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Connecting different sensors for speed and cadence at the same time (smart trainer)

I just bought a smart trainer and use it together with my Edge 520. Pairing was pretty smooth and everything seems to work properly. However I was wondering which speed and cadence information is actually shown on my device.
I have a seperate Garmin speed and cadence sensor on my bike, which is paired with the edge but the smart trainer is calculating speed and cadence, too. So, how do I know which information are shown - the ones from my seperate sensor or the ones of my smart trainer? I would assume that the ones of the seperate sensor are more accurate so I would like to make sure it takes these rather than the other.

Thanks in advance!

0 schinder over 7 years ago

Neither one is accurate since speed and distance are both zero on a trainer. Which to pretend to believe comes down to which one suits your needs better. The cadence should be the same from both or something is wrong. It's hard to say which one your 520 is showing; that information is probably in the FIT file but I don't know of any simple site/software that can show you the source. But it doesn't matter in the end, they're equally wrong. If it were me, I'd believe the smart trainer, since it may be doing some funky stuff taking power, resistance, and pretend incline into account to fake a "realistic" distance. But in the end, distance isn't useful on a trainer, and isn't that useful outdoors (but at least it means something real outdoors).

0 thg_ over 7 years ago

I don't understand how the cadence of my trainer can be correct at all. This is totally dependend on my currently selected gear - something that the trainer can't know.

0 PubBike over 7 years ago

How it determines the cadence depends on the trainer and how smart it is. Every time you press on a pedal with either leg there is an observable change in the rotational speed of the crank. The trainer might be analysing irregularities in the crank speed to determine the cadence, so doesn't need a conventional cadence sensor with either a magnet or an accelerometer. This can be achieved through signal processing.

0 thg_ over 7 years ago

Thanks PubBike. I wonder if my trainer is really that smart, but it does make sense.

Selecting the trainer sensor in my garmin, I found a setting for the gear ratio. Is this somehow connected to calculation of cadence? Why do I have to specify a certain gear ratio? Am I supposed to cycle in the same gear on a trainer all the time?