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Discussion Starter #1
My apologies if this has already been submitted, I did a search (albeit not a very thorough one, but one nonetheless) and couldn't find the info I was looking for.

I just got my 2017 LT Volt (in Kinetic Blue) yesterday and have connected the car to the Chevrolet app that gives me a diagnostic on the vehicle, including the tire pressure.

At the dealership, the tire pressure was good, even though all tires were lower than the recommended 248 kPa. I parked my new car in the garage, and overnight I checked again and all tires were lower still, with the back right tire being below the average and a notification that it had low tire pressure.

I drove it to work (about 24kms) and when I got to work, checked it again, and all tires went back up into the recommended range.

It's been 3.5 hours since I parked it and the tire pressure for both rear tires has gone down to 224 and 228 respectively.

According to my dealer, the tires have nitrogen in them and are covered, but I'm concerned that in less than 24 hours, the tire pressure has depleted so much. Is this normal for tires with nitrogen? Can I expect the tire pressure to increase as i drive it and decrease when it's parked? Is this happening to anyone else? Should I bring it back to my dealer to have them fix it?

Any info you can offer would be great!
Thanks!
 

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Q: Can I expect the tire pressure to increase as i drive it and decrease when it's parked?

A: Yes, this is normal. I always set my tires PSI to 2 pounds OVER what is recommended when they are COLD. I usually check them first thing in the morning and add air as I said.

Then as you drive the tires heat up causing the air to expand and your PSI to increase. Even in the heat of the summer they will only increase another 2 to 4 PSI.

If you follow motor sports you will hear how tire temps affect tire PSI's.
 

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Nitrogen expands and contracts, just not as much as regular air.

Now if they continue to loose pressure over a period of days with similar temperatures then worry.
 

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I did a conversion since I am familiar with PSI. The recommended 38 PSI is equivalent to 262 kPa, 40 psi is equivalent to 276 kPa and I am currently using 45 PSI which is equivalent to 310 kPa. I use higher PSI to get better range and MPG. This may be too high for some to feel comfortable so you can adjust to what you feel comfortable.

I can see 5 PSI difference between a cold tire and a warm tire. Also in winter the pressure will decrease so I will add air to what I want to maintain. Some people in cold climates with snow recommend lower tire pressure to get good grip with snow, so again depending on your needs adjust pressure accordingly.
 

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Your dealer didn't fill your tires to the recommended pressure, fairly typical. You could take it back to them and have them give you some more of that expensive nitrogen, or you can just add some free nitrogen yourself (air is approx. 80% nitrogen). Just another scam by car and tire dealers.

VIN # B0985
 

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I did a conversion since I am familiar with PSI. The recommended 38 PSI is equivalent to 262 kPa, 40 psi is equivalent to 276 kPa and I am currently using 45 PSI which is equivalent to 310 kPa. I use higher PSI to get better range and MPG. This may be too high for some to feel comfortable so you can adjust to what you feel comfortable.

I can see 5 PSI difference between a cold tire and a warm tire. Also in winter the pressure will decrease so I will add air to what I want to maintain. Some people in cold climates with snow recommend lower tire pressure to get good grip with snow, so again depending on your needs adjust pressure accordingly.
Note Gen II Volt recommended pressure is 36PSI. I run mine at 40PSI. Max cold sidewall for Gen II Michelin energy savers are 44PSI.
 

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Discussion Starter #9
Your dealer didn't fill your tires to the recommended pressure, fairly typical. You could take it back to them and have them give you some more of that expensive nitrogen, or you can just add some free nitrogen yourself (air is approx. 80% nitrogen). Just another scam by car and tire dealers.

VIN # B0985
Thanks, I think that's what I'll do. I keep checking and I see the pressure fluctuate for the rear tires from good to low.
 

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It is a normal part of routine car maintenance to need to add some air pressure from time to time. Yours are just a little low. Nothing unusual about that. Check the pressure when the tire is cold (not having been driven for at least 3 hours). Use a quality hand held tire pressure gauge (rather than relying on the TPMS sensors). Add pressure to the recommended level or to some higher pressure as some owners advocate. I have found I need to do this at least several times per year, so I check monthly, and I have the equipment I need at home.

Or you can take it to a service center, but that is time consuming. And as you have just found out, they are often sloppy with this adjustment.
 

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Discussion Starter #11
It is a normal part of routine car maintenance to need to add some air pressure from time to time. Yours are just a little low. Nothing unusual about that. Check the pressure when the tire is cold (not having been driven for at least 3 hours). Use a quality hand held tire pressure gauge (rather than relying on the TPMS sensors). Add pressure to the recommended level or to some higher pressure as some owners advocate. I have found I need to do this at least several times per year, so I check monthly, and I have the equipment I need at home.

Or you can take it to a service center, but that is time consuming. And as you have just found out, they are often sloppy with this adjustment.
Thanks! I think I'm going to get myself a hand held pressure gauge.
 

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I'm not seeing anything in the GM or Onstar app that indicates PSI levels, only kPa levels. I'm getting that these are basically two different ways of measuring the same thing.
If you want to see PSI, you have to put measuring units to Imperial or US instead of Metric. It's under App info on the upper left corner (3 bars) of the Onstar app
 

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Q: Can I expect the tire pressure to increase as i drive it and decrease when it's parked?

A: Yes, this is normal. I always set my tires PSI to 2 pounds OVER what is recommended when they are COLD. I usually check them first thing in the morning and add air as I said.

Then as you drive the tires heat up causing the air to expand and your PSI to increase. Even in the heat of the summer they will only increase another 2 to 4 PSI.

If you follow motor sports you will hear how tire temps affect tire PSI's.
My tires can be the same pressure in the garage and I've noticed while driving that the front tires often increase a lb, maybe two from the increase heat of pulling the vehicle ahead, and I also see the side the sun shines on is often higher.
 

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I have my tires at around 39-40 psi COLD and I'm in Texas, so it may rise up to 4 degrees F. I don't dare keeping it at 45 cold as the potholes would make all my fillings fall off my teeth or make my dashboard creak and crack :)
 

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According to my dealer, the tires have nitrogen in them and are covered, but I'm concerned that in less than 24 hours, the tire pressure has depleted so much. Is this normal for tires with nitrogen? Can I expect the tire pressure to increase as i drive it and decrease when it's parked? Is this happening to anyone else? Should I bring it back to my dealer to have them fix it?

Any info you can offer would be great!
Thanks!
Cold tires should be set at the recommended levels. As the nitrogen molecules inside the tires get squished every rotation, they increase in heat and expand raising the pressure inside the tire. That's NORMAL. The dealer should have pumped your tires up to the recommended level when cold.

During Winter, the ambient temps drop, obviously, and you will need to add air to get the tires up to recommended levels. And, conversely as the temps warm up, you should have to bleed some air to reduce the cold pressures to recommended levels. Of course, some people experience a little air leakage over time, so you may have to add nitrogen.

Some people may find one or two of their tires increasing in pressure more than the others when driving. That's also common, as roads are cambered for water drainage. That slight camber can affect tire wear as well as pressures. The side getting more work, typically the right, would see a greater temp rise. Also, the fronts typically get worked more than the rears, also leading to higher temp rise. That's totally normal.
 

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I find it interesting that some people say to not rely on the TPMS sensor readings. But guess what the Volt will use to indicate the tire pressure is too low? That's right, it will use the TPMS sensors, NOT your hand held pressure gauge. So should you ignore what the TPMS sensors indicate? In my case the TPMS sensor are spot on and agrees with a hand held pressure gauge that I have compared to a instrumentation quality pressure gauge.

VIN # B0985
 

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If your TPMS is accurate then you are ok to go by that. Most people find they are a little off, so a gauge is a little better in general for most people. TPMS has some limitations such as not being able to compensate for altitude, and also temperature effects are a little different. Both methods are way better than the old standby of looking at the tire.
 

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I'm not seeing anything in the GM or Onstar app that indicates PSI levels, only kPa levels. I'm getting that these are basically two different ways of measuring the same thing.
They are American (PSI) and SI (kPa) measures of the same thing. You can change between systems in both the app and on the car.
 

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kPa is just metric system. PSI is Imperial (English) system. Don't worry about a little up and down, that's going to happen with temperature. 228, 248, 270... Especially with a 3 digit gauge. The 3rd digit really isn't significant. Just watch the long term number when cold. New tires can also leak a little when new as the tire bead settles on the rim. I was topping mine off every 2-3 weeks during the first 6 months. Now not so much.

Whether gauge or TPMS, each is probably accurate only to within 1-2 psi, or 10kPA (that's why the third digit in kPA really doesn't matter). My cars TPMS is within 1-2 psi of my digital gauge. And you'll also see differences tire to tire, even if all 4 are actually exactly the same. All normal. Even just parking the car with one side facing the sun can cause (temporarily) one side to read higher than the other.

Gen 2 (Michelin) recommended is 36psi/248kPa, 44psi max cold. Gen 1 (Goodyear) was higher. Many gen 1 owners run higher, including myself (42-44 psi), for longer wear and firmer handling, and yes, longer all-electric range (although I haven't tested that one myself).
 

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Cold tires should be set at the recommended levels. As the nitrogen molecules inside the tires get squished every rotation, they increase in heat and expand raising the pressure inside the tire. That's NORMAL. The dealer should have pumped your tires up to the recommended level when cold.

During Winter, the ambient temps drop, obviously, and you will need to add air to get the tires up to recommended levels. And, conversely as the temps warm up, you should have to bleed some air to reduce the cold pressures to recommended levels. Of course, some people experience a little air leakage over time, so you may have to add nitrogen.

Some people may find one or two of their tires increasing in pressure more than the others when driving. That's also common, as roads are cambered for water drainage. That slight camber can affect tire wear as well as pressures. The side getting more work, typically the right, would see a greater temp rise. Also, the fronts typically get worked more than the rears, also leading to higher temp rise. That's totally normal.
Sorry, that's not where the heat comes from. The pressure in the tire is exactly the same on all parts of the tire and the nitrogen moves around as the tire rolls and doesn't get compressed any differently depending on whether it is on the top of the rotation or the bottom. What causes the heating up is the flexing of the tire itself, which then warms the air in the tire, which increases the pressure (Ideal Gas Law, from your high school physics class.)
 
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