Bimmerfest BMW banner

1 - 20 of 36 Posts

·
Registered
Joined
·
172 Posts
Discussion Starter #1
so i checked my tire pressure 2 weeks ago and the temperature here in canadian winter was -10 celcius ish.
my tires were around 32 front 35 back, give or take a psi
and then about 10 days ago the temperature fell down to -30 celcius on average, and ranged from -25celcius all the way to -33 celcius ever since that day.

i visually look at my tires everyday before i drive off, and they did look lower then usual but nothing alarming

yesterday i was driving and i got the low tire pressure warning finally, and i decided to fill the tires before i went home at night, but then when i was leaving the parkade a couple hours later,
my rear right tire was flat and my front right was considerably lower

so i got a buddy to bring a pump, and we began to fill the tires.
the front right tire showed 14psi, the rear right showed 0 psi
front left showed 24 psi
rear left showed 32 psi

so im wondering why the big change? and how come one tire just went flat?

they all filled up fine and they seem to hold air for past 24 hrs of driving,

is it prob just leaky valve stem? or did my right rear go flat cuz it leaked so low that it couldnt hold air anymore?
 

·
Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
Joined
·
17,461 Posts
All things being equal, tire pressure changes about 1 PSI per 10 degree temperature change.

I think leaked so low that the bead un-seated.

I was just telling the story the other day of a cold snap where I was visiting the made the bead unseat for shrinking so much. I never would***8217;a thought of that but my host said it was common at the first cold snap there.
 

·
Registered
Joined
·
257 Posts
I don't know about the physics Mr. Huffman claims to apply, but my BMW has FAR greater pressure variation than any other car I've owned. Every year in the winter when the temps drops i have to get out my pump because I go from 33 down to like 25 or less. It's amazing how much it drops. I've never seen 14, but I can believe it.
 

·
Registered
Joined
·
1,193 Posts

·
Registered
Joined
·
10,671 Posts
I don't know about the physics Mr. Huffman claims to apply, but my BMW has FAR greater pressure variation than any other car I've owned. Every year in the winter when the temps drops i have to get out my pump because I go from 33 down to like 25 or less. It's amazing how much it drops. I've never seen 14, but I can believe it.
That's o.k. I don't know much about the French I took...

https://www.youtube.com/watch?v=37Ai9pdWNpI


https://en.wikipedia.org/wiki/Ideal_gas_law

Dougie forgot to specify that the rule of thumb (1 PSI = 10 degrees) refers to degrees Fahrenheit.

Pressure and temperature are absolute values. At sea level, the absolute pressure is the gauge pressure plus 14.7 PSI. Absolute temperature, degrees Rankine, is the temperature in degrees Fahrenheit plus 459.67.

The Ideal Gas Law can be written as PV=mRT, where R is the gas constant for the particular gas, and m is the mass of the air within the volume.

It's a reasonable approximation that a fully inflated tire has the same volume (V) as an under-inflated tire, and that the mass of the air stays constant for short periods of time (no leakage).

So, given a given pressure P1 (in PSI) at a given temperature T1 (in degrees Rankine), you can determine the pressure P2 at temperature T2.

(P1)(V1) = mR (T1) and (P2)(V2) = mR (T2)

Divide the second equation by the first. The m's, V's, and the R's cancel out, giving...

(P2) = (P1) (T2)/ (T1)

But, you have to convert absolute pressure to gauge pressure, and absolute temperature to Fahrenheit.

P2 + 14.7 = (P1 + 14.7) (T2 + 459.67) / (T1 + 459.67)

or...

P2 = (P1 + 14.7) (T2 + 459.67) / (T1 + 459.67) - 14.7

If you set P1 to 35 PSI (typical pressure for a passenger tire) and T1 to 70 F, and then start changing T2 in ten degree increments from T1, you will see that P2 goes up or down about one PSI each time.
 

·
Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
Joined
·
17,461 Posts
TL;DR. That says it all....
 

·
Dave
Joined
·
134 Posts
All you have to do is become a Costco member, then have the tire shop do a nitrogen change and refill on your tires. Then they won't be subject to wild pressure swings and you can forget about the "winter and summer air" that grandpa used to talk about for your tires.
 

·
Registered
Joined
·
10,671 Posts
All you have to do is become a Costco member, then have the tire shop do a nitrogen change and refill on your tires. Then they won't be subject to wild pressure swings and you can forget about the "winter and summer air" that grandpa used to talk about for your tires.
No.

God has not granted nitrogen an exemption to the Ideal Gas Law. The pressure of a tire with nitrogen in it also goes up and down about one PSI with every ten degrees Fahrenheit.

One of the advantages of nitrogen (N2) is that it leaks out slightly slower than air (which is 78%... wait for it... nitrogen). Consumers Report did a simple test and concluded that pure N2 leaked out of tires at a rate of about 80% of air. That's because the other 22% of air is mostly oxygen (O2) and water vapor (H2O), and those molecules are smaller than N2 molecules.

The other advantage of pure or almost pure N2 is that it will slow down the deterioration of the tire's rubber from the inside. It might make some sense to fill a spare with nitrogen. But, you still have to periodically top it off, and doing that with N2 would be a pain in the butt. To get the N2 sufficiently pure inside a tire, you have to fill it and bleed it back down to zero pressure several. maybe ten, times. Go tell the tire Bubba down at Costco that you want him to fill and bleed your tires ten times. He will go get a big wrench and beat you about your head.
 

Attachments

·
Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
Joined
·
17,461 Posts
The only advantage to nitrogen N2 in tires is the lower concentration or absence of oxygen and water, both of which accelerate the aging of the tire structure. Fill gas is the only parameter of aging over which the user has any control. There is legislation coming to limit the age of tires in use to six years - sooner or later.

Tire Aging and Service Life NTSB Tire Safety Symposium Dec. 9 - 10, 2014

https://www.ntsb.gov/news/events/Documents/2014_Tire_Safety_SYM_Panel_4b_Kane.pdf
 

·
Registered
Joined
·
1,281 Posts
I don't know about the physics Mr. Huffman claims to apply, but my BMW has FAR greater pressure variation than any other car I've owned. Every year in the winter when the temps drops i have to get out my pump because I go from 33 down to like 25 or less. It's amazing how much it drops. I've never seen 14, but I can believe it.
I have no doubt that BMWs commit pressure loss more than other cars!! You have got to be kidding!
 

·
Registered
Joined
·
10,671 Posts
I had an eight year old mini-spare fail the first time I drove on it. Before that, the only time I used it was as a place holder when I was rotating tires. I'm going to start replacing my spares every six years. All my cars, including my BMW's, have spares.

All of my tires lose pressure. I top them off every two or three weeks with a bicycle pump, and they usually need a half to one PSI, but more or less if there's been a big temperature change. Last time, I had to bleed a half-PSI out of the Cobalt's tires. I have to do all this in my driveway because my garage is so cramped that I can only get to the driver's doors of the two cars in there. My nosy neighbors are always asking me "Do you have a flat tire?"
 

·
///Monkeyazz Duck
Joined
·
7,631 Posts
You engineer types thing you're so smart. But Roger Goodell says you are wrong, and that the Ideal Gas Law is fiction. Just ask Tom Brady.
 

·
Registered
Joined
·
1,193 Posts
N2 might also help minimize TPMS sensor corrosion as water content is reduced.
 

·
Registered
Joined
·
218 Posts
That’s given for winter. I work as a dealer mechanic and ALL cars that I bring in have the pressure at 25 or less psi. The worst ones are the AWD Toyota Sienna vans with RFTs. Majority of them come in with 20psi
Even the tires in my BMW lose pressure. There were 28 the last time I checked.


Sent from my iPhone using Bimmerfest
 

·
Registered
Joined
·
218 Posts
That’s given for winter. I work as a dealer mechanic and ALL cars that I bring in have the pressure at 25 or less psi. The worst ones are the AWD Toyota Sienna vans with RFTs. Majority of them come in with 20psi
Even the tires in my BMW lose pressure. There were 28 the last time I checked.


Sent from my iPhone using Bimmerfest
 

·
Registered
Joined
·
10,671 Posts
N2 might also help minimize TPMS sensor corrosion as water content is reduced.
That makes sense.

The service manager at my favorite dealership said years ago that BMW told them to fill tires with N2.

There's a Michelin office building right next to the Marriot hotel that BMW puts you up in when you're picking up a car or attending a driving school at Spartanburg. I took a friend up there to pick up a car back in 2014. The night before picking up his car, he went for a cigar-and-farting walk after dinner over to the Michelin building, and he said they had an N2 dispenser in the parking lot.

After picking up my friend's M235i and participating in all the "King For A Day" events at BMW, we went to Chipotle Grill for dinner. We were standing in line, and there was a hottie right behind us. My friend, about 60, actually pulled his butt cheeks apart with his hands, stood on one leg, and farted as loud and as hard as he could. Seeing the look on that hottie's face was actually as much fun as tear-assing around in one of BMW's M235i's that morning. I said "Hey, Clint... Do you do that kind of **** back home in Panama City Beach?" My friend's a knucklehead, but he's fun as hell to be around. It's like being twelve years old, again.
 

·
Registered
Joined
·
10,671 Posts
That’s given for winter. I work as a dealer mechanic and ALL cars that I bring in have the pressure at 25 or less psi. The worst ones are the AWD Toyota Sienna vans with RFTs. Majority of them come in with 20psi
Even the tires in my BMW lose pressure. There were 28 the last time I checked.


Sent from my iPhone using Bimmerfest
An acquaintance owned a string of quick-oil-change stores. He said that his oil-change Bubba's always had to put more air in tires in the fall than in the spring. It's that Ideal Gas Law thing, again.

Most people never check their tire pressure. That's why the federal government mandated that cars have $400 worth of pressure sensors on them... that have to be replaced for another $400 before the car's finished with its service life.

I never agreed with much that Obama said. But, he once said that if people would check their tire pressures it would save all the oil we could get by drilling in ANWR. I doubt the numbers add up exactly, but he was on the right track.
 
1 - 20 of 36 Posts
Top