rear motor

Hello!, I have found Ancheer ebike for a really good price. Motor and controller was working but it needed some love!. I get it and started to work on. The first thing I did was to change the rear tire tube because it was torn (literally). However, after changing the tube, the motor stop...

I've just bought one of these and i'm really happy with it, except that the torque is pretty poor. I'd happily fork out a bit more for a decent rear wheel motor if it was compatible with the existing battery and controller set up. I don't need to go far...