The invention is directed to a pneumatic tire that can be mounted on a rim (wheel) to assure good engagement with the rim while preventing the occurrence of rim offsets. The bead portion 4a (as indicated by a solid line in FIG. 1) on the front side of a tire 1 which is later mounted on the rim has a bead base diameter .phi..sub.1, a toe portion angle .phi..sub.1, a contact angle .alpha..sub.1 , and a heel portion radius R.sub.1, whereas the bead portion 4b (as indicated by a dashed line in FIG. 1) on the back side of the tire which is first mounted on the rim has a bead base diameter .phi..sub.2, a toe portion angle .theta..sub.2, a contact angle .alpha..sub.2 and a heel portion radius R.sub.2. The bead portion 4a on the front side has a different shape than the bead portion 4b on the back side and the following two relationships hold between the two bead portions; the angle of .theta..sub.2 of the toe portion on the back side should be greater than the angle .theta..sub.1 of the toe portion on the front side, with the difference between the two angles being not more than 4.degree. (4.degree..gtoreq..theta..sub.2 -.theta..sub.1 >0.degree.); and the bead base diameter .phi..sub.2 on the back side should be greater than the bead base diameter .phi..sub.1 on the front side (.phi..sub.2 >.phi..sub.1); preferably, the difference between the bead base diameters on the two sides (.phi..sub.2 -.phi..sub.1) is 2 mm or less (.phi..sub.2 -.phi..sub.1 .ltoreq.2 mm).