Question on ERG mode

Hi all

I have been using TR since a couple of years now and completely satisfied with it, except for the mode of ERG. I am currently doing the Base phase and I don’t seem to understand how I can choose a preferred gear while using ERG.

In the past my chain was on the small chainring in front and one of the larger cogs in the back. However in one of the olther treads on this forum I read that you should simulate outdoor rides where i mostly ride on the big chainring in front. When changing to the big chainring in front in ERG mode, my power rises, and where i would expect that the software would start to match target to power, nothing happens. I tried to re-calibrate my trainer, re-installed it etc but I cannot seem to figure out, how to match riding in the real life situation vs inside without riding on the smaller chainring.

probably worthwile to mention, I am riding a Tacx Flux 2.

I also use this model of trainer.

Before I start my TR workout, I adjust my gearing. I’m always in the big chainring (up front) and middle of the cassette (out back). I believe that a straight chain line is important with regards to reducing friction and general chain wear.

Once the workout has started, I DON’T change gears. Whilst I don’t pretend to fully understand the mechanical side of ERG, I believe that changing gears can cause the trainer to struggle with the required resistance changes. Going from the small chainring to the large chainring (during a workout), unless you’re in a recovery phase, must really confuse the unit.

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The whole point of ERG mode is that you shouldn’t have to change gear, if you want to change cadence for the required power output just pedal faster/slower and allow the trainer time to adjust the resistance accordingly.

Changing gears will just cause the trainer to struggle to make the required resistance adjustments to get your power to where the workout wants it.

I kind off feel sorry for smart trainers these days as a lot of users expect a perfect power curve which is not really possible given the amount of power changes going on in a riders pedal stroke, chuck in gear changes and it gives the trainer little to no chance.


Thanks for your reply. I tried the same method without any success: I changed gears before my workout started but still my power rises and power vs target is not met. I tried to maintain it for a longer period of time to give the trainer time to adapt, without any luck.

When pedaling faster the only thing what happens is that my power goes up and the trainer does not adjust, resulting in blowing up my legs after two minutes (when on the big chainring in front and middle cog in the back).

Sounds like there may be an issue with your trainer, are you 100% sure Erg mode is engaging? sorry I am not familiar with the Tacx Flux but I would suggest contacting TACX for some after sales support.


For how erg works watch this - its the best explanation I’ve found to date…

Though it seems like you may have an issue with your trainer or how TR is communicating with it. Have you tried shooting a question over to support at TR they are incredibly helpful and I’ve noticed lately on the beta version I’ve had random issues, not using the same trainer as you though, and the issues seem to have have gone now but I experienced similar.

Hope you get it sorted as there is nothing more annoying than jumping on the trainer and it just not working as it should…

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What is your FTP?

If it is relatively low, you may be exceeding the capability of the trainer to hold a low power in a high gear.

No one has mentioned it yet, but some trainers have what are called Wattage Floors and Ceilings. These are limits of max or min power that exist in certain gear combos.

The Flux2 is a trainer with known limits, and you may well be hitting it with your particular power needs and selected gearing.

As mentioned, it could be a pure trainer problem, but I think we need more info.


Are you finding you are changing your cadence frequently, perhaps chasing higher and higher cadences by “pedalling faster” and “faster.”

With ERG you need to pick a cadence and hold it as close to that as possible. If your cadence is changing, ERG will adjust the resistance and if you are changing it constantly, ERG will never settle down. Lots of people find that ERG initially leads them to spin faster and faster until they spin out, but you need to resist the urge to spin faster and just stick to a number. Erg will adjust accordingly.

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My FTP is 295 watt.

I don’t seem to have any particular issues when I am training on the small chainring and have to increase/decrease cadence and the power is adjusting to that.

I only have issues with the ERG mode when wanting to train on the big chainring.

I have a pretty solid cadence, around 92 RPM on the trainer. As replied to Chad, I only experience issues with my trainer when wanting to ride on the big chainring. On the small chainring my trainer is doing well, power comes down when cadence increases and vice versa.

I will try tonight to have a fairly high cadence and hold it for a while on the big chainring (if I don’t blow my legs up that is)

There’s a high probability you are hitting the trainer’s minimum resistance. The Tacx Flux series has a relatively high minimum power. At a given freewheel speed, the minimum resistance attainable by the trainer corresponds to a non-zero power, and that power increases as the freewheel rotation speed increases. The trainer is trying to reduce resistance to match the workout’s power demand, but can go no lower - hence power increases above the demand, and increases as you increase cadence.

Simple solution: switch to an easier gear.


Then just use the small ring. It isn’t going to make a massive difference in your training. I train exclusively using the small ring indoors but ride outdoors in the big ring because it is flat here. I find no difference in power output or ability to spin the pedals this way. Stick to what works imo.


Thanks for the advice. I am going to invest in an powermeter to use the functionalities of Trainerroad as well and this should also give me an idea on the accuracy of my indoor trainer and influence of using only the small ring.

Whenever you get that power meter, I’d recommend using it both indoors and out. Don’t try to compare the numbers between it and the Flux. You’re likely to pull your hair out trying to make them line up with each other. Just stick to one source and be consistent in how you operate and calibrate it. Powermatch is your friend.


This is the Flux power curve, for 39:19 gearing. At 95 rpm, the minimum power is approx 150W. If you go to 50:15 gearing and spin above 90rpm, you can easily get to 300W minimum power.

Note that in real operation, the minimum power curve drops with trainer temperature - it’s common to see workout results on Tacx Flux trainers with power during the first few recoveries hovering above the target, and eventually meeting the target in later recovery intervals.


This issue is probably a trainer floor issue. Your gearing doesn’t matter. I would aim for a straight chainline in a gear that is middle of the road. You can test to see where you hit those limits and then learn when you need to shift (if you need to shift) to avoid those limits if your trainer doesn’t have a wide enough range to support all types of work. One way you can test this theory is when you hit this limit, shift up on the rear cassette and see if you can get closer to the target.


I did some testing last night without any significant success, it almost looks like my trainer ‘learned’ itself that I use the same gearing in the past and that he takes that gearing as baseline for the target power at the recommended cadence (I hope this makes sense, English is not my first language).

I will follow the suggested recommendations here: just use the small chainring and in the meanwhile I will get in contact with Tacx to see if there are missed software updates or so.

Thanks for the advice everyone, I highly appreciate it

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I can guarantee you there is no “learning” from the trainer end. It’s a dumb control loop. Receive power target from the app, modulate resistance until measured power = target power. Control systems 101.

The limits you reach are a function of the trainer spindle speed (axle rotational speed, virtual wheel speed, freewheel speed - call it what you want). A longer gear will make you hit the low limit at a lower cadence.

I use a Tacx Flux S - a slightly less powerful version of your trainer. I do all the warmups and recovery segments on the small chainring, large cog (the shortest gear), and I still hit the low limit once in a while. I switch to small chainring/middle of the cassette for most of the intervals, and use the big chainring for short sprints. So I’m changing gears quite often. That’s the price you pay for a cheaper trainer :smile:.


It has to do with flywheel speed. Smart trainer don’t do well with high speed flywheel and they struggle to be accurate in that instance. That is why it is recommend to stay on the small chainring for erg mode. There are no advantage in using the big ring.

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