Tire pressure sensor behavior

[alohart]

On Saturday, I swapped my Giga wheels R <-> L so that their rotation directions look correct and like the Tera wheels. To me, the way BMW mounts the Giga wheels makes their rotation direction appear to be backward when driving forward. It's not obvious to me how the rotation direction would affect drag, air flow, etc., but there must be some reason why BMW chose to mount them as they did. Any opinions?

On Sunday, I drove 30 miles up the coast and parked for several hours while I completed a tough hike. When I returned and started my car, I was presented with a "Check tire pressure" warning that stated:

"Check tire pressure and correct if necessary. Afterwards, perform Tire Pressure Monitor reset (TPM). See Owner's Manual for further information."

My first fear was that I had suffered a punctured tire as has happened to so many i3 owners, but everything looked normal visually. So I started driving home and immediately looked at my tire inflation pressures in iDrive. All pressures were normal.

So I'm assuming that the TPM was confused by the changed locations or rotation directions of the tire pressure sensors after I swapped wheel positions. Each tire pressure sensor must have a unique ID so that each sensor's pressure can be associated with the correct tire. Maybe the TPM is aware of the rotation direction of each sensor as the car is moving forward but was confused because my sensors were now rotating in the opposite directions. I don't know how a TPM reset corrects this situation, but apparently it does.

Would someone like to enlighten me on how the TPM system works and why swapping wheel positions confused it?

 

[jackt]

When you swap you should do a reset before driving off, so it forces the car to relearn the tyre sensors positions. If you don't you get messages like you describe, as TPMS is getting different data to what it was expecting - if you go into IDrive (When parked) you can do the reset from TPMS menu.

 

[jadnashuanh]

Not all markets get actual TPMS sensors...some use the anti-lock brake wheel rotation sensors to determine of a tire is low. The USA does get physical TPMS in their i3. While the TPMS will show the tire pressure, it may not be associated with the right wheel location nor will it be set for the 'normal' pressure unless you follow the reset procedure correctly. If you've driven too far and warmed up the tires, you do not want to do a reset them since the currently read pressure is set as the baseline. It will then look for a drop from that pressure to indicate a problem, and it could be starting more than a few pounds high if you've driven it more than a mile or so. As opposed to older vehicles that had an actual receiver at each tire location, I was told that on the i3, the actual receiver is the key fob, and it talks to the car. This saves weight. It's a little complicated how it figures out which report is coming from which wheel, but eventually, it does. My guess is it knows when you've turned the steering wheel, and the tires on the inside path will travel a shorter distance than those on the outside, so the timing of the various reports will change.

 

[Bunter]

Did you leave the tyres on the the wheels? Because the tyres are directional (non-symmetrical).

Bill