Model 3 Tire Pressure

[TT97]

My door panel says 42 psi, service center just inflated them to 45-46.
I've read through this thread... seems like 42 is comfort, 45-46 is range... I'm taking a long car trip so I guess I should leave them at the 45?

Funny, I like them at 45 yet the service center reduced them to 42.

I also had a mobile service last month to rotate the tires and asked him to have the tires at 45 but said he was required to inflate (or really, deflate) to 42 as the door panel says 42.

 

[EVnut]

I also had a mobile service last month to rotate the tires and asked him to have the tires at 45 but said he was required to inflate (or really, deflate) to 42 as the door panel says 42.

This is just unbelievable. I'm sure you were told this for some nebulous liability reasons. But the door sticker is not the determining factor here! Not only has that sticker varied (on the Model 3 specifically, but on other cars as well), but that pressure is a compromise between safety, handling, customer comfort, tire wear and efficiency. The max allowable pressure for tire safety is clearly printed on the sidewall of every tire. Anything at that pressure or below (though of course not TOO far below!) should be acceptable to any service center.

 

[StealthP3D]

It's worse if you live high above sea level, because then the TPMS is also off for that.... it treats the tire pressure as if it's at sea level and ignores that real tire pressure that is read with a meter at 6,000 feet above sea level.

They could either make TPMS altitude aware by using the car's GPS or they could just lower the pressure warning for those of us who want a more compliant ride and live somewhere above where Venice Beach is.

It's not true that the TPMS treats tire pressure as if it's at sea level. Like all tire pressure gauges, it measures the difference in pressure between the atmospheric pressure and the pressure inside the tire.

If you inspect the TPMS, you will see it has a double barrel which acts as a passageway for the atmospheric pressure to enter the body of the TPMS.

I've found the best grip and cornering performance at pressures a little above the recommended cold PSI of 42. Basically, the best handling of the 18" MXM4's is around 44 PSI cold. Higher pressure will offer more impact protection and protect the rim from damage as well as increase your range. It's OK if the warm tire pressure goes above the 50 PSI maximum pressure while driving because the 50 PSI limit is only for cold tires.

Don't use the TPMS to determine tire pressures, use a couple of gauges that agree with each other and give consistent readings and then you can monitor air/pressure loss with the TPMS if you know what it should read first thing in the morning. Be aware that it will provide the most accurate readings on smooth, level, straight roads but handheld gauges are still more accurate.

Also, don't fret if the TPMS doesn't report the same pressure for every tire, remember, each tire uses a separate measuring device. If you take 4 dial gauges (or digital or pencil) they are also unlikely to all read exactly the same PSI on one tire. That's why it's most accurate to set the pressures using one hand-held tire gauge (so you're using the same gauge for all tires).

 

[ECCtechguy]

Looks like I’ll be taking a trip to service tomorrow this came on when I switched to the TST 18” ugh what a “painless” process

Tsportline has not gotten back to me, maybe once the sale is done we disappear?

 

[Feathermerchan]

Perhaps the TPMS need sensors need activation. You would think TSportline would have done that.

 

[AlanSubie4Life]

It's not true that the TPMS treats tire pressure as if it's at sea level. Like all tire pressure gauges, it measures the difference in pressure between the atmospheric pressure and the pressure inside the tire.

If you inspect the TPMS, you will see it has a double barrel which acts as a passageway for the atmospheric pressure to enter the body of the TPMS.

How certain are you of this? There have been reports, which seem to align with what one would expect, that indicate that absolute pressure is what is measured (the car reads ~2.7PSI lower than an accurate gauge does, at 5000 feet, is the specific report, which suggests that the car might be subtracting a constant 14.7PSI).

I'd be a little surprised by an alternate path, as that would be a potential leak path. And exposure to atmospheric would depend on the quality of the seal on the valve stem cap I would think (though usually I would expect it to equalize to atmospheric...).

But, I have no idea, and I always take what I read on this forum with a grain of salt. I have not been able to find definitive information elsewhere.

 

[StealthP3D]

How certain are you of this?

Fairly certain. Otherwise, there would be no reason to have two barrels on the valve stem.

 

[AlanSubie4Life]

Fairly certain. Otherwise, there would be no reason to have two barrels on the valve stem.

Ok! Mysterious. I do wonder if something is wrong with @voip-ninja 's sensors then. Intriguing; it's nearly as interesting as vampire drain.

FWIW, I run 45PSI cold in my PS4S. I get 270Wh/mi driving efficiency on my daily 20-mi roundtrip commute (500 feet net elevation gain on the way home, about 800 ft cumulative), and the expected wall-to-wheel efficiency of 380Wh/mi, for that same 270Wh/mi driving efficiency (40Wh/mi charging losses, 70Wh/mi standby losses (which breaks down into 10 Wh/mi charging loss, 60Wh/mi from battery)). Sweet. When I went from 42 to 45PSI in my crappy 20" wheels, perhaps the efficiency improved a bit, but at most 10-15Wh/mi. One of these days I should do a careful controlled experiment I suppose.

 

[Feathermerchan]

I also went from 42 to 45 psi and have seen an improvement of efficiency.

 

[TT97]

This is just unbelievable. I'm sure you were told this for some nebulous liability reasons. But the door sticker is not the determining factor here! Not only has that sticker varied (on the Model 3 specifically, but on other cars as well), but that pressure is a compromise between safety, handling, customer comfort, tire wear and efficiency. The max allowable pressure for tire safety is clearly printed on the sidewall of every tire. Anything at that pressure or below (though of course not TOO far below!) should be acceptable to any service center.

Yes, he even stated it was for liability reasons. I did mention the earlier 3s had 45 psi on the door jamb but to no avail. He was very friendly and knowledgeable and I could tell he wasn't thrilled with having to inflate to 42 psi when I preferred 45 psi so I didn't push the matter and just inflated them back up as soon as he left.

 

[AlanSubie4Life]

Fairly certain. Otherwise, there would be no reason to have two barrels on the valve stem.

Checked three of my cars with TPMS. I guess I see what you are saying about the separate gap on the outside of the valve stem, but one of my cars with TPMS just has a regular looking rubber valve stem (the Chevy Spark EV). Only the metal stems have the outer gap; I suspect it is a feature of how those metal stems are assembled. It seems like that other gap could get filled with junk too, submerged in water, etc. I really can’t see it as a path to the inside pressure, separated only by a differential sensing element that would allow water/moisture ingress into the sensing cavity - and an easy leak path if the extremely fragile MEMS membrane were damaged. But who knows?

Seems easier to just make a MEMS membrane, make it hermetically sealed behind the membrane, and then just calibrate it at the factory to read absolute pressure accurately.

Someone who has worked in a tire shop could probably set the record straight easily.

 

[StealthP3D]

Someone who has worked in a tire shop could probably set the record straight easily.

Well, if you learn anything, let us know.

 

[gilscales]

Just from my limited experience, with the 19" stock Continental tire you would have to run approx. 39 to 49 psi. to get even tread wear across the tire, running at 45 psi. would wear out the center section early due to over inflation unless you carried the max load everywhere you went.

 

[StealthP3D]

Just from my limited experience, with the 19" stock Continental tire you would have to run approx. 39 to 49 psi. to get even tread wear across the tire, running at 45 psi. would wear out the center section early due to over inflation unless you carried the max load everywhere you went.

But 45 is between 39 and 49!

 

[MacGreiner]

Don't use the TPMS to determine tire pressures, use a couple of gauges that agree with each other and give consistent readings and then you can monitor air/pressure loss with the TPMS if you know what it should read first thing in the morning. Be aware that it will provide the most accurate readings on smooth, level, straight roads but handheld gauges are still more accurate.

Which is exactly the reason why the TPMS low pressure alarm should not be set to such a high trigger threshold for those of us who drive through cold winters. The temp differential from cold PSI to driving temp PSI can be +5 PSI going on TPMS readings.

 

[StealthP3D]

Which is exactly the reason why the TPMS low pressure alarm should not be set to such a high trigger threshold for those of us who drive through cold winters. The temp differential from cold PSI to driving temp PSI can be +5 PSI going on TPMS readings.

You have a fundamental misunderstanding of the manufacturer's recommended tire pressures.

The tire pressure should never be below the recommended PSI no matter how cold it gets. That's why it's called "COLD" PSI and also why alert drivers add air to their tires to compensate for a big temperature drop before the alarm goes off.

If your TPMS alarm is going off it means you need to add air. I'm shocked at how many people think "soft" is good. In my experience, even the cold PSI recommendation on the door pillar is too low for sporty driving or safe evasive maneuvers. People who understand how their car responds typically go above the "comfort" recommendation of 42 PSI.

Those who run their tires on the soft side experience a greater incidence of bent rims, flat tires and uneven treadwear. But at least their tushy will feel lush.

 

[TT97]

Just from my limited experience, with the 19" stock Continental tire you would have to run approx. 39 to 49 psi. to get even tread wear across the tire, running at 45 psi. would wear out the center section early due to over inflation unless you carried the max load everywhere you went.

Mine at 45 psi have been wearing evenly, and I would appreciate no fat jokes.

If it ever stops raining in L.A., I will do a chalk test to check for sure.

 

[StealthP3D]

Mine at 45 psi have been wearing evenly, and I would appreciate no fat jokes.

If it ever stops raining in L.A., I will do a chalk test to check for sure.

It's important to note that the chalk test tells you as much about the PSI you were running previous to the application of chalk as it does about your new PSI. In other words, the chalk test is commonly misused and of limited value.

 

[gilscales]

Mine at 45 psi have been wearing evenly, and I would appreciate no fat jokes.

I would never tell a fat joke to you, you must have enough on your plate as it is.........rim shot

 

[gilscales]

Sorry about the typo on my post but it should read 39 to 40 psi, I have been running 42, at times before I adjust air it gets down to 40 psi and after measuring my tread I am still slightly lower (not by very much) in the center which suggests to me a slight over inflation condition, I have run a lot of my 17k plus miles loaded down with extra people and or luggage but most is with 1 or 2 people in t he car.