Although it was not possible to directly measure the vibration of the wheel rim where the TPMS system would sit, it can be inferred from the motion of the axel as the wheel is robustly attached to the axel. A DJB 100mV/g A/130/V Tri-axis Piezoelectric Accelerometer was used to measure the vibration. It was housed in a die cast box to protect it from the elements (fig 2a) and the box attached to the car axel swing arm (fig 2b). The accelerometer was mounted on a wedge in the box to ensure that it was level when the car was stationary.