Originally Posted by
Litespud
I was pretty skeptical about the need for a Varia, but I wanted a decent rear flasher that lasted more than the 4 hours I was getting from my current flashers. I already had a Garmin 530 head unit. However, the radar is really impressive - since it works on speed difference, it will "see" cars behind the group. It's not perfect - it can be flummoxed if the car is maintaining distance rather than overtaking, the car can disappear off the radar. Also, while it can graphically represent multiple approaching cars, if one car happens to be in the preceding car's "radar shadow", it won't show up initially, only popping up out of nowhere when the first car has passed. The Varia will also register fast-approaching bikes, with no way if distinguishing bike from car. However, I think, when used in conjunction with a rear-view mirror, it's a great addition, but it's important to make allowances for its shortcomings. On balance, though, I don't think I would ride on the road anymore without it. The audible alert means you don't have to constantly monitor your rear-view to avoid being startled by overtaking traffic, which is really nice. I recently travelled to Ireland for a couple of weeks and rented a road bike while I was there, so I could punish myself in the Wicklow Mountains. I brought my Garmin and Varia with me to install on the rental. The Varia worked great - alas, Ireland seemed to flummox the GPS - I ended up navigating by Google Maps (I used to do it with an Ordinance Survey map in my jersey pocket, so this is progress, I suppose).
Ok, this must be a Doppler radar, at least as a primary sensor. A Doppler reacts to the doppler effect and looks at the difference in frequency between the radar signal beeped out at the traffic behind, and the returned signal that bounces off the traffic behind you. That difference indicates how fast a car is approaching you, and can be analyzed to indicate a threat. If a car behind is moving at your speed (congrats for having 45 mph legs --lol!!!), then first it is not a collision risk, and secondly it should return to the radar display after the speeds diverge (either you slow down or the car speeds up), and thirdly the radar may have been built to hold the now-innocuous target in the display for some time, for your information.
I say these things because if my experience designing automotive safety radar-based systems. I don't have any direct experience with any Garmin stuff. I've been using a Wahoo on my bike, and actually the Navi and ride tracking functions are not very interesting to me. Bio monitoring (HR, cadence, performance history) are interesting, as is iPhone status.
Can Garmin devices compatible with the Varia also drive a Wahoo Snap indoor cycling stand? That's one of my other blockages to pulling the Garmin trigger, because what you folks say this little radar does sounds pretty good to me!
Human-machine interfaces are still a big problem in cars, and not surprised if there are still improvements for Garmin to make - like volume and warning style.
As far as other cyclists go, I also hate the nanny-like response where the person dinks around slowly until I pass them, regardless of whether a pass is safe. If bikes had cooperative safety systems perhaps there could be better rider cooperation, but this is still very advanced for cars.