Two times out for a test-date

I used last week to run Zwift on two of my outdoor runs. On Monday I did a little over 14km through the Bavarian dark. The second run, what also was the first Zwift Academy Tri Workout, was on the training schedule for Saturday.

Today you will get a little evaluation from me and what I noticed during and after the runs. For those who want it short: Zwift + Stryd show similar values for endurance pace as my Garmin with GPS. In the case of intervals, the pace differs more in the individual intervals. But Now: Have fun while reading.

The initial situation

A few details to start with: I have the current version of the Stryd and have calibrated the pod with my Garmin on the track. Instructions can be found here. I have the latest version of Zwift on my phone. I ran with my Garmin 945 and had the Asics DS Trainer 25 as my shoe for the 14k run. I also wore the DS Trainer during the calibration run for the Stryd.

For the second training session – 6×4 minutes with an increase in pace – I ran the Nike Next%. I had the chip on the same side of the foot. Still, there is a difference in position. Also this time the cell phone was on the handlebars of my mate (thanks Max). Maybe that’s relevant too.

So I would consider the two runs not to be directly comparable. Especially when I go into details like mean deviation or .. . To do this, I would have to run the same route a few times with the same shoe and the Stryd. Or do the calibration run on the track for each of my shoes and adjust the factor on the Garmin before each workout. Then I could make even more precise statements. But: I haven’t, because .. Yes, cause of lazyness.

How did I run the 14km?

I ran the 14km as an easy, moderate endurance run through the forest after work. In the picture you can see the kilometers and in the background the distribution as it is displayed on Zwift. Green are the kilometers I ran normally and the deviation between Zwift and Garmin is okay. It wasn’t exactly the same pace for a single kilometer. The best KM (# 1, # 4) had a deviation of one second. All others were up to 6 seconds apart. Due to the different length of the KM (if I have 4.46 on the Garmin and 4.43 on Zwift), all the following KM move accordingly. That definitely makes it harder to compare the KM here.

Therefore two things I draw from it:
1. The kilometers need to be clocked based on the app, probably based on Zwift. Only then pace and time per interval can be compared properly.
2. Relative comparison: Looks ok (not good, but ok) for the easy endurance run: 14.3km on the Garmin in a 4.45 pace to 14.5 in 4.47 pace on Zwift.

I can also write something directly about this deviation: The intervals marked in yellow are deviations that I can understand. Because there was a break in these intervals (standing, walking or something). I usually stop breaks on the Garmin. On Zwift, however, my avatar takes a few steps further. So I can explain the difference in the distance to myself. Only when the avatar Zwift stopps the time stopped there and the pace was no longer added to the avgerage.

I cannot explain the deviations marked in red. A difference of 15 seconds in a KM is a large number. And the last KM home has a few vertical meters and a traffic light on the way. But I don’t understand that the Stryd shows so much less speed here.

The Zwift Academy workout

The workout on Saturday consisted of (even more) intervals. I was hoping that these would be easier to compare, as I can stop precisely with my watch. I forgot that the intervals on Zwift are 4 minutes with a pace of under 4 minutes. Accordingly, thanks to Auto-Lap, I now have 1000m segments and a few 15 to 30 second laps on Garmin. I don’t want to make a comparison here, because of the pace deviations on the already easy endurance run. It would not make sence. I need better data to do that.

What worked very well, however, was the teamwork between Max on the bike and me on the road. How should I hit the intervals with my cell phone on my arm when the Stryd shows different values ​​and pacing is difficult? In my opinion, not at all.

So I asked Max to give me the currently required pace and the currently displayed pace. After a few exercises at the beginning and the coordination on the announcements, everything went smoothly. My favorite quote of the day: “I think I’ll pick it up and then I’ll become a running coach”. The way he sometimes shouted instructions to me in a fraction of a second – like “Faster”, “This is a little too slow for me now” or “Stop, 14.4kmh now” – he can definitely do that.

11/12 stars. With pleasure again

In the end, we got 11 of the 12 intervals checked with a star on Zwift. The minimum requirement for the academy workout was fulfilled and the test passed successfully. Workout 1 finished while running. The second workout is due this weekend. But this time on the treadmill.

A few more facts about the second run:

  • Average speed: Zwift 4.00 / Garmin 4.05
  • Fastest KM: Zwift 3.28 / Garmin 3.26
  • Distances recorded: Zwift 13.18 / Garmin 13.01 (this time no pause that could explain a difference)
  • The heart rate is the same because it was the same data source
  • Power, the values are also the same. Again, the Stryd was the data source

How would I condcut more tests

I would definitely take someone on the bike again for further tests. Then the intervals must be defined on Zwift and Auto-Lap off on the Garmin. Lap must always be pressed at the exact time when the interval changes to Zwift. Then the KM can be compared. And I would measure the calibration factor for the pod again on the track beforehand. In addition, the running route should be flat and the surface should always be the same. A lap-circuit would be optimal.

In conclusion: I imagined the values ​​a little better than they came out in the end. But I’m also very happy that I was able to do the first workout on the street. To sum it up: No negatives on first sight. And I think for anyone who can handle a small difference in pace between Zwift and watch, it is a possible way to run virtually outside.

I hope you took a little something with you. What else are you interested in about the test or the academy? Just text me. Until then, all the best, your Tom

Tom Hohenadl