How to record actual mph

During the FTP booster workouts I’m not getting the actual mph. For instance, I’m pedaling at 16mph but Zwift is showing the avatar moving at 2mph. Today I rode the 54 minute FTP Strength segment and Swift recorded I rode only 5.6 miles. This is absurd.

Which device says 16 mph? Your speed in Zwift is changing with the route (you are slower uphill, for example).


Adding to the information in the last two posts – “speed” and “mileage” will also be affected by using erg mode on smart trainers, as used for workouts.

When you’re pushing X watts, Zwift will move you in-game at the speed X watts would get you in that situation, given your Zwift weight, Zwift height, Zwift bike frame, Zwift wheels, and given the environment: incline, road surface, drafting or lack thereof.

Meanwhile, the speed sensor on your actual bicycle (whether separate or inside your trainer) is recording how fast the rear cassette is turning and deriving road speed directly from the cassette speed. That calculation isn’t affected by erg mode. You may be turning the cassette around at speed Y by pushing 50 watts or 400 watts; in the same gear it all depends on the resistance that erg mode applies. Erg can also apply 400 watts in your biggest gear or your smallest gear; erg mode is (outside of extremes) independent of gearing. But in your biggest gear you’ll be turning that rear cassette around something like 5 times faster than in your smallest gear, while producing the same power.


Very same issue here! Very disappointing and no apparent answer???

Plenty of answers have already been given in this thread.

No-one reporting this issue in this thread has provided any sort of information about their setup, so with nothing to go on then there aren’t going to be highly specific answers.

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This could help you:

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Using compatible speed and cadence sensors. Using Nasbar fluid trainer.


Short answer your garmin and Zwift won’t show the same speed. Long answer, @Paul_Allen posted above.


Hi Bill. I am a Novice to ZWIFT. I’m setup on the Wahoo Kickr and have done the ZWIFT group rides which almost always show the actual mph. I know that Garmin reads different.

I’m doing the 6wk FTP Builder training program. Although I completing the workouts as established, my actual workouts are not reflected.

For instance, yesterday I successfully completed the 58 minute Strength Training segment of the FTP builder. During most of the ride Zwift’s avatar was riding at 2mph. Didn’t matter how fast I was spinning or the power output. Why?


What course were you on? Are you using ERG mode?

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ERG is off per the training program instructions.

Most, if not all, workouts use ERG mode which is only concerned with the power and cadence you’re putting down. I’ve done workouts on flat Zwift roads and to get the power level called out for by the workout (110 watts, IRRC) ended up spinning at 110rpm in top gear for a wheel speed approaching 70kph (I think that’s what it was). And then I’ve done Zwift Academy workouts on The Alpe and ended up going 8kph while putting down 200 watts. When in ERG mode wheel speed has nothing to do with how fast you’re really going in our little fantasy world.

Interesting. Not aware of the EGR mode??

@Bill_Epperson check this post out on Zwiftinsider. ERG mode is only available on smart trainers however.

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Okay Bill.

While riding the strength training portion of the FTP Builder there’s a segment where you ride 205w for 10seconds. Prior to the segment you are instructed to turn off ERG mode.

No matter if you use ERG or not.

If the workout ask you to do 70w and your avatar is on a climb then your avatar will go very slow. Even in a workout zwift will still adjust your speed based on your power and the terrain.