Next generation of smart tires will improve the safety and stability of the vehicle by monitoring road parameters, such as pavement and rolling conditions, with sensors placed on tire surface. Between the tread and the metal belt of the tire there are only few millimeters of rubber, therefore high miniaturization is necessary to withstand at the extremely high accelerations and to fit in this very limited room. Such kind of miniaturization poses huge limitations on antenna efficiency and available power likely provided by energy scavengers. Therefore, the optimization of the wireless power budget is crucial and it passes through the study of the communication channel. This paper presents a characterization setup that measures the path-loss from the tire surface to the inside of the car where the standard RF receivers, such as RKE at 434 MHz and Bluetooth at 2.4 GHz, are usually located. A calibration procedure has been employed in order to de-embed car-body-effects from the overall path-loss. Moreover, a 4.1 GHz UWB radio has also been considered in this study motivated by the extremely low-power consumption reached by UWB transmitters. The measurement results reflect a complex propagation environment where the car body attenuation plays a marginal role. Instead, the antenna pattern and the reflections from the environment cause the largest attenuation. Moreover, the observed link budget margin is larger and more suitable for implementation within the ISM bands than for the UWB band.