Actually, you're forgetting one important point.
The Ideal Gas Law says that for *any* gas:
PV = nRT
Where P = pressure, V = volume, T = temperature, n = number of moles of
the gas and R = some garbage constant to make the units fit.
So, looking at this equation, you can see that raising the temperature
(T) of the system will raise the pressure (P) and/or the volume (V).
The amounts of these two effects depends on the container, in this case,
the tire, but at least one of them must increase to make the equation work.
Now, the problem with your assertion that both "air" and nitrogen gas
have the same delta(PV) given the same delta(T) is that you're assuming
that the number of moles (n) of the two gases is the same. Thankfully
for Jason Hartberger, air is more dense than nitrogen gas, meaning that
V cubic centimeters of "air" contains more molecules than V cubic
centimeters of nitrogen gas.
So the theory that nitrogen-filled tires expand less under the same
increase in temperature actually holds.
Regards,
Jon Heese
Ron Childs wrote:
> Also remembering maybe HS chemistry, all gases expand and contract
> the same amount with the same changes in temperature or pressure.
>
> -Ron
>
>
> ----- Original Message ---- From: G Kerby Haltom
> <g.kerby@sbcglobal.net> To: D. Mallinson <dmall@mwonline.net>;
> shotimes@autox.team.net Sent: Tuesday, August 1, 2006 12:36:55 PM
> Subject: Re: [Shotimes] Nitrogen-filled tires
>
>
> If we remember our Middle School science class...
>
> Plain old air is 78% nitrogen to start with.
>
> Kerby
>
> "D. Mallinson" <dmall@mwonline.net> wrote: What Ron said..... it is a
> waste for street cars, or even track day cars. A pro driver in a pro
> race circuit maybe. Otherwise, use plain old air.
>
> Don Mallinson
>
> Ron Porter wrote:
>
>> Besides the marketing angle to make a few $$$, the only possible
>> benefit are for clueless folks who never check their tire air (I
>> can think of a few family members as I write this). They have a
>> better chance of keeping a consistent tire pressure over the 6-12
>> months before the tires get checked again (most likely at oil
>> change time).
>>
>> For the rest of us who check tires more regularly, it's a waste.
>>
>> Planes and race tires are the useful applications for it that I can
>> see.
>>
>> Ron Porter
>>
>> I know we talked about this on the list a while back.
>>
>>
>> http://news.yahoo.com/s/ap/20060731/ap_on_bi_ge/nitrogen_tires
>>
>> "Skeptics will question how much can be gained by filling tires
>> with pure nitrogen when the air we breathe is 78 percent nitrogen."
>>
>>
>>
>> Being a skeptic (and an engineer) I will and do question this.
>> Correct me if I'm wrong, but when a tire is mounted on a rim,
>> doesn't "regular air" get trapped inside???? Even if pure Nitrogen
>> is used to "pop" the tire bead onto the rim there's still "regular
>> air" inside that will be mixed with the Nitrogen. Soooo, you don't
>> end up with a tire filled with 100% Nitrogen. The only way to
>> ensure 100% Nitrogen inside the tire is if the tire mounting
>> machine were inside a sealed room filled with Nitrogen and the
>> installer had to wear an Oxygen mask. Is that what the tire dealer
>> purchases for $3,000 to $12,000 dollars? What am I missing here?
>>
>> What if it's Sunday night and my tire(s) are a few psi low? If the
>> local Gas 'n Sip doesn't have Nitrogen, then what good is having
>> Nitrogen in my tires?
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