Bridgestone Tube - Straight Metal Stem (80/90-21) Bridgestone has best-in class tires engineered with advanced tire technology for those moments when you need it most. That's why their engineers are very passionate about researching and developing new tire technologies, including inner tubes. Discover the technologies that fit your performance needs. Bridgestone Tubes are designed for light or standard street and off-road applications.Tube Specifications: Tube size: 80/90-21. Valve type: TR-4 (straight metal stem (8 mm diameter)).