400GreyBike is a public community for owners and enthusiasts of 400cc Japanese domestic market motorcycles. Built around a shared passion for these bikes, the site invites visitors to join its forum, introduce themselves, and connect with other members. Its content celebrates the enjoyment of owning a 400cc motorcycle, while recognising the challenge of finding examples in good cosmetic and running condition. The community also considers which models may become sought-after classics as well-preserved bikes grow harder to find.

400GreyBike supports members with a document archive and shares news about community activities and events. Past highlights include a classic track day, a Spain and France rideout, and photographs from a group meet at RAF Cosford in May 2010. The site also provides information about the community, advertising, and frequently asked questions. Whether visitors are long-time owners, prospective enthusiasts, or simply interested in the Japanese 400cc motorcycle scene, 400GreyBike offers a dedicated place to exchange knowledge, follow events, and celebrate these bikes.