Foundation MTB Tube Having extra tubes with you is always a good idea because you never know when you will need to change a tire when on the trail. These tubes are lightweight and were designed for cross country and trail riding. The Foundation MTB Tube is available for 27. 5" and 29" tires and can fit 2. 1"-2. 4" or 2. 2"-2. 5" tires respectively. Features27. 5" x 2. 1"-2. 4" 48mm valve29" x 2. 2"-2. 5" 48mm valve | Foundation | Mtb Tube (Non-Packaged) 27. 5"(650B) X 2. 1"-2. 4", 48Mm Prestavalve