Looks like legacy took a page out of the GT-R book

[Cereb Daithi]

Well I had no idea about this until I was workin on an 09 Legacy today. The Legacy Limited sedans are equipped with...


*drumroll*


Nitrogen filled tires......

I was down by the tire when I noticed these bad boys on the valve-stems



Thoughts?

[complacent]

Wow, color me impressed. I do believe the gas is catching on...

[Cereb Daithi]

Ironically enough we have had no real official notification of procedures when dealing with nitrogen. Noone else at the dealership really knew these were even equipped with nitrogen. I assume we will be receiving some sort of TSB and compressors or SOMETHING so that we can refill nitrogen. Should be in interesting month or two as this develops.

[Mr Kleen]

I remember seeing coverage (autoblog maybe?) about sporadic local newscasts talking about filling your tires with nitrogen as a way to improve gas mileage last summer but it didn't seem to get any traction with the general public. (see what I did there?) a few shops in the DC area will do it but not many. IMHO it's not worth the trouble for a daily driver.

[Cereb Daithi]

Found out some more info.. apparently this is NOT an OEM off the factory floor setup. Only a handfull of subaru dealers do this and it has not become standard for the models. Still pretty neat though. in the more northern states this might actually be something valuable due to the colder climates.

[Katya4me]

I want to say that some Mazda dealerships are doing this with the new SUVs, but they are charging over $10 to top them up. Not worth it to me. Is your dealership going to charge, do you know?

[Cereb Daithi]

I haven't heard any official news but basic intuition points to yes we will charge. It's a stealership. It's what they do.

[Mr Kleen]

It's a stealership. It's what they do.

it's funny because it's true.

[drwrx]

There was an article on Nitrogen filled tires a few years back in one of the many mags I read (MT, R&T, C&D). There were a series of tests done and their conclusion was that it did NOTHING! It didn't improve gas mileage, it didn't lower tire temps, it didn't reduce rolling resistance or weight. It did NOTHING!

[zaxrex]

It has better pressure maintaining characteristics. It might not keep the temperature from changing, but the pressure won't change as much when you have temp fluctuations.

So if you can be driving a car and feel the difference in 5 psi tire pressure, then you are a better man than I, and are probably driving a race car. Race apps is coincidentally where this is used. Go fig.

[ElZorro]

It has better pressure maintaining characteristics. It might not keep the temperature from changing, but the pressure won't change as much when you have temp fluctuations.

What part of PV=nRT or P1V1/T1=P2V2/T2 explains that?

[GaToR]

It has better pressure maintaining characteristics. It might not keep the temperature from changing, but the pressure won't change as much when you have temp fluctuations.

What part of PV=nRT or P1V1/T1=P2V2/T2 explains that?

An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of zero volume, with no intermolecular forces, where the constituent atoms or molecules undergo perfectly elastic collisions with the walls of the container and each other and are in constant random motion. Real gases do not behave according to these exact properties, although the approximation is often good enough to describe real gases.

[ElZorro]

I agree, those formulas aren't perfect, but as it says the approximation is good enough, there are systems designed, built and used based on them. The boundary conditions are where it would break down, extreme cold heat pressure etc. The tire of a street car is a pretty tame environment in the scope of the universe.

[GaToR]

I agree, those formulas aren't perfect, but as it says the approximation is good enough, there are systems designed, built and used based on them. The boundary conditions are where it would break down, extreme cold heat pressure etc. The tire of a street car is a pretty tame environment in the scope of the universe.

True, but also near phase change they start to act like real gases. Now that might sound rediculous since Nitrogen boils at
-200C (77K), but you'd be surprised how little pressure it takes to liquify a gas. (if I'm anywhere close to accurate on this)

P1 = atmospheric pressure
T1 = boiling point of N2 at atmospheric pressure
P2 = pressure required to liquify N2 @ raod temperature (what we want to know)
T2 = standard temperature @ street temperature

if P1/T1 = P2/T2,

14.5 psi/77K = P2/300K ; P2 = 55psi

So as you approach 55psi on a road tire, it starts behaving like a real gas (theoretically). I seriously doubt any race car tire will be pumped that high, but even at half of that pressure the relationship would start to taper off into a curve and no longer be linear.

Now I have no idea what the difference between real gas properties of air and straight N2 are, but maybe if you did the full Van der Waals equations for both, it would start to be apparent? Don't know.

Although it is entirely possible that I'm full of

[ElZorro]

I don't think the calculation that you carried out shows what you think it shows... that formula will tell you if you have a gas at a given state (P1 and T1) and you change the T to T2 the P becomes P2. This works from PV=nRT knows that V, n, and R are all constants. So the calculation you have would be good for estimating a hot tire pressure from a cold tire pressure (tires are 70F and at 35psi, when you get them warmed up to 80F or 90F they would increase in pressure to P2... but even this is fuzzy because you may find some volume change with the expansion of the tire)

And yea, I agree, I'm probably talking out of my @$$ as well. One year of physical chemistry and a semester of thermodynamics almost 10 years ago doesn't not make me an expert.

[GaToR]

I don't think the calculation that you carried out shows what you think it shows... that formula will tell you if you have a gas at a given state (P1 and T1) and you change the T to T2 the P becomes P2. This works from PV=nRT knows that V, n, and R are all constants. So the calculation you have would be good for estimating a hot tire pressure from a cold tire pressure (tires are 70F and at 35psi, when you get them warmed up to 80F or 90F they would increase in pressure to P2... but even this is fuzzy because you may find some volume change with the expansion of the tire)

And yea, I agree, I'm probably talking out of my @$$ as well. One year of physical chemistry and a semester of thermodynamics almost 10 years ago doesn't not make me an expert.

Yeah, I'm in the same boat. My only reason for thinking you could realate one temperature/pressure set at phase change to another is the phase-change line moves upwards (near-linear) with temperature and pressure. So as you increase both simultaneously along the phase-change line, the ability for a phase-change does not diminish.



But since phase-change is one area where gases act 'real', the line is not linear.

[GaToR]

Behold my mighty photoshop skillz with Matt's crazy theoretical numbers added: (not to scale)



True, the tire will expand and/or asplode before you ever hit phase-change. But the point is that 'real gas properties' follow along that phase-line. So if you know at what temp N2 boils at 14.5psi, you can 'guestimate' what pressure it will continue to act 'unideal' at average track temp.

Now that still says nothing about what the actual difference between air and N2 is. That requires Van der Waals calculations

After that's done, you'd know what pressure change relates to temperature increases for each of the two gaseous mixutes. Under normal driving conditions, they are probably acting ideal and it won't make any difference whatsoever.

[ElZorro]

[GaToR]

Yarp