Ah ok, thanks fredaroony, it’s the same as Redrick’s. Literally I’m just looking for a rally pack size whatever that means.
Bit late in to this, the Endurostan tail pack on my bike is 8ltr, if I was to put a tool kit compressed and disk lock in you might squeeze in a pair of gloves. It’s not that big.
It’s bomb proof, and totally waterproof, good as a day bag but it would be a bit tall if it way on the pillion seat.

