Tire Pressure Too High? - Page 2 - Bimmerfest - BMW Forums



Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > F10 / F11 (2011 - 2016)

F10 / F11 (2011 - 2016)
The sixth generation of the BMW 5 Series Sedan (F10) was produced from 2011 - 2016 with LCI updates arriving in 2014. In the US BMW offered a hatchback 5 Series Gran Truismo (F07) and the rest of the world also go a Station Wagon/Touring version F11.

Reply
 
Thread Tools Display Modes
  #26  
Old 09-25-2019, 07:05 PM
Pete_NZ Pete_NZ is offline
Officially Welcomed to the 'Fest
Location: New Zealand
 
Join Date: Jan 2018
Posts: 112
Mein Auto: E61 530D E91 330d E46 328
Nitrogen vs air. If someone suggests they fill their tires because of an apparent "massive" variance in pressure over temperature changes consider this: The owner's manual and door card stipulate cold pressures. They also know that cold pressure thus gives the correct pressure when at operating temperature.
So here's the rub.. if you're filling with Nitrogen because you believe it minimises cold to hot pressure variance, then by necessity of your argument you are running pressures at operating temps that are lower than recommended by the manufacturer.
Boom! Air-roasted.
Reply With Quote
Sponsored Links
Advertisement
 
  #27  
Old 09-25-2019, 07:11 PM
Pete_NZ Pete_NZ is offline
Officially Welcomed to the 'Fest
Location: New Zealand
 
Join Date: Jan 2018
Posts: 112
Mein Auto: E61 530D E91 330d E46 328
Quote:
Originally Posted by Autoputzer View Post

How old is that BFG report? I can remember when passenger car tires took 20-something PSI of air... back in the 1970's.
1980
https://www.jstor.org/stable/4463244...n_tab_contents
Reply With Quote
  #28  
Old 09-25-2019, 07:11 PM
Autoputzer Autoputzer is online now
Officially Welcomed to the 'Fest
Location: NW Floriduh
 
Join Date: Mar 2014
Posts: 8,656
Mein Auto: 2014 535i + 2018 X3 30i
Quote:
Originally Posted by Pete_NZ View Post
Nitrogen vs air. If someone suggests they fill their tires because of an apparent "massive" variance in pressure over temperature changes consider this: The owner's manual and door card stipulate cold pressures. They also know that cold pressure thus gives the correct pressure when at operating temperature.
So here's the rub.. if you're filling with Nitrogen because you believe it minimises cold to hot pressure variance, then by necessity of your argument you are running pressures at operating temps that are lower than recommended by the manufacturer.
Boom! Air-roasted.
The charges for nitrogen are sort of a tax on those who weren't paying attention in high school physical science class.

I had somebody tell me he has them put nitrogen in his tires because it makes the car ride better.
Reply With Quote
  #29  
Old 09-25-2019, 07:16 PM
Autoputzer Autoputzer is online now
Officially Welcomed to the 'Fest
Location: NW Floriduh
 
Join Date: Mar 2014
Posts: 8,656
Mein Auto: 2014 535i + 2018 X3 30i
Quote:
Originally Posted by Pete_NZ View Post
That's a pretty cool link... read six SAE papers free each month.

As expected, the article is from before the "P Metric" generation of high-pressure passenger car tires.
Reply With Quote
  #30  
Old 09-26-2019, 05:19 AM
surly surly is offline
Officially Welcomed to the 'Fest
Location: Toronto-ish
 
Join Date: May 2008
Posts: 608
Mein Auto: '11 F10 535xi
Quote:
Originally Posted by Autoputzer View Post
That's a myth, probably mostly propagated by tire salesmen selling nitrogen.

Dry air and nitrogen both obey the Ideal Gas Law. Air with a lot of water vapor in it would deviate slightly from the Ideal Gas Law. The Ideal Gas Law is where Dougie's "ten degrees F equals 1 PSI" rule of thumb comes from.
Huh? I said the pure nitrogen difference is "very minor", meaning the promotion of using nitrogen to reduce pressure variance is bogus, which agrees with what you say.

Ambient temperature certainly does have an effect. One mid-winter weather system and a few psi are lost or gained.

I don't understand why my statements are "myth" and "bogus".
Reply With Quote
  #31  
Old 09-26-2019, 06:55 AM
Autoputzer Autoputzer is online now
Officially Welcomed to the 'Fest
Location: NW Floriduh
 
Join Date: Mar 2014
Posts: 8,656
Mein Auto: 2014 535i + 2018 X3 30i
Quote:
Originally Posted by surly View Post
Huh? I said the pure nitrogen difference is "very minor", meaning the promotion of using nitrogen to reduce pressure variance is bogus, which agrees with what you say.

Ambient temperature certainly does have an effect. One mid-winter weather system and a few psi are lost or gained.

I don't understand why my statements are "myth" and "bogus".
O.k. Then, what you said could be taken two ways and I picked the wrong way.


Dry air and nitrogen both closely follow the Ideal Gas Law: PV=mRT, where:

P = Absolute Pressure (gauge pressure plus the pressure of the atmosphere)
V = Volume (inside the tire)
m = mass of the gas
R = The Ideal Gas Constant (for the particular gas)
T = Absolute Temperature (Kelvin or Rankin, not Celsius or Fahrenheit)

If you assume the volume inside the tire is constant, the V, m, and (pertinent to our discussion about nitrogen) R all cancel out and you get:

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

Plugging in the Ranken to Fahrenheit conversion and adding the ambient pressure at sea level (14.7 PSI):

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

Pick a starting pressure (P1) and temperature (T1), and then vary the temperature (T2). The new pressure (P2) will go up or down about one PSI for every ten degrees F. Here's a table starting with a gauge pressure of 35 PSI and an ambient temperature of 70F, and then varying the temperature from 30F to 110F.
Attached Thumbnails
Click image for larger version

Name:	20190926 ideal gas law starting from 35 psi & 70F.jpg
Views:	9
Size:	20.0 KB
ID:	865795  

Last edited by Autoputzer; 09-26-2019 at 07:17 AM.
Reply With Quote
Reply

See More Related BMW Stories


Forum Navigation
Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > F10 / F11 (2011 - 2016)
Today's Posts Search
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On



Forum Jump


All times are GMT -7. The time now is 06:30 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
© 2001- VerticalScope Inc. All rights reserved.