Racing, moving to the next level Options

[Randal]

OK, all you big time racers out there, what is the correct procedure to purge air out of a tire before filling it with nitrogen?

The reason I ask is that any moisture mixed with nitrogen will create nitric acid, or some such vile stuff, if I remember correctly.

What about using air tools? Looks like a job for rubber gloves.

[SirAndy]

what is the correct procedure to purge air out of a tire before filling it with nitrogen?

i hear the benefits, if any, are neglectable (is that a real word?) ...

i'd say find something else to do on your car that will yield better results.
(IMG:style_emoticons/default/smash.gif) Andy

[jridder]

> any moisture mixed with nitrogen will create nitric acid,

OK, I'll be nice and simply say that this is wrong. BTW, air is 80% nitrogen. Why would replacing the 20% oxygen with another 20% nitrogen help? Maybe you should have the air cyrogenically treated instead.

Jonathan

[seanery]

the nitrogen benefit (IIRC) is that it won't gain as much pressure as regular ole atmosphere air, so therefore, tire pressures can be maintainted easier.

[Randal]

The other benefit is that I can run air tools. Nice to have an impact wrench to change tires.

test

[SirAndy]

that it won't gain as much pressure as regular ole atmosphere air

the word is that that is a big pile of bologna ...

(IMG:style_emoticons/default/wink.gif) Andy

[brant]

andy,

I've always heard this is legit...
actually I've already met with a gas outfitter and put him on the hunt for the remaining parts I need to finish out my conversion to nitrogen...

the benefit is that in a lapping session, your tire pressures don't change as radically as they do with air... ie: if I start the session at 26lbs, I can finish the 30minute session with less than (hopefully) the 35lbs I have experienced in the past....

Randal,

from my research (and not actual experience), I understand that just removing the core and letting the air out is inadequate... you have to mount the tire from the beginning with nitrogen...
I hear this is a pain in the #$%, to haul your bottle down to your favorite tire shop with you....

I've been told by multiple sources that if you take a pre-mounted or used tire and try to purge it that there is still condensation and that it doesn't work...

your mileage may vary..
my new car will be set up this way though...

brant

[Brad Roberts]

So gang... why does Airgas bring over 1000 bottles of Nitrogen to EVERY single pro racing event (ALMS/GrandAM)... it works. Air expands when heated... Nitrogen expands but expands a lot less. It has to do with the moisture in the tire. Randal they sell a small purging device. Every Indy car team uses Nitrogen...

It is much easier to maintain consistan tire pressures when utilizing Nitrogen.


B

[MattR]

well from a beginning level of chemistry I can tell you;

PV=nRT

that is the Pressure times Volume equals number of moles (or molecules) in the gas times a constant times the temperature.

It would make logical sense that, assuming n, R, and V are going to stay the same (because no air escapes and volume doesnt change), as temperature increases, pressure increases. To combat that, you would have to decrease the number of molecules in the gas (a property of the gas) to make the pressure less sensitive to temperature. I dont have any values on me, and this problem would be very complex because n of ambient air varies a lot, but I can say the atomic mass of oxygen is 16 and nitrogen is 14. Now if you were to go to hydrogen or something (atomic mass of 1) there might be a noticable difference, but I think 2 molecules would be considered neglegable.

But what do I know...

[914werke]

I can tell you from experiance this is something we do on race bikes religiuosly as the heat expansion of the specifically rear tire on a bike can actually "grow" the tire and change the steering geomitery (sp).

(IMG:style_emoticons/default/smile.gif)

[JWest]

The first reason nitrogen is used is that it is the cheapest gas you can get in large quantities to take to the track.

Next, once processed, it contains little to no moisture. Moisture is a bad thing in extreme temp - freezes when cold (bad in airplane tires at altitude) and creates vapor when hot (raises the tire pressure much more than the ideal gas PV=nRT).

Also, if a tire explodes, regular air has a higher oxygen content that will support combustion if ignited.

There is nothing magic or particularly special about using nitrogen in tires - it just has a couple nice benefits at relatively low cost.

[SirAndy]

It is much easier to maintain consistan tire pressures when utilizing Nitrogen

ok, here are some numbers ...

At a temperature of 0°C and a pressure of 1 atmosphere, the densities of air, nitrogen and oxygen are:

Air: 1.293kg/m3
Nitrogen: 1.250kg/m3
Oxygen: 1.429 kg/m3

Notice the very small difference between good ole Air and Nitrogen?
less than 0.043 kg, that's a whooping 43 gram per m3 !

now, let's look at some more numbers, comparing Nitrogen and Oxygen:

	O2	N2
Normal boilingpoint at atmospheric pressure, oC	-183	-196
Ration of volume of gas tovolume of liquid, measured at  15oC and absolute pressure of 101.3 kPa	842	682
Relative density of gas at101.3 kPa and 25oC (Air = 1)	1.105	0.967
Liquid density at absolutepressure of 101.3 kPa, kg m-3	1141	807
Latent heat ofevaporation, kJ kg-1	213	199

mind you, we're actually interested in how AIR compares to Nitrogen, not Oxygen to Nitrogen, so we need to take the above numbers and put them into a 80/20 split in favor of the Nitrogen ...

bottomline, the expansion rate of pure Nitrogen gas compared to normal Air is about the same ...

now, that doesn't mean that someone can't make a shitload of money selling that stuff to racers who would sell their firstborn to get 1/100th of a second ahead.

flames on (IMG:style_emoticons/default/cool.gif) Andy

[brant]

hmmm...

Brad elaborate further on the small purging device
(I did not know this)

is it pricey?

brant

[Downunderman]

So back to the original question; just inflate with nitrogen and let down 3 times one after the other and reinflate with nitrogen. You can use a purge device if you like but you don't really need one.

[Britain Smith]

As Andy said, the comparison here is between Nitrogen and AIR. It is my understanding that the reason "dry" Nitrogen is used in racing tires is because the rate of expansion and contraction is more consistend when compared to that of AIR. This is a results of the composition of AIR which is 78% N2, 21% O2, and 1% of lots of other stuff, including varying amounts of water vapor that changes as a function of the relative humidiy of the environment. It is this water vapor that tends to be inconsistent in its rate of expansion and contraction and therefore gives varying amounts of tire pressures. By using "dry" air, it eliminates the variability of the tire pressures from one venue to another and allows the teams to set the tire pressures and forget about them.

-Britain

[JWest]

bottomline, the expansion rate of pure Nitrogen gas compared to normal Air is about the same ...

The problem is that you can't buy "air" that has been processed with the moisture removed, but you can buy nitrogen cheaper than any other gas.

Now, lets see how smart you guys are: why not use helium (or hydrogen!) because it would be lighter? (I'm not saying you should, just seeing what the response will be (IMG:style_emoticons/default/wink.gif) ).

[Britain Smith]

Check this product out...it allows you to purge all four tires at once...

Tire Squid

(IMG:http://www.clparts.com/amotorsports/msimages/squidoncart.jpg)

[Britain Smith]

(IMG:http://www.clparts.com/amotorsports/msimages/humdtable.gif)

The above data was collected using industrial grade nitrogen, inflated to 20 psi on non-inner liner 15” Goodyear tires.
Ambient temperature 73.5f, ambient humidity 44%.



Should I purge after the tires have been hot lapped, qualified or practiced?
It would be a good thing to do. Moisture and other tire manufacturing elements may have been released from the tire during that first heat cycle. Also if the tires have been sitting in the sun after purging (usually the impounded qualifiers) it’s a good idea to purge them again before putting them on the car

[Britain Smith]

Why purge?
Humidity inside your race tires causes the pressure to increase when heated. If the amount of humidity is decreased the tire pressure buildup is decreased. After each purge the humidity held in the air is replaced with a dry inert gas, such as nitrogen.


Why purge more than once?
Each successive cycle dilutes the remaining air until most, if not all, humidity laden air is replaced. A vacuum pump could be used but they are expensive, time consuming and you risk breaking the bead.

Why worry about pressure increase?
An increase in tire pressure changes the dynamics of the tire. The circumference of the tire may change and therefore change the stagger. The pressure change also changes the effective spring rate. If the pressure change can be minimized the tire will perform more consistently allowing the crew to concentrate on other areas of the cars’ performance.

[Randal]

Andy,

Your a smart guy Andy, but I just wonder if racing teams would really be going to all that trouble if it wasn't worthwhile.

Yea, everyone will buy stuff to go faster (OH MY GOD is that me!) but the big racing teams have so much experience they must see a difference otherwise I can't believe they would be messing around.

Well I do know what my tires typically heat up to in a 60 second (15-20 turn) autox, so I'll check and report my findings.

I'll do the test at WWC.

I just need to find a purge device (that I can afford!) to get the air out of my existing tires.

Randal