They go under your seat! We have four options and you basically want to choose based on what size you want, or what size you can actually fit on your bike. You will need to measure the empty space between your seat and your tire to figure that out. There are dimensions listed under the ‘specs’ section of each page and also an instructional ‘fit check’ video on the seatpack page. From small to large, our product line goes Mini Saddlebag, Rolltop Saddlebag, 10.5L Seatpack, and 16L Seatpack. Hint: the Mega Bar Bag works on your saddle too! Contact us if you need help figuring out what works for you!