3 ms·

>Wait the TPMs also send temperature reports? Tire pressure measurement doesn't make sense without temperature.

throwaway201103 6y ago
Yep. pV=nRT. This is why if you are checking your tire pressure manually you should do it when the tire is cold, and not immediately after a drive. "Cold pressure" is how the vehicle manufacturer's recommended tire pressure is specified. You'll still get some seasonal variation in most temperate regions.
ufmace 6y ago
I get what you mean, and I haven't had a car in a while, but the last one I had, the TPM didn't seem to correct for temperature at all, and would flag all the tires as being low on first start on cold days. I would have thought it would be better and easier to do environment temp monitoring and some heuristics in the central controller rather than put a temp sensor on every TPM and add temp data to the transmission protocol. Ex expect lower pressures when the exterior temp is cold and the engine is cold, expect higher when the engine is hot, etc.
- gumby 6y ago
  What makes you think the pressure wasn’t low at start? After driving some distance your tyres will warm up and the pressure will increase.
  - ufmace 6y ago
    That's the point. It was low, but that should have been expected due to the low environmental temperature. The warning system should know that it will increase to the proper levels when the tires warm up some and should not request that I inflate them further.
    - gumby 6y ago
      I guess that depends on what the software that reads the sensors should say. If you like automatic transmission, perhaps you’d like the sensory to report inflate/just fine. While if you prefer to shift gears yourself you might prefer a more direct reading so you can decide for yourself.
    - birdyrooster 6y ago
      So conversely would you want to be warned that your tires are too low when its warm because if it were cold they would be under pressure?

throwaway201103 6y ago

Yep. pV=nRT. This is why if you are checking your tire pressure manually you should do it when the tire is cold, and not immediately after a drive. "Cold pressure" is how the vehicle manufacturer's recommended tire pressure is specified. You'll still get some seasonal variation in most temperate regions.

ufmace 6y ago

I get what you mean, and I haven't had a car in a while, but the last one I had, the TPM didn't seem to correct for temperature at all, and would flag all the tires as being low on first start on cold days. I would have thought it would be better and easier to do environment temp monitoring and some heuristics in the central controller rather than put a temp sensor on every TPM and add temp data to the transmission protocol. Ex expect lower pressures when the exterior temp is cold and the engine is cold, expect higher when the engine is hot, etc.

gumby 6y ago
What makes you think the pressure wasn’t low at start? After driving some distance your tyres will warm up and the pressure will increase.
- ufmace 6y ago
  That's the point. It was low, but that should have been expected due to the low environmental temperature. The warning system should know that it will increase to the proper levels when the tires warm up some and should not request that I inflate them further.
  - gumby 6y ago
    I guess that depends on what the software that reads the sensors should say. If you like automatic transmission, perhaps you’d like the sensory to report inflate/just fine. While if you prefer to shift gears yourself you might prefer a more direct reading so you can decide for yourself.
  - birdyrooster 6y ago
    So conversely would you want to be warned that your tires are too low when its warm because if it were cold they would be under pressure?