The suspension on a Brompton is provided by one of these polyurethane blocks mounted between the main frame and rear triangle. Lightweight and effective, it smooths out the lumps and bumps and helps to avoid excessive bounce.
Suspension is important on small wheeled bikes such as the Brompton, but with the standard block sometimes they can feel a little too soft at the rear.
If you find the back of your bike feels spongy and sags under rider weight then the sportier firm block is for you.
Easy to fit using the bolt and washers etc from the original block.