In late 2000 stan developed a method of converting an existing mountain bike rim and tire to tubeless use by removing the traditional tube and replacing it with a molded rubber rim strip to seal the spoke bed of the rim and a liquid tire sealant to seal the tire and prevent punctures a whole world of opportunities was created the cross country 29er kitformerly the plus 4 kit will fit most 29 cross country rims including but not limited to bontrager