Bakcou Puncture Proof Fat Tire LinerEven with top of the line tires and added upgrades like improved tire tubes, flat tires are still an unfortunate reality of riding a bike. Tire liners are an optional upgrade to help avoid the inconveniences of a flat tire while out in the field. A thin piece of extruded plastic that sits between the tire and the inner tire tube, a tire liner protects the tubes from being punctured by thorns, goat heads, or any other obstacle you may encounter on a