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With the summer heat here in Vegas my TPMS was acting up constantly. I've reset it and checked out all the sensors etc - no problems. Finally had the tires filled with nitrogen and this seems to have fixed the problem since the nitrogen expands less with heat.
TPMS
TPMS - The Tire Pressure Monitoring System provides early warning of any drop in pressure by continuously monitoring the pressure in each tire and alerting you in the onboard computer display in the event of a pressure deficiency. It communicates the exact pressure of each tire and/or their deviation from ideal pressure. This does away with the need for regular air pressure checks at the service station, which often prove highly inconvenient.
How much did it run you to get your tires filled with the nitrofill/nitogren? I live in Phoenix and recently noticed with 75degree mornings and 112 days i am starting to get eratic readings on my TPMS. Sounds like this might also help me since our weather is pretty close to the Las Vegas weather.
TPMS
TPMS - The Tire Pressure Monitoring System provides early warning of any drop in pressure by continuously monitoring the pressure in each tire and alerting you in the onboard computer display in the event of a pressure deficiency. It communicates the exact pressure of each tire and/or their deviation from ideal pressure. This does away with the need for regular air pressure checks at the service station, which often prove highly inconvenient.
I hate to keep beating a dead horse, but this is a myth. Boyle's law, Charles' law and the ideal gas law we all learned in high school chemistry are all independent of which gas is involved. PV=nRT, rearranged gives P=nRT/V, and since n, R, and Volume don't change, you're left with deltaP=deltaT (and the constants cancel out).
The only real advantage is that gas compressed to 5000 psi, like Nitrogen or even air from a scuba fill cascade, will be drier (less water vapor) and nitrogen fill may possibly be less corrosive since the 20% oxygen has been removed, so can't oxydize components in the tire. I doubt this is significant, despite the ongoing myth in the auto industry. Apparently the new Nissan GTR is to come with Nitrogen fills from the dealer...
Another advantage being touted is that O2 allegedly diffuses faster through the wall of the tire than N2, hence tires remain inflated to the inflated (redundant?) pressue longer when filled with N2.
Also, allegedly, Costco is using N2 at all its facilities. But charging $12 a tire? I will check my tires regularly for free.
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RobMason
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I would like to see some data to support the nitrogen argument. No, testimonials from race drivers won't do it for me due to sponsorhip issues. Compressed air is a MIXTURE, containing mostly (>70%) nitrogen. As far as "permeation" is concerned, if the pressure loss rate is higher for air than pure nitrogen, it is still very slow and is easily counteracted by adding more air, available at most gas stations (for free). Just look at your tires. They stay pretty well inflated for months. If they don't you probably have another problem not on a microscopic level: a bad valve or a puncture. Most sports cars have alloy rims, the interiors of which suffer minimal corrosion due to oxydation. Besides, any leakage due to corrosion would have to occur at the rim/tire bead interface, which experiences little contact with the filling gas. Will tires inflated with nitrogen maintain pressure longer? Probably, but on a scale that makes it's usage at $12/tire questionable. Lastly, the argument that tire wear is reduced by using nitrogen (by lessening expansion and contraction), I would have to see some data. I suspect that this supposed benefit is minimal, most tires discarded in shorter time frames due to tread wear from the road surface. If someone has numbers, I'd like to see them, then maybe I'll reconsider.
I hate to keep beating a dead horse, but this is a myth. Boyle's law, Charles' law and the ideal gas law we all learned in high school chemistry are all independent of which gas is involved. PV=nRT, rearranged gives P=nRT/V, and since n, R, and Volume don't change, you're left with deltaP=deltaT (and the constants cancel out).
The only real advantage is that gas compressed to 5000 psi, like Nitrogen or even air from a scuba fill cascade, will be drier (less water vapor) and nitrogen fill may possibly be less corrosive since the 20% oxygen has been removed, so can't oxydize components in the tire. I doubt this is significant, despite the ongoing myth in the auto industry. Apparently the new Nissan GTR is to come with Nitrogen fills from the dealer...
Greg
Doctor I must disagree. The constants don't cancel. Molecular weight is different for oxygen and nitrogen. The n in your equation IIRC. Since air is something like 79% nitrogen it won't change a bunch going from air to 100% nitrogen but change it will. So the resulting delta P for a given delta T will differ a bit.
Enough to be significant I can't say without remembering more chemistry from 30 years ago then I'd like.
Grins! Never mind! This is way to complicated. Besides,I look for things to check on the Cayman.
I swore I'd not mention this again but, I wish it had a dipstick!!
I have to agree with Greywolf. The equation is dependent on the density of the gas.
Quote:
Originally Posted by Greywolf
Doctor I must disagree. The constants don't cancel. Molecular weight is different for oxygen and nitrogen. The n in your equation IIRC. Since air is something like 79% nitrogen it won't change a bunch going from air to 100% nitrogen but change it will. So the resulting delta P for a given delta T will differ a bit.
Enough to be significant I can't say without remembering more chemistry from 30 years ago then I'd like.
gemars was correct in that the real culprit here is water. Compressed air from your local gas station usually has a significant amount of water vapor in it. When the tires are cold, this water vapor can condense into liquid water. You then adjust your tire pressures when the tires are cold and everything looks great. However, when the tires heat up, the water vaporizes and adds a SIGNIFICANT amount of pressure. If you could get really dry air, it would work as well as bottled nitrogen.
BTW, some F1 teams are now using CO2 in their tires. Not sure why, but the higher molecular weight (n) might have something to do with it.
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-= Rick =-
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