[Boxdur-S]

My apologies if this has already been covered before. My manual tire pressure gauge shows 33 pounds for all 4 tires, but the car display shows 33 and 35 pounds. Not sure why that is.
Has anyone else had this experience?

Dan

 

[GTS]

Yes. My car is similar. I have a high quality tire pressure gauge, so I tend to trust it over the car.

 

[duegatti]

I believe the system is fundamentally set up to report to a tenth of a bar. Here are some relevant pressures:

psi	bar	rounded
33	2.275	2.3
34	2.344	2.3
35	2.413	2.4
36	2.482	2.5
37	2.551	2.6
38	2.62	2.6

I never see my car report pressures of 34 or 37 pounds - because they are "covered" by rounded pressures of 2.3 and 2.6 bar, respectively. Since 0.1 bar is more than a psi, we effectively lose resolution in our units.

I wouldn't expect either the car or a gauge to be perfect. A good hand held gauge may be accurate to 1% of its full range, say 0.01 x 60 = 0.6 lb. But I will admit that my car does agree with what I believe to be my most accurate gauge.

One explanation for you observations would be that the true pressure in your tires is in the vicinity of 2.350 bar, let's say. A tire that is just slightly on the low side would then read 33 psi on the car, and one that is just slightly higher would be reported as 35. 34 is skipped.

2.35 bar is 34.08 psi. Your gauge would need to be reading 1.1 pounds low - which I think is a very common level of gauge accuracy.

 

[Boxdur-S]

My apologies if this has already been covered before. My manual tire pressure gauge shows 33 pounds for all 4 tires, but the car display shows 33 and 35 pounds. Not sure why that is.
Has anyone else had this experience?

Dan

I believe the system is fundamentally set up to report to a tenth of a bar. Here are some relevant pressures:

psi	bar	rounded
33	2.275	2.3
34	2.344	2.3
35	2.413	2.4
36	2.482	2.5
37	2.551	2.6
38	2.62	2.6

I never see my car report pressures of 34 or 37 pounds - because they are "covered" by rounded pressures of 2.3 and 2.6 bar, respectively. Since 0.1 bar is more than a psi, we effectively lose resolution in our units.

I wouldn't expect either the car or a gauge to be perfect. A good hand held gauge may be accurate to 1% of its full range, say 0.01 x 60 = 0.6 lb. But I will admit that my car does agree with what I believe to be my most accurate gauge.

One explanation for you observations would be that the true pressure in your tires is in the vicinity of 2.350 bar, let's say. A tire that is just slightly on the low side would then read 33 psi on the car, and one that is just slightly higher would be reported as 35. 34 is skipped.

2.35 bar is 34.08 psi. Your gauge would need to be reading 1.1 pounds low - which I think is a very common level of gauge accuracy.

Thank you, this is helpful!

Dan

 

[sevencyclist]

I believe the system is fundamentally set up to report to a tenth of a bar. Here are some relevant pressures:

psi	bar	rounded
33	2.275	2.3
34	2.344	2.3
35	2.413	2.4
36	2.482	2.5
37	2.551	2.6
38	2.62	2.6

I never see my car report pressures of 34 or 37 pounds - because they are "covered" by rounded pressures of 2.3 and 2.6 bar, respectively. Since 0.1 bar is more than a psi, we effectively lose resolution in our units.

I wouldn't expect either the car or a gauge to be perfect. A good hand held gauge may be accurate to 1% of its full range, say 0.01 x 60 = 0.6 lb. But I will admit that my car does agree with what I believe to be my most accurate gauge.

One explanation for you observations would be that the true pressure in your tires is in the vicinity of 2.350 bar, let's say. A tire that is just slightly on the low side would then read 33 psi on the car, and one that is just slightly higher would be reported as 35. 34 is skipped.

2.35 bar is 34.08 psi. Your gauge would need to be reading 1.1 pounds low - which I think is a very common level of gauge accuracy.

This is great. Thank you!

 

[jimmuller]

FWIW, my car w/20" wheels does the same thing. Sometimes a tire will read 1psi higher or lower than the others. I don't worry about that small a variation.

 

[Naptown]

If you park with one side in the sun those pressures will read higher after a while. I ignore it since it goes away. I check the car's display, looking for consistent changes rather than anything else. Cold they have been 35# since I picked up the car in May and haven't changed cold (Michelin PS4s on 20" wheels). They go up when I drive, maybe to 38 depending on how I drive.

 

[roundtail]

A question in a bit of a different direction on this subject: How much do we even need TPMS?

Most of us drove for decades before the little gizmos were invented. Are they a sales gimmick, I wonder, that started as a nice option only to become standard? Or are they essential for the track?

The reason I ask is that my experience with low-profile radials is that they have basically two modes, okay and spectacularly failed, lol. The old creeping, slow bead leaks of the past seem to have largely been eliminated. But then, I’m not tracking, so I wonder if that’s where they help most.

 

[DPC]

I like having the TPMS because, not having a spare, I feel I can get a heads up on a slow leak from a nail. And then maybe being to save the tire.

 

[antennahead]

I like having the TPMS because, not having a spare, I feel I can get a heads up on a slow leak from a nail. And then maybe being to save the tire.

This is why I like it. I always check my pressure screen once or twice during a drive for the warmed up pressure and to make sure I have no slow leaks. On a return trip home from my girlfriends condo, where some construction work is going on, I noticed the right rear was low. When I got home it was 4 PSI below the left rear and the usual warmed pressure. Inspected the tire and found the nail. I immediately plugged the tire. Had I missed this I might have gone out the next day to very low tire.

 

[Naptown]

A question in a bit of a different direction on this subject: How much do we even need TPMS?

Most of us drove for decades before the little gizmos were invented. Are they a sales gimmick, I wonder, that started as a nice option only to become standard? Or are they essential for the track?

The reason I ask is that my experience with low-profile radials is that they have basically two modes, okay and spectacularly failed, lol. The old creeping, slow bead leaks of the past seem to have largely been eliminated. But then, I’m not tracking, so I wonder if that’s where they help most.

I find it useful if I have a persistent low reading on my other vehicles.

 

[Choppen]

Go to the tpms display and scroll down to fill info. This will often be different from the tpms info. My SA and my experience say that the fill info display is reliable while tpms may not be.

 

[DriveInHouston]

A question in a bit of a different direction on this subject: How much do we even need TPMS?

Most of us drove for decades before the little gizmos were invented. Are they a sales gimmick, I wonder, that started as a nice option only to become standard? Or are they essential for the track?

The reason I ask is that my experience with low-profile radials is that they have basically two modes, okay and spectacularly failed, lol. The old creeping, slow bead leaks of the past seem to have largely been eliminated. But then, I’m not tracking, so I wonder if that’s where they help most.

I drove from Houston to NYC with a tire that was losing about 3 psi/day due to a tiny nail. I found very comforting to have TPMS to detect if the rate of loss suddenly increased (because the nail was ejected). I had the tire repaired at the shop of my choice in Queens.

It is even more important to be warned about the loss of pressure in run flat tires, because the tire does not change shape, but prolonged use with no pressure will destroy the tire.

Arguments like 'I am driving for 40 years and none of my previous cars had TPMS' do not hold any water for me. It is like saying 'It's been two thousand years from the birth of Christ and no previous generation used the polio vaccine'... Well, duh...

 

[roundtail]

Arguments like 'I am driving for 40 years and none of my previous cars had TPMS' do not hold any water for me.

I didn't mean it like that. I wasn't looking for an argument, just others' opinions. Sorry it came across that way, I didn't word it very well.

 

[DriveInHouston]

I didn't mean it like that. I wasn't looking for an argument, just others' opinions. Sorry it came across that way, I didn't word it very well.

Neither did I (word it very well) an argument in this case is a piece of logic, not that we are having an argument as in verbal fighting. Sorry about this, I came across as aggressive when I wasn't intending to be....

 

[jimmuller]

Having had one slow leak event from a nail I can attest to the value of tpms.

 

[GTS18BGTS]

My TPMS was all wonky this morning. Alarm went off and front left tire showed to be the culprit at -4. I check visually and the tire looked fine. Drove a bit and it didn't change. I then turned off the car and restarted. Came back the same way. I turned the car off a few more times and then all four showed 30psi?! So I pulled over again and checked the tire by rolling forward, checking the tire visually until I was satisfied there was nothing in the tire. Then I visited a nearby station to use the air pump as I had yet to put a gauge in the car which would enable me to check the pressure myself. Set the pump to 33psi and not one tire took air. Tires couldn't have been very warm as I hadn't gone very far. Started up at the station and all was normal again.

I somewhat agree with @roundtail in the idea that sometimes all of these systems create issues when there are none and they can be disconcerting. There are also more systems to fail and or send false information to the computer.

All I wanted to do was pick up some fresh corn at a farm about 25 miles away. Good excuse for a drive on a sunny Sunday morning

I guess I'll just keep an eye on things to see if it reoccurs.

 

[DPC]

I am on my second 718. I had one isolated incident with my'17. It showed one of my tires was low. I carry a pressure gauge and pulled over and checked the tire, same pressure as the others. It only happened once. I haven't had that happen in my '18.

 

[rasetsu]

Most of us drove for decades before the little gizmos were invented. Are they a sales gimmick, I wonder, that started as a nice option only to become standard? Or are they essential for the track?

TPMS is actually a US federal mandate stemming from the whole Firestone and Ford Explorer roll over debacle. https://en.wikipedia.org/wiki/Tire-pressure_monitoring_system

 

[roundtail]

TPMS is actually a US federal mandate stemming from the whole Firestone and Ford Explorer roll over debacle. https://en.wikipedia.org/wiki/Tire-pressure_monitoring_system

Ah. Thanks for that info.