Erg mode on a turbo trainer..am I misunderstanding how it works?

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  • Erg mode on a turbo trainer..am I misunderstanding how it works?
  • tpbiker
    Member

    I assumed it worked as follows..

    The app (ie trainer road) sets the target power and then changes the resistance, so No matter your cadence you stick at the prescribed power. Ie if it prescribes a 200 watt effort and you give it the beans the app will simply reduce the resistance to accommodate this..

    In reality..when im in erg mode the resistance changes automatically per interval but doesn’t appear to change resistance if I pedal harder or softer. Ie the interval could be at 200 watts but the app doesn’t stop me putting out 300 if I pedal hard. It’s working pretty much like I’d expect it to do in zwift when the gradient changes, ie I’m dictating the power rather than the app.

    Trainer is a tacx flux if it makes any difference

    Thanks

    whitestone
    Member

    Sounds like you haven’t actually changed to ERG mode.

    Within reason ERG mode will keep you at the target power, there’ll be a little, say +/-2W variation but otherwise you’ll be on target. What happens when you come to a step change in what the app is asking for?

    Premier Icon tomnavman
    Subscriber

    There are limits on how much / little resistance the trainer can give – I find I sometimes need to change gear in ERG mode to bring the power up / down. This is on the flux.

    I think these limits are greater on the more expensive trainers.

    Premier Icon Kryton57
    Subscriber

    The only time my direto allows that is if I put in a quick sprint, then assuming I maintain that sprint it quickly adjusts the resistance to equate to watts required for the interval again.   200w intervals are 200w intervals regardless of cadence and only fluctuate briefly if I slow / speed up before accosting back to 200w.

    stevious
    Member

    I use a flux and spend most of my time in the smallest few gears, even for threshold efforts. If I’m in too big a gear then I just end up doing loadsawatts*.

    *still not many watts, but more than I should be.

    As above-I find ERG works best in a very low gear do trainer. Flywheel then spins slower which means it’s easier for trainer to control power. At a high gear the flywheel has too much momentum to control and breaks out of erg mode more easily.

    Premier Icon nickdavies
    Subscriber

    Yours works like mine does, if I am too low or too high, it tells you to add/reduce power. Makes sense when you get the ERG loop of death when you can’t make the power so the erg asks for more power which makes it worse. You’ve still got to put out enough power, and if you give it the beans and put out 400w then you’re still putting out 400w.

    That’s my understanding anyway, although I don’t think my old wheel on job is great. New wahoo could be totally different!

    mtbtomo
    Member

    Mine adjusts the resistance compared to the cadence. So if you pedal at higher RPM, the resistance reduces a little so the power is roughly maintained. Pedal at a lower RPM and the resistance goes up to maintain the power. Takes a moment or two to adjust, its just a feedback loop not absolutely instantaneous.

    Premier Icon mattbee
    Subscriber

    Tacx Flix user here, it can take a bit of gear changing to keep within the power outputs in erg mode.
    Interval sessions for example with large differences in power can need a change up or down a few gears as the turbo struggles to maintain the wattage.

    It does seem to be able to do so more easily if I stick in the small ring though.

    tpbiker
    Member

    Thanks..so it’s meant to work how o thought it does..clearly doesn’t however.

    For example just having a play around on it earlier, 130 watts warm up for 2 min, I was about 150 and the turbo did nothing to compensate.

    Premier Icon speedstar
    Subscriber

    My H2 will adjust within a few seconds regardless of what cadence or gear I put in. Can occasionally make it waver about 30-40 watts.

    jonnyboi
    Member

    Thanks..so it’s meant to work how o thought it does..clearly doesn’t however.

    For example just having a play around on it earlier, 130 watts warm up for 2 min, I was about 150 and the turbo did nothing to compensate.

    Could be your gearing is preventing the wattage going any lower.

    To get below 130 watts on a flux you will need to be in the inner front ring and possibly no smaller than 19T on the back

    tpbiker
    Member

    Unfortunately it Lets a me put out whatever wattage i like when its meant to be 130. I dropped it down to about 80 by soft pedalling, then shifted it into big cogg and had it at 300.

    It doesn’t feel like it’s even in erg mode tbh, i may try an update on the firm wear. At the moment it feels like I’m in resistance mode, even though it clearly says erg on the screen

    andrewreay
    Member

    Newbie here, but I just noticed a huge difference tonight by shifting into the big ring for the first time (Direto user).

    The workout I did had big cadence and power changes, and I could tell that the trainer was struggling to cope. It’s never been a problem before in the small ring.

    I was finding it took ages to settle into the new power and cadence (10-15 seconds) during which time I was getting unreadable amounts of ‘Reduce power’ Spin faster’ type messages from the app.

    Shifted down to the small ring and found the trainer coped far more quickly and smoothly with the cadence and power changes. Normal service was resumed.

    Lesson learnt for me!

    Definitely use the small ring to avoid ERG feedback loops of excruciating length.

    Good luck resolving your issue.

    Did a couple of Zwift ERG sessions last night, using my 4iiii for power and cadence, alongside my Direto. Power matching for 30sec 315W intervals was awful (~280W-ish average for 16 intervals)! Due to not using Direto for power and cadence?

    Premier Icon Kryton57
    Subscriber

    NOTG – have you performed a steady state tested and offset the 4iiii to match the Direto though?   I did this and they were remarkably similar.

    Premier Icon tillydog
    Subscriber

    Not seen it mentioned: Have you got power averaging switched on?

    whitestone
    Member

    OP – you mention Trainerroad as the app. Might be worth contacting their customer support to check if there’s something they can see in your power files.

    Also are you trying to stick to the prescribed target power or are you putting in a lot of effort and assuming that the system will pull you back to the required value? What you haven’t stated is what happens when you try to stick to the target power not break away from it. It’s as if you are saying “I’m trying to break it and it breaks!”

    tpbiker
    Member

    Originally I was trying to keep to the correct power but found it near impossible.

    Not sure I’ve mentioned im using a stages to provide the power output rather than take it from the flux. Kryton appears to suggest there is some additional calibration required to use the power meter?

    TiRed
    Member

    What power are you trying to maintain. I find erg mode most helpful for 3w/kg efforts and run the SST workshop on Zwift. Normally in small ring. Power is force x angular velocity, so spinning faster at lower force is the same power as grinding at high force. The trainer can however hit the erg floor or ceiling and will be best at about 90 rpm.

    Premier Icon richmtb
    Subscriber

    I’ve got a Tacx Vortex and the only issues I have in ERG modes is it can feel a bit choppy at lower cadences – like 65 rpm out the saddle efforts – above 80 its fine and changes the resistance pretty seamlessly.

    Premier Icon swavis
    Subscriber

    I use the Tacx flux and only ever seem to need the small ring when doing a warm up/down. Anything over 130 watts and I’m in the big ring. When I have to up power to say 600 watts I have to change up a couple of gears (down the block) and give it beans. I take it this is how it should work and what you’d do on the road, no?

    I need to do another calibration on the Direto, a while ago the figure went ~10 under the factory value but then returned to ~3 below.

    When new, the Direto and 4iiii figures were identical or as good as.

    Premier Icon robbo1234biking
    Subscriber

    If using ERG mode and assuming that the turbo doesn’t have a wattage floor or ceiling that prevents it you should use the front ring most appropriate to the type of riding you do:

    MTB – tends to be small front ring so do your turbo training in this ring so you are not grinding gears (as you generally do on the MTB)

    Road – tends to be the larger ring (Unless you live somewhere very hilly).

    You get more fly wheel inertia with the bigger ring so it can make the ride seem a bit easier in my opinion. This is only relevant with ERG mode though and not Zwift (as you wouldn’t go very fast sitting in the little ring).

    With my Direto I can sit in the little ring on the front and middle cog on the rear and go down to about 70W and as high as about 500-600W which has been ample to complete TR workouts. I don’t need to change at all.

    On my Tacx Vortex I had to change down from big ring to little ring in rest valleys to be able to reach say 100W otherwise the lowest it would go in the big ring was 130W.

    whitestone
    Member

    @swavis – in resistance mode you’d do as you say but in ERG mode the trainer does its “smart” thing and adjusts the resistance so you get the change in effort without you having to change gear. There is a bit of lag, maybe a couple of seconds depending on the trainer, and resistance changes are a very steep ramp rather than a step though when tired there’s not much difference!

    Reading on the Trainerroad forums it seems that the preferred setup is small chainring and middle of the cassette. Using the big ring lets the flywheel in the trainer provide too much inertia. As noted above not all trainers can handle the full range of power in one gear but that does depend on what you as an individual can put out: if 600W is your range you should be fine; if it’s 1200W then you’ll either need to change gear or get a better trainer.

    Premier Icon GHill
    Subscriber

    I use the Tacx flux and only ever seem to need the small ring when doing a warm up/down. Anything over 130 watts and I’m in the big ring. When I have to up power to say 600 watts I have to change up a couple of gears (down the block) and give it beans. I take it this is how it should work and what you’d do on the road, no?

    I had to fish around in the gears to get in the correct power region when I had a Tacx Flux. Changed to a Direto when my second Flux died, and I don’t need to shift.

    Premier Icon swavis
    Subscriber

    Hmmm, food for thought, I’ll give it a try tonight in the small ring making sure ERG is on.
    I can definitely feel the resistance changes from the trainer, especially when doing an FTP test so I know it works. I’m using Zwift but that shouldn’t matter I suppose.

    Jase
    Member

    I use the Tacx flux and only ever seem to need the small ring when doing a warm up/down. Anything over 130 watts and I’m in the big ring. When I have to up power to say 600 watts I have to change up a couple of gears (down the block) and give it beans. I take it this is how it should work and what you’d do on the road, no?

    I also have the flux and have to do exactly as you. I tend to want to use big ring and 3rd sprocket at the back. But for my warm up/cool down even with a cadence of 80 the Watts are too high in this gear so I have to shift down to small ring.

    Once I’m into the session I can stick with my big ring for most of it and trainer will adjust resistance fine.

    Premier Icon swavis
    Subscriber

    @Jase yep, definitely the same as me then. I’m happy with it as it seems to simulate a real workout which is what I got it for 😎

    tpbiker
    Member

    Well something still isn’t right

    Just did a ramp test and I don’t think at any point I was putting out the correct wattage. Always above or below..trying to match it really detracted from the entire point of the test. At the end it wouldn’t even increase resistance enough so I had to be in big ring small cog hammering 95rpm to put out the required power.

    Power match is set to auto, I’m definitely in erg mode. I think a tacx flux is basically just a fairly rubbish trainer.

    tpbiker
    Member

    Just tried the erg mode in the tacx app, worked fine – just as I thought it would. Then tried it again in the trainer road app without the power meter and it still didn’t work.

    sweaman2
    Member

    I’d drop a note direct to trainer road then as they might be able to offer tech support.  They’ve always been very good when I’ve had issues.

    servo
    Member

    I use a Tacx Flux with trainer road and have just started my winter training. Used it for the last 2 winters but last summer I bought a 4iiii power meter and thought it would use the power from that for indoor training to. It was rubbish, just as you said. Ended up disabling the 4iiii in the TR device menu and just used the Flux power. Someone above said that you can do a long term steady test comparing your power meter to the Flux output and apply a correction factor. I’m not that bothered as long as I’m progressing.

    Just use the Tacx Flux power to do the Erg mode, it seems to work well.

    Premier Icon mattbee
    Subscriber

    So it’s a trainerroad issue really then not a Tacx one?

    jonnyboi
    Member

    Check your firmware version on the Tacx?

    As above I no longer use the 4iiii for anything other than cadence when indoor training, and I find just using the flux gives me a much smoother change in power that follows the workout exactly.

    There is a variation though, my ftp using the 4iiii is 18W higher than the Tacx so I alter my FTP for outdoor training

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