2014 macbook air vs iphone XS

i have been running zwift on my iphone XS for a while (ever since my ipad air 2 gave up the ghost) with mostly positive results. i’m using a CycleOps (Saris) Magnus trainer, a Wahoo TICKR heart rate strap, and Wahoo Blue SC speed cadence sensor, and use the speed from the trainer rather than from the wahoo sensor.
my main beefs with this setup are the small display and the unreliability of uploads of screenshots triggered from the companion to Strava. (Companion is running on a Samsung Galaxy Tab A which is too underpowered to run the main app.)

yesterday, i rearranged my basement training space and added a table i could set my laptop on. tried zwift that way (with the same companion on samsung deal).

early 2014 Macbook Air, MacOS 10.15.7, current version of zwift app. freshly rebooted so no debris running to compete for cycles.

  1. the cadence numbers were consistently low - with the iphone they are so far as i know pretty accurate. where i should have been seeing high 70s or low to mid 80s, on the macbook i was seeing 61 with a brief glimpse of 62 rpms. not really acceptable, as i’m working to bring my cadence up and i need to know.
  2. the graphics slowed down a lot about 2-3 minutes into the ride, and the cadence numbers were in the 30s when i damn well know i was in the high 70s.
  3. the heart rate and power seemed ok, it was talking to the Magnus fairly well through out.
  4. screen shots taken through the companion app failed to upload to Strava properly, but then, it doesn’t work well from the phone either.

so i guess i’m back to the phone for the time being.

at the suggestion of a friend, i ordered an inexpensive ANT+ USB dongle. have used it twice; the cadence numbers are still wrong, but differently so.