Ok, tore apart my crankset to change from a smaller (elliptical) chainring to a larger circular. Unbolted everything (dzero spider included), cleaned, greased and locktite’d as appropriate. “New” chain… waxed… has some more links than the collection I used for the smaller chainring. I then did a quick spin around the neighborhood to make sure everything was happy. Quarq app shows offset went down slight – from 585 to 541**. I repeated the offset calibration multiple times and it was always +/- 4. At rest, the torque reading would cycle between 0.00 and 0.18 Nm or so. Very slight pressure on the crank would increase the torque, as expected, but no way to validate the accuracy. What I should do is get the tacx neo thru-axle adapter so I can get a comparison, but I’m less convinced that’s $50 well spent.
** Yes, the number is a bit high… went wonky when I bricked a small log jump in a race over a year ago. Doh! but it’s been very stable at this higher offset and feels about right. What little I’ve seen said up to 500 is fine, even under 1000 is probably fine. Outside that, definitely something wrong. Maybe I should ring up sram about it, but seems fine. I’d rather not worry about it unless someone at sram is reading this and wants to send me a new one!