| 摘要 |
A pneumatic radial tire for a motorcycle capable of increasing steering stability in cornering at high speeds while holding various performances such as high-speed durability and straight running stability. The radial tire including a tread portion 2, side wall portions 3, bead portions 4 is provided with a carcass layer 5 and at least one layer of steel spiral belt 6 formed by spirally winding substantially in parallel with the equatorial plane of the tire. The flatness ratio (SH/TW) of the height (SH) of the tire in cross section to the maximum tread surface width (TW) is in a range from 0.50 to 0.85. Among bending rigidities of the tread portion 2, the lateral out-plane bending rigidity (Sb) is in the range from 4.9 to 7.7 N/mm and the peripheral in-plane bending rigidity (Sa) is in the range from 5.1 to 7.8 N/mm. The belt surface rigidity equilibrium value (K) expressed by a bending rigidity ratio (Sa/Sb) is in a range from 0.90 to 1.10.
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