I recently got a C-line to replace my Raleigh Stowaway. Almost every aspect was an upgrade except for carrying luggage when being off the bike. I have a wire basket mounted on the Raleigh where I used to pop my very comfortable, large backpack in and out in a split second, thus freeing my hands to operate the folded bike over stairways and train and underground stations.
Brompton's backpacks are tiny, and the large borough bag was the only real option for me volume-wise. Over the first few commutes, I realised that carrying it one hand and the Brompton in another was not really sustainable. Carrying it on the shoulder strap is uncomfortable when fully loaded and causes you to be off-balance, making carrying or manoeuvring a rolling folded Brompton much more difficult than it needs to be.
So, I started playing around with the idea of adding backpack straps to the bag. After searching high and low, I found HARDY, a manufacturer of backpacks made to order ( https://hrdy.pl/en/ ), who were up for the challenge. They came up with the brilliant idea of using the loops in the sewn-in light grey strap as the anchor point for the top of the straps (I was surprised that it is strong enough for it; so far so good!), and they added loops of their own on the other side of the bag at the edges by the external large pockets. They added 4 of them, 2 by each of the pockets to allow for rotating the straps 180 degrees in case of uneven loads. Brompton's sewn-in strap has symmetrically placed loops, so the anchor can be easily placed on the other side. You can see it in detail in the pictures. Note that the anchor includes a stabilising velcro with a plasticky thing underneath to prevent the straps from sliding freely.
I thought I'd post this in case anyone else was interested in the idea. Obviously, this does not turn the bag into a comfortable trekking backpack to carry on your shoulders for the whole day, but the solution wears surprisingly comfortably for short periods of time. Most importantly, it does the job of freeing-up your hands when you are on public transport. The minimalistic straps are fine and helpful for not getting in the way when closing the bag for cycling, but padding could potentially be added to them for some extra comfort.
by Veganfloyd