It is possible that the monitering system can work with aftermarket wheels. You are correct that the moniter is part of the valve stem, but if the aftermarket rims valve stem placement is much different than the stock rims valve stem placement it is possible the sensor would not fit properly in the new rim. If you bring in a wheel to your local lexus dealer they should be able to tell you wether or not the sensor will work with it. O and talk to a service manager, as a salesman probably wont be too helpfull.
