A machine comprising: an outer member; an inner member mounted for rotation about an axis relative to the outer member; and a seal system comprising: a seal housing mounted to the outer member; one or more seal rings (120, 122) held by the seal housing and having an inner diameter surface; and a seal runner mounted to the inner member and having a first outer diameter surface portion contacting or facing the inner diameter surface of the one or more seal rings (120, 122), wherein: the seal runner has a circumferential array of mounting features; and one or more weights are mounted to one or more of the mounting features; wherein the seal runner has: a mounting section mounted to the inner member; a sealing section including the first outer diameter surface portion radially outwardly spaced from the mounting section; a first hub between the mounting section and the sealing section, wherein the first hub is an aft hub extending from near an aft end of the mounting section radially outwardly and forwardly to merge with a forward end portion of the sealing section so as to leave the remainder of the sealing section axially cantilevered aftward to a free distal aft end; a balancing section including the mounting features; and a second hub between the mounting section and the balancing section, the second hub extending radially outwardly and forwardly to merge with an aft end of the balancing section, wherein the mounting section, the sealing section, the first hub, the balancing section, and the second hub are formed on a single metallic piece, and wherein the one or more seal rings (120, 122) are carbon seal rings. an outer member; an inner member mounted for rotation about an axis relative to the outer member; and a seal system comprising: a seal housing mounted to the outer member; one or more seal rings (120, 122) held by the seal housing and having an inner diameter surface; and a seal runner mounted to the inner member and having a first outer diameter surface portion contacting or facing the inner diameter surface of the one or more seal rings (120, 122), a seal housing mounted to the outer member; one or more seal rings (120, 122) held by the seal housing and having an inner diameter surface; and a seal runner mounted to the inner member and having a first outer diameter surface portion contacting or facing the inner diameter surface of the one or more seal rings (120, 122), the seal runner has a circumferential array of mounting features; and one or more weights are mounted to one or more of the mounting features; a mounting section mounted to the inner member; a sealing section including the first outer diameter surface portion radially outwardly spaced from the mounting section; a first hub between the mounting section and the sealing section, wherein the first hub is an aft hub extending from near an aft end of the mounting section radially outwardly and forwardly to merge with a forward end portion of the sealing section so as to leave the remainder of the sealing section axially cantilevered aftward to a free distal aft end; a balancing section including the mounting features; and a second hub between the mounting section and the balancing section, the second hub extending radially outwardly and forwardly to merge with an aft end of the balancing section, wherein the mounting section, the sealing section, the first hub, the balancing section, and the second hub are formed on a single metallic piece, and wherein the one or more seal rings (120, 122) are carbon seal rings.