Polyester tire cord and radial tire using same

1. A radial tire comprising:

a pair of parallel bead cores;

at least one radial carcass ply which is wound around the bead core;

at least one inclined belt layer laminated on an outer circumference of the at least one radial carcass ply; and

at least one cap ply layer laminated on an outer circumference of the inclined belt layer in a tire circumferential direction,

wherein the cap ply includes a dip cord manufactured using a yarn containing 90 mol % or more of polyethylene terephthalate,

wherein the dip cord has a shrinkage rate of 3.0 to 4.0%, a load of 2.5 to 3.0 g/d at 5% elongation, a breaking strength of 6.5 to 7.5 g/d, and a shape stability index of 5.8 to 6.5,

wherein the dip cord is generated by twisting 400 to 2200 d yarns containing 90 mol % or more of polyethylene terephthalate by 1 or more plys, and

wherein the dip cord's nominal denier is 1,300 to 2,600, and the dip cord's twist coefficient, which is a number of twists multiplied by a square root of nominal denier, is 9,000 to 18,000.

2. The radial tire of claim 1 , wherein the dip code has an intermediate elongation of 2.1 to 4.0% at 2.25 g/d and an elongation at break of 8.0 to 16.0%.

3. The radial tire of claim 1 , wherein the cap ply layer is reinforced with one or two layers.