Variability between trainers?

Went into new 12 week custom plan using FF numbers from April on my Kickr. Started the plan using Kickr bike - thanks prize minions!- and it was hard and higher intensity intervals had to be dialed back in third sets, but I figured that’s to be expected. Outdoor was spot on power per my crank based power. Was kicking climbs that were previously very hard and carrying speed on flats Nicely. Did recovery and FF prep week at the end and numbers per kickr bike dropped 10-12% . That was discouraging so I waited two days and did HM on kickr and numbers were up vs previous . Should there be that much variation between trainers? Makes it difficult to decide what numbers to use as some videos like climbing can be done but maybe I was using numbers that led to some overtraining?

Steve, are you talking about two different trainers and the power numbers between them, or are you talking about your power numbers being lower due to fatigue?

I think the power accuracy of the kickr and kickr bike are probably +/-2% at most (I haven’t checked the exact numbers that Wahoo posts). So at the extremes maybe 4% difference.

I would think most likely it was your condition the day you tested.

But a couple other things could be at play, FF and HM are different tests and should produce very similar numbers, but maybe there is some variance due to the test applied. And, is your kickr bike dialed in similar to your trainer bike? Small changes in the fit could be affecting your comfort and power as well. Was it hotter in your training environment when you tested lower?

Quoted accuracy is one thing, how accurate a training is under different conditions is another. I believe there can be some significant differences between trainers, especially moving from wheel off to wheel on trainers. When I spent time on Zw**t (:wink:) it wasn’t unusual to see a decent A cat racer drop at least a category when they bought a new trainer. Unfortunately improved accuracy almost always equalled lower power which led to a lot of disappointed people who hadn’t figured out their superstar Zwift performances didn’t match up to their times up local climbs. If you want to deep dive trainer/power meter accuracy then check out Shane Millard YouTube channel.

I should say that I’m not putting you I that category at all Steve, in fact quite the opposite, but just that there can be more difference between trainers, or power meters than the claimed accuracy would suggest. I’d also watch things like ambient temperature and warm up etc - I don’t know if those are relevant for the Kickr bike, but my Direto will drift 10w if the temperatures get too cold. Fingers crossed for power matching on the Suf before the winter!

Thanks - I’m talking two trainers on different days. Basement pain cave with stable temps - finished training plan and road performance was up in real terms . Higher gears and tolerating steeper climbs. Then as per plan after recovery week did HM and trainer numbers were way down including LTHR so I figured fatigue was issue . Did FF prep week and numbers on FF were about same though LTHR went back up to about previously levels . Both those tests were on kickr bike. 36 hours later did HM on kickr and numbers jumped 12% . Bike does not have spin down and is supposed to be accurate all time . Did do spindown on kickr. I have to assume it’s difference in trainers . At some point I’ll do a test on kickr with crank based PM and see how that compares to be sure . Went into training plan with numbers based on FF using kickr wheel off trainer then got kickr bike just before starting the 12 week plan.

Thanks for thoughts - this is comparing wheel off kicker to kickr bike . I don’t Zwift and it’s a basement pain cave with air conditioning and fans so it’s pretty steady ambient temperature. Bike is within a few mm of outdoor bike set up. I put more detail in my response to Joel si I won’t repeat it here . I probably should have done FF on kickr bike after it came in before doing the 12 week plan but had done it just a couple weeks earlier and couldn’t get excited about a repeat. Numbers are just numbers, and performance got better in terms of attacking climbs and using bigger gears outside . It becomes a question of how to set up outdoor training and watching power meter to see if you’re going too far into red On a climb for example if one trainer gives you 12% lower numbers .

Trying to answer these one by one, as there’s a few things going on possibly.

  • big thing is as the team have mentioned it’s easy to have a one off different result in different temp/conditions/fatigue state etc. though the latter I’d not think as relevant as you did the prep week.

  • so the numbers changed between April and August (down). The only hardware variable being the trainer. Yes trainers can be different is the answer to that question — but I’d not expect top end hardware to be that different. Does the Kickr need calibrated and the bike doesn’t? Does that introduce anything. Assuming all calibrated though then I’d go as far to say as those should be pretty much the same (assuming as others have said both are fitted exactly the same - same crank to saddle, same reach and reach angles and so on)

  • HM numbers on Kickr were above April numbers? well that to me points to maybe that FF above not being a ‘good day’ in line with others comments. Do you have a power and HR set of graphs from the April and Aug FF’s?
    HM is a bit different and some rider types end up with lower outcomes and some with high but that’s very individual. Try a HM on the Kickr bike sometime?

  • the last question … the only numbers that matter are the ones from your most recent run on your current trainer I’d say. Unless you’re always going to be switching between them?

You can’t have had numbers too high in April because you produced them (unless the Kickr was broken). 4 months is a long time though and the best numbers for you to use to train with could easily change in that time - again dep on what your load is obvs and so on. When did you switch across to the Kickr bike to start training on?
I’m assuming you’re not expecting them to have decreased though.

It kind of feels like you will benefit from using just one trainer, set up the way you want it, testing using that and then training on those numbers. And at that point any previous numbers are forgotten as the numbers are only in the system to enable us to have effective workouts at the den of the day.

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I see your problem. I think checking the kickr vs your power meter is a good idea. That would point to either the kickr reading high or the kickr bike reading low. Your indoor and outdoor numbers will probably be different anyway to a greater or lesser extent, but it’s not helped if the numbers are different on your different power sources. At least knowing whether it’s the kickr reading high, or kickr bike reading low will help. One last thing, have you updated the firmware for all your tech? And are your crank lengths set correctly in the software for the kickr bike?

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Thanks - cranks are same . I will check firmware, though I think it’s up to date. I should probably have done another FF on the kickr bike just before staring the training plan but didn’t think it would be that different. The whole object is to get some good numbers so that I have a good feel for what will put m in the red outside and cause a blow up on long rides and climbs like in Pyrenees etc as I climb like a troll and have to work near the limit sometimes to just not fall over . I only kept the kickr because you can’t wind up cadence drills on 5e bike since it’s rev limited. Love the bike and I think all this will work itself out in next training plan.

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I made a similar switch this june. I went from a KickR Core to a KickR Bike - mid plan. I didn’t notice a big difference at all. In fact, after two or three workouts it felt almost the same.

Sorry I can’t help pinpoint the real problem. But I’m guessing it’s not really related to your trainer. Maybe the firmware or the old KickR calibration, but I doubt it.

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To add to this conversation, I have just switched from a dumb trainer (Elite Qubo Power Fluid) to a Wahoo Kickr v5.

Previous FTP and MAP scores from the Elite were:
HM 6th June: FTP 134 MAP 172
FF 4th July: FTP 158 MAP 210

With the Kickr yesterday I did the HM and finished the whole of the ramp test without too much difficulty. I don’t think that my LTHR was set correctly as a result and my final results were FTP 214 MAP 265. I’m going to set my FTP and MAP scores higher than that and re-do HM tonight so that I at least don’t finish the ramp test. FF is planned for 2 weeks time.

Overall, I’d like to believe that the virtual watts reported in the app for the dumb trainer were way off and the much higher numbers from the Kickr are correct, but it’d be foolish not to question it, right?

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When I changed from virtual power to pedal based power meter, despite reading on almost every cycling forum that my ego would take a massive hit and my watts would go down, my watts went up by a massive amount.

I would definitely trust the Kickr over virtual power across all 4 metrics.


Thanks @titanicus Will do! I bumped up my numbers from the “failed” HM and did not get to the end of the ramp this time. I like my new higher numbers but it’s a shame that it’s only/mainly down to the new equipment rather than any fitness gains on my part :disappointed_relieved:

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I’m sure it’s both. It’s impossible to say how much of it is one more than the other.

It’s important to bear in mind that, for training, numbers are just numbers. If you are finishing workouts gasping and sweating, then the workouts are doing their job and you will be improving.

Also worth keeping mind that your numbers are yours alone - no one else’s and not really comparable.

Good luck with your training!


If you have a Garmin bike computer there’s a Connect IQ App that records both power sources simultaneously. You can then plot them both and see the difference. My crank powermeter (Power2Max gen 2) and trainer (TACX Neo2) are very close when the drive chain is clean.

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