Tire inner tube with a bent 90 degree valve stem that is perpendicular with the rim. Commonly referred to as a TR87 valve stem.Inner tubes are donut-shaped rubber balloons that are inserted into the tire and inflated to retain air pressure. An inner tube is required when a "tube-type" tire is being employed. You can determine if you have a tube type tire by looking at the tire description on the sidewall. Tube-type tires are identified by a "TT" after the tire size.The other type of tire is "tubeless," which can be identified by a "TL" after the tire size. An inner tube is not required when a tubeless tire is being employed, but can give extra prevention of a flat tire.