tldr; Zwift ERG is noticeably different from TR ERG
There are some past threads about this topic, but now that the Zwift/TR integration is official I want to re-open this can of worms. I’ve done ERG workouts in TR for over 10 years. I was really excited to see the Zwift integration go live, primarily to try something new this offseason and keep motivation up. The TR FAQ for the launch included this question:
Why does power ramp up slower in Zwift compared to TrainerRoad?
Zwift’s power transitions are more gradual than TrainerRoad’s. This is normal and won’t significantly impact your workout quality or Adaptive Training.
The above point makes intervals less than 60 seconds long completely unusable in Zwift. It takes several seconds for the target power to ramp, then it overshoots, which then causes an overcorrection. It takes at least 30 seconds for it to “calm down” and get on target.
I attempted Mills on Zwift yesterday, and the 45 seconds at 120% of FTP were all ~20 watts off target. I tried to keep cadence as steady as possible, but it didn’t seem to have any effect. I know a lot of people say that you shouldn’t use ERG for shorter intervals in either platform, but I’ve never had a problem in TR. Note: I have a Neo2T and am power matching from a Quarq power meter.
Are there any suggestions? Is my brain just too accustomed to how ERG works in TR? If this is just how ERG works in Zwift I may have to continue using TR for any workouts with intervals under 60 seconds.
Thanks in advance
Additional tech info: I’m using a Windows PC to run both TR and Zwift. All devices connected via ANT+ USB dongle.
As you mentioned, this is something we’ve heard a lot about.
I personally haven’t had as many issues as some others, and as a matter of fact, my first TR workout on Zwift was Leons which went really well for me. I did experience some weird issues with the resistance being way to high for the power targets after pausing the workout twice which you can see below, but the 1 minute intervals actually worked really well.
I have not noticed any discernible differences between ERG mode in Zwift and TR (Saris H3 trainer).
I do wonder if this is trainer specific since, from my understanding (from the recent TR podcast), TR sends different timing signals to the trainer depending on the brand / model. IF Zwift just sends the same timing signal, then it may feel different depending on the trainer you are using and how they are programmed to ramp up.
Forgive me if my opinion is informed by anecdata that’s 10 months old as it’s been that long since I last rode on Zwift, but…
… I hated Zwift’s erg mode to the point that I wouldn’t use it at all, not for endurance, not for short intervals, not for threshold or SST. What it felt like to me was their dynamic control was way too slow to adjust, so this would even make threshold intervals get quite a bit harder than they needed to be at times.
Say I was doing a 3x20, and let my mind wander for a little bit, power started coming down a bit, usually it would be allowed to come down more than what I experienced with TR or erg driven by my head unit. To compensate, Zwift would ramp up power more slowly eventually peaking out at a higher point, sitting there and then compensating back down more slowly than other platforms. This gave intervals - at times - the feeling like pedaling through molasses. I had a few wacky looking erg diagrams on Zwift where if I zoomed in enough I could literally see this waveform, and it just seemed like the control tolerances were quite a bit wider and response was quite a bit slower than other platforms.
TR’s erg in-app is far superior, and then head unit direct control (Wahoo Elemnt Bolt) of my Saris or my Kickr were better, but not quite on par with TR’s interface. So when I let my sub to TR lapse, I used Zwift for a little bit, but eventually settled on simply using Zwift for the eye candy and driving my TrainingPeaks-based workouts from my head unit.
My coach at the time told me he thought Zwift’s erg mode was like “pedaling through sand”, and he is a professional bike racer and holder of national records on the road and spends a TON of time on his trainer, so this is not really a one-off.
Maybe things have changed there and Zwift will invest more in better control in erg, but I don’t think that’s really their primary concern. I have a few athletes who use Zwift erg, but most either use head unit or TR to control intervals indoors.
I actually wonder if that’s the case with Zwift too, since they have a list of trainers they consider “Zwift Ready” or “Zwift Cog Compatible”, meaning they support virtual shifting, but it’s possible their erg mode is optimized for these models in a way that it’s not for other trainers.
With my Wahoo Kickr Move, my experience is closer to @Power13’s than @kurt.braeckel’s; it does take noticeably longer to reach power targets, especially during VO2 max workouts where the delta between the recovery interval and the work interval is pretty large. In TR, erg mode seems to be on target within a couple of seconds. In Zwift, I’ve seen it take 8–10 seconds, and almost always results in the “more power!” prompt. Zwift is also slower to adjust to things like coming out of the saddle and back, which usually results in spikes and dips I rarely see on TR. But all those things feel relatively minor, nothing that measurably affects my workouts or my ability to complete them. I haven’t experienced the “pedaling through sand” phenomenon, for example; I really can’t tell any difference in pedaling feel between the two apps.
I’m on a 1x12 setup. In ERG I keep the chain in the middle of the cassette to maintain a straight chainline. In sim-mode I have “trainer difficulty” at 10%, so I don’t shift that much.
So with SIM you are more to the smaller cogs than the middle?
If so, flywheel inertia (greater in smaller cogs) is a likely factor to that slower feel (mid cassette).
If you want to try a test, do ERG in the same gear you use most in SIM (flat road as one example) and see if the feel differs.
Maybe its the trainer, who knows. I tried a TR workout in Zwift and decided to go back to running TR on its own. Zwift Erg was just errrrgggggg in comparison.
I’ve found the exact same problem. I’m on an original Tacx Neo, and the Zwift workout resistance control is terrible. Erg is waaaaay too slow to respond, at both ends of the interval, and incline mode is like pedaling through wet concrete. I’ve never had a problem in normal, non-workout mode. TR’s resistance control is much better. I can do short intervals in erg and stay pretty close to target, at least as close as I do in manual mode.
While I will do TR workouts in Zwift, they’ll be mostly Z2 or longer steady-state intervals. Anything below about 2:00 for either work or rest intervals will be TR, with a side-by-side running of Zwift, as I’ve been doing all along.
Were you using the smart trainer for power measurement AND control? I have always used my Garmin Rally 2-sided pedals for measurement and the Wahoo KICKR CORE for control. This combo seems to hace very slow control response vs what you get if you use the KICKR for power and control. Your power curves look like KICKR/KICKR, the Rally/KICKR combo is much sloppier; they look like PID control vs a simple thermostat type of control.
Well I do notice a difference between erg modes on my Hammer1 (as the only power source) - definitely a ramp up in zwift, and maybe it fluctuates a bit more around target, but I can’t say it’s worse, just different.
Haven’t done anything on-off yet, but I always found I was under for an interval in TR too - I assume while resistance may have been more immediate, it still took me time to ramp up my output
I’ve noticed something very similar. The slower ramp up isn’t a big issue most of the time, but it will definitely hover ~10 watts or so above the target for a bit before settling back down. It’s not as big of an issue with longer steady-state intervals, but my VO2 Max workout yesterday with 6-second microbursts was completely impossible in ERG. I had to switch to resistance mode for the microbursts and then back to ERG for the remainder.
Same here, I tried TR Workouts in Zwift but it’s not as good an experience as native TR (I also miss the blue graphs) so I just run them both. I sorted my workflow with 2 ANT+ dongles years ago
