I think I don't understand ERG mode

Hi guys (and gals).

I read a lot of posts, articles on ERG mode.
Thought I got it.
Seems to be hard to grasp.

I really need your help on that one.

I read many topics here, but it doesn’t seem to look like what I experienced.

To understand my situation, I need to explain from the beginning because I received a lot of questions on other platforms asking me more precision to better explain the context. So here it is.

In September, I started by trying some rides on Zwift with an Indoor Bike (Mekbelt SM36).
Great bike.
One belt (that doesn’t stop like on our road bikes, no rattle of the cassette so first time I almost got thrown out of the bike), cadence sensor and speed sensor incorporated into the bike with easy pairing with Zwift, right of the box.
I started to train for FTP a couple of weeks later and got it at 149 at the first try.
We all need to start somewhere.
I have to turn a knob to increase/decrease the power during the workouts and trainings.
I do my best to not overshoot or undershoot.

At some point, having to set it at a certain wattage for 10 seconds, then go back down at 85W/85RPM, then go up at 180W/100RPM for 5 seconds, etc, didn’t give me enough time to pedal, increase the power on the knob and keep the cadence at the same time. I did my best.
I talked about it with my wife.
She bought me a Wahoo Kickr Smart Trainer V5 for my birthday.

Great pleasure to ride on my own bike.
But it is also needing a getting used to and to add to that, now I have my brain comparing the power in my legs (the work I had to put in) on my Indoor bike with the effort now I have to put on the Kickr and they are really not the same.

What I experience is that my Kickr is too easy.

I’m on the 6 weeks workout FTP Builder. When the workout ask me to warm up, it starts at 65W/85RPM and increase power from 65 to 120W, by 5W during 10 minutes.

I cannot feel any difference between the 65W and the 120W, not even the 4 min at 145W. Because I can compare with my Indoor bike (which didn’t have ERG mode), my legs were hurting, so, if I want to compare, 145W on my Kickr now is about 95W on my Mekbelt then. My heart rate don’t event go higher than 135BPM, and I was at 185BPM on my Mekbelt.

So today, I turned the ERG off.
Now it is harder, but it is also all over the place.

Power felt by the Kickr make it react (and sending me messages to increase/decrease cadence/power) but that’s what I want to do but if I go faster, this means I have to put more power on the pedals but now I push at 460W, when the training phase is at 125W. So the Kickr freaks out.

Just to give you an image, I started a new FTP tonight. Went to 240W, steady ( as much I could so I overshooted at 280W and back at 245W) and in the end, my FTP was increased slightly at 163 (ERG turned off). But when I started the warm up, I needed to be at 85RPM for the 65W. Each leg stoke were at 145W to be able to keep RPM at 85 ??? I don’t even know what to do. I changed gears but, when I did, I lost everything because power go down to 30W and I was pedaling at 100RPM. Changed gear again and now I’m at 640W, so I have to change gear again until I can feel and get to the right power and cadence.

I thought that I would only have to stay on the same gear and adjust the cadence and ERG would take care of the rest. But now, I don’t understand anymore.

I also asked Wahoo if I need to calibrate the Kickr but Wahoo told me that it calibrates itself.

So everybody,

How can I get my Kickr, in ERG mode, to have the right power as in ERG Off mode ?
What do I do wrong ?
What do I don’t understand ?

(ERG On is more stable than when ERG off).

By the way, Trainer difficulty is at MAX in the settings.

I’ve never heard of the Mekbelt, but I just did some poking around. Honestly, one possibility is just that the Mekbelt was not giving you very accurate power numbers. A lot of customer reviews remark that it’s study, which is good. But it’s currently on Amazon for $319, and there isn’t a single professional review that I can find. Meaning, a review that is from someone whose actually used it and tested the accuracy and such. It may be study, but my first thought is that it was just wrong about your numbers.

Regarding your bike on the Kickr, can you give some details about your bike? How many speeds is the cassette (how many gears in the rear cluster of gears, and how many in the front by the pedals)?

Shifting multiple gears at once will likely cause big swings like you’re describíng. But shifting just one gear at a time in the back should provide a much smoother transition between power output and cadence.

You post is a little difficult to follow. Can you do the below and then post up the workout “graph” that is posted in the summary screen after end ride?

  1. Got to the workout library and select a workout with long, steady intervals - for example “2x15 FTP Intervals” from the “Less than 60 minutes to burn” folder.
  2. Select the workout, make sure ERG mode is ON (option at the bottom of the screen)
  3. Do the workout, and during the workout STAY IN ONE GEAR and do not change gears
  4. At the end of the ride, make sure you take a screenshot of the workout graph, it should look like the below, and post it here:


That will help us understand what you are seeing a lot more clearly.

The best I can explain workout in ERG mode is that it should keep you at a solid power:

  • The power should be constant during an interval
  • The trainer will do this by reducing resistance if you are pedalling at high cadence, increasing resistance at low cadence
  • This means that “high torque + low cadence” gives you the same power as “low torque and high cadence”
  • You should not need to change gear.

Some tips in using ERG

  • When an interval comes up that is higher power than the previous one the resistance will get “heavy”/difficult very quickly. It is important to “attack” the start of the interval as it comes up, increasing cadence and getting ready for effort. You may feel an initial spike in difficulty but it will settle down if you just keep pedalling for a few seconds and keep your cadence up.
  • Do not change gear
  • Use the “small” ring at the front if possible

It is actually the opposite way around

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The first rule for any data collection and analysis when you change the means of measurement is to take a new baseline measurement.

Your previous trainer/ bike may not have been accurate. Therefore your FTP is probably too low (based on your feedback).

My advice would be to do a couple of free ride sessions with your new Wahoo trainer to get a feel of it with your own bike set up. Then do another FTP/ Ramp test and get a new accurate figure.

I expect that once you have a new FTP that workouts in ERG will feel much better.

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Hehe yes apologies, fingers moving faster than brain - I’ll edit

Ok, I will try this this week.