Running a TPMS in the spare

[GTGallop]

Are your wife or kids out cruising while you are sleeping?

Nope.....
I hit the little refresh button in the App, the truck makes a muted "ching ching" sound like a bell under a pillow from the firewall area and then it updates my air pressure and stuff.

Sponsored

 

[GTGallop]

I would guess it’s the last known pressure when it was active. After all the system is designed to give you a warning if the vehicle is moving not while sitting with the engine off. Here’s a test. Check all 4 pressures when you get home. Then air down one tire say 30 minutes to an hour after the truck has been sitting. Then update and see if it reads the same as when you parked or the lower pressure.

Nope again...

It will display last updated 5:30 PM (when I parked the truck) and tires all around 32 PSI. Then later at night or the next morning I hit the "refresh" button in the app on my phone and it takes a second, then the tire pressure changes to 28 PSI now that the tires have cooled and night has come. In that time the tires never rotated.

Somehow the TPMS in the tire is either transmitting all of the time, or the truck sends a "wake up" signal to the TPMS in the tire to sample and send data. If that's the case it can liesten or recieve information 24/7 regardless of rotation and that would use significantly less battery than transmitting all of the time, but still uses battery.

 

[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.

 

[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.

 

[Ranger_Rocks]

30psi with stock tires is the recommended factory cold PSI.

Depends on the tire.

Henry Mac's came stock with LT tires at 38 PSI.

 

[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.

Sponsored