You usually have to switch to reserve after burning about 3 1/2 gallons of gas, so the reserve is nearly a gallon. Along with being a little safer when you are in an area with a lot of distance between stations, the reason the reserve is so big is the size and shape of the tank. To keep costs down, Triumph uses off the shelf parts as much as is practical, and they are using a petcock that is designed to have the more usual 1/2 gallon reserve with a much narrower tank.
