Issues with zpower drop-outs for child's bike

Requesting help from someone who is familiar with speed/cadence sensor troubleshooting…

I recently purchased the small bike adapter for my Kurt Kinetic Road machine so that my son can use Zwift as well. I set up a free Child’s account for him and installed the adapter, but now i have two problems:

1. Signal dropping when child uses
I’ve set everything up correctly and installed the Garmin cadence and speed sensor on his bike. However when he pedals it seems as though Zwift is only getting his signal intermittently. He goes from 0 watts to 30 watts to 50 watts when back down to 5 watts, then 15 watts then 5 watts, etc. I had no signal issues with my bike previously and i’m wondering what’s happened.

2. My bike watts have greatly reduced
When i put the sensors back on my bike and try to use Zwift, i can generate constant power, unlike my son, but my power has been drastically reduced. ie. I can normally hold 200 watts pretty easily but now i can’t seem to hold much past 80watts.

Any thoughts?


Maybe the distance between the speed sensor and the magnet? You could try a stronger magnet and see if that helps.

Sorry this comes across as a silly question, but…is the speed sensor the one that attaches to the hub of the back wheel? And if so, where is the magnet you’re talking abut?


Yes, the ones I have used have a magnet that attaches to the spokes of the rear wheel and is the sensor and the magnet are too far apart you will have intermittent readings.

Thanks. I managed to notice that my wheel size was set to 20inch wheels when i was on which is probably why my speed was incorrect.

So, now i’m just left with one problem. Why would the signal be ok for my bike but become intermittent when my son is on his bike? We’re using the exact same sensors and his wheel size was set to 20 inch. Would the revolution speed of the tire affect the signal?

Which speed sensor are you using? My guess is still the distance between the sensor and the magnet on the spokes.

Hi Paul,

I’m using this one so no magnets i dont think:

The only thing i can think of is perhaps the revolution of the cadence sensor is shorter for my son because his crank is obviously shorter so maybe that’s why zwift is having difficulty sensing the power sometime.


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Zwift does not use cadence for power calculation, only the speed sensor.

Test the sensor with your bike computer and see if it does give constant speed.

OK, it just sits on the hub.

Are you using the same device to run Zwift for your son and you?
Is the setup in the same location?

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Yes, same device. Same location.

i’ll try again this evening and do some troubleshooting. Perhaps it was just a bad night for the wireless. I’ll report back. I appreciate your help.

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