Motor thud while slowing down

[BKing]

2019 RadCity with 2600 miles. Started noticing this awhile back on Wife’s bike but thought it was bumps reverberating through the wooden box mounted on the rear while riding. It’s not bumps. I have noticed both bikes have always made a slight thud when running the motor while leaning on the kickstand during the last two seconds before the wheel stops. You don’t hear these while riding, only the occasional loud thud from one bike as it’s slowing way down. It does not do the loud thud every time, maybe every 5th test from either a pedal start or throttle start then let it wind down to a stop. It sounds like a medium slap on a desk top when it happens. There is zero power going to the motor when it happens. The wheel rolls freely mechanically. Anyone seen this problem on a rear hub motor?

 

[J.R.]

This is just a thought that came to mind as I read your post. Make sure the axle is tight in the rear dropouts, nuts are tight and torque arms or washers are properly in place. I don't own a Rad so I don't know if they use torque arms or torque washers. I've seen a couple hub motor ebikes over the years that weren't tight at the axle, eventually rounding off the dropouts. One local guy I knew had that slap/thud you describe. He ruined the frame dropouts because the motor was loose and the steel axle rounded the aluminum dropouts.

 

[BKing]

It has both torque washers and one torque arm. The thud is coming out of the motor or caused by a sudden jolt of EMF as it slows to a stop. On the kickstand unloaded or riding both. But not very often.