What's a Brompton Rack Sack? How do you use it? I don't think we need to have whole page about this Brompton accessory, do you? So long as you know what it's all about and how to use it I don't have to quote lines of poetry about it. Suffice to say: the Brompton Rack Sack is the easiest way to expand the cargo capacity of a Brompton folding bike with a rack.
You can still fold up your Brompton and keep the Rack Sack attached, though you wont be able to fold it up all the way. Most of the way, but not all the way. Then again the Rack Sack is more of a bag you'd take on long distance rides or out grocery shopping. It's not so good for every day commutes because you have to spend an extra 10 seconds on folding, but if you have to go 40 miles and need a good spot to pack lunch and a bottle of wine the Brompton Rack Sack is perfect.
Just to be clear, the Brompton Rack Sack is ONLY COMPATIBLE with R type Brompton folding bikes with fenders and a rack.