I bought online a Cube Nuroad Race FE 2021 that comes full with fenders and dynamo lights. The front light is the Supernova E3 Pure and, although not stated clearly on Cube's site, the rear light should be Cube Pro-D dynamo mudguard rear light that includes stand light function according to Cube's site.

Now when the bike moves, both lights shine brightly and all is well. When I stop however (even after a long ride), the front stand light works, but the rear stand light does not. I noticed however a very very dim light in it.

I have asked Cube for help, but I am really wondering what is going on and whether there is a way to troubleshoot this. I know that this is not a bad component issue, since other users report the same behavior.

Also a minor note: I checked Supernova's manual and the only interesting thing I found was that the rear light should NOT be grounded to the frame. I checked it and could not see any ground cabling on the rear.

There are two wires going back to the rear light.

  • The bike is brand new, and as a Cube customer you are almost certainly in Europe, likely Germany. Let Cube deal with this problem. It's covered by European consumer rights. – gschenk Oct 12 '20 at 23:04
  • Asked the shop I got it from. They said that there is no stand light on this bike. Pretty much a disappointment for a 1.8k bike! I have asked Cube as well but they have not replied for several days now. Note that on their site, Cube does not claim that there is stand light functionality in the rear light, so I cannot make any claim unfortunately. – Kostas Oct 14 '20 at 7:46
  • Well, than everything is all right with the bike and the light, only your assumption was wrong. Simply buy the stand light and install it? – gschenk Oct 14 '20 at 9:01

It would seem likely there's a problem with the rear light's capacitor. I'm a generator light user and nerd but not a real electronics person, so maybe someone else can answer better, but my understanding is that what you're seeing (everything works but the standlight is dim) indicates a capacitor that's barely functional. You could open the light up and try following standard methods to test and then replace it. Dropping in another fender mounted tail light is also an option, but they each have their own needs for where to drill the holes to get a good angle, so you might give up some of the integrated look of the stock light on that bike.

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    Thanks for the answer. It actually looks that other users of the bike have the same issue, so it is either a bad assembly, or simply that the rear light somehow does not work with the front light. – Kostas Oct 11 '20 at 18:07
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    Given this light has issues, I'd absolutely recommend a second rear light, autonomously battery powered too. – Criggie Oct 11 '20 at 18:34
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    I thought that when the standlight went on my B&M Secula+ that got immersed in water. Replacing the capacitor didn't help, and the old one tests fine. I'm not saying it definitely isn't the supercap this time, but it's by no means certain – Chris H Oct 11 '20 at 19:54
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    @Criggie: I spent 200 euro more and added about 1 kg of weight just so that I do NOT care about batteries. So sing battery lights does not make sense, unless I strip and sell the dynamo wheel and the dynamo lights. – Kostas Oct 12 '20 at 8:06
  • @kostas you're in Europe then, where Dynamos seem to be much more accepted. In 5 mins I can't even find a seller in my country listing a price for a Son dynamo. – Criggie Oct 12 '20 at 11:13

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