Abstract: A conversion system for converting an all terrain vehicle (ATV) for use in snow and in other adverse condition, the system including an endless track assembly. Endless track assemblies are comprised of a drive cog mounted on the rear axle, having teeth for engaging a track, and a slide rail assembly for guiding and tensioning a composite track. The drive cog is uniquely designed to provide optimal power to gear ratios to be used with the drive gear of the ATV. The standard ATV axle may be replaced with a stronger axle. The track mount assembly is mounted by a bearing housing support constructed to fit the axle. The drive cog is constructed with bolt patterns compatible with bolt patterns on existing ATV axle mounts. A unique motion-limiting device keeps the track assemblies properly positioned when riding over uneven terrain. The track mount assemblies provide a dual track construction that replaces the ATV drive wheels and converts the ATV to a vehicle that can transverse terrains such as snow and mud.