[Paddlewise] Nitrogen in Racing Tires

Just to keep the "nitrogen in racing tires" debate going a little
further...here are some snippets I pulled from various web sites dealing
with racing.  The primary reason seems to be that the water vapor in air
is what causes the most expansion as tire temperature rises.  For other
applications, such as air in tires with steel rims and perhaps also
inside things like shock absorbers and struts, it avoids oxidation
problems.

Tom

======

Kiekhaefer, an eccentric German and the genius behind the Mercury
Outboard
 Motor dynasty, had burst onto the NASCAR scene in 1955, using the sport
as a
 tool to market his outboard motors. A perfectionist like the sport had
never seen,
 Kiekhaefer revolutionized what until then had been strictly a
shade-tree
 mechanics' sport, instituting such sweeping innovations as team
transporters and
 extensive testing as well as seemingly innocuous improvements like
using paper
 air filters and filling tires with nitrogen to maintain air pressure. 

===

We have switched to nitrogen when
inflating the tires. Unlike air, nitrogen contains
almost no moisture, so heat does not cause the
tires to expand like those filled with air. This
allows us to maintain more control of tire sizes.

======

Use nitrogen to fill your tires, it has a much higher expansion rate. It
will not expand
under greater heat generated by track temperatures and friction created
by a tire
burn-out. This keeps the tire from growing, allowing for a better foot
print and
more consistent times. 

===============

> There is a reason nitrogen is better than air. I'm told the problem
with
> air in tires is that the water vapor in it expands drastically when
> heated, causing a big change in tire pressures as the tires heat
up.(I've
> seen it change by 4 lbs during a single lap in an autocross.) Bottled

So it's not the nitrogen, but the water vapor?  Air of course is 79% 
Nitrogen, 20% Oxygen and 1% trace gasses.  The pressure in a tire 
increases 1 psi for every 10 degrees outside temp (tire carcass or
ambient 
air temp) from what I've heard (I've never done the calcs for that one 
Mac) regardless of the minor difference represented by the 20% oxygen.
Thus 
Matt R correctly referred to the ideal gas law.

> nitrogen is dry, and expands very little when heated, therefore the
tire
> pressures are much more stable. It's also a very inert gas, so it
doesn't
> rot the tires. 

I'll go along with that.  The 20% oxygen is probably slightly more
active 
than the if it were another 20% nitrogen.

====
Q.  I always hear about problems associated with
 pressure build-up in the tires, and expensive
 gadgets to prevent this, like bleeder valves.
 Why don't they just use an inert gas like
 nitrogen?

A.  Everybody uses nitrogen in their tires. There is still
 pressure built up by heat when the race track
 meets the tire, but it is not as much as regular air. 

===

By the way, race-car and aircraft tires often are filled with nitrogen,
which is inert. An added bonus of this, of course, is that when the
tires
blow, they don't add "fuel," i.e., oxygen, to the fire, so to speak. 


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