I’m coming from a classic trainer with a speed sensor. Using that I would tell Zwift the resistance level of the trainer and then I would use the gears on my bike to adjust the difficulty and resulting watts during a ride.
I recently purchased my first smart trainer, a Wahoo Kickr Snap, and I did a workout with ERG mode. It handled all the resistance for me, no need to change my gears.
I’m now wondering how to control the resistance of the trainer during a free ride or race. It seems that I can change my gears like I did on my classic trainer but I’m wondering if there is some more automatic way or some way through the companion app, etc. I know there is a trainer difficulty setting but I believe that deals with inclines. I’m wondering how to control the overall resistance, like on a flat.
Basically when in ERG mode the trainer tries to maintain the desired power level regardless of what gear and/or rpm you are turning. In SIM mode the trainer simulates riding outdoors by recreating the resistance you would feel riding up a hill and you choose the amount of power based on the gear/rpm you are turning.
In other words in ERG mode the trainer will try to hold say 175 watts regardless of your input or what the road looks like in Zwift. Uphill, downhill, and flat will all feel like the same resistance to hold that 175 watts. In SIM mode you will have to adjust your gearing and cadence just like you would going up/down hills and riding a flat road outside.