As you may imagine, the Tubi is sized for tubular or ”sew-up” tires. It works great for the clincher aficionado who likes to carry just a little more than is usually necessary. To fold a tubular for a good fit in the Arundel Tubi Seat Bag, use your fist as the form to roll the tire around. As one folds the tire, the length of four fingers is about right for this first fold. It takes a little more effort to fold the tire right but the end result is worth it: A small and tidy seat bag that doesn’t flop around on the back of the seat. The CO2 cartridge can be placed inside the first fold or on the side; your choice. The Tubi has a zippered side pocket if you prefer to separate your money, I.D. or key(s). The Tubi is skinny, so as not to touch you or your Castelli shorts. The strap is double sewn so you can cinch the bag tight and prevent it from swaying gently in the breeze.