The Dual is small enough to nestle under a seat without scraping against your thigh, yet it&&';;s big enough to hold two 700C tubes and two CO2 cartridges, plus an inflator. So, why two spare tubes? Because you never know what&&';;s up the road, and it&&';;s nice to know that you&&';;re prepared. That extra tube will make the rest of your ride that much more enjoyable knowing that you won&&';;t have to use your cell phone if another flat occurs.