Material decrease in RPE on similar workouts after switching from fluid trainer to smart trainer

I’m entering the second half of general build after completing sweet spot base low volume 1 and 2. Every ride prior today was done on my Kinetic Roadmachine 2 smart which is an on wheel fluid trainer. Yesterday I picked up a Kickr core and today, completed my first ride which was Avalanche Spire +1 a 1:15 over/under workout.

I did a spindown yesterday when I setup the Kickr and also did one this morning before starting Avalanche Spire. It felt way too easy today. My RPE today was probably a 5 or 6.5 at the very max but I was putting out the same power as I had done on prior workouts of similar format… In the past on my Kinetic Road Machine, my RPE for over/unders was an 8 or 9 and a far more difficult but also satisfying workout. I will admit that my cadence was around 100 for 3 of the 5 sets which was above the 85-95 range suggested. I did 95 for the final two but still do not think that the lower cadence and harder grind for 3 intervals would have made up the difference.

Has anyone had a similar issue when switching to a smart trainer?

I’m thinking that either the Kinetic was overestimating my power output or the Kickr is underestimating. However, I performed a spindown calibration before every workout with the Kinetic too. I’ve got 1 more workout prior to my rest week then a ramp test at the beginning of the second half of general build so will be interesting to see what my FTP is at that point. I’m currently 6’2 175 so my FTP of 259 is 3.26 w/kg. Would love it if I am actually a stronger rider than my Kinetic was reading but that is yet to be seen.

You’ll have to do a new FTP test. You can’t compare trainers/power meters. Since you’re near the end of this training block, just raise the intensity of the workouts to match the RPE for what’s expected for that type of workout.

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As mentioned above, you need to do a new Ramp Test whenever you change your power measuring device. Despite claims of accuracy, there is more different than common between many power devices. That is especially true with “Virtual Power” that you were getting from the KKRMS trainer. It is a guess at best. Sometimes it’s close, other times not at all.

Point is that you need to ignore the old power numbers and effectively reset based on your new trainer.

I recommend creating a new season from the day you started with your new trainer. That will help you get more up to date tracking on your Personal Records, as well as flag the timing of your change in power devices.

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Thanks - this is helpful. I’ll go in and start a new season to delineate between the two trainers.

One point though, is the Kinetic trainer I had previously considered “virtual power”? It’s a Road Machine 2.0 Smart and has the little dental floss shaped reader next to the rotor. I’m assuming this was really just reading cadence and estimating power then?

Also - is it likely that my real FTP is higher than previously thought since the same power output on the Kickr that I had been doing previously was easy?

  • Yes, it is “Virtual Power” since there is no actual power sensing device.
  • It’s not measuring cadence, because that is your pedaling RPM.

  • The InRide pod from Kinetic is measuring the trainer roller RPM.

  • “Virtual Power” from TrainerRoad is using a wheel speed sensor and the input wheel circumference, along with their measurement of the trainer power curve, to estimate power. It works, but is subject to variables like actual wheel circumference, tire flex, tire pressure, roller pressure and such.

  • The Kinetic Inride is a very similar system. The difference comes in where they are taking the RPM. By switching to the roller, they know exactly how fast the resistance unit is spinning. That makes for a more direct and potentially more accurate estimation of power, because it eliminates many of the variables from the TR equations above.

  • And the fact that the KK can also be calibrated, increases the chances of getting more accurate power data. But at the core, there is still no actual power measurement taking place. It is all very fancy guesswork. That is muddy water created by Kinetic to make their trainer seem more comparable to other smart trainers.

  • Your FTP has not changed in any way. It is exactly the same as the moment before you touched the Core trainer.

  • The only thing that has changed is the “tape measure” you are using. You might as well have swapped from Imperial to Metric measurements, because you can’t really compare power in this case. It’s dangerous to assume even two power meters are close, and when Virtual Power is part of the equation, all bets are off.

  • At the very least, you would need a power meter on the bike, that can measure power at the same time as your trainer. People sometimes record data from two apps and devices, and then load the files to compare the differences. That would be needed with a pass on each trainer, to even have a realistic comparison. Your RPE is likely valid, but far from useful in talking “real” power comparisons.

Hence the recommendation to start a new season. The past is the past and that is all it should be. Ignore the prior numbers and focus on the new meter and working from that new baseline.

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Thanks again this is all very insightful

I’ll do another FTP test in a day or two to see where Kickr puts me. Would be a nice surprise if the measurement of my FTP is higher on the Kickr since, if I’m reading correct, it seems to be a more accurate measurement than virtual power I wa spreviously using .

I’m planning to get a Power2Max NGECO for my bike soon and will compare this against the Kicr.

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But it doesn’t make any difference. Your abilities haven’t improved because you’ve bought a new trainer. It’s the interpretation of that ability that has changed by way of a new measuring tool.

The absolute fundamental and most basic part of training with power is comparing like-for-like. So don’t compare real power with virtual power. Don’t even compare power from 2 different power meters. It doesn’t matter whether your trainer says your ftp is 100 or 100000, what’s important is that you can train according to a repeatable number.

Just to be clear, I’m not expecting to have a higher ability or be stronger just from getting a new trainer. Agree with you on interpretation of the ability and its just a difference in measuring tools.

I’m simply saying that if my FTP was previously understated with a less accurate trainer, and it is now measured higher by a potentially more accurate method, I’d be excited to have a higher w/kg than previously thought.

Just to follow-up on my post from yesterday - I retested this morning and my FTP on the Kickr Core is 276 or 3.48 w/kg.The last FTP test was 4 weeks ago and this is prior to rest week. This seems to be in line with the FTP progress I’ve made in the past so maybe that ride was just easy that day for whatever reason or the Kinetic was slightly lower than Kickr. Too many variables.

Will retest once the second half of build block starts on February 3rd.

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True, that many smart trainers do not have a “power meter” in the sense of a strain gauge based system.

  • The first exception is the OTS (Optical Torque Sensor) in the upper end Elite trainers. This is a “real power meter” and has very good accuracy.

Most of the other smart trainers are using the combination of testing along with the fancy calculations housed within the electronics and resistance brake system.

  • It’s all a bit over my head, but the basics are a foundation of circuits, resistance and such, and using that info with power testing to establish a “power meter” of sorts.

  • The main point being that it is a very advanced system of measurements within the electrical system to back figure the power values.

  • And admittedly, all “smart trainers” are not created equal. Some of the really bad ones do different or just plain bad execution of any method and report terrible data (looking at you Elite… for all you Muin junk). While others are mid level and capable of good results, and bad results (Tacx Vortex) and then we have the standard makers like the original Neo 1/2 and more recent Kickrs.

  • It is all more complicated and typically more reliable when compared to the simple “spin a drum and count the revolutions” approach of the Kinetic system.

  • There is sure a range of accuracy that can be found in them, but I would tend to trust most mid level and higher smart trainers above and beyond the Kinetic Virtual Power.

In the end, from a training perspective and with using the one device, the most important aspect is that it is consistent and repeatable to itself. The issues arise when we try to compare data from one source to another.

That usually leads to head scratching, as was the case here. In those cases, questioning the device least likely to provide “accurate” data is a starting point. But it is entirely possible that a “smart trainer” could be giving junk data too. So there is no real answer without a 3rd data point.