Bridgestone – Bridgestone Tire Tubes - 18-80 in. Rim, including TR4 tubes in 80/100-21 and 80/90-21 front sizes, 2.75B350-21 fitments, 70/100-19 and 110/80/90-19 sizes, 2.50-18 and 100/100B-18 rear tubes, is where full-size dirt and dual sport wheels are served. Large spoked rims see the hardest life a tube can get. A 21 inch front slaps into rocks and ruts all day, and an 18 or 19 inch rear absorbs every landing and every bit of spinning torque, which is precisely how thin tubes get pinched or torn at the stem. Bridgestone's TR4 heavy duty tubes answer with a thick, evenly gauged butyl wall and a strongly bonded valve stem, so pressure stays put and the tube tolerates the flexing that off-road riding demands. Riders running lower pressures for traction gain the most from the extra material. Sizes cover the standard motocross, enduro and dual sport combinations, letting you replace a tube whenever a tire is changed rather than reusing one that has already been stretched. Torque the rim lock properly and check the stem angle after seating the bead, because a stem pulled sideways is the most common cause of tube failure.