Abstract: A flywheel system includes an annular rim mounted for high speed rotation on a flywheel hub. The hub has a radially splined exterior surface facing radially outwards. The rim includes an annular rim liner having an axis of rotation coinciding with the axis of rotation of the hub, and having an inner surface facing radially inward. The inner surface of the rim liner has integral splines projecting radially inward and extending axially. The rim liner splines mate with the hub splines. The flywheel rim liner has a modulus of elasticity el, and a density ?l, and a liner ratio Rl equal to El/?l. The flywheel rim has a modulus of elasticity er in the hoop direction and a density ?r; and a rim ratio Rr equal to Er/?r. The materials and configuration of the rim and rim liner are designed so that Rl is less than or equal to Rr, so said flywheel rim liner grows radially with the rim.