I believe you're actually supposed to use the bigger ring in erg mode - it means a lot less stress on the tire since the tangential force at the roller will be much smaller. If the tire is doing 10km/h, the braking force from the roller needs to be 3x higher for a given power level than if the tire is doing 30km/h. This means more slippage (or more clamp-down force to prevent slip), more heat, and more wear. On both my kickr and CT I usually do my erg workouts in the fastest gear that doesn't generate too much noise. In several thousand km, I haven't popped a tire due to external problems on the CT (usually installation problems from rushing my trainer tire on).

More on-topic: My kickr is still reading crazy high, but it has been consistent from workout to workout at least.

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STAC Zero Trainer - Zero noise, zero tire contact, zero moving parts. Suffer in Silence starting fall 2016