Why not air?

[perdidochas]

Wher have you been hiding? The Nascar media is selling nitrogen to the public, people are buying it! I'm openning a helium tire fill station, add wiil state "Make your car lighter on the road and save gas money"

Nitrogen is used because it has a slightly larger molecular size than oxygen, hence, ideally nitrogen should leak slower. Helium would leak much faster.

 

[RTodd]

Nitrogen is used because it has a slightly larger molecular size than oxygen, hence, ideally nitrogen should leak slower. Helium would leak much faster.

Okay totally off topic but I will go ahead and correct the bad information. Leaking less than air over the course of a race is meaningless. The reason for nitrogen is that it reacts less to heat than the O2 in air so the pressure of the tire from cold to hot stays more stable. You generate a great deal more heat in tires on a track than driving around town. Tire pressure is important to handling and performance even at the amateur level of racing.

 

[Vie]

The reason for nitrogen is that it reacts less to heat than the O2 in air so the pressure of the tire from cold to hot stays more stable. You generate a great deal more heat in tires on a track than driving around town. Tire pressure is important to handling and performance even at the amateur level of racing.

Totally of topic - in racing, you want the tires to heat up quickly (to optimal working temp.) but not overheat over a race distance. Last year Ferrari (and this year as well?) filled their Formula One cars' tires with CO2. Admittedly the Bridgestone tires used in Formula One is rather different from those used on automobiles driving around town...

 

[lamont]

EAN32 reaches a PPO2 of 1.2 at 91'. Doesn't a MOD of 100' for EAN32 break their own acceptable PPO2 levels?

Tom

i believe all GUE mods have +/- 10 fsw attatched to them. so EAN32 is 90 +/- 10 fsw.

someone is now going to mention 100% being 20 +/- 10 fsw is a fairly poor idea.

and i agree, but the +/- 10 fsw rule as a GUE standard was conveyed to me by bob sherwood (who pretty much wrote the current version of these rules) in the context of a no-deco course. unless he pops up here and clears it up, i'm assuming that the +/- 10 fsw rule refers to bottom mix only. i've also tried to and failed to find these rules on the GUE website, i think they're private for instructors only.

 

[lamont]

also, i'm very dubious about nitrogen in tires on typical passenger vehicles:

The Straight Dope: Is it better to fill your tires with nitrogen instead of air?

 

[Jason B]

The underlying principle is that in GUE we are thinking divers. The reasons for the gasses choose are:
1. Acceptable PPO2 (Unbendable rule: 1.2 max working, 1.4 contingency max working, 1.6 max resting deco)

My class was taught 1.2 PPO2 average, not max.

 

[RTodd]

Totally of topic - in racing, you want the tires to heat up quickly (to optimal working temp.) but not overheat over a race distance. Last year Ferrari (and this year as well?) filled their Formula One cars' tires with CO2. Admittedly the Bridgestone tires used in Formula One is rather different from those used on automobiles driving around town...

Okay, ambush the silly thread time. I think the nitrogen reason is mostly about the lack of moisture in pure nitrogen and less expansion, etc. Any idea why CO2 other than the importance of race temp in those tires? There is an episode of TG where Hammond I think, a fairly good driver, takes an older Formula One car out for a few laps and the tire temp actually drops from what the tire warmers bring them up to. So, "up to temp" on these tires must be pretty ridiculous.

 

[RTodd]

I feel guilty and will provide real world answers too. A standard gas of 32% which is what is needed for most diving allows you to learn deco or minimum deco limits and have them in your head. Basic min deco is obviously easy but if you always dive the same gas you will gain a better understanding with what you can do multi-level wise for minimum deco too which is a big plus. As long as it is only one or two dives in a day and depths are in the 30 +/- a bit depth range it usually doesn't matter. However, even that has some caveats. Start doing multi hour long cave dives with lots of ascents to really shallow depths or even surfacing to traverse stuff and you get to a level where you want 32% for even the shallow stuff in Mexico.

 

[Rainer]

My class was taught 1.2 PPO2 average, not max.

We were also taught average, not max.

 

[Charlie99]

We were also taught average, not max.

Jason B and Rainer -- were you also taught a max allowable limit ppO2, or was the only limit an average ppO2 ?