The capacity of backpack  is not too big. If we ride, the back will be too big, and it will swing from side to side. There will be more cars on our roads, which will affect your riding. So the foreign guys like to wear tight clothes. Don't wear a skirt like a ride. If you scrape a branch, it's not good. In fact, if the bag is too big, it will hit the car or the branch. It is recommended that the best 5L or 10L, there must be a chest buckle, a waist buckle, it will be very close.