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:

Hi Midwest,
Didn't know you lived in Minnesota. I was in Minneapolis in January a few years ago and thought that I would die. I've got some friends in the Minnesota Orchestra and they tell me stories about having to use electric block heaters in their cars. Wow. I lived at Interlochen, Michigan for several years, but never got nearly as bleak and cold as Minneapolis. But since I do drive back up to northern Michigan several times a year, perhaps your suggestion about nitrogen is food for thought. I drove up there last February when it was 65 here in DC and 20 at Interlochen, and my nitrogen filled Mercedes tires only changed by 1 psi. But with run flats, maybe this is all moot?

I think that's the key -- we have RFT's...I love the change of seasons, but winters here are too long..Am ready for Spring by end of Feb :cool:

Sorry I forgot to look at your X6 specs and saw that you have the 20" OEM performance run flats. I was told by my PA dealer that if I plan to drive up north a lot in the winter to go for the 19" all season with the sports package. Maybe he was wrong. My hat is off to you for dealing with the bitterly cold weather in Minnesota. Beautiful in the summer, but it does take a strong constitution to deal with that winter. Garrison Keillor loves to make jokes about the Minnesota winters in his books and radio show. I thought he was exaggerating, but then I had the "winter experience". Do you go ice fishing" I did it once when I taught up in Michigan, and somehow managed to fall in. Students were laughing their heads off. To add insult to injury, I only caught one three inch fish after standing out on the lake for two hours before putting my right leg into an open hole in the ice that had been snowed over. Best of luck to you with your amazing X6 (it is beautiful), and you do a fantastic job if keeping it clean.
It is wonderful to be back in the BMW fold. BMW people are much more interesting than the Mercedes crowd.

JB essentially answered it, but the fault here is my short/cryptic post.

To explain the physics, as I said in my post, air expands when heated just like nitrogen does. They are essentially equal in that respect. However, moist air (which includes water vapour) expands much more, comparatively speaking. It is also the moisture that causes the corrosion problems with the rim.

Racers use nitrogen, and remember that they can get tires much hotter than street use. This isn't because the nitrogen doesn't raise the pressure compared to air but rather that it does so in a much more predictable manner. Racers will measure hot pressures (they have to) and wet air will produce much more variance in hot pressures than either dry air or nitrogen. In those cases, nitrogen is just easier to use. For those of us not measuring hot pressures and bleeding tires down in between laps, but rather driving on the street, using nitrogen is nothing more than a way to get a green valve stem cap.

Thanks for the explanation. Makes a lot of sense. When I had nitrogen put into my recently retired Mercedes E class (which they did for free) I talked the dealer into not putting on those rather ugly green valve stem covers. Those things would definitely not look acceptable on any BMW.

My tire place put nitrogen in my Toyo's when I had my tires replaced a few years back. I would have never asked for it, but I have noticed that even after two years and 30,000 miles, I have only had to top off the pressures once or twice to maintain spec. Also, the tire shop that installed the tires offers free checks and top ups, so there was no extra cost.

As you said, performance benefits on the street are nill, but I do see how it could be a slight safety benefit to someone who doesn't check their air pressure as much as they should. Especially an SUV.

I had the same experience with my now retired Mercedes. Had nitrogen put into the Conti tires when car was new, and didn't have to have any top up whole two years I was driving it. But if you do have a leak, or lose some pressure somehow, you cannot top up nitrogen fill with regular air.

What happens if you do this? It just negates the point of the nitrogen, correct?

I am going to have to replace my tires in the next few months and I was actually thinking about just topping up with regualr air if the levels happen to below instead of making a trip to thetire place and waiting.

I was told by the Mercedes dealer (who may or may not be correct) that you should not top off a nitrogen filled tire with regular air. That, according to him, will introduce some water into the mix, thus negating the effectiveness of the "dry" nitrogen.

I don't buy it. Who's going to run around looking for a N2 top up when their tire is low? The important thing is to not drive around with underinflated tires, not whether or not you may have 10% regular air vs pure N2.

Introducing water is another thing. Even if you have regular air in your tires you should avoid poor quality air (moist). I've seen gas stations that had water dripping out of the air hose. :yikes:

That is what I figured. With only a few months of life left on my tires, I am not too worried about that.

That is the thing. You only have to do it once or twice over the typical life of the tires. You probably end up saving time over the long run of having to find an air compressor every few months.

This is indeed a common problem. Probably best thing to do is either get a good 12v air compressor (I've never seen one that actually worked) or a tank of compressed air to use when adding air to the tires. I always used regular air until i got my last, now retired Mercedes with free nitrogen fill from the dealer. Never had to adjust air pressure in any of the tires in two years I owned the car, even when I drove up to very cold northern Michigan. But since I've never had rft's before (will find out in two weeks when I get my new X6), people (thank you Midwest for your help) with much more experience with rft's than I have suggested that the nitrogen is totally unnecessary for street use.

I apologize if this post is redundant. Save your money. Nitrogen is used in aircraft tires for two reasons. Extremely high pressures, I've seen some on airliners as high as 120 psi. Also because of the incredible temperature variations the tires are subjected to. Let's say it's 100F on the surface coupled with a 10,000 foot take off roll on a heavy airplane and then a -60F at 39,000 feet for hours at cruise. I guess nitogen does not expand and contract as much as good old air. No, I never used a laptop computer in the cockpit. I did sleep and read the paper though. It's a long way from NY City to Tokyo. Most importantly, when it comes to pilots, the old cliche' "you get what you pay for" is truly profound!!

OT...
I rode on those flights 2 dozen plus times...maybe you were driving up
front?! ;)

I have been using a 20+ yr old Black & Decker portable, to pump up the
rides in the Stable; never a problem with fill or moisture.

This is the newer version, I have at the FLA Joint. My orig., still being used, is the older version.
GL,mD

http://images.lowes.com/product/conv...77578422md.jpg

What the heck. For forty bucks with tire-life free refills, I went ahead and had my dealer do the nitrogen on my new 2010 X6. 5.0. That's what it costs for three people to have lunch at the local generic Garbage Burger. We did 41/42 PSI front/rear and since I do a lot of driving between warm Virginia and very cold Michigan (!) every winter, I decided that it certainly couldn't hurt. After spending so much on this vehicle, and paying to have a 3M clear bra installed, why not splurge? I'll save those forty bucks just by not going to Starbucks for a week (good reason to get out of that habit since I hate their coffee anyway).

Not sure about the X6, maybe it is different, but the X5 has a spec of 32 psi front and rear, even loaded, unless you are regularly travelling at autobahn speeds (and even then they don't recommend 41/42). All it can hurt is premature wear on your tires, and a harsher ride, but it's your call.

The owners manual for the 2010 X5/X6 recommends 33/33 for the X6 19" all season tires, but states that "for sporting driving and speeds over 100 mph" that 41 front/42 rear is recommended. My mechanic who races BMW's also suggested this setting. The ride is not too harsh, and the vehicle handles extremely well. He also mentioned that 33/33 will probably cause cupping with rft's.

I only have access to a 2009 owner's manual for the X6 5.0, so perhaps they have changed the recommendation. In that manual, over 100 mph sustained speeds, with four passengers, the recommendation for 19" tires is still 33/33. You have to go to the maximum gross vehicle weight (4 passengers plus a full load of luggage), and sustained speeds over 100 mph, to get up to 36/39 psi front/rear. You need all of those conditions, plus the 21" tire option, to get to 42 psi for a BMW recommendation. No worries, run them where you like, but I have never seen 33 psi cause cupping with any of my BMW vehicles, including those with RFTs. I have seen 39 psi and over cause accelerated wear in the centre of the tread.

On page 234 of the 2010 X5/X6 owners manual, it lists the recommended tire pressures with the stock 19" 255/50 R19 107 HM+S XL for speeds exceeding 100 mph as 41/42 front/rear. The ride at this setting is not at all stiff, and handling (with active steering) is amazing. My 2010 came with Michelin rft's, which may have something to do with the good ride quality. I asked the head master mechanic (Todd Thomas, who is rated by BMW as one of the ten best in the USA) at my dealer, SunMotorCars BMW about the possibility of this setting causing premature center tread wear, and he said that this should not be a problem. In fact, he strongly suggested running with the 41/42 for best tire life. So far, so good.

BTW, for what it's worth, I find the active steering option to be amazing. There has been a lot of negative stuff flying around about BMW's active steering, but once I drove my new X6 off the lot, there was no doubt that i made the right choice. The 2009 X6 that I test drove (at another dealer) did not have active steering, and even with the 20" performance tires, did not handle nearly as well.