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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > Check your tire pressure!



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      09-23-2005, 06:21 PM   #23
fdc
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Quote:
Originally Posted by espo89
Well it's actually 78.11% Nitrogen (I work for an air seperation company that "makes" the nitrogen that you would use for your tires, the oxygen that you get at the hospital, and the argon that fills the panes between your house windows).

The biggest problem with standard compressed air is not really the fact that there is oxygen in it, but there is water. The water is what creates the greatest increase in pressure as the tire heats up. If you don't want to use nitrogen, they you could use DRY compressed air and that would get you most of the way there....
espo89: Great explanation. This makes perfect sense. The nitrogen vs air didn't make much sense to me. Also the fact that the permeability to oxygen is 4 times more than nitrogen means that
after some months I would have had a greater % of nitrogen anyway.

Your comment about the water is what was actually missing and
explain clearly the great change of pressure with temperature and
the real reason is good to use nitrogen.
That's why airplanes use it ...

thanks

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      09-23-2005, 10:37 PM   #24
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when i got my 325i, my dealer told me the tire pressure should be around 40psi. WTF?? "isn't that a little too much, i thought it was supposed to be around 30psi," i asked the dealer. anyways, im plannin on checkin the pressure tomo.

BTW, how much does a tire pressure gauge cost? and where can i get it (pepboys, autozone,...?)
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      09-23-2005, 11:10 PM   #25
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Pressure gauges are only 5-10 bucks.

Try to get the analogue (non-digital) ones that read 20-50psi that have deep "necks" with rubber seals. They are more accurate/consistent and the narrower psi range gives finer precision. The deeper necks prevent excessive air leaks while you're checking pressure.

Whatever you do, don't get the cheapest one! Ask me how I know...
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      09-23-2005, 11:24 PM   #26
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thx dude
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      09-23-2005, 11:48 PM   #27
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This actually just happened to me. I have about 2000 miles on the car and all of a sudden on the way the work the tire pressure monitor chimed on. Checked my tire pressures, and they were fine all the way around. Tried to initialize the sensor...but nothing worked. So I have an appointment with BMW on sat so we will see...
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      09-24-2005, 12:49 AM   #28
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Just checked my pressures, 40psi all around. :mad:
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      09-24-2005, 01:02 AM   #29
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i have the 325i ZSP, so can you actually feel the difference between driving with 40psi tires and 30psi tires? i dont think i can, the driving seems smooth and i havent had any problems yet driving with 40psi tires

Last edited by cannonspike22; 09-24-2005 at 01:52 AM.
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      09-24-2005, 01:08 AM   #30
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36psi front
40psi rear
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      09-24-2005, 09:08 AM   #31
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This is my first experience with Runflats.
So I don't know how to monitor them.
How do you tell if they are leaking?
Shouldn't they still look inflated if they are deflated?!?!
I'm going to try different configs (different psi) for the next few weeks to see what I like best.

Personally, I still have yet to have a good experience with Bridgestones.

My Michelin's never had this issues of leaking.

If it doesn't work out, I'm gonna swap them with regular All season Pilot's. (Since I'm in the NE)
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      09-24-2005, 12:22 PM   #32
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Yes, I live in CA and yes, I still have to check my pressure when I feel there's a need for it. There's NorCal and SoCal - I've lived in both and they're two totally different places in terms of arrant temperatures.

Most good drivers can feel a difference if the pressure is off. Most good drivers know when it's needed to check the pressure (i.e. dramatic temperature changes). If you can't feel a malady while driving, obviously the pressure is ok. If you feel a shimmy, pulsing, or recalcitrant behavior of the wheel, it could be the tires.

Downsides of nitrogen - if one tire is off in pressure, you'd have to go to a place that provides nitrogen. You can fill up with plain air from a "free air" gas station, but now you have one tire filled with lowly, normal air that can 'permeate' as easily as Nikkie claims. So now you have to check that defective tire as normally as you would had you not filled up all 4 tires with nitrogen in the first place.

Trust me, if nitrogen was *that* beneficial, gas stations and commuters would have been using it since the Ford T models rolled out.

But, wait, nope. It's unnoticeable to regular Joe Blo commuters. Race cars use nitrogen mainly because nitrogen is pressurized - they won't have to use a compressor to fill up tires - that would shave off ever-so-precious milliseconds off of pitstops. You think racecars worry about permeablization when they wear out the tires in about 30 (NASCAR) laps? Same goes with pressure - unless there is a leak in the tires, they don't expect loss of pressure due to permeablization and those folks already know what pressure they need to hit per tire contingent to the temperatures at the race tracks.
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      09-24-2005, 03:56 PM   #33
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Here's another tip. I just had my tires rotated by my dealer. I checked them today, just to make sure... and sure enough - 38 front, 33 rear. They rotated the tires but didn't adjust the pressure accordingly! Make sure you check this when you have tire work done.
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