Why can't Zwift apply gearing to resistance?

I have SRAM eTap which communicates the gear I’m in via ANT+.  Couldn’t Zwift use this to set resistance on the road to provide the most realistic ride?

You already change the resistance you are feeling because you’ve changed gear. Otherwise no idea what you mean.

I mean it’s not realistic to be doing 55 kph (35 mph) in a 36-19 gear doing 90rpm cadence.  But I get it now, in Zwift it’s power only.  OK fine.

Hi Claude,

eTap will not transmit power, as it is only transmits a gearing choice. To communicate power, you’ll need a power meter or a smart trainer.