Abstract: There is provided an apparatus for measuring forces acted upon a tire in which a radial force and a peripheral force acting to the tire, which are required for the high precision measurement of a friction coefficient on a road surface, are simply measured in a high precision by detecting a magnetic field formed by a magnet fixed to a tread portion of the tire by a magnetic sensor fixed to a rim and measuring the forces acting to the tire from a variant pattern of a magnetic flux density detected un the rotation of the tire and without influencing upon the balance of the tire, which contributes to the high precision measurement of the friction coefficient on the road surface.

Abstract: A change of magnetic characteristics of a magnetic circuit constituting body or a composite magnet arranged in a necessary portion of a tire is detected by a magnetic sensor detecting a magnetic field leaked from the magnetic circuit constituting body or a magnetic filed from the composite magnet, while a temperature in the necessary portion of the tire is directly measured or a degree of heat deterioration is directly measured by using a tire temperature sensor or a tire heat deterioration detection sensor constructed so as of change the magnetic characteristics of the magnetic circuit constituting body or the composite magnet dependent on the temperature or the degree of heat deterioration in the necessary portion of the tire, whereby it is possible to attain an early identification of the abnormality on the possibility bringing about the troubles of the tire. Also, there is provided a tire temperature sensor or a tire heat deterioration detection sensor causing no fear of the early battery drain.