"ThisRecommended Practice encompasses the significant factors which determine the effectiveness of a seat system in limiting spinal injury during vertical impacts between the rider and the snowmobile seat system. The recommended practice is intended to providea tool for the development of safer snowmobile seats. It is recognized that the seat is only a portion of the entire vehicle protective suspension system. It is@ however@ usually required that the seat serve as added protection to the suspension system@ since the latter may ""bottom out"" during a severe impact. The term ""seat"" refers to the occupant-supporting system not normally considered part of the vehicle suspension or frame system. In some cases@ it may include more than the foam cushion. Thisrecommended practice provides the minimum requirements for performance of a general seat system@ and a description of specific means of evaluating the shock-absorbing characteristics of foam seat cushions using a specific testing procedure and a companion seat evaluation chart. The test input and means of interpreting the results are unique to the seats of typical recreational snowmobiles. Therefore@ this document is to be used for snowmobile seats only and is not to be used to evaluate seats of any other type of vehicle. In addition@ it should not be applied to seats of snow vehicles of significantly different design@ dimensions@ construction@ or intended usage from the typical recreational snowmobile illustrated in SAE J33. Purpose-The purpose of this SAE Recommended Practice is to facilitate the development of seats used on snowmobiles to minimize occupant spinal injury during impacts of: (a) The occupant on the snowmobile seat. (b) The snowmobile and seat on the occupant. Operators and passengers of snowmobiles can be subjected to high levels of impact with the snowmobile seat under riding conditions. This document was developed to identify the cushioning properties of snowmobile seats. Information on the technical development of this recommended practice is contained in SAE J89a."