Why does my car have green topped valve covers?

[justatroll]

Originally Posted by mav1178

... if someone went through the trouble of using only nitrogen in their air compressors, it just means the air will have less moisture and more stable air pressures that don't fluctuate as much when temperatures change.

-alex

Oh and there's killing yourself in the garage while using your porting tool

[Tcoat]

Originally Posted by mav1178

So I am gullible enough to pay for such a scam, even though the car came with it from the factory when I took delivery of it?

Just because it doesn't work for you doesn't mean it doesn't work for others. Nitrogen-filled is just a marketing thing, but if someone went through the trouble of using only nitrogen in their air compressors, it just means the air will have less moisture and more stable air pressures that don't fluctuate as much when temperatures change.

-alex

Weall paid for the scam when we bought the car. They didn't do it for free and it is built into the price of the car (at a profit)
It is a tank there Mav not a compressor. A simple drier on an air compressor will give the same results as far as moisture goes. The temp fluctuations are minimal at best and only really apply under very heavy use. In a race car it may make sense. In a street driven car there is zero benefit.

[mav1178]

Originally Posted by Tcoat

Weall paid for the scam when we bought the car.

Possibly, however the car was not serviced at the dealer (Heuberger) prior to me taking it.

-alex

[joe strummer]

Originally Posted by mav1178

it just means the air will have less moisture and more stable air pressures that don't fluctuate as much when temperatures change.
-alex

Assuming that's true, why does it matter to you?

[Packofcrows]

Any pics? I dont see anything green in my car....well.....anything legally green....

[strat61caster]

Originally Posted by joe strummer

Assuming that's true, why does it matter to you?

Tire pressure changes can dramatically alter the handling of a vehicle, with standard atmospheric air the temperature increases lets say 3 psi after an autox run or lapping session. By using dry air (typically accomplished with nitrogen) you can reduce the pressure change, lets just make stuff up and say it reduces the increase by 1 psi.

To the average person, doesn't make a lick of difference.

To the hardcore competitive guy that means he starts his day +1 psi over standard air, he's 1 psi closer to his optimal temperature, the tires will react more predictably sooner in the run, if there's an unanticipated handling problem (under/oversteer) that would heat up the fronts or the rears disproportionately or unexpectedly with nitrogen/dry air the pressure change will be lessened reducing the impact of the problem vs. atmospheric air.

I remember doing some testing about a decade ago, these were go kart tires and my dad had access to a house sized nitrogen tank at work, nobody would miss a bit here or there, one of the perks you could say. We saw maybe 0.5 psi difference at the absolute most and our methods weren't very scientific. We deemed it wasn't worth the hassle and after a season of messing with it dropped it and put our efforts into more valuable testing time. The local championship and track records came long after we stopped bothering.

I fear I may have misinterpreted your post, oh well, already wrote it.

I wouldn't hesitate to use the desiccator I linked a few pages back but at this point it's not on my radar for minimizing variables, if I were to use it I'd have to spend a day re-confirming my air pressures...

Originally Posted by Packofcrows

Any pics? I dont see anything green in my car....well.....anything legally green....

Edit: Easy DIY test, take one tire filled with nitrogen (courtesy of your local dealership, costco, american tire, NASA, whatever) take one tire filled with atmospheric air (stop off at a gas station on the way home drain a tire flat, fill it up with the air compressor there), let them sit in the garage overnight, equalize the pressure in the morning, let 'em sit in the sun for a few hours and measure the pressures again. You could be fancy and measure every half hour and make some nice Excel graphs, of course make sure they get equal sunlight and aren't close enough to influence each other significantly.

Might do this if I get my next set of tires at costco, lets see if they offer any trackable compounds aside from RE71R and MPSS...

[Packofcrows]

Originally Posted by strat61caster

Tire pressure changes can dramatically alter the handling of a vehicle, with standard atmospheric air the temperature increases lets say 3 psi after an autox run or lapping session. By using dry air (typically accomplished with nitrogen) you can reduce the pressure change, lets just make stuff up and say it reduces the increase by 1 psi.

To the average person, doesn't make a lick of difference.

To the hardcore competitive guy that means he starts his day +1 psi over standard air, he's 1 psi closer to his optimal temperature, the tires will react more predictably sooner in the run, if there's an unanticipated handling problem (under/oversteer) that would heat up the fronts or the rears disproportionately or unexpectedly with nitrogen/dry air the pressure change will be lessened reducing the impact of the problem vs. atmospheric air.

I remember doing some testing about a decade ago, these were go kart tires and my dad had access to a house sized nitrogen tank at work, nobody would miss a bit here or there, one of the perks you could say. We saw maybe 0.5 psi difference at the absolute most and our methods weren't very scientific. We deemed it wasn't worth the hassle and after a season of messing with it dropped it and put our efforts into more valuable testing time. The local championships and track records came long after we stopped bothering.

I fear I may have misinterpreted your post, oh well, already wrote it.

I wouldn't hesitate to use the desiccator I linked a few pages back but at this point it's not on my radar for minimizing variables, if I were to use it I'd have to spend a day re-confirming my air pressures...






Edit: Easy DIY test, take one tire filled with nitrogen (courtesy of your local dealership, costco, american tire, NASA, whatever) take one tire filled with atmospheric air (stop off at a gas station on the way home drain a tire flat, fill it up with the air compressor there), let them sit in the garage overnight, equalize the pressure in the morning, let 'em sit in the sun for a few hours and measure the pressures again. You could be fancy and measure every half hour and make some nice Excel graphs, of course make sure they get equal sunlight and aren't close enough to influence each other significantly.

Might do this if I get my next set of tires at costco, lets see if they offer any trackable compounds aside from RE71R and MPSS...

Thanks! I walked around my car probably 8x's now and throughout the day looking for something green. Mine are all black.



Reading online it says it can help mpg and handling. I might try it if i ever go to track again for fun.

[joe strummer]

Originally Posted by strat61caster

I fear I may have misinterpreted your post, oh well, already wrote it.

Not at all. Thank you for the explanation. Very interesting.

Originally Posted by strat61caster

Edit: Easy DIY test, take one tire filled with nitrogen (courtesy of your local dealership, costco, american tire, NASA, whatever) take one tire filled with atmospheric air (stop off at a gas station on the way home drain a tire flat, fill it up with the air compressor there), let them sit in the garage overnight, equalize the pressure in the morning, let 'em sit in the sun for a few hours and measure the pressures again. You could be fancy and measure every half hour and make some nice Excel graphs, of course make sure they get equal sunlight and aren't close enough to influence each other significantly.

Or I can take your word for it.

[mdm]

Originally Posted by strat61caster

By using dry air (typically accomplished with nitrogen) you can reduce the pressure change, lets just make stuff up and say it reduces the increase by 1 psi.

It would be great if we did not just make stuff up here, but have some sort of physics-based estimate, even a crude one.

Because if it is 1 psi, then someone may care (again, in a race car, I am not sure if most handheld tire pressure metter have accuracy better than 1 psi). If it is 0.05 psi, it's another story.

[nickmerronesucks]

In before a year from now when OP cant get chrome caps off of his tpms cause their frozen on

[mdm]

Originally Posted by strat61caster

the temperature increases lets say 3 psi after an autox run or lapping session. By using dry air (typically accomplished with nitrogen) you can reduce the pressure change, lets just make stuff up and say it reduces the increase by 1 psi.

OK, here is an attempt at estimating these effects.


We want to estimate how different is the response of tire pressure to temperature changes depending on the gas used to fill the tire.


You are guesstimating that using regular moist air will cause the response to be 150% compared to dry air or pure nitrogen (3 psi vs. 2 psi).


Now we all now that PV=nRT.


So the response of pressure to temperature change will depend on nR/V. V is constant for our purpose (there may be changes of tire volume with pressure and temperature, but they are minute and more importantly will not differ between different gases). Therefore the response will depend on nR only.

n is the amount of gas in moles, so for a given volume it will be determined by the gas molar volume, which only slightly between water vapor (24.5), oxygen and nitrogen (both 22.4)


For R the difference is bigger, 0.297 for O2, 0.26 for N2, H2O vapor 0.462.

(all figures taken form the internets ;-)

Now I am making a few assumptions here, which may be not generally correct, but I think they are close enough to correct for our purposes. If there is a physicist in the room, please stand up and correct me.

First, I am assuming that n and R change with temperature and pressure will be either negligible or its difference between our gases will be tiny.

Second, I am assuming that n and R of a mixture of gases can be approximated by the weighted average of n & R of component gases.

Third, I am assuming that dry air is 79% nitrogen and 21% oxygen, and that's it.

Fourth, I am assuming that moist air is 5% water vapor + 95% dry air. This is a worst case scenario, there is this much water vapor in the air at 100% relaive humidity at 40C (104F). Normally,at lower temperatures and lower RH there will be much less.


Fifth, I may have mixed up volumes and masses somewhere, but I think these are similar enough between our gases to ignore this.


Now, to the results. nR for dry air is 6.0, for nitrogen 5.82, for water vapor 11.32. this would indicate a huge difference in response of pressure to temperature change, with water vapor's response about 189% of dry air response, and about 194% of pure nitrogen response.


BUT let's not forget that we do not have pure water vapor in the tires, we have 5% max, usually much less.


For 5% water vapor in air my figures are 104% compared to dry air and 107% compared to nitrogen. This is FAR less than 150%, and once again, I assumed using insanely tropical air, normally the effect will be much smaller.

[mav1178]

Originally Posted by joe strummer

Assuming that's true, why does it matter to you?

It doesn't matter to me.

It will matter if you are into autocross or professional racing, where consistency is key.

-alex

[strat61caster]

Originally Posted by mdm

It would be great if we did not just make stuff up here, but have some sort of physics-based estimate, even a crude one.

Because if it is 1 psi, then someone may care (again, in a race car, I am not sure if most handheld tire pressure metter have accuracy better than 1 psi). If it is 0.05 psi, it's another story.

If you read my entire post I do reference personal experience of seeing ~0.5 psi difference between Nitrogen and atmospheric air in go-kart tires (5-6" diameter, 5"-9" wide) we typically ran at around 10 psi and saw a ~2psi gain after coming off track.

I do appreciate you chemistrying it up though.



Edit: I do have some reservations about your math as I am not saying there is a 150% difference, rather my example is ~3% difference between the two scenarios (~30+3 vs ~30+2), but I am not too bothered by it. Like I said, I'll actually run an experiment if I ever get my tires filled with nitrogen.

[justatroll]

Originally Posted by mdm

First, I am assuming that n and R change with temperature and pressure will be either negligible or its difference between our gases will be tiny
.

This immediately set off a red flag in my head that perhaps you do not understand something.
For a sealed system (tire), n (number of moles) and R (ideal gas constant) will not vary AT ALL.
They are constants and by definition will not change during this experiment.