Originally Posted by
twocicle
Alcanbrad, most of those concerns are inconsequential. Pedal power meters will record the wattage effort YOU apply to the pedals regardless of whatever the stoker does, and does not measure power applied to the drivetrain as a whole. Sure the stoker input level could make it easier or harder for you to maintain a certain speed, but there is nothing to stop you from adjusting your effort level accordingly.
This. I've been training with power for 10 years now, and 2 years on the tandem. I've used a powertap and Quarqs on single bikes, and Look Power pedals and Garmin Vectors on the tandem.
Any interference in one rider's power reading from the other rider's efforts I believe is deminimis. I base this on a couple of things. If I pedal at a constant effort and my stoker unclips, my power remains pretty much constant (although speed drops). If I unclip, and my stoker continues to pedal, my power meter will show some power, typically 0-3 watts. So there's a tiny influence. Additionally, the readings appear pretty consistent with perceived effort.
I do find that my power is lower on the tandem than on the single bike. However, I don't believe this is from interference from the stoker. I think its more a function of difference in calibration of the different meters, subtle position differences, and just the dynamic of riding a tandem.
And what's most significant is that the Garmin on the tandem is consistent and repeatable. So, even if it reads lower than the Quarq on the single, it does so consistently. And the key point for training with power is consistency, which is more important than absolute accuracy.