The invention provides an assembly of a pneumatic tire and a rim. The tire has at least one carcass ply 2 and a belt layer 8. The ply 2 is composed of ply cords and has end portions. The belt layer 8 is composed of belt cords provided outside of the ply 2. Each belt cord extends in a direction intersecting the ply cord. Each of the end portions is held in the rim 12. The width of the tire is maximum in a circumferential cross section “T” with a cylindrical shape with respect to the center axis “D” of the tire. The cross section “T” extends through the rim 10. When the tire is rolled under a load and a stress is applied on the tire as an arrow “X”, a neighboring portion 2d near the end portions 2a, 2b is considerably bending-deformed as arrows “Y” to absorb the stress. The roundness of the belt layer 8 is thus preserved to reduce the rolling resistance of the tire considerably.