STANDARD TUBE MOTOZ 80/100-21 90/90-21 90/100-21 3.00 X 21 3.25 X 21 INCHOur tubes are made from 100% high grade Natural Rubber. Designed to fit motorcycle tyres at maximum volume, so they? re under the least amount of stress (not stretched and thin when inflated). The raw material we use is #1 Smoked Rubber sheet, which stretches like a surgical glove and can be compressed under load without splitting. This is super important for avoiding pinch flats. Many tubes are made of Butyl (synthetic) rubber which is artificial and