Tire replacement warning device

A tire includes a tread (20) and two sidewalls (21) are located on two sides of the tread (20). The tread (20) has multiple tread grooves (22, 23) defined therein and a safety face (30) protrudes from the inner end of one of the tread grooves (22, 23). A sensing device (40) is located in the tread (20) and has a sensing line (41) which is located beneath the safety face (30) and emits wireless signals when the sensing line (41) is exposed after the safety face (30) is worn out.