I don't know what L capacity my rucksack has but is on large side for cycling with measurements of 50cm x 35cm x 25cm. Will this cover fit or be too small?
The height of 50cm and width of 35cm would be OK but the depth of 25cm might make it a tight fit. There are elastic straps that cross diagonally to secure in place. You can always return the item if it's not suitable.