Garmin Edge 800 Problem

[Michael Katz]

Having an odd problem with my new Garmin Edge 800. I have it set up with the rear wheel sensor, cadence and heart rate monitor. When I am at a dead stop, it often shows a speed fluctuating from .1 to .3 mph and then may return to zero. Happens in a variety of locations, with no correlation to the presence of power lines, other bikes, garage door openners, etc. Has anyone else encountered this? Solutions?

[jdhansen63]

This happens to me too. I assume you are riding with the GPS on. If so, the Garmin uses this to calculate speed not the wheel sensor.
JH

[csm]

mine does that too. it doesn't seem to add to the mileage.
I think I read somewhere that they all do that.

[KF9YR]

If you have the speed/cadence sensor installed there is an algorithm used to calculate the correct wheel circumference and then the magnetic pulses picked up from the spinning wheel is used to calculate your speed.

If you have the wheel circumference set to manual you need to input the wheel/tire rollout as in the manual.

If you have the unit in your hand and it is not receiving signals from the cadence/wheel sensor it will revert to calculating speed from the gps signals. When the unit is stationary it may show the speed varying a little bit as the gps receiver calculates position. Basically it thinks you're moving a tiny bit because the signals received from the satellite vary (you may be "jumping" 10+ feet in position since the accuracy of the position isn't able to be calculated to the inch).

An earlier version of the firmware didn't have this "problem" but they probably just didn't display the results of small movements and wanted to improve accuracy by displaying all movements.

Bottom line... This is normal with the current version of the software and if you use the cadence/speed sensor the speed should be calculated using the sensor and not the gps.

When my sensor battery goes low I have seen my speed to drop to 50% of my current speed then jump back to correct speed. This happens on and off as the sensor signal is getting weak and the head unit is only picking up around 50% of the transmissions. If I check my ride stats after riding a loop I ride all the time my recorded distance will be short. After a couple of rides like this I change the sensor battery and it starts working correctly again.