Four points fixation, more reliable. This bag requires your rear rack to have at least four fixed points and support poles on two sides. Top adjustable fixing straps fix on the rear seat, two side velcro fixing straps fixed the the sides of the rack. The rear rack width needs to be 16cm. Installing 22L bag requires the rack length of 28cm, installing 40L bag requires the rack length of 32cm, and installing 50L bag requires the rack length of 34cm.
Top expandable strap can storage tent, sleeping bag, moisture-proof mat, top bag, etc. Two side elatsic rope can be used to tie wet items such as clothes, towels, gloves, etc. Separate storage compartments for internal small items such as ID card and miscellaneous items.