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TPMS & Cold Weather (cold in SoCal at least.)

Discussion in 'Model S: Driving Dynamics' started by PTADO, Nov 17, 2016.

  1. PTADO

    PTADO Member

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    New owner, and my TPMS lights all came on last night. I assume it's the cold (if you could call it that), but it's not 85 degrees so I'll call it cold.

    All four tires are reading 38psi.
    Per the sticker, all should be 45psi.

    From what I know, these are nitrogen filled tires so adjusting the pressure isn't as easy as it once was with traditional air as far as letting a little out in the heat, and pumping them up when it's cold.

    What do most of you do in this situation? Just ignore the beacon and dinging, or adjust properly accordingly with nitrogen?
     
  2. ColdRauv

    ColdRauv Member

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    Unbelievable. Add air to your tires.
     
  3. PTADO

    PTADO Member

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    Air, or nitrogen? I don't think that deserves an "unbelievable".

    Can you add air to nitrogen tires
    When you add compressed air to the tire, the water comes along for the ride. As the tire heats up during driving, that water changes to a gas, which then expands, increasing tire pressure. Because nitrogen is dry, there is no water in the tire to contribute to pressure fluctuations.

    My point in asking the question is should I top-off my tires to 45psi of NITROGEN just to turn off the lights? Because when it gets hotter again, I could be pushing 50+psi which isn't recommended.

    @ColdRauv - I was asking what OTHERS' do. Clearly, your one answer "just add air" is wrong, so I'll wait to see if anyone else chimes in.
     
  4. BrokerDon

    BrokerDon Member

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    I've had to add air at least 3 times in 20,000 miles of driving this past year in our 2015 Model S P85D with Tesla 21" wheels and Continental "ContiSilent" tires. This becomes an issue when the outside air temperature drops and the tire haven't been "topped off" for a couple of months. Not that unusual, and from my experience more if an issue with low profile / high performance tires since the volume of air in them is lower than "standard" or "high" profile tires like the HEAVY thick sidewall 35" 315/75R16 tires on our lifted Jeep Wrangler.

    Whether its worth adding Nitrogen or just plain old atmospheric air (which is 79% nitrogen) is up to you and your wallet's threshold of pain. Since I'm in SoCal too, I just drop by an America's Tire every couple of months in all our vehicles and have them "top off" our tires with good old atmospheric air for FREE.

    YMMV

    Closed course, professional driver.

    You won't lose your doctors, you won't lose yhour insurance, and your insurance won't increase. WAIT that isn't me... That was our lame duck POTUS. LOL
     
  5. BrokerDon

    BrokerDon Member

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  6. Don85D

    Don85D Member

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    Yesterday I had one tire show low pressure and it was a cold morning. When I checked pressure I found that the other three were at 45 while this one tire was lower. I have a feeling there is minor rim leak and that air vs nitrogen is not the issue. I topped them all up to 50 psi (cold) which may improve range. The ride was not adversely affected.

    I don't use Nitrogen and I have a large compressor at home but there is one tire that leaks a little and that may be the symptom that is happening in this discussion.
     
  7. St Charles

    St Charles Member

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    Passenger car tires being filled with nitrogen is garbage pseudo-science. Properly inflated tires are 100% what you should be concerned with.
     
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  8. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    I agree with St. Charles, I think there's very little benefit to filling tires with nitrogen vice air.

    Nitrogen changes pressure with temperature somewhat less than air does, but I don't really think that's an advantage. Inflating the tires with air to the recommended pressure when cold will then mean that the tire pressure will increase when it heats up, which is already accounted for in the manufacturer's specs.

    Nitrogen can inhibit corrosion because the oxygen is not inside the tire to react with any corrosion-susceptible components. Usually this means the steel in the wheels/rims. However, all Tesla wheels are aluminum, so there's very few exposed components inside the tire that can benefit from the lack of oxygen. Plus, if the air is dried using a desiccant at the air compressor (most industrial air compressors have some sort of dryer to remove the moisture), then even air won't corrode anything.

    Nitrogen doesn't diffuse through the tire's rubber as quickly as air, so nitrogen-filled tires supposedly maintain pressure longer. But in the average tire, very little internal gas escapes by diffusing through the rubber. You get a lot more slow leakage from imperfections in the wheel/bead seat, valve stem to wheel seal, and the valve seat itself.

    Also, to the OP, did you have the tires specifically filled with nitrogen somewhere? To my knowledge, Tesla uses standard air, not nitrogen. Most locations that fill tires with nitrogen specifically indicate this by using a green valve stem cap. If your car doesn't have green valve stem caps, I'd bet they're filled with air, not nitrogen.

    Like St. Charles said, it's far more important for handling, tire life, and safety to fill the tires to the recommended pressure, regardless of your choice of gas.
     
  9. St Charles

    St Charles Member

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    Yeah. The big reason that Formula cars use Bottled Nitrogen is because it's the cheapest and safest way to remove moisture from the inside the wheels. Bottled Nitrogen is considered "dry" and has practically 0% water vapor which is important for the heat and stresses that Formula cars place on the wheels and tires in a race. This environment is not possible to duplicate on a passenger car and thus, the primary benefit is useless to us.

    The whole concept of anti-corrosion, inherent stability, and diffusion properties if Nitrogen are either patently false or not remotely relevant. The outside walls of the tire will fall apart well ahead of the inside. Unless someone were to pour a corrosive liquid inside the tire at mounting, the inside will look practically brand new when compared to the outside after the tread is worn down. Diffusion is negligible compared to air leaking past the valve stem and contact points with the wheel.

    Finally, pressure variance. Google University would indicate that in a best case scenario Nitrogen has about a 5% difference in how it reacts to pressure vs Oxygen. That said, standard pressurized air is already 77% Nitrogen and 23% Oxygen. this means that the actual best case difference is about 1% difference in pressure variance as temperature changes. If you watch your tire pressure through the TPMS system in the car, it varies about 3lbs/sq in as the tires warm up in normal driving. Applying the math, the real difference would be 0.03lbs/sq in. It's highly doubtful there is a consumer grade tire pressure gauge that is accurate enough to measure this difference. This is best case scenario, assuming you actually have 100% nitrogen in your tires, which isn't possible.

    Keep your tires properly inflated and your alignment straight. Everything else is placebo.
     
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