Export the file and do the calculations yourself. Or you can use the head unit that takes speed off the hub. Is there no option for the Garmin to do this as well? Or does the Garmin only take speed off of it's GPS or speed sensor.
A computer program can only do so much. Golden Cheetah works very well if you are using it with the PT head unit. This is really the Garmin's fault for not taking speed readings from the hub.
I just looked at the PT manual (I don't know if you have a PT or what, but I assume it's similar across the powermeter spectrum)... Is there any way you can get the Garmin to accept speed and torque info from the ANT+ stream? Apparently the hub will transmit this data ("torque at wheel" message, whatever that means, which gives you torque, speed, and distance from the hub unit). The other option is "power at wheel" which only transmits power and cadence, no speed, which is apparently what you are using.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter