Speed sensor 2 on two wheel sets - autocalibration?

no one knows how the autocalibration works? 

I would go with manually entering the 'Wheel Size' and remembering to update it when you change the wheels.

How well automatic calibration works depends on your local conditions. For the calibration period if the track is a straight line on level ground with a clear view of the sky (for optimum satellite reception) it should be fairly accurate. Anything less and the accuracy declines.

thanks for your answer, but the question was not if the autocalibration is accurate or not, but how it works.

Do Garmin autocalibration every ride, also if the wheelsize was already set by autocalibration? 

That would reflect change of wheels, but if not,do I have to do something manually to trigger autocalibration after change of wheels? 

Automatic calibration of 'Wheel Size' works by comparing the revolutions of the wheel against GNSS distance until a consistent value for the wheel circumference is arrived at. For a given set of environmental conditions, how long this takes and to what degree of accuracy will be head unit specific.

When in 'Auto' the Garmin head units will perform an automatic recalibration when they detect a difference in distance compared to the GNSS distance. What the threshold is will be head unit specific. If the difference in circumference between the two wheel sets is not very much, it may not be sufficient to trigger an automatic recalibration.

If the change of wheel set does not trigger an automatic recalibration, then apparently on Garmin head units it can be triggered by changing 'Wheel Size' from 'Auto' to 'Manual' then back to 'Auto'.

Or you could just get another speed sensor and have one on each wheel set.

Thanks again ;-)

Actualy, my question shut be formulated a bit diffrent:

Do Garmin comparing the revolutions of the wheels against GNSS distance every ride, also if the wheelsize was already set with autocalibration? 

If and when then the autocalibration will be triggered it an another topic. 

BTW: I already have two speed sensors vers2 - on MTB and ROAD bike, but I also have a more wheelsets for ROAD bike. 

Garmin head unit users on other forums have stated that when they changed wheels/tyres an automatic recalibration of 'Wheel Size' was triggered during the next ride which suggests it is probably done at some point during every ride.

Automatic calibration and recalibration only happen if the 'Wheel Size' is set to 'Auto'.

If 'Wheel Size' is set to 'Manual' the head unit takes the value for wheel circumference you enter and uses that without verifying it against GNSS to see if it is in any way accurate.

What calibration method you choose to use in the end comes down to whether you are primarily interested in speed data or distance data from the Speed Sensor 2.