With a rack on your Brompton folding bike you have the option of using a Rack Sack to carry extra loads on the rear wheel. But how does it work? How do you use it? That's exactly what this video shows you. The Brompton rack sack is a good way to get some extra cargo capacity out of your folding bike. If you're building a Brompton folding bike to order you may want to try out our Custom Brompton Folding Bike Builder. With 52 in depth videos covering every option, our Brompton builder is the easiest and fastest way to build a custom Brompton folding bike.