I do a lot a MPG tracking and have done 21K miles with a combination of having summer tires with and without Nitrogen fill and having winter tires without Nitro.

Nitrogen filled tires yields 1 MPG better then being without the NitroFil.

Summer tires yield 1 MPG over winter performance tires.


The first 7500 miles on the car were Summer w Nitro and I averaged 21.6 on 70% spirited highway.

this winter without NitroFil I did about 8000 miles and averaged 19.2

In spring I had the Summers swapped out but didn't want to pay for Nitro. I put on 4000 miles and averaged 20.0.

While getting my oil changed I had them go ahead and do the Nitro and so far I've put on 2K miles and I'm back to 21.9 And on one trip I tried to baby it as best as possible and I averaged 25.1 during 110 miles @ 80MPH.

My driving is all consistent. I'm now a believer that Nitro does improve MPG.

 

From what I understand Nitro simply does not expand or contract as much as air due to tire heat and outside temp. TPMS also help remind you to keep your tires inflated properly. Snow tires or A/S will be much grippier that summer tires due to sipes, therefore more rolling resistance. Summer tire are tackier on hot days but have less rolling resistance. That's my thought. Your stat might be right and that's very interesting. I like to think I am independently wealth and that prices don't affect me, but these gas prices do p1$$ me off. For the record I drive in town 95% of the time and I average from 16.9 to 17.8 mpg. These cars suck down gas.

 

Wow, you only put 8k on ur tires.
Mine lasted about 44k or so before I changed mine. But then again, I had the RS-A's

 

I admire the kring's effort in trying to verify this , but I still question the vaildity of the conclusion. There are too many variables to consider ... engine oil viscosity, oil temperature, environmental conditions, etc. All these can also affect the a vehicles mpg. Remember ... the air we breathe is already almost 80% nitrogen. The bulk of the rest is oxygen.

I think the only way to do this experiment is in a lab by measuring rolling resistance.

IMHO, I wouldn't go out of my way to get a nitrogen fill on my daily driver.

 

+1 (and terry said it quite elegantly ). Also, the described benefits of NitroFil also really what you state here; it's supposed to heat up less (so less tire pressure increase, and not lose pressure as fast due to the larger molecules).

Shouldn't your mileage actually be the same or BETTER as tire pressure gets higher? Beyond a certain point the contact patch gets smaller, so less rolling resistance - which means for mileage you actually want your tires to get hot and increase. Agree with terry though, there are too many other variables, as the tires get hotter they might get relatively stickier etc.

 

I'm no scientist just a casual observer but my assumption is that oxygen being the majority of the rest of the make up of air (20.95% - I was going to say 23% until I checked) must cause the expansion of air. The presence of Oxygen may cause this where the absence of oxygen will not. If your tire pressure is the same all the time under all temperature condition you will have a more consistent shape to your tires keeping your car rolling at an optimal MPG.

I have noticed more on this car since using Nitro than on any other car, not using it that my tire pressure is much more consistent. 15,500 mile and never once has my TPMS come on due to low tire pressure. I can't say that about any other car I've owed.

If you inflated your tires to 50 pounds your have a harder ride but probably better MPG, but MPG is not everything, other wise we’d be using solid lawn mower tires.

I agree to many variables. It sound plausible though and if someone did the research I think they'd find this is mostly true.

 

What was the tire pressure with NitroFil vs without ?

 

Thanks for the data, but I'd have to disagree with your findings. That 1mpg has to be included in the tolerance of your data. That 1mpg could come from anything. Wear in your tires, engine, engine oil weight that the dealer used at the time, air filter clogging up, air filter replacement, computer learning your driving habits, the fact that you consciously know that your tires are or are not nitrogen filled you subconsciously drive differently, drafting behind more truck, suv's, and big rigs in one period vs. drafting behind mostly cars in another period, etc. I know you probably tried to keep it as controlled as possible, but there are too many factors that are just simply out of your control when experimenting in the real world.

But. I'm not discounting N filled tires. There are benefits. The main one being that N is processed. It has to be purposely extracted and contained so in the process humidity and moisture is controlled. When that's pumped into your tires, tire pressure differnetial due to heat is less affected. That's why racers use N, so that they can control that variable and be more consistent in racing.

 

Nitrogen filling has little or nothing to do with oxygen. It is water that is the issue. Oxygen and nitrogen behave as (almost) ideal gasses and therefore their pressure changes linearly with temperature. Double the temperature (in degrees Kelvin) and you will double the absolute pressure. Any difference between O2 and N2 is tiny and can be disregarded.

But water vapor - now that is the poster child for a non-ideal gas. It behaves quite a bit differently than O2 or N2. This alone would not be a problem. The problem is that the amount of water vapor in the air changes all the time, so each time you fill your tires, you have a different amount of water in them. Hence, if you fill your tires on a low humidity day, then get a leak and refill one tire on a high humidity day, that one will react differently to heat.

But here's the most important part: to a street driver, none of this matters at all. The differences are very small compared to things like the tires themselves. Heck, strap a case og beer into the passenger seat and you'll have a greater effect on performance. The only reason it matters to anyone is that racers are concerned with very small differences. Hence, crew chiefs want to remove variables. One of these variables is the pressurizing agent in the tires. Bottled N2 is widely available enywhere in the nation and is always exactly the same. It is N2 and only N2 - no water or anything else. If air that had been bottled at STP an 50% RH were readily available, they'd use that- if it were cheaper.

The only possible way I could see nitrogen pressurization effecting MPG is if the hysteresis of the gas was a whole lot less than damp air. But I seriously doubt that this would have more than a fraction of 1% effect, since rubber's hysteresis is so large.

 

Oh, and Nitrogen is #7 on the periodic table, whereas Oxygen is 8. They are almost identical in size.

 

I want to agree but I also want to disagree. It feels like the tires have stayed rigid longer(ie less pressure lost)over the past 2 months that I've had nitrofill on. I only considered nitrofill because of the winter season. My car's low pressure light would pop every 2 weeks forcing me to constantly go to fill the tires up, I guess the real test will come in a few months.

 

+1. It's the water. Dry gas is dry gas. Nitrogen is inert and cheap so it's used for the application.