I understand the equation, what I don't understand the actual real life results. If what you said was the case, we would have still gotten tire pressure warnings on some of our loaners at some point over the past two years. If this was only checked over a few days I would see your point about recording temps over a long period and then evalutating, but this has been for 2 years now and that's long enough. No, I don't have the actual recorded temps in the shop and outside at those specific times but I think after 2 years it's fairly obvious. If you saw the line of people out the door before we even open up in the winter you'd see what I'm talking about first hand. In some way the oxygen has to be causing something to happen which sets off the monitor. Otherwise just as many cars with nitrogen would be lined up outside, and they'd all want a refund for the nitrogen. The machine is approx 3ft sq. around and 5 ft tall and should produce a good sized flame. While we're over there, let's ask Bridgestone what they are using in their racing tires and why.
I suppose that's a possibility. I am not familiar with BMW's tire pressure monitoring system. If it uses something that measures oxygen content instead of pressure (They've done weirder things in the past), well there ya go! I guess one indicator would be whether you EVER get a low pressure signal with a nitrogen-filled tire, even if it's obviously down on pressure. Hmmm ... Oh, hell, we can't burn anything that damn big! They'd probably call out the Plymouth F.D. How would you even haul it up here? Besides, the one chemical property nitrogen has that is supported by the science is that it doesn't support burning!
Another possibility is moisture content and condensation. Air compressors just grab whatever air is handy and compress it--trace gases, water vapor and all. A nitrogen generator produces dry nitrogen--near-zero relative humidity. (Compressed air dryers do exist but they're not common around auto shops. For most uses of shop air--running tools and whatnot--they'd be overkill as moisture content doesn't much matter.) An air-filled tire could experience condensation inside the tire when the temperature drops (think: dew), depending on the temperature change and the relative humidity of the trapped air charge. It might be possible for that to have a temporary, adverse effect on a pressure sensor. This is somewhat speculative--I don't know that TPM sensors are upset by condensation--but it's a plausible hypothesis that fits your data.
http://www.mpt.org/motorweek/goss/2924.shtml Pat Goss, MotorWeek's resident master technician, helps consumers understand car problems and how to speak the same language as their technician. As cars becoming increasingly complex, fewer repairs can be accomplished at home. Effective communication with a repair shop is vital to keeping consumer and operating costs under control. From rattles and squeaks to leaks and drips, Pat covers a myriad of issues designed to keep cars on the road and out of the repair shop. Tire Pressure Monitoring Systems Pat Goss All cars now come equipped from the factory with tire pressure monitoring systems, and the majority of them use a sensor like this. This is the actual sensor; this is the valve stem. They go into the wheel like this-they fit through and you see the stem portion of it. The sensor portion is inside the tire. They do a very, very good job, but they do have some problems. Number one is that many of these succumb to corrosion. The stem portion is made out of aluminum and it doesn't take much in the way of moisture to cause the aluminum to deteriorate, and many times when you have to have tire service performed - well, the sensor can't be salvaged and you have to put new sensors in the car. Well, you always had to put the entire sensor in until recently, and now Dorman Products has this unit right here. This is a two-piece unit. It has the sensor just like it always has, but the stem is replaceable. It's held in place by a hollow screw. So, if the aluminum portion gets damaged, all you need to do is to buy the aluminum stem, not the entire sensor. This saves a lot of money. This comes in a kit with a whole variety of stems and repair parts and so on, and it is from Dorman Products. Now, when you have service done-tire rotation or anything like that-in most cases, the sensors have to be re-programmed to the computer on the car. In some cars, it will simply require a round magnet like this that's designed specifically for that purpose, or on others you may have to use an electronic unit such as this that interfaces the computer on the car. The big thing here is, if you're going to have tire service done, make sure that the shop that you're using has the proper equipment to do everything without damaging anything on the car. And, if you want to prevent a lot of the moisture problems, here's what you look for. You look for nitrogen, and you have nitrogen put in your tires just like they do on airplanes. Nitrogen from a good machine, like this Nitro-Fill machine, is completely dry, so you do away with all of the moisture-related problems. Not only that, but the molecules in nitrogen are bigger than oxygen, so what happens is, tire pressure remains constant longer and it's more stable. It's something that I would look for, because it can increase the life of your tires, it can prevent TPMS problems, and overall you might get a little better fuel economy.
As I mentioned in the very first post in this thread, it's a lot cheaper to put a moisture trap on a compressor to do this than to pay for bottled or generated nitrogen. Also addressed in my very first post. Let's put it in a 'folksy' Pat Goss-type example: Say you have one hundred footballs - because molecules of two oxygen and two nitrogen atoms are longer than they are around. Seventy-eight of 'em are 23.9 inches around the middle and the other twenty-one are 23.2 inches around. [One is a soccer ball we'll call 'trace'. It won't fit through the hole.] Now, you're going to start randomly throwing these footballs at a hole in a wall that's 23.8 inches in circumference. Not carefully stuffing through the ones that fit, but tossing them from ten feet away - because that's how gases work. How many of those smaller footballs do you think you'll get through that hole? That's how much oxygen (73 picometer molecular radius) will escape compared to the nitrogen (75 picometer molecular radius). If that exercise alone doesn't convince you, then figure out what the odds are that you'd find a perfectly round hole smaller than 23.9 inches but bigger than 23.2 inches to throw them through. In terms of your tires, what are the odds that there are holes smaller than 75 picometers and bigger than 73 picometers? Even if this theory were true, simply refilling with regular air will do this: The first time, you will be up to 94% nitrogen because the air refill will be 78% nitrogen, or 16% of the 21% you lost when the oxygen left. The second time you refill (assuming you could actually tell that the tire lost 6% of its pressure), you'll be up to over 98% nitrogen in there - all without ever actually filling the tire with pure nitrogen. The third time you refill, you'll know you have a hole big enough to let the nitrogen out ... Now, let's say you start throwing baseballs at a slightly smaller hole, about 20 inches in circumference. None of the footballs will fit through, but you'll do reasonably well with the baseballs, especially if you keep trying. Eventually, you'll get most of them through. This is what happens with a helium-filled rubber balloon. Rubber's pores are smaller than 'football-sized' molecules like nitrogen and oxygen (so an air-filled balloon stays inflated for a very long time) but helium is baseball-sized by comparison - so your balloon goes dead in a day or two. So, does that explain the 'escaping smaller molecules' myth away?
I can think of TWO uses for nitrogen in tires A) Jet aircraft use it due to the friction created by coming in for a landing at more than 100 miles an hour. Nitrogen is a relatively inert gas not likely to ignite from the 21 percent oxygen of regular air when that jet comes in for a landing. Last thing you want when your plane touches down is for the friction to ignite and detonate your tires as soon as they hit the ground. B) Plan on locking your car up in a museum for decades? All nitrogen in your tires is less likely to lose pressure over time and less likely to build up condensation due to temperature changes. So if you're not going to be doing landings and takeoffs in your automobile, and you don't plan on storing your car away for decades, I'd say forget the nitrogen, keep an eye on your tire pressure, and enjoy your BMW along with the rest of your life.
While seeing the combined gas law on a car forum causes me to wretch and regret logging in, I do have to ask how you got from chemical researcher to lawyer?
You know, I've wondered the same thing. We may have our very own BMW CCA "Renaissance Man" (or at least a reasonable facsimile thereof). Maybe we can rent him out for parties......
Whoa, this is rapidly becoming a full-service bar............. The plan was to legally anesthetize Krieger and avoid the subject. Now, everyone's going to be impaired and talking about nitrogen. That's just not right.
You'll have your chance at Siebkins in August. To answer your question: BFGoodrich R&D paid my way through law school at about the same time as I came to the conclusion that I was done inhaling stuff that would probably kill me in a few years. Chemical research (I'm good in a lab.) was just a 'saleable skill' I had as I paused for a few years between college & law school.
Brecksville, Ohio. Additives & Specialty Polymers, at that time. Did basic research work on antioxidant and UV stabilizers for plastics.
I can understand the comments made by both sides...but I did have the tires in my '05 Focus filled with notrogen and the car was easier to steer around corners (less effort on the sterring wheel). Did not do anything else to the car. Can't explain it - have no idea why. But it something I noticed, and after a few days - I didn't notice it anymore. Makes no sense to me - and you probably think I'm crazy but that's my experience and I'm sticking to it.
