Tire Size and Calibration Puzzle ?

Reported on this or another thread: In similar weather (it is much colder now where I live), in full HV mode always, I got 55-62 mpg on full tanks versus 44-50 (at best) with the stock 19s (horrible especially for me coming from a Gen4 PP where I was consistently getting 62-67; averaged 62-63mpg over 18K miles) To note: I am not an aggressive driver and drive about 5 below speed limits on freeways (just keep away from the crowds) but on a A to B basis, this is what I have found so far. Inexact of course but a significant trend is there in the switch I made.

My latest tank run yielded 51.7 (so there has been a drop from the relatively warmer weather of October (just have had the car since mid-September).

 

It doesn't know what size it's fitted with now, sure, if the owner's fitted something different.

But it knows what it came with and what it's specced pressure is, and that's all it offers you as the preset. It doesn't offer you choices for different sizes. It only offers you the original pressure(s) for one size. So the pressure choices on your actual tyre label. Not for the other tyre size.

The only choice you get is the normal or high speed pressure for the 17", if that's what you car came with, or no choice for the 19, if that's what your car came with.

Hoping I've said it enough for the point to be grasped. Which is that there is not a single programming of the dash for both sizes. Increasing the chance that it uses this knowledge for the speedo and odo.

It's possible the US UI is different, I guess.

 

Of course the car does not know what tires the car came with, but the assembly workers do. They set the TPMS accordingly when they assemble the car. I am pretty sure they use the same TPMS transmitters for all tire sizes. Likewise, the speedometer is set accordingly when it is assembled in the factory. I am sure somewhere in the speedometer firmware there is a parameter to set the tire’s revolutions per mile, which is done during or before assembly.

 

By the way, I really like the Dunlop Enasave 01 A/S OEM LRR tires on my 2021 Prius Prime Limited. It is sad to hear Sumitomo Rubber Industries has closed the New York Dunlop factory. Mine were made in Japan though.

New York factory that makes Dunlop tires shuttered by Japanese owner

 

And I'm saying that having a selection for the TPMS is not evidence as to whether there are such settings for the meters, cause there is no need to tie the TPMS software to speedometer or over displays.

All the car's computers need to know for the TPMS is a pressure set point to compare the sensor readings to. Toyota could have used car trim or pressure value instead of tire size on that display.

 

If that is the case, then perhaps Toyota calibrated the speedometer for the 17” tires for all trims, resulting in the LE/SE showing a higher speed on the speedometer for a given actual speed, which is normal behavior for Toyota speedometers.