STURDY:This bike carrier rack is made of durable aluminum alloy,strong and well built bike rack for carrying lots of weight.QUICK RELEASE:Quick release mount at seat post.Easy to install and come with tools and installation instruction.LARGE LOAD:This carrier rack is made of quality aluminum alloy,lightweight,but carries up to 115 lbsW-SHAPED & ADJUSTABLE DESIGN:Design with W-shaped bars to prevent pannier from hitting the tires,keeps your pannier safe.The adjustable shelf and bottom rods,fits 18"-27.5" mountain bike type and road bike type.NOTE:Does NOT fit Suspension bike,Fat tire bike, Women’s cruiser bike,Bike seat,ect.The included nuts are locking nuts.When you installed the nut,The rubber inside the nut will prevent you from tightening. Just use a tool to tighten nut.Requires 2"Height and 30mm Seat PostThe main bracket needs a height of 2" attached to the seat pole.If your seat pole is at the lowest height, please confirm that you are still suitable for riding after raising