Speed sensor 2 wheel size storage location?

On the 830.

The sensors don't receive data. 

You can configure the wheel size in the Speed sensor 2 if paired as a device in GCM however this is only used in an activity which the speed sensor has recorded itself. If you are recording an activity on the edge as dpawlyk said the wheel size is for each sensor is stored on the edge

Thank you both. That is what I thought. I am getting a replacement edge. So, i will need to recalibrate each sensor.

No problem. If you back up your settings & transfer them to your replacement edge. All your sensors should be set up as they were previously

The wheel size might be stored in GCM and not on the sensor. 

You might be right.

I did a test where I changed the wheel circumference from the default in GCM on my phone & synced. I then removed it from GCM/GC & paired it with GCM on the phone again. The wheel circumference on the initial setup screen displayed as I'd changed it.

I then removed it from GCM on the phone & paired it with GCM on my tablet. The wheel circumference on the initial setup screen had reverted to the default setting.

Next I removed it from the GCM/GC on the tablet & paired it with GCM on the phone again. This time the wheel circumference on the initial setup screen had reverted to the default setting.

So it's plausible that there may be some settings held in GCM on different devices & with your Garmin Connect account. So whichever version of GCM is paired with the sensor the settings on that version determine the initial settings of the sensor when paired even if it is deleted from GCM on one device & added to another 

From a design standpoint, it's much simpler to have sensors only send data. If they also receive data, you'd have to wake them up to get them to receive it. It makes more sense to keep software off of the sensors because there isn't any provision to fix bugs on the sensors (so, they have to be as simple as possible).

Essentially, GCM becomes a head unit (something that works like an Edge). It's easy to update GCM.

It seems like a plausible solution.

TBH I don't have the Speed Sensor 2 paired with GCM normally. I'm waiting (probably in vain) until Garmin do something about the creation of separate activities every time the sensor is woken from it's sleep state. Even just wheeling the bike a short distance, the next time it syncs it'll upload a 0.02 Km ride lasting 30 seconds. There really needs to be some distance/time threshold, which can be set where activities, which don't meet the criteria are discarded 

The sensor typically just sends wheel clicks when paired with a head unit, but the new speed sensor can be used without a head unit and will record distance for users that have configured it on the sensor. When GCM communicates with the sensor it will upload the FIT file from the sensor and send it to Garmin Connect. In this mode the wheel size is stored on the sensor so that it can compute distance,

If the sensor is paired and in communication with a head unit then it does not record the activity locally. The head unit sends a message to the sensor to tell it that it is using it. This disable the local recording of distance on the sensor.

aweatherall said:

If the sensor is paired and in communication with a head unit then it does not record the activity locally. The head unit sends a message to the sensor to tell it that it is using it. This disable the local recording of distance on the sensor.

Hi thanks for the description. However last weekend I did a 250km ride. After 115km I stopped for 5 min to fill my bottles & put the edge to sleep. I then had a longer stop after 200km for a coffee where I did the same. When the SS2 synced later it uploaded a 115Km ride but not the other parts of the ride.

So if correct there may be a caveat to what you said, which is if the sensor wakes up even if it connects to the head unit if the head unit isn't currently recording an activity ie at the start of a ride then the SS2 begins recording itself