Hi John -
It takes a little bit of tinkering, but it is actually possible to do this. It requires you to manually edit your workout files after you’ve created them in the workout editor. I’m going to give you step by step breakdown to start the process.
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Create your desired workout in Zwift and save it (you’ll probably want to start this well ahead of your planned ride time), and exit Zwift
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Navigate to Documents/Zwift/Workouts, and find the workout you wish to edit. Click once to select the file, then right click and on Windows select Rename, or on Mac select Get Info
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Remove the .zwo from the end of the workout name, and replace it with .xml . Use the Enter key to save your change.
Now that the workout file is in .xml format, you will be able to edit it. Right click the file and select Edit on Windows, or Open With TextEdit on Mac to make your changes. When editing your workout file, be sure to pay attention to the format and keep your changes in line with that formatting to ensure you don’t break the file.
For normal segments, you can specify power with:
PowerLow=“0.5” PowerHigh=“0.75”
That means the power zone is 50% of ftp to 75% of ftp. You can adjust this as tightly as you like.
For intervals, it is:
PowerOnHigh=“0.5” PowerOnLow=“0.4” PowerOffHigh=“0.3” PowerOffLow=“0.2”
which would give an ON-Interval of 40% to 50% and an OFF-interval of 20% to 30%.
So, for example, I want to adjust the ranges of my workout to keep me within 5% of my target wattage on any interval:
Original workout:
<workout>
<Warmup Duration=“600” PowerLow=“0.2545” PowerHigh=“0.75449997”/>
<SteadyState Duration=“300” Power=“0.81449997”/>
<IntervalsT Repeat=“4” OnDuration=“60” OffDuration=“300” OnPower=“0.75449997” OffPower=“0.50449997”/>
<Cooldown Duration=“600” PowerLow=“0.75” PowerHigh=“0.25”/>
</workout>
To adjust the range on the normal interval,
<SteadyState Duration=“300” Power=“0.81449997”/>
would be changed to
<SteadyState Duration=“300” PowerLow=“0.76” PowerHigh=“0.86”/>
To adjust the range on the over/under intervals,
<IntervalsT Repeat=“4” OnDuration=“60” OffDuration=“300” OnPower=“0.75449997” OffPower=“0.50449997”/>
would be changed to
<IntervalsT Repeat=“4” OnDuration=“60” OffDuration=“300” PowerOnHigh=“0.7” PowerOnLow=“0.8” PowerOffHigh=“0.45” PowerOffLow=“0.55” />
After you finish editing your workout file, be sure to save your changes to the file. Zwift will read the files in either the .xml or .zwo format, so as long as you’ve preserved the proper formatting, the workout will appear in your Custom Workouts menu as usual.
As for your second suggestion, I’ve added it to our request list for consideration as we continue to expand and improve Zwift.
I hope all this helps! Ride on!