The Gmac motor is a collaboration between Bikeswift and Grin with Mac motor. It is one of two geared hub motors with a locked clutch so you can use regen. Because of the 5/1 ratio of the motor to the wheel. You can set it up with 10%-15% regen vs only about 5% regen on a direct drive motor. You need not file or dremel out your rear stays, because it uses a solid 10mm rear axle. Grin has an extensive right up on it
Here .