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.

The mounting pivot has spacers that can be arranged to adjust the chainline. The Melvin works best, of course, with Paul hubs, but the chainline spacers allow it to work with most other hubs too. In addition to the pivot spacers, the pulleys have side to side float to quiet slight variances in chainline.

The pulleys are made of extruded and machined aluminum and have sealed bearings for durability. They are 2.25mm thick at the tooth which fits inside most narrow 6 through 9 speed chains, and the pulley cage is wide enough to allow 1/8″ single speed chains as well. Chain tension is optimized when the chain length is cut so that the pulleys are aligned vertically. For 1/8″ cogs Paul recommends the silver SRAM PC-1 chain. For 3/32″ cogs we recommend any 8 speed chain. If you are having problems with skipping and are using a Surly cog, try another cog before contacting Paul. Paul isn't sure why, but 9 out of 10 times that’s the issue.