Just thought I'd chime in... as far as I know you should always check your tires cold, as you will get a different reading if you have been driving for a while. At least my Acura owners manual agrees. According to it, you should wait 3 hours for your tires to cool after a long drive to get an accurate cold tire measure, or your measurements could be 4psi higher then they would if you waited. If this is wrong, cool.. thanks for the correction, but remember, if you're going to flame something... flame Acura, they wrote it.

 

That is absolutely true.

In a closed container of gas (a tire) increasing temperature will increase pressure. Driving increases pressure.

The falsity in this thread was the "theory" that nitrogen would expand less than air given the same temperature change for both tires. This is incorrect.

 

No. They are absolutely right. If you drive for a while, your tires will heat up. And if you drive on them hard, they will heat up more. My buddies and I run a couple racecars and we set the tire pressures hot. Because on a track, you want your tire pressure correct while it's being used, not before and hours later. This drastically effects the performance and wear of the tire. And it changes from track to track, season to season, and tire brand to tire brand.

 

see below

 

HAHAHHAHAHHAHAH!!

 

http://www.nitrofill.com/

 

Another scam website. Good on you for looking out. Thanks for the link!

 

Not true. You're getting confused between Molecular Weight and Molecular Size, which don't always correlate. In the case of O2 vs N2... Yes O2 does have a higher Molecular Weight, but it is indeed a smaller molecule, which does allow it to permeate through the polymer chains of rubber 3 or 4 times faster than N2 will.

I believe the mpg increase claims for N2 are based solely on maintaining correct tire pressure (most people neglect checking tire pressure regularly, therefore end up driving on tires underinflated by 4-5psi most of the time, which will take a few % from your mpg). You can get the same mpg increase using air if you periodically check and adjust your tire pressures to keep them at the correct pressure.

I use air, by the way and don't plan on switching to N2, but I do carpool with a guy that has bought into the N2 hype.

 

Yeah, that website says that to ensure you are getting the benefits of Nitrogen, you have to have > 95% N2 in your tire. Of course, they are saying that to promote the high purity N2 (close to 100%) that they offer.

However, they fail to mention that because of the 1Atm (absolute) of air that's in the tire to begin with (at 21% O2), you'd have to fill your tire to 4Atm (absolute) to get the O2 down to 5%. That means your tire would have to be inflated to 45psi (gauge). That would make for a rough ride.

 

I do "nitro conversions" at work (Lexus). All of our new cars have TPMS (tire pressure monitoring system). Thanks to Ford and the tire blowouts now all new cars have to use this system. We put nitro in the tires because temperature has less of an effect on the pressure (that's good up here in the Northeast), and it's denser (so it leaks less?).
We get alot of cars coming in with tire lights on and most of them are due to all the tires being low. Once in a while I'll find a nail or screw in a tire. Even with this system nobody checks the tire pressure themselves. Now with a visual alert, there should be less blowouts from people driving with under inflated tires.

Me, I just use regular air and check them every so often.

 

You are correct here. I indeed missposted and thank you for the correction.

 

No. All gasses behave the same.

 

Correct me if I'm wrong, but don't only ideal gases behave as predicted by the gas laws. Its been a while now...

 

This is why NASCAR uses Nitrogen
Most of the teams remove the air from the tires and replace it with nitrogen. Compressed nitrogen contains less moisture than compressed air. When the tire heats up, moisture in the tire vaporizes and expands, causing the pressure inside the tire to increase. Even small changes in tire pressure can noticeably affect the handling of the car. By using nitrogen instead of air, the teams have more control over how much the pressure will increase when the tires heat up.

 

The water is already vapor though, or else it would be a liquid.

I have seen the testing that has gone into the NASCAR stuff online, and agree that when they fill their tires with Nitrogen, it gives them more consistent results.

In a regular car, it is irrelevant.

 

This is true. At temperatures and pressures around STP, all gasses are ideal gasses. You have to get very close to absolute zero, or up to extremely high temps to get gasses to behave differently.

 

I want it to be clear that I'm not trying to put anyone down or be a jerk.

Certainly I don't expect to be believed on spec, but please look into it for yourselves, as this stuff is readily available with a simple google search.

 

I thought otherwise, but its been a couple years since I thought about it, so I'll have to look it up again obviously.

 

The ideal gas law ignores molecule size, but at low pressures like in a tire, it makes a negligible difference.

 

yes, but it's also easier for NASCAR to carry around several bottle of compressed nitrogen instead of lugging around a couple huge compressors. And they can run their air tools off the bottles as well.