Tire Pressure system accuracy

[dweeks]

Does anyone know the required accuracy of the tire pressure system?

On my late 2017 S100D, the the car shows all tires consistently 3-5 PSI below the pressure shown on two different handheld gauges. When I inflate to the recommended 45 PSI cold pressure using the handheld gauge, the car shows 42-41 PSI.

So, any pressure drop in the tires will make the car think the pressure is below 40, and that give the low pressure warning. But the real pressure is still well above 40.

Is this adjustable by a service center, or need it be replaced under warranty?

 

[Bill Price]

Does anyone know the required accuracy of the tire pressure system?

On my late 2017 S100D, the the car shows all tires consistently 3-5 PSI below the pressure shown on two different handheld gauges. When I inflate to the recommended 45 PSI cold pressure using the handheld gauge, the car shows 42-41 PSI.

So, any pressure drop in the tires will make the car think the pressure is below 40, and that give the low pressure warning. But the real pressure is still well above 40.

Is this adjustable by a service center, or need it be replaced under warranty?

On my 2018 SP100D, I inflate the tires with this...........Digital Tire Inflating Gun - Griot's Garage

The car always shows the exact same pressure as the gauge.

 

[dweeks]

On my 2018 SP100D, I inflate the tires with this...........Digital Tire Inflating Gun - Griot's Garage

The car always shows the exact same pressure as the gauge.

Well, that tells me your TPMS sensors are more accurate than mine...

 

[jerry33]

My good Longacre gauge shows approximately the same pressures as the display. However, what you want in the display is consistency. If it happens to differ from a known-to-be-accurate gauge, that's okay as long as it's consistent and you know the difference. A $20 gauge is not likely to qualify as a known-to-be-accurate gauge--regardless of the reviews you might see.

BTW. If the comparing is done incorrectly--driving for a bit and then checking the handheld gauge--the warm tires can increase the pressure very rapidly after stopping. The correct method is to inflate the tires, and then check shortly after driving. (I'm sure you know this, but just in case.)

 

[dweeks]

All good points. But recall my frustration is that the correct inflation pressure of 45 from the handheld gauge shows just over 40 from the car sensors, so with normal pressure drops the car thinks the pressure is below 40 and I get what are really false low pressure warnings.

 

[jerry33]

All good points. But recall my frustration is that the correct inflation pressure of 45 from the handheld gauge shows just over 40 from the car sensors, so with normal pressure drops the car thinks the pressure is below 40 and I get what are really false low pressure warnings.

Recommended pressures are a set of assumptions based on some standards and what the engineers think the conditions the car is going to be driven in--with input from marketing. Change any of the assumptions as you get a different pressure recommendation.

A standard assumption is that the temperature is 18C (65F) first thing in the morning when you check. If it's warmer than that, pressures should be increased.

Assumptions that the engineers make involve speed (presumably Tesla targets the high end) and the normal load expected (often for cars just one person, rather than GVW).

Marketing input is often "please lower pressures for ride quality".

Most people drive backwards. That is they use the speed limit as the minimum they should be going and the tire pressure recommendation as some kind of maximum that can't be exceeded. I like to think of the tire pressure recommendation as the pressure that you never ever want to go below except in special circumstances. (Unless you're into buying cheapo tires, then you're on your own, because tires are not the place to go cheap).

 

[Bill Price]

Well, that tells me your TPMS sensors are more accurate than mine...

No....what that should tell you is that the TPMS sensors on my car agree EXACTLY with what that particular gauge reads, which is a good thing of course. I ALWAYS set the pressure in my car's tires to 45 psi when the tires are cold. That is to say, when the car has been sitting for several hours. The only caveat to this is if it is EXTREMELY cold. I may set the pressure to 46 in that case because if it's zero or below outside, I know the pressure will decrease as the temperature of the tires decrease.

 

[jerry33]

No....what that should tell you is that the TPMS sensors on my car agree EXACTLY with what that particular gauge reads, which is a good thing of course. I ALWAYS set the pressure in my car's tires to 45 psi when the tires are cold. That is to say, when the car has been sitting for several hours. The only caveat to this is if it is EXTREMELY cold. I may set the pressure to 46 in that case because if it's zero or below outside, I know the pressure will decrease as the temperature of the tires decrease.

It's going to take a lot more than one psi to make up the difference.

 

[dark cloud]

Well, that tells me your TPMS sensors are more accurate than mine...

I think it is more likely both of your handheld gauges are off by the same amount, than your TPMS system being out.

If you are really curious yet cheap drive to at least 2 different tire stores and ask to use their most accurate gauge and compare against your car readings.

 

[animorph]

There was a thread discussing apparent TPMS problems with altitude differences. TPMS was OK at sea level but off at high altitudes. It seemed to them that TPMS was using an absolute pressure reference rather than an external relative pressure. If you are in Flagstaff that would definitely apply to you. I didn't follow it long enough to see if there was a resolution.

ETA:
Model 3 Tire Pressure

Model 3 TPMS sensors are junk

 

[Barry]

On my late 2017 S100D, the the car shows all tires consistently 3-5 PSI below the pressure shown on two different handheld gauges.

The answer is:
ELEVATION ABOVE SEA LEVEL

When I got my car, it was spot on. When I got new tires and re calibrated in Denver, it consistently reads 3 PSI low. TPMS sensors have no external reference. There's a full explanation somewhere on tirerack.com

I just add 3 psi whenever I want to know the real pressure. If it really bothers you, drive to sea level and recalibrate.