How to match specified power without erg/auto mode

I have come to the conclusion that erg mode doesn’t work, or at least isn’t optimal, due to lag between trainers and apps. Too slow to reach target watts and constantly making micro adjustments based on power readings which are seconds old.

So what does everyone do? Particularly these complex workouts where you have to do short hard efforts. Maybe work out what power will result from x cadence in y gear?

I’m an XC mountain biker so said complex workouts are one of the reasons I’m choosing Xert. Punchy efforts are


I tend to use exclusively slope mode set to 2-5% slope when short (or up to 1 min) hard efforts are required, even for the recoveries as gives me more of a road like feeling.
Can check out this for details:
What Trainer Modes Are Available in Xert’s Workout Players? – Xert (


Depends on your brand/model trainer as some are very quick to respond.
Many short punchy workouts use MIXEDMODE (AUTO to Slope) to avoid trainer transition response issues (or death spiral). Same for sprint intervals.

SMART interval targets work whether you’re in AUTO or Slope mode.
Only difference is you’ll need to use gears/cadence to hit and maintain target watts and that requires monitoring the EBC rainbow gauge to align the chevrons (iOS) or arrowheads (Android). Or view the SP rainbow gauge for same purpose.
In either case, no harm switching to Slope mode then vary % slope to determine what number works best with gears/cadence required to complete the interval set. You’ll discover an effective % range that works with your trainer/cassette combo.

Power chart graph won’t be as exact as ERG trainer control, but you’ll get the job done.


Which workout(s) are you having trouble with? Typically any smart trainer will lag for short (<20s) intervals. Usually the lag applies to both sides of an interval though, so while I might take a few extra seconds to get up to the target power, it also usually takes a couple of seconds for the trainer to drop the resistance at the end of the interval.

My personal choice when riding in slope mode is as follows:
Sprints: ~5% slope
VO2/5 min efforts: 2.5% slope
Threshold/Endurance: 0.5-1.0% slope

You’ll get a feel for what gear(s) you’ll need as you go!


Thank you for replies!

My trainer is a Tacx Flux S. What I think the problem is is the power reading: either my crank based Stages PM or the trainer one - I prefer to use the Stages one so I can do zone 2 rides outdoors with it and I want to have consistent readings.

I think a lag in reading power changes makes it impossible for the trainer to increase resistance in time for short efforts as you said, less than 20 seconds. I think we’re talking around 5 seconds lag. It seems it makes more sense to use the gears and slope mode. Do other people have different experiences with this? My garmin HU and the Stages app have similar lag on returning power readings.

Thanks for advice!

I use a Saris H3 trainer for ERG + 4iiii single-sided pedal for power. The lag is tolerable (3s?), but more than if I were to use my trainer for power as well. I dislike this because it reads ~3% lower and confuses things in my fitness signature. For punchy workouts, I’ve experimented with using the trainer for power and the workout feels better, but I absolutely have to lower the workout intensity to 95% or I cannot complete harder intervals. There’s no great answer.

One thing I’ve also done is use all trainer for running the workout, but record pedal power with my head unit (Wahoo). Then I upload after the fact so that the data matches my outdoor signature. It’s all sort of a game, really, so this sort of nonsense is somehow pleasing to me. Others would find it ridiculous.

Good luck!

But if you use your 4iii power meter all the time, wouldn’t it at least be consistent and therefore the workouts correct?

Yes, the only reason to avoid my 4iiii pedals is the bit of extra lag and “settling time” compared to my trainer. Almost every setup I’ve tried has been tolerable but I like to fiddle with things… :person_shrugging:

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