Tire / Tyre Nitrogen

Ladies and Gents,

Do any 355 owners (or any Ferrari owners) use Nitrogen instead of air? Is there a voodoo about it because of the rims? I have used it in my 911 and 928 and feel the difference in the ride.

Thanks.

Boaf

 

I am very curious as to what differences you feel between air and nitrogen.

I have a nitrogen tank a few feet away from my 348 but I don't bother using it in that car because I'm not tracking it.

 

No offense but there is no physical way you feel the difference in the ride unless you have some super human, extra sensory perception that none of us regular animals have.
Placebo effect. Nothing more.

Only real benefits of using Nitrogen is the pressure is more stable during variations in ambient and tire temperature. So under racing conditions, as the tires get hot or cool, the tire pressure stays almost the same as when the suspension was set up.

Unless you are on the track or running super hard in the back roads Nitrogen has little benefit on the street. Marketing is a powerful tool.

 

All true, Jack. There is another slight advantage to nitrogen in that its larger molecules result in less pressure loss due to osmosis, but that benefit isn't really noticable except in very thin, light racing tires.

Even the difference in pressure rise versus regular air is fairly small, but every little bit helps in my case since I'm running 255 cross section tires on a 3100 lb car, meaning tire temps are extreme and pressure rise is substantial.

 

First of all, dry nitrogen is actually very slightly more sensitive to temperature changes than dry air. Given that initially the temperature and pressure are T1 and P1, if the temperature rises to T2, then P2 = P1 x (T2/T1) ^ (k/(k-1)) where K is the ratio of specific heats and is 1.4067 for air and 1.3997 for nitrogen. So the exponent for air is 3.46 where as for nitrogen it is 3.502. (Commonly k is taken as k=1.4 for both, which would yield an exponent of 3.5 with result that there would be no difference in temperature sensitivity.) Also, while the heat content of nitrogen is slightly greater than that of air, the density, at the same temperature and pressure, is less. The result is that for a given amount of heat generated in the tire, the temperature rise will be about the same for both. As for molecule size, air has 22% O2 and 78% N2. So if you fill your tires with air to 30 psi and the O2 leaks out the pressure would drop to 20 psi. Then you top if off with air back to 30 and the new O2 leaks out and the pressure drops to 27.8. Top it off again and that O2 leaks out and the pressure drop to 29.5. So after 3 top offs you pretty much have N2 in the tire. That said, how often do you have to add air to the tires on you street car? With tire pressure monitors on my Porsche it comes down to about once a year they loose about 2 psi when filled with air. Of course, over time both O2 and N2 leak out, but if O2 leaks out faster than N2, then over time, as you top off the tire pressure, you do end up with mostly N2 in the tire.

The real benefits of nitrogen are that nitrogen from a cylinder is (supposed to be) dry, i.e. no water vapor content compared to air from a typical compressor at a gas station, and it does not degrade tires from the inside since there is no O2 to oxidize the rubber. But for pressure stability, it is the moisture content in the air that makes it less stable to temperature changes.

The bottom line is that for street use, N2 filling is just a way for the tire shop to make a little more money.

 

Snake oil/placebo effect for a street car.

 

I had to use nitrogen in my aircraft tires, no way id bother using it in a cars tires.

 

+1

 

I can only tell you what I feel when I am driving a 4000 LB 928S at high-way speed and hard turning. It seems the the pressures do not expand at highway speed as compared to air (then again, I wont be driving this car in the winter time either). I do feel it in the steering over bumps. Also, a Porsche is no Ferrari and vice versa. I do feel a difference; (must be my sensitive Italian bottom).

So sounds like a resounding "Nyet" on the nitrogen for the 355. I'll just maintain the proper pressure. Thanks for the feedback, good stuff.

Boaf

 

John,

Now that is cool stuff right there. Three top offs and you are N2? I do sometimes drive the 928 in the cold and if there is moisture in the air (tire), that is when I sometimes feel a change in handling. Might be just me but had the 928S for 12 years and got use to it...

Thanks,

Boaf

 

Yep, ambient temperature is when I can feel the difference between stability. Same roads, highways in cold months vs. warm months makes a difference.

Guess I'm not the regular animal, oh well, dare to be different.

Thanks

Boaf

 

Better yet, instead of swapping the gas yourself and stating "I can tell the difference by feel", have someone swap the gas for you, with you being "blind" as to which gas is in the tires. Drive it. Do this 5-10 times and see if you're truly actually able to discern the difference. Otherwise everything you're telling yourself (and now others) is anecdotal.

 

Well, that's a hypothetical. But if N2 leaks out less than the O2 and any H2O vapor, then eventually you have to end up with mostly N2 in the tire. But by that time you may need new tires.

 

I feel a difference too through the seasons, but more from the tires- my ferrari has summer sport tires (so definitely notice worse adhesion in cold weather), but even in our daily drivers (all season tires) there is a some handling difference with cold vs. warm months.

A quick question- when you changed from oxygen to nitrogen, did you also have the tires mounted/balanced? I believe you would feel a difference from that vs from having nitrogen vs. oxygen, and maybe that is what your are noticing?

I know when I add say 1-2 PSI to my tires (say the same range of pressure increase that might occur with the normal driving of a car between oxygen and nitrogen) I feel no difference, thus I don't think I could possibly notice any difference between any variation of PSI range from oxygen vs nitrogen (again on street driving- I don't have track experience so can't speak to that)

 

Now temperature has a huge effect on rubber and how tires drive. Like the difference between winding up with a smile on your face or in a ditch. Ask me how I know.
Age of rubber is also a major factor that seems to be seldom discussed in performance circles.

 

True. Lots of difference in feel between winter & summer, but a whole bunch of it is down to tires. Also, the oil in the dampers becomes more viscous in cooler temps so the car usually feels stiffer and better damped as a result of that.

 

In my opinion, it's essentially impossible to fill a car tire with nitrogen, unless you manage to do it in a vacuum chamber. When the tire is mounted onto the wheel it already has a volume of air in it, at around 14-15 psi at sea level. All you can ever really do regardless of what gas you use is top it off with another 15-20 psi. The ambient air in the tire when mounted isn't being evacuated as the nitrogen is being filled. Given the capacity of a car tire, topping it off with nitrogen I doubt will have any effect, even if the car is being tracked, there just isn't enough volume to make a difference.

 

You flush the tire with nitrogen before the final fill and the results are obvious in the pressure readings. The difference is not huge but every little bit helps when pushing the tires extremely hard. Nitrogen is cheap and a source of dry propellant is really handy to have around, so even a couple of psi at the top end justifies its use for serious track people, especially considering the fact that it takes lots longer for your slicks to go flat.

No real point in it for street car tires, but I do use nitrogen in my 348-- it's clean and dry (unlike shop air) so I use it to clean the car inside & out (but not in the tires... yet).

 

I was thinking the same. I've had nitrogen in one of my vehicles and didn't notice a difference.

 

My car does best with 78% nitrogen.

 

Yep 78% nitrogen mixed in with about 21% O2 seems to be the sweet spot. The last 1% is carbon dioxide just to be proprietary...

 

Guess this is a good opportunity to point out the importance of using a paste tire lube and NOT soapy water when mounting a tire. It always pains me to see poorly trained/poorly equipped tire techs struggling to mount low profile high performance rubber by using copious quantities of water, some of which inevitably winds up inside the tire. Not only can that create an impossible to solve imbalance, it'll make for higher pressure rise on the track. If your tire & wheel place is too cheap to spring for paste, bring your own or find another tire shop. Little things mean a lot on a high performance car.

 

There actually is a sweet spot. It depends on pressure. For example, if the tires are inflated to 32psi then if you have anything over 93.39% Nitrogen will result in O2 actually infiltrating the tire. Similarly, if whatever in in the tire is "dry" water vapor from outside will also infiltrate the tire over time. It's a 2 way street. It has to do with partial pressures.

 

N always sounds cool if you are into the latest and greatest thing, but for the casual street driver, I could take it or leave it. I think I had one mechanic that filled my tires with N to try and get me to come in for regular refills (hey kid, the first hit is free), but I didn't bite.

 

Or you can just vacuum the tyre before filling with Nitrogen, it is quite possible...(?!)
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