This seat pack uses too many velcro straps to attach it to the seat. However, the velcro that is supposed to close the opening is too short. If you use this pack with its full capacity (with the extension), it won't even close securely. It is very odd that the closing velcro strap is facing down when installed. It doesn't make any sense. When you hit a bump, it easily opens up. I LOVE specialized bikes and helmets, but they have to up their game with storage gear.