Newbie questions on Speed and Power measurement


I used Zwift yesterday for the first time, having bought an Elite smart turbo trainer this week.

I know the Turbo can provide a power measurement, but I decided to use my 4iiii Precision (crank arm) power meter instead to provide the power data - have I done the right thing?   I presumed it would be more accurate and of course at least it’s the same as when I ride on the roads in terms of power measurement.

Also, I noticed that when pairing sensors, you get a choice of Power or Speed.  I’m a bit confused by that, I have a Garmin ANT+ Speed sensor attached to the rear hub, but it seems it isn’t being used.   Is Zwift calculating the speed some other way?   Obviously I chose to pair my power meter rather than the speed sensor.   Perhaps Zwift simply looks at how far you’ve ridden and the time, to calculate the speed?   Or does it use the power data too somehow?


Go with the Power (crank arm) , ask your ? speed That for  Zpower  Noobs fake in game power. I would take the speed sensor off, killing the battery doing you 0 good.

I would also use the 4iiii so you can compare in-door and out-door rides. If you have a power meter or smart trainer paired Zwift will not connect the speed sensor on your bike and it will not be used for in-game speed.

Speed within Zwift is estimated based on watts, the weight you entered, in-game bike used, in-game drafting, and virtual elevation changes.


Thanks for the replies.  I’ve done another ride this evening, just the 30 minute workout ‘Jon’s Short Mix’.

I’m not sure why, but there doesn’t seem to be enough resistance, I found that I spent most of the ride in top gear (52T x 11T) just to sustain the required power figures for the different bits of the workout.   Bizarelly though, during the cool-down at the end of the workout, I changed down several gears to drop the power to 60W, cadence was higher of course but my speed went up…very odd.

I’ve got the trainer paired over ANT+ FE-C, I do realise that during Zwift workouts the gradients aren’t used (so the resistance doesn’t change) but the ‘base’ resistance just doesn’t seem to be enough - I’m spending all the time on the big cog (52T) and just switching between the top 3 (smallest) gears at the rear.   I’m no superman btw, my FTP on the road (using the same power meter) is 225W.

Any thoughts?   I have my 4iiii power meter calibrated, and am using that for power and cadence.  Obviously no speed sensor paired.

Maybe I’m still learning about how Zwift deals with power/speed but something doesn’t seem right.

Further to my post above, I’ve now seen that  There is a ‘Trainer difficulty’ setting on Zwift.

I presume setting this to 100% may solve my problem…does it increase the resistance on the flat as well as up hills…?

Trainer difficulty: it does increase hilly resistance it will kick in much harder. one down side  going down hill you will be free wheel more.