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From: Tegger on 18 Oct 2009 18:28
dr_jeff <utz(a)msu.edu> wrote in
news:_pKdnZ3BAMbVEUbXnZ2dnUVZ_vednZ2d(a)giganews.com:

> Mike Hunter wrote:
>> As someone said the air inside the tire, as well as the air OUTSIDE
>> of the tire, is already nearly 80% nitrogen. ;)
>
> Air has something that nitrogen doesn't have: water. Water can
> condense or evaporate, causing changes in the pressure of the tire
> faster with air than with nitrogen.



But you can get water-free air. That's what the FAA specifies for aircraft
tires when nitrogen is not available.

Any garage with a drier on their compressor can provide water-free air. Dry
air is what any garage /should/ have, because it prolongs the life of air
tools and helps keeps them from spitting oily goop all over the place.


>
> However, the difference is pretty small; IMHO, not worth the extra
> cost. (Note: If you're a NASCAR crew chief, please disregard what I
> said. The differences are important for NASCAR cars.)
>


And for aircraft, whose tires may need to go from -100F to 100F in an hour.

Nitrogen, for road-going passenger cars, is a nice frill (especially with
those funky green valve caps), but far from essential for safety or
anything else.


--
Tegger

From: dr_jeff on 18 Oct 2009 18:43
Tegger wrote:
> dr_jeff <utz(a)msu.edu> wrote in
> news:_pKdnZ3BAMbVEUbXnZ2dnUVZ_vednZ2d(a)giganews.com:
>
>> Mike Hunter wrote:
>>> As someone said the air inside the tire, as well as the air OUTSIDE
>>> of the tire, is already nearly 80% nitrogen. ;)
>> Air has something that nitrogen doesn't have: water. Water can
>> condense or evaporate, causing changes in the pressure of the tire
>> faster with air than with nitrogen.
>
>
>
> But you can get water-free air. That's what the FAA specifies for aircraft
> tires when nitrogen is not available.
>
> Any garage with a drier on their compressor can provide water-free air. Dry
> air is what any garage /should/ have, because it prolongs the life of air
> tools and helps keeps them from spitting oily goop all over the place.
>
>
>> However, the difference is pretty small; IMHO, not worth the extra
>> cost. (Note: If you're a NASCAR crew chief, please disregard what I
>> said. The differences are important for NASCAR cars.)
>>
>
>
> And for aircraft, whose tires may need to go from -100F to 100F in an hour.
>
> Nitrogen, for road-going passenger cars, is a nice frill (especially with
> those funky green valve caps), but far from essential for safety or
> anything else.

I suspect that an air drier provides air with reduced water rather than
no water. So with an air dryer, there still is some water left in the
air. Unless you're a NASCAR driver or crew chief, probably not enough to
make a difference. However, a lot of gas stations have air hoses with
small compressors that provide the air. I doubt that the small
compressors have air driers on them. Nor do the small pumps that are
plugged into the 12-V power ports in cars.

Jeff
From: Tegger on 18 Oct 2009 19:21
dr_jeff <utz(a)msu.edu> wrote in
news:yq-dnafQ09q5B0bXnZ2dnUVZ_hCdnZ2d(a)giganews.com:


>
> I suspect that an air drier provides air with reduced water rather
> than no water. So with an air dryer, there still is some water left in
> the air. Unless you're a NASCAR driver or crew chief, probably not
> enough to make a difference.



The FAA seems to think the same.

And even "pure" nitrogen is never purer than about 95%, which is all
commercial nitrogen generators are capable of making.



> However, a lot of gas stations have air
> hoses with small compressors that provide the air. I doubt that the
> small compressors have air driers on them. Nor do the small pumps that
> are plugged into the 12-V power ports in cars.
>


That's true, but those little compressors don't generally have large
reservoirs that accumulate big puddles of water that could make their way
into tires (or air tools).


--
Tegger

From: dr_jeff on 18 Oct 2009 19:41
Tegger wrote:
> dr_jeff <utz(a)msu.edu> wrote in
> news:yq-dnafQ09q5B0bXnZ2dnUVZ_hCdnZ2d(a)giganews.com:
>
>
>> I suspect that an air drier provides air with reduced water rather
>> than no water. So with an air dryer, there still is some water left in
>> the air. Unless you're a NASCAR driver or crew chief, probably not
>> enough to make a difference.
>
>
>
> The FAA seems to think the same.
>
> And even "pure" nitrogen is never purer than about 95%, which is all
> commercial nitrogen generators are capable of making.
>
>
>
>> However, a lot of gas stations have air
>> hoses with small compressors that provide the air. I doubt that the
>> small compressors have air driers on them. Nor do the small pumps that
>> are plugged into the 12-V power ports in cars.
>>
>
>
> That's true, but those little compressors don't generally have large
> reservoirs that accumulate big puddles of water that could make their way
> into tires (or air tools).

Yeah, I know. Instead, the water ends up in the tires, which causes the
tire pressure to vary too much for a given temperature change (although
that's important for NASCAR, not regular drivers). (The compressed air
in those 12-V compressors is also hotter than noncompressed air, which
helps keep water from condensing in the air hose - that why water
doesn't drip out the end - air in the big compressors has more time to
cool down to room or ambient temperature.) If you don't believe me that
the air gets hot, just feel the bottom of foot pump after you use it to
fill a bicycle tire.

The accumulated water with the big air compressor is also a pain in the
winter, when it freezes in the air hose before it gets into the tire.

Compressed nitrogen is also used in hospital operating rooms for use
with the power tools there, like the drills used to put holes for screws
into bones by orthopedic surgeons or holes in skulls by neurosurgeons.

Jeff
From: Mike Hunter on 19 Oct 2009 11:17
Did it ever occur to you dr., that although the air inside the tire, as well
as the air OUTSIDE of the tire, is already nearly 80% nitrogen, that there
is far more water OUTSIDE the tire than is ever INSIDE the tire? LOL


"dr_jeff" <utz(a)msu.edu> wrote in message
news:_pKdnZ3BAMbVEUbXnZ2dnUVZ_vednZ2d(a)giganews.com...
> Mike Hunter wrote:
>> As someone said the air inside the tire, as well as the air OUTSIDE of
>> the tire, is already nearly 80% nitrogen. ;)
>
> Air has something that nitrogen doesn't have: water. Water can condense or
> evaporate, causing changes in the pressure of the tire faster with air
> than with nitrogen. And, water can also be absorbed and released by the
> rubber of the tire. So tires that are filled with nitrogen tend to
> maintain a steadier pressure than tires filled with air.
>
> However, the difference is pretty small; IMHO, not worth the extra cost.
> (Note: If you're a NASCAR crew chief, please disregard what I said. The
> differences are important for NASCAR cars.)


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