Question on TPMS Reset vs Odometer/Energy graph

Al Sherman said:

If I put the 21's back on after Winter, and I tell the TPMS reset screen that they're 21's (vs the 19" snow tires) does the whole car know that I have 21's? The Odometer? The Energy graph?

Or, do I need the Service Center to tell the Odometer functions that I have the 21's back on?

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The 21" and 19" have roughly the same outer circumference, so no adjustment is needed for the odometer. (35 aspect 21" vs. 45 aspect 19")

FlasherZ said:

The 21" and 19" have roughly the same outer circumference, so no adjustment is needed for the odometer. (35 aspect 21" vs. 45 aspect 19")

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True, but I wonder why the car needs to know that (in the TPMS settings) anyway. Don't the sensors just measure the pressure? Do the 19's use different pressure than the 21's? Both my summers and winters are 19".

mknox said:

True, but I wonder why the car needs to know that (in the TPMS settings) anyway. Don't the sensors just measure the pressure? Do the 19's use different pressure than the 21's? Both my summers and winters are 19".

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19's and 21's have different pressures on the door plates (although I run both at the same pressure anyway).

I ran both at 3.1 atmospheres. The rating given by the manufacturer is the MINIMUM you should be running. The tires themselves have for example a max rating of 3.5. So instead of running 2.9 or 3.0 my tire shop put it at 3.1 to make sure that no matter how the temperature varied I'd have a decent pressure in all.

Al Sherman said:

Thanks Flasher. Do you run both at 45 or both at 42? Or, some other number?

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I tend to run both at 48 (3.25 atmospheres).

FlasherZ said:

19's and 21's have different pressures on the door plates (although I run both at the same pressure anyway).

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Ahhh... I never thought to look there. I just assumed it would only list the pressure for the 19" tires that came on my car.

mknox said:

Ahhh... I never thought to look there. I just assumed it would only list the pressure for the 19" tires that came on my car.

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Sorry - clarification - it does list the pressures for the wheels your car was delivered with; I don't believe it lists both.