Model 3 TPMS sensors are junk

[mongo]

Tires aren't particularly flexible, and their volume changes very little with changes in pressure. I don't see how the balloon analogy works here.

That vid showed the impact of differential pressure.
Denver is 12 psi ambient vs 14.7 at sea level. 2.7 over pressure psi due to altitude is the same as 2.7 psi over at sea level due to over inflation.

The tire contact patch size is highly dependent on the load on the tire and the tire pressure. 35 psi differential vs 33.3 psi differential is a 5% change in contact area needed to support the same weight. It also impacts the contact shape, higher pressure puts more load in the middle of the tread, lower pressure puts more force on the outer edges/ sidewall effects.

Also, I think you are absolutely correct that the warning shouldn't kick in so close to the recommended pressure.

That's part of the issue, due to lack of altitude compensation, the warning kicks in 2.7 psi too soon.

I normally start at the manufacturer's recommendation and then adjust from there for best wear. In the last 20 years or so, that pretty much always has meant running a pressure a bit lower than that recommended by the manufacturer.

Tire pressure placards are based on max GVWR, which explains why you get better results at slightly lower air pressure.
https://www.safercar.gov/Vehicle-Shoppers/Tires-Rating/General-Information

It would be nice if someone knew how to calculate this, but it's probably a pretty specialized area of knowledge.

What calculation are you referring to?

 

[Eno Deb]

You have it easy, you're at sea level
If all 4 sensors read the same on the display, and on the handheld gauge (even if different than the gauge), the issue is the car software is not applying the correct altitude ambient air pressure compensation. TPMS sensors only deal in absolute pressure.

Well, strictly speaking the reading produced by the TPMS is also relative to something. While in science PSI is defined relative to vacuum, the sensor reading can be relative to any pressure that the sensor manufacturer chooses. As @voip-ninja correctly pointed out, it is up to the controller in the car to convert the sensor reading into a value relative to the ambient pressure (which is also what pressure gauges show). The ambient pressure can be calculated from the GPS altitude, or measured by using an additional pressure sensor that is exposed to the outside air. Apparently Tesla simply always uses 14.7 PSI.

 

[GregD60]

What calculation are you referring to?

How much the outside air pressure affects the load carrying ability and the contact patch shape of the tire versus the pressure exerted on the tire by the vehicle itself.

 

[CUBldr97]

Ya, the issue here is altitude. Looks like the Tesla isn't compensating for the lower air pressure vs. the TPMS absolute pressure readings.

You need to get the service guys at a Tesla service center to escalate the problem to engineering. It will have to be fixed in software. There's nothing the TPMS modules or TPMS system can do about it.

For those who may not be familiar with what's happening, the problem arises because tire pressures are specified as a relative pressure -- i.e. a differential pressure between the air inside the tire and the air outside. The standard tire pressure gauge measures exactly this, using the air from the tire through the valve stem, and the air outside.

However, TPMS modules have no source for the outside air. So they have to measure an absolute pressure using an internal reference. The internal reference is calibrated to sea level.

So, let's say we have a tire inflated to 45 psig (psi by gauge) at sea level. 45 psi is the difference between the absolute pressure inside the tire (59.7 psia) and the absolute pressure outside the tire (14.7 psia -- atmospheric pressure at sea level).

Now we drive to 10,000 feet elevation. Up here, the atmospheric absolute pressure is 10.1 psia. Assuming the tire has no leaks, the inside air pressure is still 59.7 psia, resulting in a tire gauge pressure reading of 59.7-10.1 = 49.6 psig. The tires are now overinflated, so you need to reduce air pressure. But the TPMS module still reads 45 psi because the inside air pressure of 59.7 psia is still exactly 45 psi over the TPMS sensor's internal reference of sea level pressure (14.7 psia).

So you drop the tire pressure back to 45 psig by the tire pressure gauge, resulting in an internal tire pressure of 55.1 psia. Now the gauge reads 55.1-10.1 = 45 psig which is perfect. But TPMS now says the tire is at 55.1-14.7 = 40.4 psig and you're close to setting off the low pressure alarm.

Telsa needs to compensate by using the map, looking up the elevation, then looking up the expected atmospheric pressure at that altitude, find the difference between that pressure and sea level pressure, and then add that offset to the TPMS readings before displaying the value and before comparing the reading with the alarm threshold. This will result in TPMS readings that are very close to the gauge pressure.

So whats different with the S and X that have been at altitude for the past 5 years, as compared to the 3?

 

[voip-ninja]

So whats different with the S and X that have been at altitude for the past 5 years, as compared to the 3?

This is apparently a known issue on S/X as well, per this thread. It might be that on those cars Tesla have just set the warnings lower so it's not annoying as many owners when the TPMS readings are off.

tire pressure monitoring sensors | Tesla

 

[GregD60]

This is apparently a known issue on S/X as well, per this thread. It might be that on those cars Tesla have just set the warnings lower so it's not annoying as many owners when the TPMS readings are off.

tire pressure monitoring sensors | Tesla

Also, did the S or X have their recommended tire pressures lowered after their initial introduction, or have Elon Musk recommend a lower inflation pressure? At the original 45 PSI recommended pressure for a model 3, having the warning come on at 38 PSI doesn't sound too unreasonable, but with the current recommended pressure of 42 PSI and Elon's suggestion of 39 PSI, a 38 PSI warning threshold doesn't seem so appropriate.

 

[voip-ninja]

Also, did the S or X have their recommended tire pressures lowered after their initial introduction, or have Elon Musk recommend a lower inflation pressure? At the original 45 PSI recommended pressure for a model 3, having the warning come on at 38 PSI doesn't sound too unreasonable, but with the current recommended pressure of 42 PSI and Elon's suggestion of 39 PSI, a 38 PSI warning threshold doesn't seem so appropriate.

The problem is compounded by the car being oblivious to altitude differences.

So, Elon musk says if you want your Model 3 to have a nice comfortable ride set the tire pressure at 39 psi. You do this at altitude (I'm at over 6,000 feet) and the car reads it as 36 psi and throws an alarm.

Either lowering the alarm threshold or fixing the car so it adjusts from a fixed PSI value for TPMS to one based on elevation would alleviate the issue....

 

[GregD60]

The problem is compounded by the car being oblivious to altitude differences.

So, Elon musk says if you want your Model 3 to have a nice comfortable ride set the tire pressure at 39 psi. You do this at altitude (I'm at over 6,000 feet) and the car reads it as 36 psi and throws an alarm.

Either lowering the alarm threshold or fixing the car so it adjusts from a fixed PSI value for TPMS to one based on elevation would alleviate the issue....

So, how do we get someone at Tesla to do this? Anyone have Elon's ear? It seems that when he talks, people at Tesla listen. This should be such an easy change to make in the programming.

 

[voip-ninja]

So, how do we get someone at Tesla to do this? Anyone have Elon's ear? It seems that when he talks, people at Tesla listen. This should be such an easy change to make in the programming.

LOL good luck.

It's not a problem for most people and nobody for who it is a problem has any influence.

Someone proved to the Broadway service center in CO that this problem existed and simply got refuted that most of the gauges used to measure tire pressure aren't accurate.

 

[GoodOmens]

Don't TPMS sensors recalibrate when they are reset? I think filling the tires to 45PSI and having a tireshop reset/relearn all the sensors should have them recalibrated for the proper altitude. If you can get a hold of a TPMS diagnostics tool you might be able to try yourself.

Tesla's auto learn sensors so it's further possible a rotation might trigger the sensors to recalibrate.

 

[nvx1977]

So, how do we get someone at Tesla to do this? Anyone have Elon's ear? It seems that when he talks, people at Tesla listen. This should be such an easy change to make in the programming.

when I contact Tesla via the form (with escalate for executive review), I tell them to pass my feedback to their Product Design / UX team. Then I explain the problem. This issue needs to reach their software development arm. A service center will be able to do nothing about this.

Not every time, but several times, the rep that responds will acknowledge that they've passed the feedback to their dev/design teams.

 

[Eno Deb]

OK, this is getting ridiculous. Note that the recommended pressure according to the door tag on my car is 42 PSI ...

 

[Buzd]

I am in Colorado as well. My tpms shows 40psi and my $100 tire gauge shows 44psi. Optimum ride and handling is in the 32-35psi range for these cars...wish Tesla would set the warning threshold lower and let owners choose whether performance/ride or hypermiling are more important to us. I have submitted complaints to Tesla online and at a service center.

 

[FloridaGary]

I am in Colorado as well. My tpms shows 40psi and my $100 tire gauge shows 44psi. Optimum ride and handling is in the 32-35psi range for these cars...wish Tesla would set the warning threshold lower and let owners choose whether performance/ride or hypermiling are more important to us. I have submitted complaints to Tesla online and at a service center.

Out of curiosity, do you have any data that you can share to support 32-35 psi for the Model 3? That is significantly different from the 42 psi Tesla recommends.

 

[mswlogo]

Out of curiosity, do you have any data that you can share to support 32-35 psi for the Model 3? That is significantly different from the 42 psi Tesla recommends.

I think he’s right and I agree. Tesla pushes the pressure a bit for efficiency.

Look at any car with similar weight and tires and they will be in the range he suggested.

I agree also that the warning range is to high.

BTW I think part of the warning detection is a sudden drop in pressure. I partly wonder if I left the pressure low, it would eventually accept it. I didn’t try very hard.

 

[dhrivnak]

Mine are working fine and yes they show low pressure warnings when in fact the pressure is low. That is just what I want them to do.

 

[Jetstreamsky]

It would help a lot of warning messages were fully dismissable for the trip, yes you can get it down to a small black circle on the left, but when any other message appears it comes back across the bottom again. An acknowledge low critical warning should remain muted unless a new condition occurs, that's how it works in aviation.

 

[dhanson865]

Since I'm still getting alarms at 45 psi I will have to go even higher, 47-49 psi just to get the idiot alarms to clear. It seems as though the sensors aren't reading very well at lower temperatures, so I'm supposed to drive around on rock hard balloons all winter because Tesla thinks we need cockpit warnings over what it thinks is 40psi but is really 45 psi. It's just sad.... at a minimum let me lower the warning to something a little more sane like 32-35 psi or something like that. It's not like I'm going to damage the car or the tires running them at 42 psi.

all these posts and you don't say what temperatures these PSIs correspond to.

42 PSI at 20F is totally different than setting a tire to 42 PSI at 50F in a garage or 42 PSI when tires are warm from driving.

Are you using your Accu-gage when the tires are cold, really cold and adjusting the PSI by 1 per approximately 10 degrees F between the temp you set them at and the coldest time of the day?

As in if the low is 10F and you want to put air in the tires in the afternoon after sleeping in and its now 40F you have to pump your tires to 45PSI at 40F to get 42PSI at 10F.

Door jamb label, owners manual, sidewall rating, TMPS warning are all based on the PSI at the coldest possible temperature you'll face in your normal travels not the current temperature, not the average temperature, not the high temperature, but the coldest temperature and only the cold temperature. Any discussion of tire pressure should have offsets for temperature and/or a temperature for each PSI mentioned.

 

[Knightshade]

OK, this is getting ridiculous. Note that the recommended pressure according to the door tag on my car is 42 PSI ...

Heh- at least it's reporting ALL your 40s as low.... I've had it report "low" from only a couple of wheels despite them all being displayed at the same PSI when it's cold (and I've had it report that at 39, 40, and 41 all at different times too).

I dunno if the sensors are crap, but the programming sure is.

 

[voip-ninja]

all these posts and you don't say what temperatures these PSIs correspond to.

42 PSI at 20F is totally different than setting a tire to 42 PSI at 50F in a garage or 42 PSI when tires are warm from driving.

Are you using your Accu-gage when the tires are cold, really cold and adjusting the PSI by 1 per approximately 10 degrees F between the temp you set them at and the coldest time of the day?

As in if the low is 10F and you want to put air in the tires in the afternoon after sleeping in and its now 40F you have to pump your tires to 45PSI at 40F to get 42PSI at 10F.

Door jamb label, owners manual, sidewall rating, TMPS warning are all based on the PSI at the coldest possible temperature you'll face in your normal travels not the current temperature, not the average temperature, not the high temperature, but the coldest temperature and only the cold temperature. Any discussion of tire pressure should have offsets for temperature and/or a temperature for each PSI mentioned.

What's your source that the manufacturer recommended tire pressure is based on "coldest temperatures you will encounter"?

Anyone who has been driving for any length of time (I've been driving for 30+ years) knows that PSI is affected by temperature. I routinely adjust inflation levels on all of my vehicles in the fall when night-time temperatures start to dip close to freezing.

The issue here is not an ignorant owner as you've implied. The issue is that Tesla has provided an incredibly narrow margin in PSI range before the sensors alarm. That is proven with photos of tires that are within 2-3 PSI of Tesla's recommended tire pressure level still alarming. That is ridiculous and Tesla needs to fix it but good luck getting them to even acknowledge that it is an issue.

As big or bigger problem is Tesla not accounting for atmospheric pressure differences at altitude which forces those of us who live at higher altitudes to over-inflate the tires to prevent them from alarming in the first place.

How you and other people don't get this part is a mystery to me.