Provides additional support and length. Provides additional hip support via wider cushion design. Integrated rear storage. Battery cover with support (860201720) required for REV Gen4 (Narrow) without battery. Battery cover (511001210) required for REV Gen4 (Narrow) with battery. 2 Summit seat posts (510006693) required for installation on REV Gen4 (Narrow) Summit. Not compatible with Battery Cover (860201407).