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Why does wheel size matter when resetting the TPMS?

Why does wheel size matter when resetting the TPMS?

Could someone in the know shed some light into this? I mean my hand held pressure gauge doesn't ask me what size/shape is the object I'm measuring...

Bighorn | 2018年12月12日

Recommended pressure is different.

Kahn | 2018年12月12日

not that i can tell new labels are 42 psi for both 18 and 19 wheels.. maybe the warning low pressure trigger point is different.

lbowroom | 2018年12月12日

The rolling diameters of the OEM setups are slightly different as well.

ReD eXiLe ms us | 2018年12月12日

The interior cross section area of the space between outside of rim and interior wall of the rubber differs dependent on the wheel and tire size. The TPMS may take that into account to determine a proper reading for PSI.

Wormtown Kris | 2018年12月13日

There isn't any way to initiate a reset/ recalibration for the TPMS from within the car, is there? We put non-OEM winter tires, mounted on wheels, from Tire Rack on our 3 around Thanksgiving. It gave the alert/ message asking if there were new tires and asking the diameter, and they seemed to work fine the first day. On the second day we started getting a low tire pressure warning on all four tires.
My tire gauge says they're at ~42# but the car is reading 28 to 30 psi. (The eyeball test says no way they're underinflated by ~35%). I've been too busy w/work, kids' activities and holiday prep to get around to calling Tire Rack, but I would like to try to reset the TPMS readings thru the car if that were possible. 18" Blizzaks on Tire Rack/ Moda rims w/ what they assert to be the appropriate TPMS, delivered mounted.

Kahn | 2018年12月13日

Sounds like the sensors u have are faulty. I got the cheap itm sensors in eBay and after a delay of a few days for the reset are reading spit in with my hand tester

George with SacEV | 2018年12月13日

I suspect, just my guess, that most of the above posters are missing what the actual reason could be:

With a reset of the TPMS system, I speculate that Tesla has simplified WHY this reset has had to take place. Many times when the TPMS system might need a reset is because of a TOTAL CHANGE IN TIRE/WHEEL SETUP. For example when changing from summer tires to a winter tire/and wheel set. In my own case, I have recently switched from the Performance 20" wheel/tire setup that came with my Model 3 Performance + to a winter/wet season set of 18" all-season tires and lightweight wheels.

The requirement to set the wheel size when the new TPMS sensors were then recognized by the Tesla monitoring system allows the speedometer and odometer to be accurate as well.

THAT is just my guess on why the wheel size must also be input when resetting the tire pressure system.

Bighorn | 2018年12月13日

@George
The reset on the Model S does not account for speed inaccuracies of the slightly different circumferences. It was for different target pressures—38/40 vs 45 in that case.

Magic 8 Ball | 2018年12月13日

The tire pressure monitors work by trapping molecules at speed. The sensors mounted at different diameters need adjustment for different speeds. The coriolus, centrifugal, centripetal, gravity constant, etc. all come into play. All explained in the missing amendments to the guide.

Bighorn | 2018年12月13日

@M8B
Maybe in the original Baolong system on the S, but not the current set up.

https://www.bridgestonetire.com/tread-and-trend/drivers-ed/tire-pressure...

Magic 8 Ball | 2018年12月13日

I guess they went to 30 Weight Ball Bearings.

https://www.youtube.com/watch?v=pbWWxGmbS9s

PECo CT | 2018年12月13日

The TPMS sensors that I got from Tire Rack in my winter wheels and tires work perfectly. As Kahn said, you may have gotten faulty ones.

Magic 8 Ball | 2018年12月13日

If you really care about TPMS design @Bighorn provided a good link for better understanding. The actual logic is most likely born from technology obtained at area 51.

Kahn | 2018年12月13日

it is defiinately not due to size. if you check in one of the online tire calculators the 18 vs 19 vs 20 should be withing .5-1.0 diameter difference that is why the width and sidewall changes for the different sizes..