I was installing OEM TPMS from stock rims to aftermarket rim by using iforged TPMS adapter. and I came up with some questions.

In OEM set up, it seems TPMS actually working as valve stem, sticking from inside to outside.
In this part, I could imagine that the air actually go through the sensor & somehow the sensor reads pressure.


but in aftermarket rim set up with adapters, the TPMS sensor is placed inside of space between rim's surface & tire, and I really don't understand how the sensor work in this set up.
Dose the sensor reads pressure by just breathing the air inside?
Maybe I am not very smart to understand this.

can someone explain how TPMS sensors work in aftermarket rim set up with adapters?

I post some pictures for better explain.

sorry for my poor English.
thank you

 

fisrt 2 pictures are aftermarket rim set up with adapters,
and 3rd for OEM set up.

 

theres two ways to do it. The cheapest way is to utilize the wheel speed sensors that already exist for the ABS system. Theoretically a tire that has low pressure will have a different diameter thus a different wheel speed than a properly inflated tire. The system detects that one is different than the others and throws a flag. However this isnt 100% reliable if you have stuff sidewall tires or low profile tires which even underinflated the diameter doesnt change much. Also if all tires lose pressure at the same rate there is no "different" tire to vote and throw a flag on. Some of the newer ones are fixing this I heard.

http://en.wikipedia.org/wiki/Tire-pr...itoring_system