[s-cars] Tire Pressures

[Robert Myers]

Yup, good old flammable hydrogen rather than nearly inert 
nitrogen.  Yup.  Makes good sense.  :-D))

FYI, any gas or mixture of gases, whether it be air or nitrogen or hydrogen 
will exert a higher internal pressure at higher temperatures and the 
magnitude of the effect will be approximately the same for most 
gases.  Hydrogen will also diffuse through the tire wall at a higher rate 
than just about any other gas.  Rate of diffusion, everything else being 
equal, depends upon the molecular weight of the gas concerned.  It is 
inversely proportional to the square roots of the molecular masses.

Nitrogen MW = 28
Hyrdogen MW = 2

28/2 = 14

sqrt 14 = ~3.74

Hydrogen will diffuse approximately 3.7 times as fast as nitrogen.  This 
means that your tire will lose pressure 3.7 times as fast if you use 
hydrogen than if you use nitrogen.


At 07:09 PM 5/19/2004, Gabriel Caldwell wrote:

>Hydrogen is the proper tire filler.
>
>Gabriel Caldwell
>
>
>-----Original Message-----
>From: Mark Strangways [mailto:strangconst at rogers.com]
>Sent: May 19, 2004 4:06 PM
>To: mlped at qwest.net; kirby.a.smith at verizon.net; 'Bill Clancy'
>Cc: s-car-list at audifans.com; NDoshi at aol.com
>Subject: Re: [s-cars] Tire Pressures
>
>That's why I use nitrogen to fill  my tires, does not fluctuate with
>temperature.
>
>Mark S
>----- Original Message -----
>From: "mlp5" <mlped at qwest.net>
>To: <kirby.a.smith at verizon.net>; "'Bill Clancy'" <clancybill at yahoo.com>
>Cc: <NDoshi at aol.com>; <s-car-list at audifans.com>
>Sent: Wednesday, May 19, 2004 11:24 AM
>Subject: RE: [s-cars] Tire Pressures
>
>
>As a for instance:  "....Keep in mind that recommended inflation pressure
>are for cold tires. This means tires that have not been driven on for
>several hours (ideally overnight). It also means tires that are at a normal
>outside temperature of about 70° F.
>
>To accurately inflate a tire, you have to compensate for changes in
>temperature. For every 10° F change in ambient temperature, tire pressure
>will change a little more than half a pound.
>
>A tire that contains 32 psi of air at 70° F will have a little over 35 psi
>at 100° F - even if the vehicle hasn't been driven. Take a quick drive down
>the freeway and heat up the tires even more, and the pressure may read 38 to
>40 psi.
>
>Likewise, when seasons change and temperatures drop, tires lose pressure.
>They haven't lost any air, but the air isn't exerting as much pressure as
>before. The same tire that held 32 psi at 70° F will have only about 28 psi
>when the thermometer hits 32° F. And when temperatures are in the subzero
>range, the loss in air pressure will be several pounds more.
>
>Altitude will also affect tire pressure. For every 1,000 feet in elevation
>above sea level, atmospheric pressure decreases about a half a pound. As a
>result, tire pressure goes up an equal amount. A tire gauge that reads
>accurately at sea level will read about 3 psi too high at an elevation of
>6,000 feet....."  from
>http://members.aol.com/carleyware/library/tirepres.htm
>
>So again Bill, how many variables are your 34-36 feels too slippery, 28-31
>too muddy, experimentation taking into account?
>
>mike
>
>PS - oh, and last but not least from the above link, "... make sure you use
>an accurate pressure gauge. Gauges are often out of calibration, so either
>get them recalibrated, or help your customers by getting new gauges...."
>Damn, nothing's easy any more .... except perhaps that humming noise coming
>out of the rear of Bob Frizzel's S4  :-)
>
> >-----Original Message-----
> >From: s-car On Behalf Of Kirby Smith
>
> >I don't think you would find Bridgestone SO-2s slippery at 36
> >psi.  I run mine around 38 psi, and the tread edges still wear
> >faster than the tread center.  Optimal tire pressure will
> >depend on tread construction and section height, not to
> >mention driving style, camber, etc.
> >
> >kirby
>
> >Bill Clancy wrote:
> >>
> >> Has anyone done any trial and error?   I did and I ended up
> >with 32 psi on
> >> my stock 16x8's.    with 34-36 the car feels slippery on the highway.
> >> 28-31 and it feels muddy -- not to mention that I am sure it would
> >> wreck the tires.
> >>
> >> I have no experience with 17's but i did spend a fair amount of time
> >> fine tuning the pressure with the 16's.
>
>
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_____
"I never give them hell. I just tell the truth and they think it is 
hell!"  Harry Truman

Bob
*****
  Robert L. Myers  304-574-2372
  Rt. 4, Box 57, Fayetteville, WV 25840 USA  WV tag Q SHIP
  '95 urS6 Cashmere Grey - der Wunderwagen   ICQ 22170244
  http://www.cob-net.org/church/pvcob.htm
*****