A runflat tire system comprising a pneumatic tire, a wheel rim and a
support ring disposed in a tire cavity is disclosed, wherein the wheel
rim comprises a pair of axially spaced bead seats, and a support-ring
seat between the bead seats; the support ring has an inner
circumferential surface fitting to the above-mentioned support-ring seat,
and an outer circumferential surface contacting with the inside of a
tread portion of the tire mounted on the wheel rim when the tire is
deflated; and one of or alternatively each of the support-ring seat and
the inner circumferential surface is provided with an ordered uneven
surface which can reduce a friction in the axial direction between the
inner circumferential surface and the support-ring seat, while
maintaining or increasing the friction in the circumferential direction.