Reduced watt/FTP output with new trainer

I am using a simple spinning bike with a heavy front flywheel, with Favera Assioma pedals, to measure my output. I have been a consistent Trainerroad user for almost 3 years, and had a typical FTP progression:

-started with an over-ambitious FTP of 240 when I first started riding;
-dialed back to 180 which was more realistic, and which allowed me to progress;
-rode my first Ramp Test after 7 months (220);
-rode second Ramp Test after 18 months (251)

I have been at 251 for more than a year now. Up until February 2022, I was still able to modestly improve my performance at various exercise durations, even though I didn’t increase FTP.

After using the same very simple friction-resistance home trainer for more than 7 years, I wanted to upgrade to a new spinning bike which has magnetic resistance. The old trainer was becoming rough to pedal due to degrading drive belt, so I assumed that this updgrade would - if anything - make it easier to produce same power at any given level.

Unfortunately this is totally not the case. I have experienced a substantial (25-35 watts) decline in my output and am frankly unable to do some workouts that I did before. Overall I feel that my heart rate is higher at corresponding wattage levels, which is surprising to me. I checked/adjusted the following parameters without great success in restoring wattage output (although each adjustment was worthwhile):

  • saddle and handlebar positions
  • cleat position
  • TrainerRoad pedal calibration
  • Favera calibration

I am out of ideas for any possible quick fixes. An additional aspect that makes me unsatisfied with this new bike, is that ergonomics are poorly thought out. Handlebars are too large and wobbly, and also block the ventilation provided by a front mounted fan I have installed. Bottle cage is too far to reach. All of these things are probably fixable, but combined with the sense that this bike is a step backwards mechanically - for some unexplained reason - make me look for another model.

Any thoughts about what else to try to ‘correct’ my wattage output? I suppose I could just re-run a ramp test, but that feels unfair. I probably shouldn’t care so much about my FTP considering it’s just a number, it will undoubtedly drop at some point anyway (I just turned 55) but I feel it’s something I earned and want to keep it as long as I can.

I have found zero references to this phenomenon, but could it be possible that watts which are measure at the pedal can can be influenced by some mechanical aspect of the resistance system, which makes it the case that ‘not all watts are the same’? I ask that with the observation that it could be something about friction vs magnetic resistance application and pedalling technique. In that sense, I notice a very subtle improvement after 6 weeks of using the new trainer, but it’s definitely not going to get me back my 25-35 watts,

Any thoughts?

The fit geometry of the new spin bike is probably substantially different than the old one, well beyond your ability to fix it with cleat position, seat height, and bar height. (E.g. new bike has you sitting less upright and farther forward relative to the pedals as an example)

Do you notice a difference in the position on the new bike?

I don’t notice a dramatically different (i.e. uncomfortable) position, but funny you should mention it - the adjustment I did before the ride yesterday was to move back relative to pedals. The result was a slightly perceptible improvement.

But overall, it feels like re-starting Trainerroad, and I have bailed on about as many workouts in the past 6 weeks as I did in previous 6 years…

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In case it was not clear, the saddle is adjustable on both vertical (slightly diagonal) axis as well as purely horizontal axis. Perhaps I could go back a bit further…

Is there a difference in crank length between the old bike and the new one that you haven’t accounted for? Is it set correctly in the Favero app?


Good one.

Good question, I think it’s the same but will double check. The other parameters are wheel circumference (in Trainerroad) which wouldn’t seem to matter…

I would consider doing a weighted calibration test if that’s not too difficult.

You don’t need to do this.

This is quite understandable and expected IMO. Rule #1 in my book:

  • Whenever you change a part of your training equipment, you should retest of FTP to set the new “foundation” for training. This includes things like new power meters, trainers, bikes, and in your case… a new trainer bike.

  • Aside from all the potential issues you mentioned (that are quite valid contributors here), you have not mentioned the resistance unit and related flywheel. I feel that can be a large factor as well, if the two bikes you had differ enough in the size, weight and speed of the flywheel and resistance unit.

  • We see this happen with people swapping from one trainer to another, where it’s quite pronounced between something like a basic wheel-on trainer to one of the top end wheel-off trainers. The difference in flywheel effect in these cases can be HUGE, even if the person using the same exact bike and power meter on both (just like your case here).

  • All that to say, you really should retest and just move forward. You clearly see the fact that ‘FTP is just a number’, but are also clearly stuck on holding to what you have now. Remember that your fitness and ability is EXACTLY THE SAME in the real world. The only thing that changed is the effective ‘tape measure’ you are using.

  • We know you have the same power meter, but the bike connected to it is a real influencer and effectively changing the results. So, you just have to accept that if you plan to keep the bike. It is likely worth addressing the fit and cooling considerations you mention, to get them as good as possible with that setup. But even if you nail that and duplicate your prior setup, I still expect the flywheel and resistance unit changes will alter the final results.


This is the correct answer. You’re going to mess around with a bunch of stuff to protect your ego. Just let the number go and reset your baseline. Nothing changed, just the bike.


I vaguely recall having measured my old trainer crank length and it being the same as the new crank length, something less than 170mm, I am not at home now but will check later.

However, if I dig further I note that Favero default crank length is 172.5mm and presumably I never changed that before. So if the new and old crank lengths were in fact the same, they are both not matching the default.

I understand how crank length could be a very rational explanation, will check!

I always forget to include this in my first post related to issues like this, but along with the reset, it can be useful to apply a new Season in your TR career. This effectively allows you to set a new starting point for power PR’s based on the new setup.

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Crank length is not going to make a 25-35W difference if they’re in the same ballpark.

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Correct, 172.5mm to 170.0mm is roughly 1.5% change up or down, which would only be around 4w delta for a 250w FTP. Definitely not the full difference here.

Thanks, good tips (all).

Indeed may make the most sense to just re-test and see where it puts me. Without biasing myself, I am guessing it will be in the 220 range, correlating with my observed output of 25-35 watts lower.

Is it reasonable then to expect that there is enough ‘physiological learning effect’ possible to return to the original FTP eventually, or does the flywheel etc. create a sort of ceiling for my progression? I realize this question may not have an answer, but I never thought about my old bike creating any resistance on my development (other than the friction on the flywheel that translated into watts)…

As you guess, there is not really an answer here. I have a theory about flywheel effect and the impact on at least superficial levels of training. We see enough differences in RPE and apparent FTP when people try high vs low gearing on the same trainer in ERG mode. Sadly, I have never heard of a study that actually looks at this basic issue in any way, and definitely not in long term aspects like actual training impact.

Based upon your wording, I strongly urge that you actively work to ignore your prior FTP and avoid using that as some sort of carrot. Maybe it’s possible, but just as likely you may not be able to hit it with the current bike setup. Motivation and targets are highly individual, so I can’t say what’s best for you. But all too often, we see people set these and have mixed results and satisfaction related to those goals.

I think you can work to make your current setup the best it is, get accustomed to it and the related FTP and move on with your training.


The spin bike has a LOT more resistance against mid-stroke power surges than a wheel on trainer and does’t not provide equal resistance for 360 of your pedal stroke. The home trainer will challenge the weak parts of your stroke less while taxing the weak parts more since you can’t surge past them.

All that matters is that the FTP is appropriate for the setup you are using , to scale your workouts appropriately. FTP is not something to compare to others or even previous setups. As long as new setup is consistent in its power measurement it’s all good. Retest and move on.

-Power measurement at the crank and power measurement at the rear wheel hub are different. This is also the reason PowerTap has disappeared from the market. Most of us use the crank’s power standard.

-Assioma is great. It also outputs very similar data compared to SRM.

-In general, smart trainers often display rather high power. This is because it is not completely free from temperature drift.

-Among the trainers that measure power at the rear wheel hub, only the NEO 2T uses a virtual resistance, so it is free from this temperature drift.

-The two NEO 2Ts I use give similar power in ERG, but I have found that they usually give out 3-5% less results.

-Actually, my conclusion is the same as the other opinions above.
It would be better to apply indoor and outdoor FTP respectively.

To wrap this issue up somewhat - I have decided to get a different spinning bike with a friction rather than magnetic resistance. I have identified a couple of models which appear to solve some of the ergonomic issues (saddle and handlebar position and stability). These will also better accommodate a fan which would be directly facing my head and upper body. This decision was made not to protect my FTP figure (‘THE PRECIOUS’) but because there is really something suboptimal with my current setup that contributes to overexertion and reduces my riding benefits. The reduced FTP was a visible output, but I also feel it continuously.

I’ll retest FTP once I have it set. Thanks again.