Busch und Muller's bicycle mirrors are the most well engineered mirrors available for bicycles. They're sturdy and have good optics. However, like most mirrors, they present a blunt face to the wind. If you've fitted such a mirror to a fast (recumbent) bicycle or velomobile you may have wondered what effect this has on aerodynamics. The mirror may be small, but a flat face to the wind is not helpful, however small it is. On a velomobile the mirror can be quite significant as it's one of very few parts of the machine which presents a blunt face to the wind. This part fits over the 50 mm Busch und Muller Cyclestar mirrors, transforming their blunt rear face into a far more aerodynamic shape. What's more, the flat edge from the print bed creates a sharp edge around which airflow will be disturbed so the air-flow past the mirror can also be expected to be improved. Fix the cover in place on the mirror using bathroom sealant. We recommend using this with the the long B&M 901 mirror for recumbent touring bikes. For velomobiles we recommend the short B&M 901/3. To fit a 901/3 to the body of a velomobile, sawn off the ball joint and cut an M thread into approximately 20 mm (this will vary depending on your velomobile body thickness) of the stalk of the mirror. Then fit one small nut so far as possible onto the mirror, use two washers to form a "sandwich" with the velomobile body and finish off with an anti-slip nut on the inside of the body. As well as making some items available for free, we sell a wide range of bicycle components online.