[T3] Tire failure?

[Jim Adney]

On 18 Jan 2011 at 9:57, Daniel K. Du Vall wrote:

> I used to work in the high purity gas control industry so the Nitrogen I
> am used to always came in liquid form from dewars. Getting it form a on
> demand machine seems to me like it would not be of good quality. I guess
> for tires it really does not matter. It is more stable than normal air
> in that its expiation rate is less I guess that would be good for gas
> mileage if your changing altitude a lot ;-) 

The ad Dennis posted the link to mentioned 95% purity, so that's 
probably a lot easier since they only have to get rid of about 3/4 of 
the Oxygen.

Over the range of temps normally seen in tires, I would expect both O 
and N to have identical expansion rates. 

I agree with Dave that the O16 molecule is probably bigger than the 
N14, but I can't swear to that. Those things don't always turn out 
the way I expect.  

N actually absorbs water vapor quite readily. It's used for that 
purpose, in underground cables, etc, just to keep moisture from 
causing problems. I don't know about O.

Yes, there's already ~80% N and ~20% O in our air, plus ~1% Argon. If 
you really wanted something inert in there, you should be going for 
the Argon, even if it's heavier.  ;-)

BTW, for bonus points: What material burns equally well in pure O and 
pure N?

There may be some point to keeping the O out of the interior, just to 
limit the amount of oxidation that it can cause, but, like Dave, I've 
wondered if that process is self limiting as the O gets used up.

I've taken a lot of old tires off old rims, and most of the time the 
rims are pristine inside, with no sign of corrosion at all. I've had 
exactly one tire where the rim was really eaten up with corrosion, 
and that one was one that had a leak and had been topped up 
frequently over a very long time. My guess is that it got fresh O and 
water every time it was topped up. IIRC, there was even loose water 
in the tire when it came off the rim. That's one very good reason to 
fix leaky tires rather than just adding air every week.

And, the rubber inside that tire still looked fine, even though the 
steel rim was a mess. I've never seen a tire where the rubber inside 
looked worse that the rubber outside.

As for preventing oxidation of the rubber over time, I suspect that 
this is mostly a scam. It may have some safety advantage in racing, 
where it's a good idea to avoid adding compressed oxygen to a crash. 
Otherwise, I can see no harm other than the $10 it costs you, and 
that sounds pretty minimal.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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