Backpack recommendations - big enough to put a helmet inside.

[b1k3rdude]

Unless I am miss understanding, that rucksack only allows storage on the outside, not the inside. I need it to be out of sight and inside the backpack unfortunatly. And I found one link that shopw the capacity at 25ltr - https://www.ghostbikes.com/2431-knox-six...ksack.html