A local tire chain has started using nitrogen to fill tires they mount. The question is, would this be good to use in my A3SO4's for autocross? Would if affect the tempurature of the tire, or the ability for the tire to heat up quickly? What about road racing? It seems like you could just find the pressure that workes best for you and leave it there for the season.

 

Nitrogen expands less for a given amount of heat, so your cold to hot pressures won't vary as much. All the pro teams use it.

 

From The Racing and High-Performance Tire: "Professional teams inflate tires with dry nitrogen. Moisture in the tire causes more pressure buildup when the tires get hot. Water inside the tires turns to steam and increaases inflation pressure. Racers on a budget too small to include dry nitrogen should consider using a dryer with replaceable cartridges on their compressors. The bottom line is that internal pressure is what supports the load on the tire. And the correct inflation pressure maximizes contact-patch area and minimizes contact-patch load variation, allowing your tires to generate more grip."

 

In fact, N2 actually expands and contracts MORE with temp than dry air does. However, it is very hard to make (or keep) air dry, and water vapor expands and contracts with temperature much more than N2 does. This is why filling the tires with dry N2 makes their pressures more temp-stable.

The problem with using it at home is that the tanks and regulators and the like are much more expensive than the actual N2. Costco, for instance, uses a machine that separates the N2 directly from the atmosphere. Makes sense for a shop, but not for a home garage.

I would say that it's probably more hassle than it is worth, especially for AX where the air temps in the tires just don't change all that much during a run. And you can always adjust the pressures just before a run.

 

I guess when I should keep the N2 in my tires that costco put in. I at first I didn't understand why, especially for road race purposes. I now see its benefit so i will keep it

 

^ I actually used to fill my tires with N2 because I had N2 in a welder's gas bottle for filling my shocks. I didn't notice a huge improvement in hot/cold temps. It just drained my 8lbs bottle Real Fast.

 

Umm, no.... N2 expands and contracts in exactly the same way dry air will.

P1/T1 = P2/T2 by ideal gas law

Since dry air is over 99.9% supercritical gases and 78% nitrogen, it behaves VERY ideally.

Before anyone says anything about nitrogen (or dry air) not being an ideal gas, it is ideal (within 0.03%) at ambient temperatures. That ideality won't change until it is cooled to near its critical temperature (nitrogen's is -147 C).

You are right however about how hard keeping air (or any gas) dry can be.

Just correcting some urban myths....
Eric

 

I've been using it in my S02's since June and the pressure hasn't changed one bit.

You obviously won't be able to "feel" the difference but there's quite a few positives to running nitrogen.

 

[QUOTE=Eric42,Jan 26 2005, 07:52 PM] Umm, no....

 

what happens if i have some nitrogen and some reg air in my tires? costco did not inflate mine properly so i had to add some normal air