

John K Jordan
12-03-2016, 11:36 PM
... When you compress air, it can't hold as much moisture as when it's at a lower pressure. That's why you get water in your tank. And the air compressors in a service station probably compress to at least 150 lbs/sq" so the air coming out of the hose is dryer than the ambient air. It isn't completely dry, but it would be very low humidity. So I'd think that moisture in the air in the tire would be a small factor.


I don't think it works like that. From what I remember from my studies long ago the amount of liquid vs gaseous water in a container is not related to the pressure but dependent on the temperature, i.e., the water doesn't come out of the air because of pressure but from when the air cools to the saturation point (the dewpoint). In that case, water accumulating in the tank would result from the compressor adding more hot, moist air each cycle coupled with the cooling cycles. Since air heats up as it is compressed, if not allowed to cool the air coming through the lines may actually have more moisture in it than the air in the room since it can pick up moisture from any liquid water in the tank. The increased moisture in hot air is why recommended installations have cooling condensers or a long length of line on the outlet of the compressor (along with a gravity trap) to allow the air to cool and water removed before use.

Perhaps a real physicist will comment or I can ask one of my scientist friends.

This page has some interesting information, especially the section at the end discussing why air doesn't actually "hold" water:
http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/relhum.html

BTW, my shop compressor compresses to about 150 psi. I use a moisture trap, a centrifugal water separator and a desiccant drier before piping the air to the outlets. (The plasma cutter doesn't like wet air.) Even though I drain the tank the desiccant drier picks up a huge amount of water and has to be changed every few months. I suspect some service stations don't even dry the air at all.

But regardless of how the water gets in the tank, my own opinion about filling tires with nitrogen is it is an unnecessary expense with marginal benefit, if any, intended to increase sales. Even if it was beneficial, how will most people add a little air to their tires when needed - hunt for a shop that has nitrogen service? Topping off with "plain" air would add oxygen. When we take our 4wd vehicles in the deep sand (beach) we let air out of the tires to 15 psi or so, then add it back when back on hard pavement - the nitrogen would be vented several times a day!

JKJ

Mike Henderson
12-04-2016, 12:56 PM
That opens up an interesting question: "Why do we get water in our air compressor tank?" When the air is compressed it heats up, but once it's in the tank, there's no place for it to absorb more water. And eventually, the air cools to ambient.

So the air going into the compressor is at some level of humidity. Here in CA, it's at a low humidity, maybe 30 to 40%. It goes into the compressor and gets compressed and because of the compression, it heats up. But once it's in the compressor, there's no place where it can absorb more moisture.

Eventually, the air in the tank cools to ambient. And I find water in my tank and have to drain it. I suspect that people who live in high humidity areas have a lot more water than I do.

So if compressed air will hold as much absolute water as uncompressed air, why doesn't the moisture stay in the air? Why do we find it in the bottom of our tank?

I didn't base my comment in my previous post on any science, just on my observation. And because of that, I could be wrong.

Mike

[And because some of the water is left in the tank, I assumed that the air coming out of the tank would have less moisture than the air that went into the tank.]

Malcolm McLeod
12-04-2016, 1:19 PM
So if compressed air will hold as much absolute water as uncompressed air, why doesn't the moisture stay in the air? Why do we find it in the bottom of our tank?

As usual, the complete answer is long, but for simplicity's sake, I believe the principal issue is not in the compression of the air, but rather in its's use. As you say, the air in tank cools to ambient. As the pressure in the tank drops due to this usage, the temperature must drop as well (see above reference to the 'ideal gas suggestion';)). If the temperature drops below the dew-point of the air in the tank/receiver, you have a mini-monsoon. In the tank.

With extreme pressure drops at point-of-use, you get even more significant cooling ...and you can get even more condensation at the point-of-use.

Industrial processes with a strict no-water requirement, will generally install a refrigerated air dryer head of the receiver. They cool the compressed air below the lowest expected temperature in the system, and so typically establish a 10-15 degF dew point (aka dry air). In a previous life, I worked in a (small) facility with 400hp in compressors. Dry air was a never ending battle.

John K Jordan
12-04-2016, 6:30 PM
So if compressed air will hold as much absolute water as uncompressed air, why doesn't the moisture stay in the air? Why do we find it in the bottom of our tank?


Again, the air doesn't "hold" water, the water is introduced and until it condenses exists in the tank as a gas, independent of the air. Water does stay in the air but some of it may and does turn to liquid in normal compressor operation. What water goes where is a dance between the humidity, the pressure, the temperature, and time.

The total pressure in the tank is the sum of the "partial" pressures of each gas in the mixture, water, oxygen, nitrogen, CO2, argon, etc. The maximum partial pressure of water vapor is dependent only on temperature and is called the saturation vapor pressure. If there is more water vapor than this the vapor turns to liquid water.

The "dewpoint" is the temperature at which water as a gas can turn into liquid water. I don't understand all the details but I think it works something like this: The water vapor in the air is compressed in the tank and gets hot. The dewpoint at a certain pressure is a certain temperature. As the tank cools below that temperature, some of the water vapor turns to liquid water. The cooling can be from the tank sitting in the room or from reducing the pressure by letting gas out of the tank. (A compressor that ran continuously would simply pass air at the same humidity as the room.) The dewpoint temperature is actually higher at a higher pressure so at a high pressure liquid water can form sooner than at a low pressure. The way I understand it, gas turns to liquid until it reaches a stable balance for that temperature and pressure. Each cycle of the compressor brings in additional water vapor from the air, more at high humidity levels and less at low, and if even a tiny bit condenses each cycle eventually there will be a lot. If the air coming in is very dry, some of the liquid water can turn into vapor increasing the humidity of that air until it reaches the stable balance. As mentioned, air straight from a compressor can be way too "wet" for a lot of things in industry and science (paint spraying, pharmaceutical processes, etc.) and must be dried. The water can also condense and freeze in pipes in cold environments. This wet air is not considered a problem for things like blowing dust, air tools, and filling tires.

Again, I'm no physicist. I did a quick refresher from a reference book but I don't claim to have a solid handle on the details. Perhaps an expert on this will chime in and straighten out any misconceptions or mistakes. But regardless of the mechanism causing condensation, it does happen and the air from our compressors can be "very" wet even if we drain the tank after every use. I still don't think this will affect tires significantly. I certainly don't worry about it.

BTW, some tires have water added on purpose. Tractor and equipment tires are often filled with liquid for the weight. In climates where it never freezes, people fill them with plain water. Otherwise, people use water mixed with antifreeze, alcohol, calcium chloride, windshield wiper fluid, or even beet juice. Some fluids are more corrosive to the wheels. I have never heard of any fillers which effected the tires. Mine are filled 75% with something but it's been so long I can't remember.

JKJ

Mike Henderson
12-04-2016, 8:10 PM
Well, my comment was that the air coming out of our compressors is less "wet" than the ambient air. Let me discuss why I believe that a bit more.

Let's take one cubic foot of air at a standard temperature - let's say 70 degrees. If we compress that to one quarter cubic foot, we know that some of the moisture that was in the cubic foot will come out of the air - because we find water in the tank. (I'm just using round numbers when I say "one quarter cubic foot")

Then, let's expand that one quarter cubic foot back to one cubic foot. The cubic foot still contains some moisture (less than the original one cubic foot because some water stayed in the tank) and the expansion cools the air, causing some of the moisture still left in that one cubic foot to condense out. If we have a water trap on our air line, that moisture will be trapped. When the temperature of that one cubic foot rises to 70 degrees, it will have less moisture than the original one cubic foot of air.

So compared to the original one cubic foot of air, the one cubic foot of air that we get out of the compressor must have less moisture in it since we have two places where it dropped moisture in the form of liquid water.

Mike

Curt Harms
12-06-2016, 7:14 AM
Probably Glycerin. It's there for use in applications where there is vibration. Very common in industry.


Like your typical consumer grade air compressor?:) You're probably right. I recall a "How it's Made" episode about making dial gauges and they used glycerin.

Kevin Barnett
12-15-2016, 3:20 AM
Again, the air doesn't "hold" water, the water is introduced and until it condenses exists in the tank as a gas, independent of the air. Water does stay in the air but some of it may and does turn to liquid in normal compressor operation. What water goes where is a dance between the humidity, the pressure, the temperature, and time.

The total pressure in the tank is the sum of the "partial" pressures of each gas in the mixture, water, oxygen, nitrogen, CO2, argon, etc. The maximum partial pressure of water vapor is dependent only on temperature and is called the saturation vapor pressure. If there is more water vapor than this the vapor turns to liquid water.

The "dewpoint" is the temperature at which water as a gas can turn into liquid water. I don't understand all the details but I think it works something like this: The water vapor in the air is compressed in the tank and gets hot. The dewpoint at a certain pressure is a certain temperature. As the tank cools below that temperature, some of the water vapor turns to liquid water. The cooling can be from the tank sitting in the room or from reducing the pressure by letting gas out of the tank. (A compressor that ran continuously would simply pass air at the same humidity as the room.) The dewpoint temperature is actually higher at a higher pressure so at a high pressure liquid water can form sooner than at a low pressure. The way I understand it, gas turns to liquid until it reaches a stable balance for that temperature and pressure. Each cycle of the compressor brings in additional water vapor from the air, more at high humidity levels and less at low, and if even a tiny bit condenses each cycle eventually there will be a lot. If the air coming in is very dry, some of the liquid water can turn into vapor increasing the humidity of that air until it reaches the stable balance. As mentioned, air straight from a compressor can be way too "wet" for a lot of things in industry and science (paint spraying, pharmaceutical processes, etc.) and must be dried. The water can also condense and freeze in pipes in cold environments. This wet air is not considered a problem for things like blowing dust, air tools, and filling tires.

Again, I'm no physicist. I did a quick refresher from a reference book but I don't claim to have a solid handle on the details. Perhaps an expert on this will chime in and straighten out any misconceptions or mistakes. But regardless of the mechanism causing condensation, it does happen and the air from our compressors can be "very" wet even if we drain the tank after every use. I still don't think this will affect tires significantly. I certainly don't worry about it.

BTW, some tires have water added on purpose. Tractor and equipment tires are often filled with liquid for the weight. In climates where it never freezes, people fill them with plain water. Otherwise, people use water mixed with antifreeze, alcohol, calcium chloride, windshield wiper fluid, or even beet juice. Some fluids are more corrosive to the wheels. I have never heard of any fillers which effected the tires. Mine are filled 75% with something but it's been so long I can't remember.

JKJ

Okay. I deal with dew points daily. Compressed air cannot hold as much water vapor as less compressed air. I'm not going into a diatribe about your theory, but if what you said was true, water would go back into vapor after compression - which it typically doesn't.

A cheap compressor will generally lower the humidity to about 9% RH from 40% at room temp.

In this discussion, unless the air line is lower in temp than the compressor tank or the compressor is malfunctioning, the dewpoint of the pressurized tire will be less than typical outside air.

I think some people feel the cold of compressed air and assume it's wet or the humid atmosphere condenses on cold skin giving the impression air that has significant moisture. Fact is, that air might be coming out at 4 degrees Celsius and 30% RH, but that's the same moisture content as room temp air at 10%.

I think a quick way to fool someone about this would be to depressurize a tire and then remove it showing the customer how "wet" it is inside. Fact is, depressurizing it would cool it down allowing moist air to condense once exposed to ambient air.

The chemist in me says 78% nitrogen is the most cost effective way to go here.

Stewie Simpson
12-15-2016, 6:00 AM
Jiminy cricket - we are heading towards the 70th post on what should be regarded as simply inflating your tyres with compressed air. Air pressure at 85% of max.tyre rating to allow room for heat expansion. 78% nitrogen !!!!Save the chemistry background for something a little more challenging.

John Stankus
12-15-2016, 10:52 AM
Jiminy cricket - we are heading towards the 70th post on what should be regarded as simply inflating your tyres with compressed air. Air pressure at 85% of max.tyre rating to allow room for heat expansion. 78% nitrogen !!!!Save the chemistry background for something a little more challenging.

Stewie - 78% nitrogen is the composition of dry air (21% oxygen 1% other gases). I think Kevin is saying just use air.

The amount of water that can be in the gas phase is the vapor pressure which is a function of temperature. At room temperature that is about 20 torr. (Note 1 atm is 760 torr). The vapor pressure is the maximum amount of water that can be in the vapor state at a particular temperature.