Running a TPMS in the spare

[seanellaz]

Then why can my Ford App give me an updated Tire Pressure at 2:30 AM that's different than when I parked it a 5:00 PM?

Tire pressure goes up when warm. Pressure will be hier after driving, and during day. @ 230 am your tires are probly rested, coolest, would expect lowest pressure then.

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[charwest]

Tire pressure goes up when warm. Pressure will be hier after driving, and during day. @ 230 am your tires are probly rested, coolest, would expect lowest pressure then.

his comment is not referring to uncertainty about why the tire pressure changes. he is referring to uncertainty about how the tpms can access that data.

i run my tires at 32 psi

32? thats not super low?

 

[GTGallop]

Tire pressure goes up when warm. Pressure will be hier after driving, and during day. @ 230 am your tires are probly rested, coolest, would expect lowest pressure then.

I know why it goes up and down.
The point is that it does go up and down so I know I'm getting a new pressure reading and not an old static one. Meaning, the TPMS is working even when the tire is not rotating. Something else wakes it up.

his comment is not referring to uncertainty about why the tire pressure changes. he is referring to uncertainty about how the tpms can access that data.

32? thats not super low?

30psi with stock tires is the recommended factory cold PSI.
32 is pretty close and keeps the on highway gas mileage good w/o cooking the tires with heat and swelling.

 

[charwest]

30psi with stock tires is the recommended factory cold PSI.
32 is pretty close and keeps the on highway gas mileage good w/o cooking the tires with heat and swelling.

oh interesting. our truck says 38 is recc for stock. im assuming we have different stock wheels, but even then didnt realize there would be such a difference.

 

[HTX1811]

If the recommended stock cold tire pressure is 30 psi, what would be the recommended cold pressure for 255/80R17 tires? The same?
30 psi is what my Ford pass app is telling me the recommended cold pressure is.

 

[geophb]

I know why it goes up and down.
The point is that it does go up and down so I know I'm getting a new pressure reading and not an old static one. Meaning, the TPMS is working even when the tire is not rotating. Something else wakes it up.



30psi with stock tires is the recommended factory cold PSI.
32 is pretty close and keeps the on highway gas mileage good w/o cooking the tires with heat and swelling.

Truck can ping the tpms whenever it feels like it. As you have noticed. Rotation has nothing to do with anything thats an internet myth. Correlation does not me causation.
*Except on some vehicles that have a tpms in the spare tire, then the module can read fluctuations in the signal while wheel rotates to determine which sensor is in the spare tire (ie the one without fluctuations or the static signal).

 

[LurchOR]

Rotation has nothing to do with anything thats an internet myth. Correlation does not me causation.

I would encourage anyone who is interested in sensors to do their own research on how -and when- they transmit information. Internet myths can be pernicious.

 

[geophb]

I would encourage anyone who is interested in sensors to do their own research on how -and when- they transmit information. Internet myths can be pernicious.

The tpms sensor in the ranger will ONLY send a signal (sensor ID and pressure reading) when pinged by a Low Frequency signal from the directional Low frequency initiators built into the TPMS module in the head liner above the passengers head.
Otherwise they are in an "off" state, more or less.

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