Manufactured with a high quality, very elastic butyl rubber to Michelin's precise uniformity standards, these tubes are optimized for competition. Each one is precisely sized to match the inner diameter of the tire for which it's intended, while Service Course uniformity and elasticity allow for the lightest weight possible; taking into account the specific purpose of each tube. This also creates enhanced rolling efficiency. 700 x 18/23. 36, 52 and 60mm valves. 70 grams.