I recently got a fancy Garmin Varia Rearview Radar Tail Light for my commuter bike, and wanted to mount it to the Surly Rear Rack that I use. Since the Garmin only comes with seatpost mounts and the Surly rack only has a center light mount, this presented a little bit of a problem. Luckily, someone had already designed and uploaded a 3D-printable rack mount for the Varia. Unluckily, it uses a 50mm two-hole rack mount, so I decided to write up how I kludged around this in case anyone else needs to do something similar.
To adapt the 50mm bracket to the single center hole on the Surly rack, you can use this $5 part from Planet Bike. Since this already has a clip protruding for attaching a Planet Bike Blinky light, it won’t mount flush to the 50mm bracket without some work. Either you can dremel off the clip, or you can be lazy and do what I did and just mount the Planet Bike bracket backwards onto the rack, so that the flat side can be used to mount flush to the Varia bracket. Basically you use a long M5 screw in the center hole, then use the two sets of M5 screws, nuts, and washers that come with the Planet Bike bracket to sandwich the two brackets together like so:
Once that’s done you can spin the whole assembly to screw it into the Surly rack. Success!
If you have a really long M5 screw and extra nut, a better approach might be to drop the nut into the Planet Bike bracket center hole before sandwiching the brackets, then screw the bracket sandwich onto the rack by threading the long M5 screw in from the back. I didn’t have a really long M5 screw though, and this works fine.
Overall, so far I’m pretty happy with both the Garmin Varia and the 3D-printed part from Shapeways. Right now I’m using it paired to a Garmin Vivoactive HR with a handlebar mount and it works well. On roads where it’s hard to use road noise to tell when a car is coming up behind you, it gives you some extra information that can be helpful for positioning yourself or preparing for an upcoming turn. You can see a good overview of how all this works in this DC Rainmaker video. Plus, the light is incredibly bright and gets even brighter when something approaches.