Every winter I like to play with some new technology and this year I chose to try out the Garmin Varia 510 Radar Taillight. It moved to the top of my list when Wahoo announced that the Elemnt GPS/Bike computer that I use now supported it. I was hoping it would go on sale before Christmas - it didn't but REI offered a weekend of double member rebate so I used that justify spending the $200, since I'd get $40 back in REI scrip.

The first challenge was mounting it. The Varia comes with a seat tube mount. On my road bike I use a Topeak saddle bag and have no seat tube space available. For my normal talilight, I just clip it on the loop on the back of the Topeak bag and it is close enough to vertical. The radar unit really wants to be vertical.

I tried a simple solution first: I opened the zipper to expand the Topeak bag, which makes the rear more vertical. I then cut a scrap wooden shim to place on the bottom of the bag to stop its natural tendency to pull towards the seat boast and get less vertical. 

I had previously bought a 3D printed adapter from Shapeways (a very cool site, kinda like an Etsy for people who make stuff on their 3D printers and lots of bike specific stuff) that mated the Garmin twist mount to a clip built for saddle bag loops. Slipped it on, and voila!

It is hard to take a picture of the display in action while riding but the above is with the Varia in test mode. When a car approaches behind you, the car icon shows up on the strip on the side (on the bottom in my rotated photo), the strip and the LEDs at the top turn yellow and there is an audible warning too. As the car gets closer, the car icon moves up the strip - when it is at the top it is just about to pass you. 

The Element has a row of LEDs on the left hand side for other functions - if you don't want to use the screen real estate, you can have the LEDs play the role of the car icon. 

I did a 30 mile ride, about 10 miles on a rail trail, 20 on roads. No false positives on the rail trail - the unit will only alarm on targets approaching you from behind and there weren't many cyclists out to see if a passing bike would show up.

On the shoulder of a busy road, it worked very well. It would alarm before I could hear an approaching car and when I looked down at my bar end mirror I could see a small dot but couldn't tell if it was moving. If there were multiple cars, multiple car icons would show up, apparently up to 8.

Part of this ride is on a service road next to MD Rt. 50, the big highway to the Chesapeake Bay Bridge. There is limited or no shoulder on the road but usually there are very few cars. On my test ride, 50 was backed up for miles due to construction on the bridge and people were cheating and using the service road - the taillight was getting a work out.

On the way back, the route is on the service road on the opposite side of Rt. 50. This time very little traffic on the road, but the 40 degree angle of the radar (which claims to detect as far back as 140m) would trigger constantly on cars in the right hand lane of 50, which was probably 50 feet to my left. I assume the same thing would happen on a trail that was next to a road - not very useful in those conditions.

For my Trek 520 touring bike, it will easily mount on my rear rack. In January I'm doing a 5 day ride from Venice FL to Jacksonville on a Jamis Renegade in more of a bikepacking set up - a big Revelate saddle bag on the back. I now have to see if I can mount the unit on the rear of that thing.

Bottom line for me: useful but not critical adjunct to my bar end mirror for my typical rides on back roads. I use the bar end mirror mostly for situational awareness - continually checking it so that I know if some varmint or human driven thing leaps out from the right whether I can swerve to the left or not, but I'm always turning and looking before making normal turns. The audible alert serves a similar purpose with the Elemnt screen display more in my normal line of vision than the bar end mirror.

For tours/rides with long stretches of  urban traffic or service roads close to highways, pretty useless. It is also YATTTWPNSU - Yet Another Thing That Will Periodically Need Software Updates. I was already charging  a taillight periodically, but now have to add it to the list of biking and home stuff that has to have firmware updated every now and then. If you are a gram weenie, it definitely weighs more than my normal taillight.

Interesting post, John.  I had considered getting one of these for touring but was put off by the price.  Then when I got my new bike and started adding things like racks and fenders, I discovered that there was no room to mount even my current little Cygolite taillight vertically on the rack--and my saddle bag doesn't have a loop.  [That's not a feature I look for because clip-mounted taillights bounce off on rough Vancouver-area streets.]

I solved my problem with a Specialized Stix taillight plus adapter.  I hope.  I haven't been out for a ride since I mounted it.

Jacquie - my Cygolite Hotshot taillight has survived many years of being clipped to saddle bag loops. That includes a good deal of gravel road/dirt towpath mileage and a few stretches of cobblestone.  

The 3D printed loop adapter is well designed with an upward curved section at the bottom on the clip, and also has holes where you can loop at zip-tie through if you want to do belt and suspenders! I'll likely use that for my 5 day Florida ride.

Maybe different saddlebags have different loops. Mine has bounced off (on a not particularly rough stretch of paved road) but I heard it and retrieved it.  I’ve seen others lying on the roadway.   I’ve also seen panniers that have bounced off, but those are always the type that rely on a bungie providing tension between opposing open hooks.