Help with Edge 800 Cadence Speed Sensor

[Nomadski]

Im planning a 55 mile ride tomorrow (furthest yet if I manage it) and installed the GSC 10 (sic?) Garmin sensor unit.

It seems fitted fine, both red and green lights come on when wheel or crank is turned, and have set Garmin's Bike Profile Setting to Spd/Cad, it has picked it up and given me the ID and says Connected.

Now my understanding was when the wheel would turn, the speed would be recorded. But my Garmin is sitting on the desk in front of me reporting 0.2 - 0.4 mph!

Im guessing it is still using GPS for its speed with its fluctuations being due to being indoors?

If so how do I tell it to use the Sensor which is stationary?

 

[Nomadski]

Oh.

So I cant follow a course / track a ride AND use the sensor to track speed?

That seems...strange.

 

[T.M.H.N.E.T]

My mistake. It will base speed off the sensor and not GPS

It can't do that until the wheel is turning of course. My unit often shows small speeds when the bike is stationary, but not enough to trigger my auto-pause setting

 

[HLaB]

For Indoors youve got to go to the settings and switch the gps to off if you dont it overides and if youve got the unit set up right and its in the open (visibility to satellites is quite good) and it auto pauses when stopped; Ive never had a problem outdoors.

 

[HLaB]

Oh.

So I cant follow a course / track a ride AND use the sensor to track speed?

That seems...strange.

Who said that of course you can

 

[T.M.H.N.E.T]

Who said that of course you can

Twas my error. I deleted the post and reposted

 

[Nomadski]

So, just to clarify, I understand if your using the sensor indoors (on a trainer) you would turn GPS off, but when Im outside following a course on my edge 800 I have to have the GPS turned on, is it using the GPS or the Speed sensor to measure speed?

Im just confused why there would be ANY small micro error in speed when the wheel isnt turning?

 

[T.M.H.N.E.T]

It uses the sensor.

 

[Nomadski]

Thanks, guess I'll have to monitor it tomorrow when Im under 'clear skies' (I'm being sarcastic of course, I live in London where clear skies are a myth at the moment!) and check its not recording speed when I'm stationary.

 

[Gary E]

Mine does the same thing if I leave the head unit turned on indoors.
The head unit will always try to use data from the cadence unit whenever possible but if the cadence unit isn't sending a signal it will default to using GPS data. GPS data isn't always that accurate (especially indoors) so as your location keeps changing slightly (according to your GPS location anyway) it records a small speed.
If the wheel isn't turning the Cadence unit will turn itself off to save power after a short time and so that's why your head unit is using GPS.
To confirm this just spin your wheel and the Cadence unit will come to life. When the wheel then stops your head unit will show 0 mph for a short while until it powers off again and the head unit switches back to GPS.
The good news is that on a ride this won't be a problem
Hope that helps/makes sense.

 

[T.M.H.N.E.T]

Thanks, guess I'll have to monitor it tomorrow when Im under 'clear skies' (I'm being sarcastic of course, I live in London where clear skies are a myth at the moment!) and check its not recording speed when I'm stationary.

Small fluctuations are standard. If it's going 30mph sitting still there is a problem

 

[Nomadski]

Mine does the same thing if I leave the head unit turned on indoors.
The head unit will always try to use data from the cadence unit whenever possible but if the cadence unit isn't sending a signal it will default to using GPS data. GPS data isn't always that accurate (especially indoors) so as your location keeps changing slightly (according to your GPS location anyway) it records a small speed.
If the wheel isn't turning the Cadence unit will turn itself off to save power after a short time and so that's why your head unit is using GPS.
To confirm this just spin your wheel and the Cadence unit will come to life. When the wheel then stops your head unit will show 0 mph for a short while until it powers off again and the head unit switches back to GPS.
The good news is that on a ride this won't be a problem
Hope that helps/makes sense.

It makes perfect sense, thanks!