A rubber-coating device for a steel wire is provided with: a heating device for heating water to a specified temperature range; heat transfer rollers, which contact the steel wire and inside which a water passage is formed; and an extruder for coating rubber on the steel wire that is heated by the heat transfer rollers.

A foldable tire includes a tire main body provided at two edges thereof with two tire beads respectively. A plurality of rings are disposed in each of the tire beads. Each of the rings has a reinforcing core, which includes a plurality of flexible steel filaments helically entwined with each other and has a diameter ranging from 0.2 millimeters to 0.5 millimeters, and a cladding layer clothing the reinforcing core, so that the reinforcing cores located in each of the tire beads are separated from each other.