Abstract: A method and apparatus for detecting a partially deflated tire on a vehicle having four tires each mounted on a wheel. Each wheel being provided with a signal generator for producing a series of digital signals or pulses spaced apart by equal increments by angular rotation of the respective tire and wheel assembly characterized by calculating from one of the series of signals reflective of the vehicle speed. The method includes selecting an appropriate interval for deflation detection, measuring the speed of rotation for each of the four wheels, storing the speeds found, repeating the measuring step for at least three consecutive successive equal intervals, averaging the speeds to produce an average speed signal for each wheel, processing the four signals in a processing unit which subtracts the sum of the signals from one pair of diagonally opposite wheels from the sum of the signal from the other pair of diagonally opposite wheels, sensing when the magnitude of the result is between 0.05% and 0.