A riding outdoor power equipment vehicle, such as for grounds maintenance, having a chassis including a support area, an operator platform for supporting a rider and supported by the chassis, and a suspension assembly. The suspension assembly is configured to resist movement of the operator platform towards the support area of the chassis and includes a biasing element having a plurality of annular portions. At least two annular portions of the plurality of annular portions are spaced apart from one another when the biasing element is in a default orientation and are moved into engagement with one another upon compression of the biasing element between the operator platform and the support area. Compression of the biasing element provides an initial deflection response that decreases substantially in response to increasing loading being applied to the operator platform.