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Discussion Starter #1
FWIW, the TPMS is a wonderful system forced upon us. Sometimes the guvmint does right by its citizens.

I've noticed the Bolt has lost 10%+ of air pressure over the three months we've owned it from 38 down to 34. A couple of my other cars with TPMS haven't lost any during that same span.

Anyone else noticing the Bolt new tires/wheels losing air pressure?

jack vines
 

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It's probably worth noting here that all cars (at least in the northern hemisphere) loose some tire pressure in the fall as the temperatures drop, and they gain pressure in the spring as the temperatures rise. Where I live in Vancouver BC it's quite normal for there to be a change in pressure of around 3 to 4 psi between the summer and the winter.
 

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I was under the impression that all rubber tires lose pressure over time. Hence the need for me to check the pressure on my bicycles after not being ridden for a while; hence the need for me to check the pressure on my motorcycle weekly; hence the need for TPMS. In my experience a 10% drop over 3 months is within the bell curve of normal, without the need to invoke seasonal temperature changes which also have an obvious effect. YPMV!
 

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I was under the impression that all rubber tires lose pressure over time. Hence the need for me to check the pressure on my bicycles after not being ridden for a while; hence the need for me to check the pressure on my motorcycle weekly; hence the need for TPMS. In my experience a 10% drop over 3 months is within the bell curve of normal, without the need to invoke seasonal temperature changes which also have an obvious effect. YPMV!
It is quite normal for car tires to lose up to 2 psi a month.

Bicycle tires will lose more than that just due to a lower actual volume and the tubes are thinner thus slightly more permeable, it is still a good example though.

So on top of temperature changes causing tire pressure to raise and lower tires just lose a little air over time.
 

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Losing pressure that rapidly is not normal on any vehicle I've owned. I'd find a leak somewhere if it dropped 2 PSI per month.

I check tire pressure twice per year; once in the winter to add pressure due to the cold, and once in the summer, but normally don't need to add or remove any air.
 

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In my experience, losing 2 psi in any one month is understandable. Losing that much month after month is very unusual. Unless the valve is defective, tubeless tires will lose air VERY slowly. "Puncture proof" tires have two layers of rubber with a liquid polymer layer between. This polymer is activated by air after a nail has gone both in and out, sealing the leak. In these tires, would losing 2 psi for any reason other than a moderate (not minor) temperature change be unusual? Should we not see a different pattern in the tires we have purchased with our Bolts?
 

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Losing pressure that rapidly is not normal on any vehicle I've owned. I'd find a leak somewhere if it dropped 2 PSI per month.

I check tire pressure twice per year; once in the winter to add pressure due to the cold, and once in the summer, but normally don't need to add or remove any air.
Losing 2 psi within a month is not fast. I've had my Bolt 8 months now and I have had to put a little air in two times so far. Pretty much about the same behavior as I have seen in all the other cars I have had. You will also notice I said up to 2 psi a month, doesn't mean they absolutely will lose that much a month. There is nothing special about the tires on the Bolt that are going to stop osmosis. Air will escape out of the tire (even with the puncture lining) no matter what. There are no non-permeable rubbers suitable for tires that I know of, which is what would be required to prevent air from slowly escaping.

If you are seeing more than 2 psi a month, then yeah you probably have a slow leak or valve issue.

Beyond that osmosis is going to let a little air out. How fast that occurs is highly dependent on where you live and what is used to inflate your tires. Nitrogen will leak slower than air, about 30% slower, because it is a larger molecule.
 

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Had the same problem, with nitrogen. Only the dead of winter (and a roofing nail) ever caused my Cherokee tires (no nitrogen) to lose pressure over three years. Took it to the dealer, suspecting TPMS was malfunctioning. Dealer said no error codes. Deflated and re-inflated the tires to 38 psi. Three mornings later all four were back down to 34. Bumped up to 37 if I did much highway driving.

Unless one tire plummets, I've decided to ignore the situation. It is what it is.

I did notice that the Cherokee dealership always inflated to 39 psi, even though the door sticker said 33. Was it their way of dealing with TPMS anxiety?
 

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Discussion Starter #9
FWIW, the vehicle which isn't losing any pressure over the same time span has 265/65-18s, which have a considerably greater air volume than that of the tires on the Bolt. Thus same volume loss would result in a greater pressure drop on the Bolt.

jack vines
 

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If the temperature is dropping, yes. Otherwise I agree with the other posters who have never seen that kind of pressure loss outside of having a slow leak.
You guys can't stop osmosis from being real just because you think you haven't seen it happen. There isn't a car tire on the road that stops osmosis. If you can invent one that does and it still retains all the favorable properties of current tires, well you will be a very rich person.

If you will notice what I typed it says lose UP to 2 psi per month. Not that you absolutely will. You could lose .5 psi one month and .25 psi the next and none the next. It is highly dependent upon weather conditions, temperature, humidity and the tires exact composition.
 

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Here is current TPMS on the right in a 7x7 mm package and the new one my company is releasing soon in a 4x4 mm package. That is a huge reduction in die size to shrink the package that much. We have very incredible equipment that we use to test these before sending them to the OEMs. Thought you guys would enjoy what you don't get to see.
 

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^ Are the sensor modules made here in the USA Steve or overseas?
 

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The silicon wafers are made in the US. Probe testing and die bond and packaging are done overseas. Final test and distribution are done in US.
 

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The final package units that the sensors go in I am not sure. By the way I grew up on LI and my brother still lives there.
 

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If you will notice what I typed it says lose UP to 2 psi per month. Not that you absolutely will. You could lose .5 psi one month and .25 psi the next and none the next. It is highly dependent upon weather conditions, temperature, humidity and the tires exact composition.
Hey, all I can tell you is that I have never seen a 2psi drop in pressure that wasn't temperature related unless the tire had a slow leak. I would definitely NOT consider a 2psi pressure drop to be "normal".
 

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Hey, all I can tell you is that I have never seen a 2psi drop in pressure that wasn't temperature related unless the tire had a slow leak. I would definitely NOT consider a 2psi pressure drop to be "normal".
Yes, you may not have seen it. Your own observations doesn't negate the science though. As I said, how much air you lose in a tire due to osmosis is highly dependent on the conditions you are in, the exact composition of your tires and the conditions those tires are in.

One thing to consider is that because of how the average temperatures go throughout the year any lose of air during the spring and summer can easily be offset by the rise in temperature. Without going to in depth and doing all the math the general rule of thumb is that for every 10 degrees of change in temperature the pressure in your tire will change by 1 psi, up for higher temp and down for lower. This is ambient temperature of the air in the tire of course, not taking into account temperature changes based on tires being used on hot or cold surfaces or any heat generated from friction and other sources.

So if you had one set of tires you put at 30 psi and they were sitting in a room at 65 degrees and you then moved them outside into 85 degree heat once the temperature of the air in the tire equalized to the outside environment you would see the pressure rise to about 32 psi.

Point being is that during the spring and early summer you will be losing air but since the ambient temperature is higher the pressure increase offsets that loss in air so you don't ever see from pressure measurements that you are losing any air.

Real world example. I park in my garage at home each night. After I plugged my car in to charge I checked to see how long it would take to charge and saw my tire pressure to be reported at 38 psi for all four tires. This morning when I got in my car to go I saw the tire pressure was showing as 35 psi for all four tires. I wasn't concerned of course because I know the 3 psi difference was due to temperature changes. Temps went down to the mid 60s last night, down about 20 degrees from the high. Granted it is probably about time to top back up to 38 psi in the garage but being within three is perfectly fine so nothing to be concerned about so i'll top them off later.

When I top the tires off back at 38 psi tomorrow or later this week it will be the second time I have put air in the tires this year, last time I did it back in June they were around 34 psi each. So between February when I got the car and June they lost about 4 psi making it about 1 psi a month. Now it is three months later and they are down 3 psi, another 1 psi per month. So far I am pretty consistently seeing 1 psi loss per month, not bad really. It is pretty easy for me to get consistent measurements throughout the year though. My garage slab is part of my foundation so it stays within a pretty consistent temperature band and with my car sitting on it all night gives it plenty of time to equalize temperature within the tire.
 
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