[J00PTv]

Hi all, 2016 340i xdrive

this morning in Chicago temps were around 15-19 degrees outside. I started the car and when I started to drive I received the tire pressure warning that it's low, checked on the idrive system and shows pressure at 30 ish give and take for all tires. after I drove for 30 mins showed the pressure at 36 back and 35 front. but the warning never went away.

something cool I noticed is that I was stuck in comfort mode only with the warning on still.

is this normal for the pressure to change that much? i do have run flats.

[AndDown]

Yes

[PhizzurpF]

Yep. I live in MN, so I can relate to this. Was -12 this morning and I was surprised I didn't get the warning on my drive to work.

[J00PTv]

Originally Posted by PhizzurpF

Yep. I live in MN, so I can relate to this. Was -12 this morning and I was surprised I didn't get the warning on my drive to work.

I did respect that the car blocks you from going into sports mode while not on the correct pressure. safety is always #1 lol

[Billfitz]

You need to inflate your tires more often. Even if they didn't lose any air 35 pounds on a September morning becomes 30 pounds in January, for everyone except Roger Goodell.

[Gen13 F36]

I check my tire pressure every time I wash my car

[J00PTv]

Originally Posted by Billfitz

You need to inflate your tires more often. Even if they didn't lose any air 35 pounds on a September morning becomes 30 pounds in January, for everyone except Roger Goodell.

if they have nitrogen can I add or mix in normal air?

[Billfitz]

Nitrogen is automotive snake oil. Regular air is just fine.

[Dave turbo]

Originally Posted by Billfitz

Nitrogen is automotive snake oil. Regular air is just fine.

It's not snake oil. If free, use it.

[WaleeF30]

If you use nitrogen it'll hold air better in cold temps.

[Billfitz]

Nitrogen doesn't make its way through the pores in a tire as fast as air, but the difference is too slight to be of any real consequence. Anyone who says otherwise is selling you a bill of goods.
https://www.lesschwab.com/article/ar...-the-cost.html

[IAmATeaf]

So logically, with 78% of air being Nitrogen and it’s the other elements that escape faster, unless the tyre goes completely flat, over the course of time with filling and escaping the percentage of Nitrogen when filling with normal air, the air in the tyre will be higher than 78%?

[chiefneil]

Originally Posted by J00PTv

is this normal for the pressure to change that much? i do have run flats.

Figure roughly 1psi change per 10F temp change. So if the last time you filled your tires to 35psi the temp was 55F, then you lost 1-2psi gradually over time, then you lost another 4psi due to the 15F weather, suddenly you’re down 5-6psi.

Good practice to check your tires every time the temp changes about 20F, or generally a little more frequently as the season changes.

[Billfitz]

Another factor to be aware of is that pressure is supposed to be measured with cold tires. If you drive a few miles before you reach a place to fill them your tire temperature will have risen, and along with it the pressure of the air in the tires. That can lead to under-inflation. If that's your situation put in an extra couple of pounds for good measure. I have a compressor, so I fill mine at home. After driving a few miles my pressure typically comes up by 3 PSI.

[J00PTv]

I thank you guys for the replies and the helpful tips.

Taking the car in for the first time to the service center here in Chicago. oil change, my cig lighter port does not work in the front and I get a random cruise control malfunction error that disables the steering wheel buttons for a few secs. looking forward to driving it after!

[eluded]

If have a Costco membership, they have nitrogen.

https://www.popularmechanics.com/car...ogen-in-tires/