Finally got around to picking up an Edge. The first thing I did was check the speed with the car and it was accurate and was very stable above 35mph (you know where we all ride).

After about 4 rides with the same results, I wanted to find if the problems I'm having are common or if I have a defective unit.

1) Speed jumps around quite a bit under "open sky" It's constantly jumping up and down even when holding a steady cadence. Not much but it can vary 1mph.

2) When going under tree lined MUP or even an overpass on the highway it can easily drop 3-4 mph for then entire time. I do not get a weak sat error during this.

3) After rides I upload to both Strava and Endomondo as they track different things. Average speed, Max speed and Duration are all slightly different (never ran into this with my phone)

At first I figured that the speed reading was just going to be an irritation and that it would get's it average speed info (I know here we go) by calculating the time and distance, but clearly not so. I do enjoy a little Strava competition with friends so this is a concern for me. One or two tenths here or there...

I suppose the next thing is to continue to use my phone for a few rides, but wanted to know if these are common issues or if it's just my device.

Thanks.

That is totally normal for any GPS device I've ever used. To eliminate it, use the Garmin GSC-10 speed/cadence sensor. Your Edge will pick that up and use it for speed instead of GPS.

https://www.gps.gov/systems/gps/performance/accuracy/

Well, funny thing for me is that even when I am at a complete stop the garmin registers 1mph and jumps up and down from 0.5 to 2 and back and up and back etc. I have a GSC10. I disabled the Cadence sensor (cadence sensor in power meter) but still have the speedo with magnet.

Endomondo and Strava probably interpret the data differently resulting in disparities. There are always differences when I load to Training Center and Strava.

https://strava.zendesk.com/entries/2...-is-Calculated

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.

is it running the latest version of the software, might pay to check for an update

Thanks!