DIR Tire Gas?

[airsix]

as long as all the car people are here...I started not using 92 in my x5 which "requires" premium gas....is that bad?

Lower octane fuel burns faster. Running mid-grade or regular in your X5 can cause knock (that 90% of the time you can't hear) but your engine has a knock sensor and will retard the ignition timing when it detects this to compensate. This protects the engine, but will reduce power and probably your mileage. You aren't likely to hurt anything, but it is not optimal.

-Ben M.

EDIT: I see that Jeff beat me to it and said the same thing more concisely. I'll also add to Jeff's comments that you can get away with lower octane at colder air temperatures as well. I have a truck that knocks with anything less than 90 in the summer months but runs knock-free in the winter on 87.

 

[miketsp]

The ONLY reason race teams use Nitrogen is because there is less pressure change for a given temperature change than with air. Tire pressure on a race car is critical for optimizing traction (a function of tire temperature and distribution of weight across the tire's contact patch). For example, using air, the tire pressure of my time-trial car after the first lap on a 1.25 mile course can increase by 12psi. That pressure swing would be less if nitrogen were used instead of air. The pressure swing on a street car is much less because you're not heating up the tires with 4-wheel drifts around every corner.
..snip..

Pure unadulterated BS.
At relatively low pressures (ie tire pressures) N2, O2 and water vapor will all behave as ideal gases, and follow PV=nRT. Pressure will increase or decrease to the same extent as the temperature increases or decreases regardless of which gas is in the tire. (Even at 300 psi, which is about 20 atm, there is little deviation from ideality.) Therefore the comments about N2 not changing in pressure as the temperature changes are without merit.

Even if you put air in the tire, it's already 78% nitrogen.

Race teams will often use nitrogen to fill tires, but largely out of convenience rather than due to any performance benefit. No ancilliary equipment needed to fill a tire if you have a (cheap) bottle of nitrogen. If you use a compressor you either need a generator or need to find a place to plug in, or need a gas powered compressor.

 

[airsix]

Pure unadulterated BS.
At relatively low pressures (ie tire pressures) N2, O2 and water vapor will all behave as ideal gases, and follow PV=nRT. Pressure will increase or decrease to the same extent as the temperature increases or decreases regardless of which gas is in the tire. (Even at 300 psi, which is about 20 atm, there is little deviation from ideality.) Therefore the comments about N2 not changing in pressure as the temperature changes are without merit.

Even if you put air in the tire, it's already 78% nitrogen.

Race teams will often use nitrogen to fill tires, but largely out of convenience rather than due to any performance benefit. No ancilliary equipment needed to fill a tire if you have a (cheap) bottle of nitrogen. If you use a compressor you either need a generator or need to find a place to plug in, or need a gas powered compressor.

I bet you are right about the ideal gas behavior. What I stated was based on what I've read and been told. I have not done testing on my own cars. Regarding convenience, I'm not so sure. It's just as easy to bring compressed air cylinders to the track as it is nitrogen cylinders. Like I said - I don't buy into it. I run air in my race tires. Now I'm tempted to go put nitrogen in one, set the pressures, and then do some laps and compare the pressure in the air tire to the nitrogen tire (making sure both werer brought up to the same temp). You're probably correct that there won't be a difference, and I'll eat crow for regurgitating false info.

-Ben M.

 

[The Chairman]

Actually, they run N2 for their impact guns as well. They have used that since the 60s/70s and the gus are usually highly polished internally and modified Ingersoll Rands. At least they were.

 

[airsix]

Here is a paper (non scientific) from the Toyo tire co. That says permiation rate and reduced oxidation are the only logical benefits, and that the oxidation benefits realy only apply to retreadability of truck and bus tires.

Here's a 4x4 club newsletter of all things, that contains a very detailed and scientific evaluation. Impressive experiment with good controls. Temps were not as high as tires experience, and humidity of the air wasn't measured, but overall it is a lot more conclusive than our yammering about it. Conclusion: what Mike said.

-Ben M.

 

[lamont]

it sounds like the major (but possibly theoretical) improvement of nitrogen is just that its dry, and dry scuba air would work just as well...

 

[Snowbear]

So air is no longer even DIR for tire gas :shakehead .... does this mean GUE will have to change the answer on the Tech1 test

 

[Packhorse]

Nitrogen is the gas of choice for tyres. Maybe they could use the N they take out of air to make Nitrox

 

[ckharlan66]

I have it in my tires.

It did increase my mpg's by about 2%

Chad

 

[lamont]

http://www.scubaboard.com/showthread.php?t=154039