Slime Smart Tubes come preinstalled with Slime Tube Sealant to instantly and repeatedly seal tread-area punctures. Installs like a regular tube and works for up to two years. Fits: 4.8/4.0-8. Don t waste time repairing a flat tire. Slime self-healing Smart Tubes are pre-filled with Slime to prevent flats for up to two years. As the Slime treated tire rotates centrifugal force pushes the sealant to the tread area creating a layer of protection repairing punctures as they occur or treating existing punctures.