“…The cause-based method, also known as the experimental method, uses sensors to measure friction-related parameters and attempts to correlate these parameters with the tire–road friction coefficient. The friction-related parameters are to use a sensor to measure anything from hub sound to road surface optical properties, and these sensors are acoustic [ 9 , 10 , 11 ], optical [ 12 , 13 , 14 , 15 , 16 ], and tread sensors [ 17 , 18 , 19 , 20 , 21 , 22 ]. Meanwhile, the effect-based method attempts to simplify the mathematical models to estimate friction [ 23 , 24 ].…”