Originally Posted by
nhluhr
Also totally normal with a GPS device. The accuracy is going to be around 3meters, but that means the position could bounce around anywhere within a 3 meter radius all the time while you're stopped. This means you'll inherently get some readings unless you correctly configure your Garmin.
If you've got the GSC-10 then your Garmin is clearly NOT set up correctly - it is still reporting GPS based speed, not wheel speed.
Here's a hour and a half on the trainer and the resulting spastic trace. If I didn't use my Powertap for speed, the Garmin would have been reporting these positional variations as speed instead:
Thank you very much for clarifying that. I'll go home tonight and set the Garmin the way it's supposed to. I use the garmin in the trainer and I just turn the GPS off, then it measures speed based on the sensor since the GPS is off.