Paul 'Melvin' Chain Tensioner

Want to build a single speed without having to buy a dedicated frame? Try the Melvin. The Melvin bolts to the frame where the rear derailleur would normally go and allows the use of a single speed rear wheel on bikes with vertical dropouts.

Vertical dropouts hold the rear axle at a fixed distance from the cranks and nine times out of ten this doesn’t put the rear wheel at the right spot for a single speed drivetrain. The result is a chain that is too loose or too tight. The Melvin takes care of the chain tension and lets you run a single speed wheel on almost any frame with a derailleur hanger, including BOOST and Fat Bikes.

The Melvin uses two pulleys, just like a rear derailleur, which gives it 20 teeth of chain wrap. This means that the Melvin will work with multiple front chain rings while maintaining proper chain tension. Of course this is no longer a true single speed, but can come in handy when two or three gears are all you need. Twenty teeth of chain wrap means that chain rings with a maximum difference of twenty teeth can be used up front.