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 Ultra Heavy Duty Tubes are designed for the harshest street and off-road applications. Constructed of ultra-heavy duty 4 millimeter thick natural rubber for superior protection against flats. Recommended for the high demands of Enduro, desert, and cross country riding or racing. Tube Specifications: Size: 100/100-18.