Originally Posted by
mattdd
Thanks, @Jipe. Looks like I need to add some hardware and bushings to make it work.
On another note, since I'm starting with nothing and building to suit, what are the pros and cons of the suspended rack, where the luggage load is cushioned by the rear suspension, and a rack that's attached only to the rear swingarm? I'm particularly curious about how a 15 kg load affects ride and handling when suspended vs not. Thanks everyone for your help!
The rack that I showed you is made by Pacific Cycles. The benefit is that it folds with the bike perfectly and stays at the back of the bike. It will touch the ground after the bike is folded and supporting the bike from the back. The down side is that you will need to install the mudguard if you want to use pannier bags. The mounting rod from the original Birdy mudguard will serve as a support for the pannier hooks.
I have been traveling on a Birdy 3 with 15KG pannier bags on the rack. Other than fitting the rack's measurement and dimensions right (since you intend to build one yourself), you will need to change to a stiffer rear suspension. The cargo weight will cause extra force on the PU suspension block. You can get the green suspension for better results.
The additional weight normally doesn't affect the ride and handling of the bike.
I could consider to find one in the second hand market instead. If you can't find one in Europe, you can consider Yahoo Auction Japan. There is a shipping partner that will help you to ship the item to your location.