Venus Wars (movie, 1989)

The new frontier of Venus has degenerated into a dystopia ravaged by the civil war between Ishtar and Aphrodia. Bubbly reporter Susan Sommers arrives in the capitol of Aphrodia just before it's captured by Ishtar. She falls in with a bunch of teen-agers who live for a sort of motorcycle version of Roller Derby. Daredevil rider Hiro and his friends reluctantly join the struggle to free Aphrodia from the invaders. Not surprisingly, Hiro proves an ace at piloting the mono-cycles that are the Aphrodians' secret weapon in the key battle.