Here are some pictures of the piggy-back frame I made to allow me to carry Ortlieb panniers on my Brompton. This was a proof-of-concept frame I knocked up in a couple of hours with no access to tube bending tools. I never got round to tidying up the welds properly nor have I painted the frame. So be warned, it is not a pretty sight. However, it has functioned perfectly whilst fully laden all summer (1100km including the Rallarvegen). The total load on the luggage system was 16-18kg depending on how full my water bag was.
1) The view from the rear of the Brompton touring bag. The frame is attached at the top with a pair of jubilee clips. Most of the weight is transferred directly to the mount at the centre of the Brompton bag frame. This mount, in turn, sits directly on the Brompton luggage block. This seemed to be the most sensible way to do it at the time. I am not sure I would do it differently now, as it still seems to make sense.
2) Close up of the lower mounting point. There is an L-section piece of metal welded onto the middle of the bar. The bottom of the L protrudes forwards and sits in a little trough at the top of the plastic mount. I don’t know if newer Brompton bag frames have the same feature.
3) View of the top of the frame and how it is fastened to the Brompton frame. The jubilee clips work a lot better than the fastenings I made myself. The clips pull the frame down so that the L-shape tongue is clamped to the plastic Brompton bag mount. One of the problems of this design is that later Brompton touring bags cover the Brompton bag frame almost completely. You’d have to unpick part of the stitching at the top of the bag to be able to get a jubilee clip or other fastener round the top bar of the Brompton bag frame.
This is one of the reasons why I plan to do away with the Brompton bag completely in the Mk 2 version. The other reasons is to be able to use Ortlieb front panniers on both sides of the frame and save the weight of the Brompton bag frame.
Any chance you could share dimensions and welding information? I don’t weld (yet) so will ask someone to do it. What is you rube size. Anything you would change having toured with this set-up?
The tube diameter is 10mm – mild steel bought from a DIY store. The height of the frame is 30cm and the overall width is 56cm. I used a MIG welder to weld up the frames. These are versatile welders you can also use for car bodywork. Easy to use – but don’t bother with gasless MIG welders. They do work but are harder to use and slow you down. A TIG welder or gas (oxy-acetylene) would be fine too except both have a steeper learning curve (particularly gas welding).
Note that this system only works with a an M-Type handlebar stem with Ortlieb Front Roller bags. This is due to clearance problems between the top of the bags and the brake levers/bottom of the handlebars. It will NOT fit a bike with an S-Type stem and I would expect clearance problems with the P-type handlebars.
Our bikes have modified handlebar stems (taller) which gives more clearance than a bike with standard M-type bars. This allows us to use the Front Packer Sport panniers on them.
Given the above this setup works fine for us. The main downside is that the Brompton touring bag is not waterproof and you cannot use the standard Brompton rain cover any more.
If I was to make another one of this type of Brompt-o-lieb frame then I would try to lower the top bar as much as possible. This is to lower the centre of gravity a bit and to make it easier to use the Brompt-o-liebs on our 20″ wheeled Dahon folders.
NOTE, if you lower the top bar too much then the bottom of the Ortliebs will foul the front wheel when it turns.
I don’t plan to make a new set of piggy-back frames for various reasons. Thus the Mark II version will be quite different, I want to be able to use Ortlieb panniers on the front instead of the Brompton touring bag. This will give us four fully waterproof panniers. Having four bags means we can pack our bags in a similar way to when we are using our full-sized tourers.
Thanks for your detailed response! I must get that welder a mask on and have a go. Your remarks are encouraging as I have the same aims. Sometimes I am cycle-touring, other I am touring with a cycle to make dealing with luggage easier. This is the Brompton appeal and the appeal of your device.