Sounds to me like it would have to be mounted in the wheel (hub). You don't want to lose the sensors everytime you have a tire blow out or replaced.

It should be suffcient to ONLY measure and report the pressures when the car is started. Dynamic tire pressure systems exist but are for expensive commercial transports.

If this were for an automobile, I submit that it is enough to only report when the car starts. The only time matters change notably during one car trip are:
(1) A tire blews - an obvious event.
(2) A tire with a knewn slow leak is re-inflated and driven.

A dynamic report would be nice in the rare case 2, but wouldn't be worth the performance most of the time. Sure driving conditions could heat the tires and increase tire pressure on long trips, but people have to pull over and get gas often and the report would be updated while parked when the ignition is turned on.

So is dynamic reporting really even needed? Static reporting at ignition simplifies communications too. For power you could use a technique similar to RFID with charged cap, or a kinetically charged cap.

-Jay C. Box