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[BrokenVert]

Ahh pv=rhoRT its always so fun to work with you. It gets even better when your an Aero and have to work in both British and SI units.


(lb/ft2)(ft3/slug)=(slug/ft3)(1716lb/(slug *Rankine))(*Rankine) how I do know thee (for air at least).

I dont know R for Nitrogen off the top of my head.

[Drlbrill]

Originally Posted by frank@wheelsto

you are correct, and I'm an idiot. I didn't really think about this when I was told why. I'm an engineer too, I should have known

No worries old man, just didn't want everyone to get excited, thinking we repealed the laws of physics.

[BrokenVert]

Originally Posted by Drlbrill

No worries old man, just didn't want everyone to get excited, thinking we repealed the laws of physics.

Nope you cant do that, even with DTC...I read that in the manual

[pkcormier]

If you use 100% nitrogen in your tires they will get The Bends.

[Cisitalia]

Originally Posted by Angry3

That's interesting to hear, since the last time I was over at my local dealer (Hendrick) they were adding the cost of a nitrogen tire fill to the dealer add sticker on much of their new inventory. I'll have to keep an eye out for that notice in the mail.

Agreed, that's the irony. BMWNA saying not necessary and Hendrick (other dealers probably as well) pushing hard to sell nitrogen. It's on Hendrick's website as well for service.

I won't be going with nitrogen fill though. Waste of money.

[BerkTechnology]

i've done nitro, it just makes it so you dont have to check your air pressure as much. and yes it is a waste of money.

[BCieslak]

I work for a tire company (not sure if I'm allowed to say which one or what I do, but for now I'll just say that my company supplies BMW and Tire Rack), and we don't recommend or dissuade you from using nitrogen. Many of you have said exactly the things that I say when discussing the subject, but there are a few more points that haven't been said yet.

All gasses do expand when heated, but it's the water molecules that expand the most. Remove the water, and the remaining gas becomes more stable. As to how the dealer would remove all of the air on an RFT or regular tire without dismounting it, I don't know.

But the reason that dealers offer nitrogen is because of two reasons. First, because it does leak out at a slower rate than air, it will keep your pressure where it's supposed to be for a longer period of time. Studies show that about 80% of all vehicles on the road have underinflated tires, defined as over three PSI below what they should be. Underinflated tires lead to premature tire wear, lower fuel economy, and decreased performance (aka safety). If nitrogen can help keep pressures where they are supposed to be, the owner could recoup the cost of the nitrogen in tire life, fuel costs, and "safety related costs", depending on the driver and vehicle.

A side benefit is that it also reduces the number of "nuisance trips" of the TPMS. Since all passenger vehicles 2008 and newer in North America are equipped with TPMS, service shops have naturally seen an increase in the number of people coming in with TPMS alarms. The shops who started offering nitrogen saw that number drop, proving that it does keep PSI where it's supposed to be for a longer duration.

Second, car dealers need to keep customers coming back for service, rather than going to the corner garage or the random fast lube place. Offering nitrogen, so the argument goes, can lead to higher customer retention because the customer has to go back to the dealer to get a refill. Many dealers offer free refills for the life of the tire.

So - the bottom line is that nitrogen does work, but it's not necessary unless you need it because you're racing, etc. If you check your tire pressures regularly, which I'd hope that a forum full of enthusiasts would be doing, then it's less of an issue for us.

But the big factor is that BMW recommends using air. That isn't necessarily a deterrent to nitrogen, but they may have done some testing to support their position, or they may have not done testing at all.

[dr.bmw]

the way to separate oxygen and water from nitrogen in the air is to turn it into liquid. you can do that by freezing it or compressing it. Oxygen and water liquify at different temperatures and pressures to nitrogen and thus can be physically separated to a very high purity.
Obviously that can't be done at a random petrol stop so most places need to pay for nitrogen cans to be delivered and there is cost involved in compressing and separating the gas mixture and that cost is passed on to customers, multiplied several fold to make a profit.

[CoolToolGuy]

Originally Posted by frank@WSTO

Another interesting point to think about. Your dealership is filling up your tires with "100%" nitrogen instead of 80% nitrogen in the air. When they fill the tire up with said nitrogen how are they getting the existing air out? You would need an extra valve to allow the air to flow out. So in the end your still only probably getting a 90% nitrogen fill anyways

Bingo!

You could, of course, do a fill with nitrogen, bleed it out, fill it again, bleed it out, on and on. Each time the nitrogen percentage would increase slightly.

Or you could go to a tube-type tire - the tube can have all of the gas removed so you really do get close to 100% nitrogen. But good luck finding the right size tubes.

Nitrogen is a nice theory, but hard to accomplish - even for the diehard racers.

Have Fun,
Rick