Nitrogen in tires?
 

Has anyone in this forum had any experience with nitrogen in their X6 or even X5 run flat tires? I had it in my recently sold Mercedes E class with regular Continental tires, and it worked very well with virtually no change in pressure between warm and cold climates. But I've never had run flats before, and am going to be getting them (whether I want them or not...probably 3rd generation Bridgestone all season) on my new X6 which is currently in production. One would assume that nitrogen would work as well in rft's as in non-rft's, except for the fact that BMW has publicly stated that they do not endorse the use of nitrogen with their vehicles. Since nitrogen is a larger molecule than regular air, does not seep out of the tire as easily, and does not change very much between warm and cold climates, why would they suggest that nitrogen should not be used? Any helpful comments would be greatly appreciated.

Don't even worry about nitrogen. It's important in race tires where the tires get pretty hot and the difference in pressure between air and nitrogen actually matters for consistency and grip. Somewhere around 1-4 psi difference at race tire temps is common, depending on lots of variables. Your tires will never get that hot on the street. The common knowledge about the difference in pressure at street driving temps is less than 1 psi (if at all under normal driving), and at that range it's tough to narrow down any differences in alignment, vehicle weight distribution, etc., all of which can have a larger effect than the type of gas in the tire. And you don't know the moisture content of the air you're putting in, so you have no idea what you're actually comparing the nitrogen to.

And I know Porsche and some other manufacturers use it from the factory. This is probably because of a few things.. First, people like to think that they're getting something special for their money, and if that means the same type of inflation gas that race cars use, fine. Second, you can generally neglect tires filled with nitrogen a bit more because nitrogen seems to seep out slower than air. Third, it makes for really low maintenance tire filling equipment because it's dry, clean, and largely inert.

So just check your tire pressure often and you'll save a lot of money on nitrogen fills. If you check your tires like you should, you'd need a bottle at your house or you'd spend a lot of time at tire places paying them to do it.

Oh, and even though it's heavily marketed, most of the stuff you hear about nitrogen is either exaggerated or doesn't apply to street driven vehicles. People say stuff like "they use it in plane tires, it must be good!", but don't think about the fact that planes have a shitload of weight, very high speeds during landing, really huge temperature swings when they land and fly, and aren't supposed to use flammable gases. That's my favorite marketing-hype example, sorry. So yeah, nitrogen is great for planes. Does your car need the same treatment? No.

It makes money for a lot of people though. Don't buy into the hype. We use it in race tires, and have a few cylinders full of it, but I don't even bother using it in my street car tires even though I can use it for free. It just doesn't have any benefits on the street. Whenever the weather changes a lot, I just adjust the pressure for free at a gas station when I leave the house. I'd have to do the same thing with nitrogen, and it's a hell of a lot less convenient.

http://www.sears.com/shc/s/ProductDisplay?partNumber=00911586000P&storeId=101 53&catalogId=12605&sid=comm_sears_productpg

Thanks for the advice. Very helpful. Now I just hope that rft's aren't as bad as I have been led to believe. Guess I'll find out.

:iagree:

Given that air is composed mostly of nitrogen, it makes sense that air and nitrogen expand and contract with temperature at the same rate.

The only benefit of nitrogen is that it is dry. Dry air vs dry nitrogen, there is no difference. The issue is that many unmaintained air compressors have wet air, and it is the moisture that is expanding and contracting, not the air itself.

As to BMW not endorsing it, well, neither J.Belknap nor I endorse it either. That doesn't make it bad, it simply means that we don't see reasons to come out promoting it. Maybe BMW is the same, becaues if they do endorse it all their dealers may well send them a bill for nitrogen filling equipment, plus thank you notes for making them purchase it for no good reason, but simply due to their endorsement.

I have had three sets on two vehicles, and have yet to have a problem. Can't understand what all the flap is about. Early RFTs could be harsh. Newer generations don't have to be, it depends on the design.

I can certainly agree with the part about dealers having to buy stuff they don't need. My Mercedes dealer (past history) had to buy tons of service equipment per Mercedes' spec that wasn't as good as the stuff they already had. My only concern with moisture is that I don't have any way of knowing how well the gas stations around where we live maintain their compressed air supplies to prevent moisture from getting into the lines.

Thanks for your experience with rft's. Word has it that the new third generation rft's from Bridgestone (with whom BMW has recently signed an exclusive for entire fleet) are much better riding (only 5% stiffer riding than non-rft's according to the press release). I think it's a great idea in theory, but with so many people complaining, and lawsuits against manufacturers (Honda with earlier Bridgestones), it has been difficult to sort the bs from fact.

Could you please explain the physics of that phenomenon?

pV = nRT

Semantics?

Yes, dry air also expands when hot. It raises tire pressure by a negligible amount, comparatively.

edit: You guys fill up with nitrogen if it makes you feel good. It doesn't "hurt", but it's certainly not needed for our applications.

Maybe not our applications, but the wifey's ES350 TPMS was going off all last winter (Minnesota) until we put the nitrogen in...And then the alarms stopped going off while the weather outside stayed frightful :dunno: