I would like to be able to use speed sensors on multiple bikes. I know the the sensors can auto calibrate so the same single sensor could be used on multiple bikes, but the consensus seems to be that on twisty MTB trails it will likely not calibrate correctly.
Yes, you should be able to pair multiple speed sensors to the E130+. Probably a bit unpredictable what would happen if both were sending signals at the same time, but presumably you'll only be riding one bike at a time 
Yea, I don't find calibrating on very twisty trails particularly accurate. I'll calibrate on a straight road or trail, and then set the manual calibration value from that. Note that on those twisty trails, the distance you get from a well calibrated speed sensor will probably give you 1% to 2% extra distance. It's probably more accurate, but won't match your buddies distance. And 1 to 2% on the trails is kind of just noise anyway.
You also would need to make sure the tire pressure is consistent from the calibration ride if you manually set because that could have a measurable effect on distance from a wheel sensor.
