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New Varia 515 - 6 or 7 misses / false negatives on 2 1/2 ride

Hi there

I recently bought an new Garmin RTL515. Before fitting it to my bike, I sat in on the wall outside my house just to test it out and its picked up everything, even cars that were further away than I’d expect.
So I fitted it to my bike and while generally on long straight rural roads it worked flawlessly, but as soon as I went through towns with more vehicles and more built up, it would miss on multiple occasions.
These two examples stood out
1) I am going down a road which bends off to the left and straightens out. Ahead of me to the right an Amazon van is looking to enter the road from a driveway. I pass the van and then it moves onto the road and then is behind me. At no stage did the van trigger the Varia and it then slowed and stopped to drop off another parcel.
2) I am approaching a junction on my left. There is another ahead car signalling right, I am signalling left. I get to the junction first and go down the road. A few seconds later the other car joins the road and is probably 20 meters behind me, but doesn't trigger. It actually was behind me for about 1/4 mile and never triggered at all until RIGHT at the end when it started an overtake.
There were several other misses but I only started paying attention to the last two. I also had two false positives which I think were caused by passing metal farm gates (extremely brief, not a concern)
I don’t think its faulty because if a car approaching from a long way away and comes into range it triggers every time, but it seems to be fooled by cars that enter the scene from a much closer range (ie the Amazon van starting to move, or the other car pulling onto the road). Dcrrainmaker mentions thar cars that maintain the same distance can be missed, but I don’t think this can be case in those two examples?
  • I wonder if both these cases involved vehicles that were travelling no faster than you (until the 2nd accelerated to overtake)?

  • The radar is only triggered by speed. If something is faster it will react. If you stop and somebody walks behind you, it will trigger. If you stop just outside of the house and close the door behind the bike, it will trigger.
    If somebody isn’t faster than you, it will not trigger. If cars run up to you, it will trigger. If they slow down to your speed and stay at that speed, it will give you "all clear“ after some time even if the car is still behind you.
    In my experience of 5 years riding with Varia, it will also detect cyclists behind you like they were cars. The Varias i have (1 510, 1 515) perform pretty solid. You will get a feeling for it, they are not totally perfect but quit helpful. 
    There is for sure a small delay built in to prevent a lot of false positives wich can mask a car like in your second case.

    You will still have to look behind before turning or overtaking. I also ride with a Beam Corky mirror on my roadbike wich i can fold out when there is more traffic or in cities. 

    Enjoy riding and don’t overthink the gadgets.